Cold-start for high-octane fuels in diesel engine architecture

Abstract

To disclose embodiments that relate generally to systems and methods of operating internal combustion (IC) engines, and more specifically to systems and methods of starting compression ignition (CI) engines when a surrounding environment is significantly colder than a normal operating temperature of the engine (i.e., "cold-start").SOLUTION: In some embodiments, the CI engine can include an ignition-assist device. In some embodiments, a method of operating the CI engine during cold-start can include opening an intake valve to draw a volume of air into the combustion chamber, moving a piston from a bottom-dead-center position to a top-dead-center position in a combustion chamber at a compression ratio of between about 15 and about 25, injecting a volume of fuel, the fuel having a cetane number of less than about 30, closing the intake valve, and combusting substantially all of the volume of fuel.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0001] This application claims the priority and benefit of U.S. Provisional Application No. 62 / 848,087, filed on May 15, 2019, entitled "Cold - Start for High - Octane Fuels in a Diesel Engine Architecture", the entire disclosure of which is incorporated herein by reference in its entirety.

Background Art

[0002]

[0002] Diesel engines, also known as mixed - control compression ignition (MCCI, or CI) engines, are an important element of the energy landscape, having several advantages over the spark - ignition (SI) engines used in conventional gasoline vehicles. The CI design of diesel engines provides high efficiency and good torque / power density. At the same time, the robustness of the design enables the high reliability and low maintenance of these engines, which can often be driven in excess of 1 million miles in on - road applications. Thus, diesel engines are optimal for long - distance and short - downtime scenarios. However, diesel engines are not without drawbacks. In addition to a higher initial cost than conventional SI engines, diesel engines have difficulty starting in cold climates, particularly with low - cetane - number fuels, due to the thermal requirements of MCCI operation.

Summary of the Invention

[0003]

[0003] The embodiments disclosed herein generally relate to systems and methods for operating an internal combustion (IC) engine, and more particularly to systems and methods for starting a compression ignition (CI) engine (i.e., “cold starting”) when the ambient environment is significantly colder than the normal operating temperature of the engine. In some embodiments, an auxiliary device such as a glow plug, a spark plug, or a plasma ignition device may be used until the engine reaches a temperature at which auto-ignition occurs during cold starting. In some embodiments, the CI engine includes an engine cylinder having an inner surface, a head surface, a piston disposed and configured to move within the engine cylinder, an intake valve, an exhaust valve, and an ignition assist device. In some embodiments, the inner surface of the engine cylinder, the piston, the head surface, the intake valve, and the exhaust valve may define a combustion chamber. In some embodiments, the piston and the head surface may define a bowl region of the combustion chamber. In some embodiments, the ignition assist device may be located within the bowl region of the combustion chamber. In some embodiments, a method of operating a CI engine may include opening an intake valve to draw a quantity of air into the combustion chamber. In some embodiments, the quantity of air may have a mass average temperature of less than about 150° C. at the instant the quantity of air passes through the intake valve. The method of operating a CI engine may further include moving the piston from a bottom dead center (BDC) position to a top dead center (TDC) position within the combustion chamber at a compression ratio between about 15 and about 25 and injecting a quantity of fuel at an engine crank angle between 0 degrees and 360 degrees. In some embodiments, the fuel may have a cetane number of less than about 30. The quantity of fuel and the quantity of air may form an air-fuel mixture. The method of operating a CI engine may further include closing the intake valve and substantially completely combusting at least a portion of the quantity of fuel. In some embodiments, at least 50% of the quantity of fuel may be premixed with the quantity of air immediately prior to ignition.

Brief Description of the Drawings

[0004]

Figure 1

[0004] Schematic diagram of a compression ignition architecture according to one embodiment.

Figure 2

[0005] Schematic diagram of the arrangement of a glow plug or spark plug in a combustion chamber according to one embodiment.

Figure 3

[0006] Schematic diagram of the arrangement of a glow plug or spark plug in a combustion chamber according to one embodiment.

Figure 4

[0007] Schematic diagram of the arrangement of a glow plug or spark plug in a combustion chamber according to one embodiment.

Figure 5

[0008] Chart showing the transition from SACI to HCCI and from HCCI to MCCI according to one embodiment.

Figure 6

[0009] Chart showing the influence of valve timing on the transition from SACI to HCCI and from HCCI to MCCI according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0005]

[0010] Chemical fuels (such as petroleum, alcohols, biodiesel) continue to be important for heavy-duty road transportation. The high energy density of chemical fuels is important for users who need to travel long distances and refuel quickly. As a result, the demand for chemical fuel diesel engines will continue for decades. However, diesel fuel prices have risen substantially over the past 30 years, and diesel fuel is a major contributor to greenhouse gas emissions. Furthermore, emission standards for nitrogen dioxide and nitric oxide (collectively referred to as NOx) and soot are becoming increasingly stringent.

[0006]

[0011] The use of cleaner, lower-carbon alternative fuels such as methanol, ethanol, dimethyl ether (DME), and natural gas has been steadily increasing in the United States' energy landscape over the past 20 years. Between 2000 and 2018, ethanol production in the United States has increased annually from 1.6 billion gallons to 16.1 billion gallons, a ten-fold increase. During the same period, natural gas production in the United States has increased by approximately 30%, and methanol production has also experienced a significant increase. While petroleum-based fuels still provide approximately 85-90% of the United States' energy demand in the transportation sector, the market share of alternative fuels (such as methanol, ethanol, biodiesel) and natural gas is expected to grow consistently over the next several decades. These alternative fuels serve not only as a means to supplement the supply of the petroleum industry to meet energy demand, but also as an attractive method to reduce greenhouse gas, soot, and NO x emissions related to the transportation sector. Fuels with approximately 80-85 wt% ethanol emit less than 40% of the carbon dioxide of conventional petroleum-based fuels per mile. Other alternative fuels experience similar reductions in greenhouse gas emissions compared to conventional petroleum-based fuels. Also, emissions of carbon monoxide, volatile organic compounds (VOCs), and NO x can be significantly reduced when these alternative fuels are used.

[0007]

[0012] The use of clean, lower-carbon alternative fuels such as methanol and ethanol in CI architectures is an important innovative step in meeting energy demand and reducing harmful emissions, but these fuels have low cetane number characteristics, meaning they require a higher temperature to achieve autoignition compared to long-chain hydrocarbons (i.e., chains of 6 or more carbon molecules). The cetane number is an indicator of the ignition quality of a fuel in a CI engine and is the temperature threshold for autoignition to occur. Due to the higher autoignition temperature, these fuel types have even greater difficulty with ignition at low temperatures compared to conventional diesel fuel.

[0008]

[0013] Embodiments disclosed herein generally relate to systems and methods for operating an internal combustion (IC) engine, and more specifically to systems and methods for starting an IC engine when the ambient environment is significantly colder than the engine's normal operating temperature (i.e., "cold starting"). In other words, starting the engine when the engine block is very cold due to the low ambient temperature is more difficult than starting an engine that has been recently (typically between 90 minutes and 2 hours) driven. Cold starting is made more difficult for a number of reasons, including: (1) lack of heat makes it more difficult for the fuel to ignite, (2) low temperatures thicken the engine oil and make it more difficult to circulate, and (3) the air-fuel ratio is affected by the cold air and thus affects the combustibility of the mixture.

[0009]

[0014] There are two types of engines most commonly used in vehicles. These are spark ignition (SI), most commonly used in gasoline engines, and compression ignition (CI), most commonly used in diesel engines. In a standard four-stroke SI engine architecture, the chemical energy in the fuel (e.g., gasoline) is converted into mechanical energy by the ignition of the fuel in the combustion chamber. The outer boundary of the combustion chamber is defined by the engine cylinder, a piston configured to move within the cylinder, a head surface, one (or more) intake valves, and one (or more) exhaust valves. During operation, the piston completes four distinct strokes while rotating the crankshaft. First, in the intake or induction stroke, the piston moves from the top position (i.e., top dead center (TDC)) of the combustion chamber to the bottom position (i.e., bottom dead center (BDC)) of the combustion chamber. Since the crankshaft rotates about its central axis below the combustion chamber, the term "dead center" indicates the relative position of the crankshaft with respect to lateral movement. During the intake stroke, the intake valve is opened and gas is drawn in through the intake valve. The gas may be an air-fuel mixture or simply air, in which case fuel is directly injected into the chamber for mixing. The intake valve is then closed prior to the second stroke, creating a sealed environment within the combustion chamber. The second stroke is the compression stroke, during which the piston moves back from BDC to TDC. During this stroke, the piston compresses the air-fuel mixture in preparation for ignition. By the end of this stroke, the crankshaft has completed a full 360-degree rotation. The third stroke is the power stroke, during which the spark plug ignites the compressed air-fuel mixture. The ignited mixture expands, pushing the piston back to BDC and creating a mechanical action on the crankshaft. In the fourth stroke, the piston moves back from BDC to TDC with the exhaust valve open, discharging the exhaust gas (i.e., combustion products).

[0010]

[0015] The operation of a CI engine is very similar to that of an SI engine. A standard four-stroke CI engine employs the same four strokes as an SI engine and has important differences in the compression and ignition strokes. During the compression stroke, the compression ratio (the ratio of the combustion chamber volume at BDC to the combustion chamber volume at TDC) is substantially higher than that of an SI engine and reaches a value of 17:1 or higher. This significant compression causes a dramatic increase in temperature and pressure, bringing the air-fuel mixture (if pre-mixed) to its auto-ignition temperature or injecting fuel into air that already exceeds the required auto-ignition temperature, so that the ignition stroke occurs without the use of a spark. This type of engine architecture generally produces a higher torque output than an SI engine architecture and is constructed to be more robust. Thus, CI engine designs provide reliable performance over a relatively long time frame.

[0011]

[0016] While the benefits of clean, low-carbon fuels are well established, one of the drawbacks of such fuels is that they have a relatively low vapor pressure and auto-ignition ability compared to gasoline. During cold periods, E85 fuel is often supplemented with a larger amount of petroleum-based gasoline than during warm periods to meet the fuel volatility requirements of winter. For an E85 blend in winter, typically only 70% ethanol is included, compared to 83% in the summer blend. As long as the E85 fuel has sufficient volatility, the cold-start systems and processes of SI engines are substantially the same as those for pure petroleum-based fuels. Ignition occurs regardless of temperature due to the vaporization of an appropriate amount of volatile fuel in the combustion chamber. However, the CI architecture increases the difficulty of achieving ignition. As mentioned above, clean, low-carbon fuels typically have a low cetane number, which makes it more difficult to achieve auto-ignition with neat methanol or ethanol in a diesel engine. These alcohols have a cetane number of about 1 to 15, so that the temperature of the air and thus the air-fuel mixture at TDC is typically insufficient to meet the ignition requirements of either alcohol, compared to a conventional diesel fuel with a cetane number of about 45.

[0012]

[0017] Examples of systems and methods for operating a CI engine with low cetane number fuel are described in U.S. Patent No. 9,903,262, entitled "Stoichiometric High Temperature Direct Injection Compression Ignition Engine," filed April 6, 2015 (the "'262 patent"). The disclosure of the patent is incorporated herein by reference in its entirety. These methods include short ignition delays and mixed control combustion that requires a pre-injection temperature (pre-injection temperature) of approximately 800°C for these fuels. As described in the '262 patent, there are many benefits to engines operating with low carbon fuels under high temperature conditions. Specifically, soot emissions are substantially lower than those resulting from the use of conventional diesel fuel.

[0013]

[0018] Regardless of fuel type, CI engine architectures experience some problems that are not common in SI engines. In a CI engine, sufficient thermal energy is required for autoignition to occur, but this is not the case for spark-assisted ignition. The '262 patent describes retaining exhaust to provide thermal energy for steady-state operation, but the exhaust cannot be used for the initial engine start, and low cylinder wall temperatures prevent the intake charge from reaching an air temperature of approximately 800°C suitable for CI low cetane number fuel autoignition. Also, starting a CI engine in a cold environment can be even more difficult given the relative lack of thermal energy available for autoignition to occur in the combustion chamber. When the ambient environment around the combustion chamber is cold, that ambient environment draws a large amount of thermal energy generated during the compression stroke away from the combustion chamber, making autoignition very difficult.

[0014]

[0019] Since low cetane number fuels have a higher autoignition temperature than diesel, cold start with low cetane number fuels (e.g., methanol, ethanol, or natural gas) is more difficult. Since CI engines using low cetane number fuels rely on high ignition temperatures and exhaust utilization, the development of cold start strategies for initiating or sustaining ignition of low cetane number fuels to reach steady state operation when thermal energy is insufficient can be challenging. That said, the high octane number of most low carbon fuels provides a unique opportunity for cold starting of engines.

[0015]

[0020] The embodiments disclosed herein relate to a system and method for cold starting a CI engine driven by a low cetane number fuel. FIG. 1 shows a compression ignition (CI) engine 100 including a cylinder 110, a piston 120 configured to move within the cylinder 110, an intake valve 130, and an exhaust valve 140. The cylinder 110, piston 120, head deck 125, intake valve 130, and exhaust valve 140 collectively define a combustion chamber 150. Both the intake valve 140 and the exhaust valve 150 can contact a camshaft (not shown) that rotates to open and close the intake valve 140 and the exhaust valve 150 according to the timing and distance necessary to achieve the desired intake. While a spring holds the intake valve or exhaust valve in the closed position, the oval shape of the cam presses against the valve at various lengths relative to the central axis of the camshaft, creating the open and closed positions of the valve. In other words, when the long side of the oval cam (with respect to the distance from the central axis of the camshaft) contacts the valve, the valve is pushed into the open position. When the short side of the cam contacts the valve, the spring pushes the valve to the closed position. In some cases, the engine employs multiple camshafts, such that one camshaft controls one or more intake valves while another camshaft controls one or more exhaust valves. The camshaft can often change the timing of opening and closing of the valves via a variable valve timing (VVT) scheme. The simplest form of VVT is cam-phasing, whereby the phase angle of the camshaft rotates forward or backward relative to the crankshaft. This changes the timing of valve opening, but does not change the amount of lift or the opening period provided by the camshaft. More complex or "asymmetric" VVT, where the lift and opening period can be modified and / or the timing adjustment of the intake valve 130 can be different from the timing adjustment of the exhaust valve 140, can also be implemented. In some embodiments, the intake valve 130 and the exhaust valve 140 open and close via hydraulic actuation, electronic actuation, or other means rather than via a camshaft.

[0016]

[0021] The CI engine 100 also includes a source of fuel 160 that is fluidly coupled to a fuel injection device 170 that injects fuel into the combustion chamber 150. The fuel 160 can include conventional fuels such as gasoline or diesel fuel, or low carbon / low cetane number fuels such as methanol, ethanol, or natural gas, or low carbon / high cetane number dimethyl ether.

[0017]

[0022] In some embodiments, the CI engine 100 can operate according to a stratified charge controlled compression ignition (MCCI) strategy. In standard MCCI operation, the fuel injection device 170 sprays a fixed amount of finely atomized fuel 160 into the combustion chamber 150 near the time when the piston 120 reaches TDC (within ~15 degrees of crank angle). The fuel 160 vaporizes rapidly but non-uniformly in the combustion chamber 150 and ignites. The fuel 160 in front of the spray stream first contacts the heat and oxygen in the combustion chamber, and the fuel 160 in front ignites first. This creates a flame front at the point of contact between the fuel 160 and the compressed air. There are drawbacks and advantages with respect to this non-homogeneous flame and fuel concentration gradient. One of the drawbacks is the potential for incomplete combustion of the fuel 160, as well as the formation of undesirable combustion products such as soot, carbon monoxide (CO), and NO x etc. To reduce these harmful emissions from the exhaust of a stoichiometric fuel supply, typically a three-way catalyst 165 is used. The three-way catalyst 165 is often disposed downstream of the exhaust valve 140 and includes noble metals such as rhodium, platinum, palladium, and some metal oxides. The three-way catalyst 165 is most effective in the supply of stoichiometric fuel 160 because it promotes the reaction between CO and NO x to produce CO2 and nitrogen gas. A fuel-rich mixture exposes more CO to the catalyst, and the CO remains unreacted. An air-excess fuel-lean mixture exposes more NO x to the catalyst, and the NO x remains unreacted.

[0018]

[0023] One advantage associated with the operation of a stratified MCCI engine is the minimization of engine knock. Engine knock occurs due to premature fuel combustion, specifically when a premixed fuel-air charge auto-ignites by compression prior to the desired timing. In MCCI operation, only air (or air with a small amount of fuel and / or exhaust) is compressed during the compression stroke, thereby eliminating the possibility of knock in the case of fuel deficiency. After injection, the stratified charge of fuel 160 through the fuel injector 170 creates locally rich points of fuel 160 that can burn in a timely manner and with a short ignition delay, avoiding knock. In other words, the timing and rate of fuel combustion are limited by the timing and rate of fuel injection. Turbulence in the flow of fuel 160 as it is injected into the combustion chamber 150 aids in bringing as many available oxygen molecules in the combustion chamber into contact with the atomized droplets of fuel 160. This reduces the physical delay between the vaporization and combustion of the fuel droplets. By delaying the air-fuel mixing and reducing the homogeneity within the combustion chamber 150, the possibility of knock can ultimately be reduced.

[0019]

[0024] In some embodiments, the CI engine 100 may operate according to a homogeneous charge compression ignition (HCCI) strategy. What differentiates HCCI from MCCI is that HCCI involves burning a substantially homogeneous air-fuel mixture. In some embodiments, HCCI operation is achieved by delivering fuel 160 through fuel injector 170 while piston 120 is moving from TDC to BDC during the intake stroke. In some embodiments, the fuel injector may be disposed near intake valve 130, just outside combustion chamber 150, to further promote pre-mixing of fuel 160 and air before entry into combustion chamber 150, resulting in a substantially homogeneous air-fuel mixture at the time of compression and ignition. There are several advantages to HCCI operation. First, the combustion of fuel 160 in the HCCI mechanism tends to be more complete and efficient. This not only improves fuel economy but also tends to produce the expected combustion products of water and CO2 more selectively. In other words, in the HCCI mechanism, NO x and CO emissions are reduced. However, HCCI operation generally has a narrow operating range in which it is the optimal combustion strategy. If the temperature in combustion chamber 150 is too low, proper amounts of thermal energy may not be supplied to create a combustion event throughout combustion chamber 150, and thus ignition performance is simply not supported. In contrast to MCCI operation, when the temperature in combustion chamber 150 is too high, knocking may occur due to an out-of-time (early) combustion event of fuel 160.

[0020]

[0025] In some embodiments, the exhaust may flow through the line that conveys the incoming fuel 160 to promote heat transfer to the incoming fuel 160, thereby reducing the loss of thermal energy from the fuel 160 associated with pre-ignition vaporization cooling. Similarly, thermal energy may be transferred from the exhaust to the intake air stream to increase the temperature for auto-ignition. Also, the gas stream in contact with the EGR cooler 195 may increase the temperature of the coolant in contact with the EGR cooler 195. Generally, a coolant reservoir (not shown) is disposed throughout the engine 100 to surround each cylinder 110, and the heat from combustion is transferred to the coolant liquid in the reservoir there. The coolant then flows to a radiator (not shown), where a blower assists in the transfer of heat from the coolant to the ambient air. In some embodiments, the circulation of the coolant throughout the engine 100 may be reduced or controlled such that the temperature in the combustion chamber 150 rises rapidly. Reducing the amount of coolant flowing through each cylinder 110 effectively reduces the amount of thermal energy transferred out of the combustion chamber 150, whereby the temperature in the combustion chamber may rise faster than with complete circulation of the coolant fluid.

[0021]

[0026] In some embodiments, in conjunction with the methods described above, knocking can be reduced by lowering the intake pressure of the engine 100. Lowering the intake pressure can reduce the amount of fuel required to maintain an appropriate air-fuel ratio while reducing the pressure in the combustion chamber 150. This lower pressure effectively reduces the overall probability of auto-ignition.

[0022]

[0027] In some embodiments, the CI engine 100 may include a thermal barrier coating 155 that helps retain thermal energy within the combustion chamber 150 to maintain a high temperature for combustion. As described in the '262 patent, the thermal barrier coating 155 may be applied to the liner of the cylinder 110, the face of the piston 120, the surfaces of the intake valve 130 and exhaust valve 150, the interior of the combustion chamber 150, and the cylinder head (not shown). In some embodiments, the thermal barrier coating 155 may be applied to the entire intake and exhaust systems of the engine 100, including the recirculation port 190 and the EGR cooler 195.

[0023]

[0028] In some embodiments, an intake preheating system may be used to assist with cold starts. An intake heater cartridge system may be installed immediately upstream of the intake valve 130 to reduce heat transfer losses between the heater and the engine. This system configuration is similar to cold start assist utilized in many commercial diesel engines. However, due to the high autoignition resistance of low cetane fuel, even higher levels of preheating are required. However, that need can be reduced by providing additional exhaust retention or other forms of combustion assistance. Similarly, a block heater (not shown) may be attached within or outside of the engine 100 to assist with ignition at low ambient temperatures. In some embodiments, the block heater may be attached within the cylinder block to heat the cylinder 100. In some embodiments, the block heater may heat an oil reservoir (not shown) near the crankshaft 180 to reduce the oil viscosity at startup. In some embodiments, multiple block heaters may be attached within and around the engine 100. In some embodiments, one block heater may be permanently attached within and around the engine 100. In some embodiments, the block heater may be removable so that its use can be seasonally adjusted.

[0024]

[0029] In some embodiments, engine 100 may include a pilot fuel injection device (not shown) that injects a high cetane number fuel into combustion chamber 150 during a cold start. A fuel with low heat insulation against autoignition can assist in the ignition of the engine during a cold start and can be slowly and gradually stopped during the transition to steady state MCCI operation. In some embodiments, the high cetane number fuel may be stored in a tank separate from fuel 160. In some embodiments, the tank holding the high cetane number fuel may be substantially smaller than the tank holding fuel 160. In some embodiments, the high cetane number fuel may be diesel. In some embodiments, the high cetane number fuel may be dimethyl ether.

[0025]

[0030] A central challenge in engine cold starting is to reach a stable idle speed (approximately 750 RPM), but it is equally important to keep the exhaust emissions during starting within regulatory limits. The three-way catalyst 165 generally has an operating temperature of at least approximately 250°C. This high temperature is an important property in the realization of the exothermic oxidation of incomplete combustion products, and in that regard, the exothermicity of the reaction can be used to sustain catalysis in a process known as catalyst light-off. Before light-off is achieved, untreated unburned hydrocarbons, CO, and NO xcan be emitted from the engine 100. Considering the low emission thresholds that the engine 100 must meet to maintain compliance, the cold start period is an important period during which harmful pollutants should be actively reduced. Thus, it is important to ensure that catalyst light-off is achieved quickly and that the pollutants emitted before reaching catalyst light-off are at a minimum level. In some embodiments, the cold start method described herein can minimize the formation of pollutants by reaching the light-off temperature in less than 60 seconds. In some embodiments, the use of the thermal insulation coating 155 throughout the intake and exhaust ports of the engine 100 can be an important component for retaining as much thermal energy as possible to assist the three-way catalyst 165 in achieving the light-off temperature. In some embodiments, a heating element can be added to the three-way catalyst to shorten the time required to achieve the light-off temperature. In some embodiments, each of the aforementioned cold start methods can help to achieve catalyst light-off.

[0026]

[0031] Achieving stable idle operation is important for any cold start strategy, but simply adopting a strategy that is suitable for adoption by the original equipment manufacturer is not necessarily sufficient. Just as emissions should be kept low enough during cold start to meet regulations, combustion should be stable enough to meet the user's expectations regarding reliability and noise, vibration, and harshness (NVH) during cold start. At low temperatures, there may be significant variations in combustion between different cycles. In some embodiments of cold start via the methods described herein, minimizing these variations can help to achieve an acceptable level of combustion stability. Specifically, the coefficient of variation of the indicated mean effective pressure (the volume-normalized work generated in the combustion chamber during the operating cycle) between cycles should be less than about 5%.

[0027]

[0032] In some embodiments, engine 100 may include a glow plug (not shown) for providing desired thermal energy to fuel 160 to achieve self-ignition by sufficiently heating the ambient air or by providing a hot surface for surface ignition. In some embodiments, engine 100 may include a spark plug (not shown) for facilitating spark-assisted compression ignition. In some embodiments, engine 100 may include a plasma ignition type device (not shown) that is similar to a spark plug but has fewer spatial constraints with respect to the boundary of high-energy plasma to assist cold start.

[0028]

[0033] The attributes of the embodiments of the foregoing method will be different with a heat-insulating coating as compared to embodiments without a heat-insulating coating. The heat-insulating coating facilitates both cold-start ignition and early catalyst light-off, as well as the CI mode of transition strategies such as SACI and HCCI.

[0029]

[0034] FIG. 2 shows a CI engine 200 according to one embodiment. CI engine 200 includes a cylinder 210, a piston 220 configured to move within cylinder 210, a head deck 225, an intake valve 230, and an exhaust valve 240. Cylinder 210, piston 220, intake valve 230, and exhaust valve 240 collectively define a combustion chamber 250. CI engine 200, cylinder 210, piston 220, head deck 225, intake valve 230, exhaust valve 240, and combustion chamber 250 may be substantially similar or identical to engine 100, cylinder 110, piston 120, head deck 125, intake valve 130, exhaust valve 140, and combustion chamber 150 described above with reference to FIG. 1. Accordingly, the details of the specific aspects of the components of CI engine 200 are not described in further detail herein and should be considered to have the same or substantially similar shape or function as the corresponding components described above with respect to engine 100, unless the description is clearly different.

[0030]

[0035] As shown in FIG. 2, fuel injection device 270 sprays fuel along line A towards auxiliary device 275 while piston 220 is at the TDC position or as piston 220 approaches the TDC position. In other words, auxiliary device 275 is located in the bowl region 251 of combustion chamber 250 and within the direct spray path of fuel injection device 270. In some embodiments, positioning auxiliary device 275 in bowl region 251 may assist in inducing surface ignition (i.e., ignition of fuel or fuel-air mixture on the surface of auxiliary device 275). In some embodiments, auxiliary device 275 may be a glow plug. In typical diesel fuel operation, a glow plug heats the air within combustion chamber 250 to enable combustion during cold start. However, in some embodiments of low cetane number fuel CI engine 200, the heat provided to the air via the glow plug may not bring the air to a temperature suitable for autoignition to occur. The advantage of positioning a glow plug within the direct spray path of fuel injection device 270 along line A is that it may facilitate direct contact between the fuel and the surface of the glow plug. This direct contact may enable ignition of the fuel on the surface of the glow plug. In other words, fuel injection device 270 can spray fuel onto the hot solid surface of the glow plug with oxidizing molecules in the vicinity to directly promote combustion on that hot solid surface. Considering that the heat capacity of the hot solid surface of the glow plug is high compared to the heat capacity of the nearby air, a greater amount of thermal energy is transferred from the glow plug to the fuel, thereby facilitating ignition. This initial ignition event on the hot solid surface may facilitate subsequent ignition events away from the hot solid surface of the glow plug. In some embodiments, the glow plug may be coated with a material that catalytically assists the combustion of alcohol, natural gas, and / or dimethyl ether, including but not limited to transition metals. As shown, fuel injection device 270 injects fuel into combustion chamber 250. In some embodiments, fuel injection device 270 may be positioned such that fuel injection device 270 injects fuel into an intake port (not shown) outside of combustion chamber 250.

[0031]

[0036] In addition to the above advantages, placing a glow plug within the direct injection path of the fuel injection device 270 along line A can have additional unique advantages compared to other possible placement locations. Considering that the glow plug is in close proximity to the fuel injection device 270, when the air-fuel contacts the glow plug, the air-fuel mixture is substantially heterogeneous. This high level of heterogeneity increases the probability of timely combustion and decreases the probability of premature combustion and knocking. However, this level of stratification in fuel injection can ultimately result in more unburned fuel and undesirable CO and NO x emissions in the exhaust stream.

[0032]

[0037] When operating the CI engine 200 using the glow plug as an auxiliary device 275, there are two time delays to consider when facilitating cold starting of the CI engine with low cetane fuel. The first time delay is the amount of time between activation of the glow plug and the first start of the CI engine 200. The first time delay is a function of the rate at which heat is transferred from the power source to the glow plug and ultimately into the combustion chamber 250. The second time delay is the amount of time between the first start of the CI engine 200 and the completion of the transition to steady-state MCCI operation of the CI engine 200. The second time delay is a function of the exothermicity of fuel combustion within the combustion chamber 250. In some embodiments, the first time delay can be less than about 1 second, less than about 5 seconds, less than about 10 seconds, less than about 20 seconds, or less than about 30 seconds. In some embodiments, the second time delay can be less than about 30 seconds, less than about 45 seconds, less than about 60 seconds, less than about 90 seconds, or less than about 120 seconds.

[0033]

[0038] In some embodiments, the auxiliary device 275 may be a spark plug, facilitating a process referred to as spark-assisted compression ignition (SACI) or spark-assisted MCCI combustion. In other words, the use of a spark plug as the auxiliary device 275 in the combustion chamber 250 can provide a local spark that helps initiate combustion when the thermal energy is insufficient for conventional compression ignition. Placing the spark plug within the direct spray path of the fuel injection device 270 along line A has certain advantages and disadvantages similar to those encountered with glow plugs. The degree of fuel non-uniformity when the fuel contacts the spark plug increases the probability of timely combustion while reducing the probability of premature combustion and knocking. However, this level of stratification in fuel injection can ultimately result in more unburned fuel in the exhaust stream and undesirable CO and NO x emissions.

[0034]

[0039] As described above, the use of alcohol-based fuels in a typical SI engine can create challenges for cold starting. However, the CI architecture utilizes a significantly higher compression ratio (i.e., approximately 17:1), which reduces the barrier to spark-assisted cold starting. Considering the high volatility and rapid vaporization of the low cetane number fuels described herein, the air and fuel may be well mixed and made ignitable even at low temperatures.

[0035]

[0040] In some embodiments, the compression ratio of the engine described herein can be at least about 15, at least about 16, at least about 17, at least about 18, at least about 19, at least about 20, at least about 21, at least about 22, at least about 23, or at least about 24. In some embodiments, the compression ratio of the engine described herein can be about 25 or less, about 24 or less, about 23 or less, about 22 or less, about 21 or less, about 20 or less, about 19 or less, about 18 or less, about 17 or less, or about 16 or less. Combinations of the compression ratio ranges referenced above (e.g., at least about 15 and about 25 or less or at least about 15 and about 20 or less) are also possible, including all values and ranges therebetween. In some embodiments, the compression ratio of the engine described herein can be about 15, about 16, about 17, about 18, about 19, about 20, about 21, about 22, about 23, about 24, or about 25.

[0036]

[0041] In some embodiments, the low cetane number fuel described herein can have a cetane number of at least about 1, at least about 5, at least about 10, at least about 15, at least about 20, or at least about 25. In some embodiments, the low cetane number fuel described herein can have a cetane number of about 30 or less, about 25 or less, about 20 or less, about 15 or less, about 10 or less, or about 5 or less. Combinations of the cetane number ranges referenced above (e.g., at least about 1 and about 30 or less or at least about 10 and about 20 or less) are also possible, including all values and ranges therebetween. In some embodiments, the low cetane number fuel described herein can have a cetane number of about 1, about 5, about 10, about 15, about 20, about 25, or about 30.

[0037]

[0042] In some embodiments, the fuel may be injected earlier in the cycle than is typical for MCCI operation. In a typical gasoline SI engine, the fuel is injected earlier in the cycle than in a CI engine. This early injection results in a more homogeneous air-fuel mixture. Given the highly reliable ignition source provided by the spark plug, the air-fuel mixture need not be as inhomogeneous as in standard MCCI operation. Further, the high compression ratio of the CI engine can facilitate vaporization, mixing, and spark-assisted flame propagation. However, a completely homogeneous air-fuel mixture may not be desirable during cold start. As described herein, a completely homogeneous air-fuel mixture will have difficulty igniting at low temperatures. This can be due to the lack of fuel-rich pockets in the air-fuel mixture and / or the lack of thermal energy in the air-fuel mixture. Conversely, a completely homogeneous air-fuel mixture can experience knock if the temperature rapidly becomes high enough.

[0038]

[0043] In some embodiments, as the temperature in the combustion chamber 250 increases, fine-tuning of the parameters of the SACI implementation can assist in achieving efficient engine performance and reducing knock. Changing the injection timing and the degree of homogeneity of the air-fuel mixture during the progression of the SACI regime is a potential strategy for achieving this effect. These changes can also enable a transition to an HCCI-type combustion strategy (where combustion is initiated by compression rather than by a spark plug) by varying the degree of stratification to limit out-of-time auto-ignition (i.e., knock). Also, a greater homogeneity of the fuel can result in a more efficient and complete fuel combustion. In some embodiments, the timing of the spark plug may be configured to fire only while the combustion chamber 250 is closed, thereby controlling the time at which spark ignition can occur. In some embodiments, a temperature sensor (not shown) anywhere within the combustion chamber 250 or within the air / exhaust treatment system can be used to control this timing scheme. In some embodiments, the air-fuel mixture within the combustion chamber 250 can be non-stoichiometric.

[0039]

[0044] In some embodiments, fuel may be injected throughout the intake stroke during cold start. In some embodiments, fuel may be injected during cold start, partially in the intake stroke and partially in the compression stroke. In some embodiments, fuel may be injected at an engine crank angle between about 0° and about 360° during cold start. In some embodiments, fuel may be injected at an engine crank angle of at least about 0° (i.e., after the start of the intake stroke), at least about 10°, at least about 20°, at least about 30°, at least about 40°, at least about 50°, at least about 60°, at least about 70°, at least about 80°, at least about 90°, at least about 100°, at least about 110°, at least about 120°, at least about 130°, at least about 140°, at least about 150°, at least about 160°, at least about 170°, at least about 180° (i.e., after the start of the compression stroke), at least about 190°, at least about 200°, at least about 210°, at least about 220°, at least about 230°, at least about 240°, at least about 250°, at least about 260°, at least about 270°, at least about 280°, at least about 290°, at least about 300°, or at least about 310° during cold start. In some embodiments, fuel may be injected at an engine crank angle of about 320° or less, about 310° or less, about 300° or less, about 290° or less, about 280° or less, about 270° or less, about 260° or less, about 250° or less, about 240° or less, about 230° or less, about 220° or less, about 210° or less, about 200° or less, about 190° or less, about 180° or less (i.e., before the start of the compression stroke), about 170° or less, about 160° or less, about 150° or less, about 140° or less, about 130° or less, about 120° or less, about 110° or less, about 100° or less, about 90° or less, about 80° or less, about 70° or less, about 60° or less, about 50° or less, about 40° or less, about 30° or less, about 20° or less, or about 10° or less during cold start. Combinations of the crank angles of fuel injection during cold start referred to above (e.g., at least about 0° and about 320° or less or at least about 100° and about 180° or less) are also possible, including all values and ranges therebetween.In some embodiments, the fuel may be injected at an engine crank angle of about 0°, about 10°, about 20°, about 30°, about 40°, about 50°, about 60°, about 70°, about 80°, about 90°, about 100°, about 110°, about 120°, about 130°, about 140°, about 150°, about 160°, about 170°, about 180°, about 190°, about 200°, about 210°, about 220°, about 230°, about 240°, about 250°, about 260°, about 270°, about 280°, about 290°, about 300°, about 310°, or about 320° during cold start.

[0040]

[0045] In some embodiments, fuel injection during cold start may begin at a first engine crank angle and may end at a second engine crank angle. In other words, the fuel injection event during cold start may be of sufficient duration such that the engine crank angle changes significantly during that fuel injection event. In some embodiments, the fuel injection event during cold start may begin at least about 0° (i.e., after the start of the intake stroke), at least about 10°, at least about 20°, at least about 30°, at least about 40°, at least about 50°, at least about 60°, at least about 70°, at least about 80°, at least about 90°, at least about 100°, at least about 110°, at least about 120°, at least about 130°, at least about 140°, at least about 150°, at least about 160°, at least about 170°, at least about 180° (i.e., after the start of the compression stroke), at least about 190°, at least about 200°, at least about 210°, at least about 220°, at least about 230°, at least about 240°, at least about 250°, at least about 260°, at least about 270°, at least about 280°, at least about 290°, or at least about 300° of engine crank angle. In some embodiments, the fuel injection event during cold start may begin at an engine crank angle of about 310° or less, about 300° or less, about 290° or less, about 280° or less, about 270° or less, about 260° or less, about 250° or less, about 240° or less, about 230° or less, about 220° or less, about 210° or less, about 200° or less, about 190° or less, about 180° or less (i.e., before the start of the compression stroke), about 170° or less, about 160° or less, about 150° or less, about 140° or less, about 130° or less, about 120° or less, about 110° or less, about 100° or less, about 90° or less, about 80° or less, about 70° or less, about 60° or less, about 50° or less, about 40° or less, about 30° or less, about 20° or less, or about 10° or less. Combinations of the crank angles of the start of the fuel injection event during cold start referred to above (e.g., at least about 0° and about 310° or less or at least about 100° and about 180° or less) are also possible, including all values and ranges therebetween.In some embodiments, the fuel injection event at cold start may begin at an engine crank angle of about 0°, about 10°, about 20°, about 30°, about 40°, about 50°, about 60°, about 70°, about 80°, about 90°, about 100°, about 110°, about 120°, about 130°, about 140°, about 150°, about 160°, about 170°, about 180°, about 190°, about 200°, about 210°, about 220°, about 230°, about 240°, about 250°, about 260°, about 270°, about 280°, about 290°, about 300°, or about 310°.

[0041]

[0046] In some embodiments, the fuel injection event during cold start may end at an engine crank angle of at least about 0° (i.e., after the start of the intake stroke), at least about 10°, at least about 20°, at least about 30°, at least about 40°, at least about 50°, at least about 60°, at least about 70°, at least about 80°, at least about 90°, at least about 100°, at least about 110°, at least about 120°, at least about 130°, at least about 140°, at least about 150°, at least about 160°, at least about 170°, at least about 180° (i.e., after the start of the compression stroke), at least about 190°, at least about 200°, at least about 210°, at least about 220°, at least about 230°, at least about 240°, at least about 250°, at least about 260°, at least about 270°, at least about 280°, at least about 290°, at least about 300°, at least about 310°, at least about 320°, at least about 330°, at least about 340°, at least about 350°, at least about 360°, at least about 370°, or at least about 380°. In some embodiments, the fuel injection event during cold start may end at an engine crank angle of about 390° or less, about 380° or less, about 370° or less, about 360° or less, about 350° or less, about 340° or less, about 330° or less, about 320° or less, about 310° or less, about 300° or less, about 290° or less, about 280° or less, about 270° or less, about 260° or less, about 250° or less, about 240° or less, about 230° or less, about 220° or less, about 210° or less, about 200° or less, about 190° or less, about 180° or less (i.e., before the start of the compression stroke), about 170° or less, about 160° or less, about 150° or less, about 140° or less, about 130° or less, about 120° or less, about 110° or less, about 100° or less, about 90° or less, about 80° or less, about 70° or less, about 60° or less, about 50° or less, about 40° or less, about 30° or less, or about 20° or less. Combinations of the crank angles at which the fuel injection event during cold start ends, as referred to above (e.g., at least about 10° and about 390° or less or at least about 100° and about 180° or less), are also possible, including all values and ranges therebetween.In some embodiments, the fuel injection event during cold start may end at an engine crank angle of about 10°, about 20°, about 30°, about 40°, about 50°, about 60°, about 70°, about 80°, about 90°, about 100°, about 110°, about 120°, about 130°, about 140°, about 150°, about 160°, about 170°, about 180°, about 190°, about 200°, about 210°, about 220°, about 230°, about 240°, about 250°, about 260°, about 270°, about 280°, about 290°, about 300°, about 310°, about 320°, about 330°, about 340°, about 350°, about 360°, about 370°, about 380°, or about 390°.

[0042]

[0047] In some embodiments, the fuel can be injected at an injection pressure of at least about 1,000 bar during cold start. In other words, the pressure of the fuel injection device 270 while the fuel is being injected can be at least about 1,000 bar. In some embodiments, the fuel can be injected at an injection pressure of at least about 1,000 bar, at least about 1,100 bar, at least about 1,200 bar, at least about 1,300 bar, at least about 1,400 bar, at least about 1,500 bar, at least about 1,600 bar, at least about 1,700 bar, at least about 1,800 bar, at least about 1,900 bar, at least about 2,000 bar, at least about 2,100 bar, at least about 2,200 bar, at least about 2,300 bar, at least about 2,400 bar, at least about 2,500 bar, at least about 2,600 bar, at least about 2,700 bar, at least about 2,800 bar, or at least about 2,900 bar during cold start. In some embodiments, the fuel can be injected at an injection pressure of about 3,000 bar or less, about 2,900 bar or less, about 2,800 bar or less, about 2,700 bar or less, about 2,600 bar or less, about 2,500 bar or less, about 2,400 bar or less, about 2,300 bar or less, about 2,200 bar or less, about 2,100 bar or less, about 2,000 bar or less, about 1,900 bar or less, about 1,800 bar or less, about 1,700 bar or less, about 1,600 bar or less, about 1,500 bar or less, about 1,400 bar or less, about 1,300 bar or less, about 1,200 bar or less, or about 1,100 bar or less during cold start. The combinations of injection pressures during cold start referred to above (e.g., at least about 1,000 bar and about 3,000 bar or less or at least about 1,500 bar and about 2,000 bar or less) are also possible, including all values and ranges therebetween.In some embodiments, the fuel may be injected at an injection pressure of about 1,000 bar, about 1,100 bar, about 1,200 bar, about 1,300 bar, about 1,400 bar, about 1,500 bar, about 1,600 bar, about 1,700 bar, about 1,800 bar, about 1,900 bar, about 2,000 bar, about 2,100 bar, about 2,200 bar, about 2,300 bar, about 2,400 bar, about 2,500 bar, about 2,600 bar, about 2,700 bar, about 2,800 bar, about 2,900 bar, or about 3,000 bar during cold start.

[0043]

[0048] In some embodiments, a portion of the fuel injected during a fuel injection event may be injected while the intake valve 230 is open during cold start, and a portion of the fuel injected during the fuel injection event may be injected while the intake valve 230 is closed. In other words, the fuel injection event may have a sufficient duration during cold start such that a portion of the fuel injected during the fuel injection event is injected before intake valve closing (IVC) and a portion of the fuel injected during the fuel injection event is injected after IVC. In some embodiments, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, or at least about 85% of the fuel, including all values and ranges therebetween, may be injected while the intake valve 230 is closed (i.e., after IVC) during cold start. In some embodiments, about 40% or less, about 35% or less, about 30% or less, about 25% or less, about 20% or less, or about 15% or less of the fuel, including all values and ranges therebetween, may be injected while the intake valve 230 is open (i.e., before IVC) during cold start.

[0044]

[0049] In some embodiments, the fuel injection timing can change from a cold start operation to an HCCI operation (i.e., the transition period between cold start and steady state MCCI operation). In some embodiments, the fuel can be injected throughout the intake stroke during HCCI. In some embodiments, the fuel can be injected during HCCI, partially in the intake stroke and partially in the compression stroke. In some embodiments, the fuel is injected during HCCI at an engine crank angle of at least about 0° (i.e., after the start of the intake stroke), at least about 10°, at least about 20°, at least about 30°, at least about 40°, at least about 50°, at least about 60°, at least about 70°, at least about 80°, at least about 90°, at least about 100°, at least about 110°, at least about 120°, at least about 130°, at least about 140°, at least about 150°, at least about 160°, at least about 170°, at least about 180° (i.e., after the start of the compression stroke), at least about 190°, at least about 200°, at least about 210°, at least about 220°, at least about 230°, at least about 240°, at least about 250°, at least about 260°, at least about 270°, at least about 280°, at least about 290°, at least about 300°, or at least about 310°. In some embodiments, the fuel is injected during HCCI at an engine crank angle of about 320° or less, about 310° or less, about 300° or less, about 290° or less, about 280° or less, about 270° or less, about 260° or less, about 250° or less, about 240° or less, about 230° or less, about 220° or less, about 210° or less, about 200° or less, about 190° or less, about 180° or less (i.e., before the start of the compression stroke), about 170° or less, about 160° or less, about 150° or less, about 140° or less, about 130° or less, about 120° or less, about 110° or less, about 100° or less, about 90° or less, about 80° or less, about 70° or less, about 60° or less, about 50° or less, about 40° or less, about 30° or less, about 20° or less, or about 10° or less.The combinations of crank angles of fuel injection during HCCI referred to above (e.g., at least about 0° and up to about 320° or at least about 100° and up to about 180°) are also possible, including all values and ranges therebetween. In some embodiments, the fuel may be injected at an engine crank angle of about 0°, about 10°, about 20°, about 30°, about 40°, about 50°, about 60°, about 70°, about 80°, about 90°, about 100°, about 110°, about 120°, about 130°, about 140°, about 150°, about 160°, about 170°, about 180°, about 190°, about 200°, about 210°, about 220°, about 230°, about 240°, about 250°, about 260°, about 270°, about 280°, about 290°, about 300°, about 310°, or about 320° during HCCI.

[0045]

[0050] In some embodiments, fuel injection during HCCI may start at a first engine crank angle, and fuel injection during HCCI may end at a second engine crank angle. In other words, the fuel injection event during HCCI can be sufficiently long such that the engine crank angle changes significantly during that fuel injection event. In some embodiments, the fuel injection event during HCCI starts at at least about 0° (i.e., after the start of the intake stroke), at least about 10°, at least about 20°, at least about 30°, at least about 40°, at least about 50°, at least about 60°, at least about 70°, at least about 80°, at least about 90°, at least about 100°, at least about 110°, at least about 120°, at least about 130°, at least about 140°, at least about 150°, at least about 160°, at least about 170°, at least about 180° (i.e., after the start of the compression stroke), at least about 190°, at least about 200°, at least about 210°, at least about 220°, at least about 230°, at least about 240°, at least about 250°, at least about 260°, at least about 270°, at least about 280°, at least about 290°, or at least about 300° of engine crank angle. In some embodiments, the fuel injection event during HCCI starts at an engine crank angle of about 310° or less, about 300° or less, about 290° or less, about 280° or less, about 270° or less, about 260° or less, about 250° or less, about 240° or less, about 230° or less, about 220° or less, about 210° or less, about 200° or less, about 190° or less, about 180° or less (i.e., before the start of the compression stroke), about 170° or less, about 160° or less, about 150° or less, about 140° or less, about 130° or less, about 120° or less, about 110° or less, about 100° or less, about 90° or less, about 80° or less, about 70° or less, about 60° or less, about 50° or less, about 40° or less, about 30° or less, about 20° or less, or about 10° or less. Combinations of the crank angles at which the fuel injection event during HCCI starts as referenced above (e.g., at least about 0° and about 310° or less or at least about 100° and about 180° or less) are also possible, including all values and ranges therebetween.In some embodiments, the fuel injection event during HCCI may start at an engine crank angle of about 0°, about 10°, about 20°, about 30°, about 40°, about 50°, about 60°, about 70°, about 80°, about 90°, about 100°, about 110°, about 120°, about 130°, about 140°, about 150°, about 160°, about 170°, about 180°, about 190°, about 200°, about 210°, about 220°, about 230°, about 240°, about 250°, about 260°, about 270°, about 280°, about 290°, about 300°, or about 310°.

[0046]

[0051] In some embodiments, the fuel injection event during HCCI can end at an engine crank angle of at least about 0° (i.e., after the start of the intake stroke), at least about 10°, at least about 20°, at least about 30°, at least about 40°, at least about 50°, at least about 60°, at least about 70°, at least about 80°, at least about 90°, at least about 100°, at least about 110°, at least about 120°, at least about 130°, at least about 140°, at least about 150°, at least about 160°, at least about 170°, at least about 180° (i.e., after the start of the compression stroke), at least about 190°, at least about 200°, at least about 210°, at least about 220°, at least about 230°, at least about 240°, at least about 250°, at least about 260°, at least about 270°, at least about 280°, at least about 290°, at least about 300°, or at least about 310°. In some embodiments, the fuel injection event during HCCI can end at an engine crank angle of about 320° or less, about 310° or less, about 300° or less, about 290° or less, about 280° or less, about 270° or less, about 260° or less, about 250° or less, about 240° or less, about 230° or less, about 220° or less, about 210° or less, about 200° or less, about 190° or less, about 180° or less (i.e., before the start of the compression stroke), about 170° or less, about 160° or less, about 150° or less, about 140° or less, about 130° or less, about 120° or less, about 110° or less, about 100° or less, about 90° or less, about 80° or less, about 70° or less, about 60° or less, about 50° or less, about 40° or less, about 30° or less, or about 20° or less. Combinations of the crank angles at which the fuel injection event during HCCI ends, as referenced above (e.g., at least about 10° and about 320° or less or at least about 100° and about 180° or less), are also possible, including all values and ranges therebetween.In some embodiments, the fuel injection event during HCCI can end at an engine crank angle of about 10°, about 20°, about 30°, about 40°, about 50°, about 60°, about 70°, about 80°, about 90°, about 100°, about 110°, about 120°, about 130°, about 140°, about 150°, about 160°, about 170°, about 180°, about 190°, about 200°, about 210°, about 220°, about 230°, about 240°, about 250°, about 260°, about 270°, about 280°, about 290°, about 300°, about 310°, or about 320°.

[0047]

[0052] In some embodiments, a portion of the fuel injection event during HCCI can occur during the intake stroke (i.e., at an engine crank angle between 0° and 180°), and a portion of the fuel injection event during HCCI can occur during the compression stroke before an engine crank angle of 320° (i.e., at an engine crank angle between 180° and 320°). In some embodiments, at least about 40%, at least about 45%, at least about 50%, at least about 55%, or at least about 60% of the fuel injected during the fuel injection event, including all values and ranges therebetween, can be injected during the intake stroke during operation in HCCI. In some embodiments, about 60% or less, about 55% or less, about 50% or less, about 45% or less, or about 40% or less of the fuel injected during the fuel injection event, including all values and ranges therebetween, can be injected during the compression stroke during operation in HCCI.

[0048]

[0053] In some embodiments, the fuel injection timing can change from HCCI to steady state MCCI operation. In some embodiments, the fuel injection event in steady state MCCI can occur completely or substantially during the compression stroke. In some embodiments, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, or at least about 85% of the fuel injected during the fuel injection event can be injected after the engine crank angle reaches 310 degrees. In some embodiments, in steady state MCCI, the fuel injection event can end during the combustion stroke (i.e., at an engine crank angle greater than 360°).

[0049]

[0054] In some embodiments, fuel can be injected with a first fuel and a second fuel during cold start. In some embodiments, the second fuel is a different fuel from the first fuel. In some embodiments, the second fuel can be injected during HCCI operation. In some embodiments, the second fuel can be injected during steady state MCCI operation. In some embodiments, the second fuel can have a cetane number of at least about 30, at least about 35, at least about 40, at least about 45, at least about 50, or at least about 55. In some embodiments, the second fuel can have a cetane number of about 60 or less, about 55 or less, about 50 or less, about 45 or less, about 40 or less, or about 35 or less. Combinations of the cetane number values of the second fuel referred to above (e.g., at least about 30 and about 60 or less or at least about 40 and about 50 or less) are also possible, including all values and ranges therebetween. In some embodiments, the second fuel can have a cetane number of about 30, about 35, about 40, about 45, about 50, about 55, or about 60.

[0050]

[0055] In some embodiments, to reduce knocking, intake air may be throttled to lower the effective compression ratio within combustion chamber 250. While the actual compression ratio of a standard CI architecture is fixed, the effective compression ratio can be reduced by throttling the engine's intake air. A throttle plate (not shown) may partially block the air flow so that the incoming air is thinner, resulting in a less dense compressed state. Also, by reducing the amount of lift of intake valve 230 during the intake stroke, the engine ultimately takes in less air. When less air moves into combustion chamber 250, the pressure that can ultimately be achieved when the piston moves back to TDC is reduced, thereby reducing the likelihood of auto-ignition during the spark assist operation period. In addition to adjusting the lift of intake valve 230, similar results can be achieved by adjusting the timing of intake valve 230 or exhaust valve 240. Intake valve 230 may remain closed during part of the intake stroke, thereby reducing the amount of intake air. To achieve similar results, intake valve 230 may remain open during part of the compression stroke.

[0051]

[0056] In some embodiments, engine 200 may include a turbocharger (not shown). In some embodiments, engine 200 may include a supercharger (not shown). In some embodiments, engine 200 may include a turbo-compounding device. In some embodiments, air may pass through a supercharger, a turbocharger, and / or a turbo-compounding device before entering combustion chamber 250.

[0052]

[0057] In some embodiments, keeping the intake valve 230 open longer can be used in combination with the backpressure provided by the turbocharger or other exhaust control device (i.e., the Miller cycle mechanism). In some embodiments, EGR may assist in diluting the fuel mixture within the combustion chamber 250. The use of EGR may be suitable for the purpose of facilitating an increase in the temperature within the combustion chamber 250 and ultimately bringing the combustion chamber 250 to a desired steady state temperature. Also, EGR can move the air drawn in during the intake stroke to dilute the overall concentration of the fuel-air mixture and increase the energy barrier against premature auto-ignition.

[0053]

[0058] As the temperature of the CI engine 200 further increases towards the desired steady-state operating temperature, the homogeneity of the air-fuel mixture becomes less desirable. As described above, HCCI operation is optimal only within a narrow temperature range. During HCCI operation, the fuel has more time to absorb thermal energy in the combustion chamber 250 and potentially can burn substantially before TDC. In some embodiments, this event at the end of the SACI regime and during the transition through HCCI can be mitigated by adjusting the timing of the fuel injector 270 to reduce the homogeneity of the air-fuel mixture. Post-injection of fuel can achieve a similar result. Additional injection of fuel can further introduce stratification (or charge cooling) into the fuel injection to create locally rich (or cool) spots of fuel to ensure that combustion occurs in a timely manner. In some embodiments, the timing of the spark plug can be retarded to reduce the likelihood of knock by the expanding spark-ignition flame front. In some embodiments, the timing of the spark plug can be retarded until after the piston 220 has moved away from the TDC position to reduce the likelihood of knock by the expanding spark-ignition flame front. The exhaust dilution-based knock mitigation measures described herein can also reduce the engine load at high temperatures. Also, each of the knock mitigation methods with injection timing, post-injection, and EGR described herein can assist in knock mitigation when the auxiliary device 275 is a glow plug.

[0054]

[0059] When operating the CI engine 200 with a spark plug, there is a time delay between the first start of the CI engine 200 and the completion of the transition to the steady-state MCCI operation of the CI engine 200. In some embodiments, this time delay can be less than about 30 seconds, less than about 45 seconds, less than about 60 seconds, less than about 90 seconds, or less than about 120 seconds.

[0055]

[0060] In some embodiments, the auxiliary device 275 can be a plasma ignition device. Plasma ignition can function similarly to spark ignition when localized thermal energy is generated that is insufficient for a standard spark plug to produce ignition. The obstacles encountered in a plasma ignition system are similar to those in a spark-assisted compression ignition system. Plasma ignition can potentially involve adjustments to mixture stratification, ignition timing, exhaust gas recirculation (EGR) dilution, and IVC timing in order to facilitate both ignition and knock prevention as desired. When operating the CI engine 200 using a plasma ignition device, there is a time delay between the first start of the CI engine 200 and the completion of the transition to steady-state MCCI operation of the CI engine 200. In some embodiments, this time delay can be less than about 30 seconds, less than about 45 seconds, less than about 60 seconds, less than about 90 seconds, or less than about 120 seconds. In some embodiments, multiple auxiliary devices 275 may be disposed throughout the CI engine 200 or one device may inject plasma in multiple directions to simultaneously stabilize combustion in multiple regions.

[0056]

[0061] Figure 3 shows a CI engine 300 according to one embodiment. The CI engine 300 includes a cylinder 310, a piston 320 configured to move within the cylinder 310, a head deck 325, an intake valve 330, and an exhaust valve 340. The cylinder 310, the piston 320, the head deck 325, the intake valve 330, and the exhaust valve 340 collectively define a combustion chamber 350. The CI engine 300, the cylinder 310, the piston 320, the intake valve 330, the exhaust valve 340, and the combustion chamber 350 may be substantially similar to or the same as the engines 100, 200, the cylinders 110, 210, the pistons 120, 220, the intake valves 130, 230, the exhaust valves 140, 240, and the combustion chambers 150, 250 described above with reference to FIGS. 1 and 2. Therefore, the details of the specific aspects of the components of the CI engine 300 are not further detailed herein and should be considered to have the same or substantially similar shape or function as the corresponding components described above with respect to the engines 100, 200, unless the description is clearly different.

[0057]

[0062] As shown in FIG. 3, fuel injection device 370 sprays fuel along curve B toward auxiliary device 375 while piston 320 is at the TDC position or as piston 320 approaches the TDC position. In other words, auxiliary device 375 is located at the outer edge of ball region 351 of combustion chamber 350. In some embodiments, the placement of auxiliary device 375 at the outer edge of ball region 351 can induce surface ignition. Since the shape of the ball affects the spray path of fuel injection device 370, the fuel can contact auxiliary device 375 after flow B is redirected by the piston ball. In some embodiments, auxiliary device 375 can be a glow plug, a spark plug, or a plasma ignition device. General considerations regarding the operating conditions of the embodiment described in FIG. 3 are the same as those of FIG. 2. However, there will be some differences regarding the placement of auxiliary device 375. In some embodiments, the placement of auxiliary device 375 at the outer edge of ball region 351 can lead to slightly delayed ignition. When fuel particles or an air / fuel vapor mixture contact auxiliary device 375 due to the longer fuel flow path created by the placement of auxiliary device 375, this can result in the particles becoming finer, more dispersed, or more thoroughly mixed with air. Since fuel particles with a higher surface area contact more oxidizing air per unit surface area, this can lead to a more complete combustion event.

[0058]

[0063] FIG. 4 shows a CI engine 400 according to an embodiment. The CI engine 400 includes a cylinder 410, a piston 420 configured to move within the cylinder 310, a cylinder head, one or more intake valves 430, and one or more exhaust valves 440. The cylinder 410, piston 420, head deck 425, intake valve 430, exhaust valve 440, and cylinder head collectively define a combustion chamber 450. The CI engine 400, cylinder 410, piston 420, head deck 425, intake valve 430, exhaust valve 440, and combustion chamber 450 may be substantially similar to or the same as the engines 100, 200, 300, cylinders 110, 210, 310, pistons 120, 220, 320, head decks 125, 225, 325, intake valves 130, 230, 330, exhaust valves 140, 240, 340, and combustion chambers 150, 250, 350 described above with reference to FIGS. 1-3. Accordingly, the details of the specific aspects of the components of the CI engine 400 are not further detailed herein and should be considered to have the same or substantially similar shape or function as the corresponding components described above with respect to the engines 100, 200, 300, unless the description is clearly different.

[0059]

[0064] As shown in FIG. 4, the fuel injection device 470 sprays fuel along curve C while the piston 420 is at the TDC position or as the piston 420 approaches the TDC position. In some embodiments, the auxiliary device 475 is located outside the ball region 451 of the combustion chamber 450 in the squish region 453. The shape of the ball affects the spray path of the fuel injection device 370. In some embodiments, the auxiliary device 475 can be a glow plug, a spark plug, or a plasma ignition device. General considerations regarding the operating conditions of the embodiment described in FIG. 4 are the same as those of FIG. 2. However, there will be some differences regarding the arrangement of the auxiliary device 475. In some embodiments, arranging the auxiliary device 475 in the squish region 453 can reduce the possibility of surface ignition. In some embodiments, arranging the auxiliary device 475 in the squish region 453 can create a heating effect in the combustion chamber 450. The overall thermal effect and ignition impact of arranging the auxiliary device 475 in the squish region 453 may not be as clear as arranging it in the ball region 451. In some embodiments, arranging the auxiliary device 475 in the squish region 453 of the combustion chamber 450 can lead to a slightly delayed ignition. When the auxiliary device 475 aids in the initiation of ignition due to the longer fuel flow path caused by the arrangement of the auxiliary device 475, the fuel particles can be made finer and more dispersed. Since the fuel particles with a higher surface area contact more oxidation air per unit surface area, this can lead to a more complete combustion event.

[0060]

[0065] Figure 5 shows how the ignition timing can evolve with increasing engine temperature from cold start assisted combustion to HCCI operation and ultimately to steady state (i.e., unassisted) MCCI operation, according to some embodiments. The transitions presented herein can apply to any of the cold start strategies described above. The level of fuel stratification can affect the ignition timing. In the case of SACI or spark assisted MCCI, the spark timing can also affect the ignition timing. As shown in Figure 5, the curves represent the engine pressure as a function of the engine crank angle (i.e., the time or movement from the compression stroke to the combustion stroke). In this first exemplary mode, the curve with the inflection point at the lower x-axis value represents cold start and steady state MCCI operation. The curve with the inflection point at the higher x-axis value represents HCCI operation, while the inflection points along these curves represent the point at which the ignition event occurs and the pressure begins to increase. The ignition event can be a self-ignition or a spark assisted ignition event. As the engine temperature initially rises, the engine operation operates in a combustion assisted cold start strategy. In some embodiments, this strategy can control the ignition event using a spark plug. As the engine temperature increases, the spark timing has to be retarded to avoid knock, and the ignition event is shifted to a later time (right side of Figure 5). Eventually, the temperature rises to a level that enables a compression ignition event with a long ignition delay, at which point the engine begins to operate in HCCI mode without additional combustion assistance. Further temperature increase shortens the required ignition delay until it eventually reaches the point of MCCI operation (shifting the combustion back to the left side of Figure 5). There is no specific temperature or event in the combustion chamber that marks the transition from cold start to HCCI or from HCCI to steady state MCCI. Instead, the combustion evolves along a continuous spectrum as shown in Figure 5. If the engine has to sustain low load or idling for a long period, the engine may make a transition back to the assisted combustion mode and the ignition timing may be adjusted appropriately. However, in such cases, the elevated engine temperature achieved by long term operation will enable a transition back to a more rapid MCCI operation as the load demand increases.

[0061]

[0066] In some embodiments, the operating mode may vary based on the mass average temperature of the contents (e.g., air or air and fuel) inside the combustion chamber at the time of IVC (for simplicity, this temperature is referred to herein as the IVC temperature). In some embodiments, the operating mode may vary based on the mass average temperature of the air as it passes through the intake valve (for simplicity, this temperature is referred to herein as the intake temperature). In some embodiments, the engine may operate in a cold start mode when the IVC temperature and / or the intake temperature is less than about 200°C, less than about 190°C, less than about 180°C, less than about 170°C, less than about 160°C, less than about 150°C, less than about 140°C, less than about 130°C, less than about 120°C, less than about 110°C, less than about 100°C, less than about 90°C, less than about 80°C, less than about 70°C, less than about 60°C, less than about 50°C, less than about 40°C, less than about 30°C, or less than about 20°C, including all values and ranges therebetween.

[0062]

[0067] In some embodiments, the engine may transition to HCCI when the IVC temperature and / or the intake temperature reaches at least about 50°C, at least about 100°C, at least about 150°C, at least about 200°C, at least about 250°C, at least about 300°C, at least about 350°C, at least about 400°C, or at least about 450°C. In some embodiments, the engine may operate in HCCI when the IVC temperature and / or the intake temperature reaches a value of about 500°C or less, about 450°C or less, about 400°C or less, about 350°C or less, about 300°C or less, about 250°C or less, about 200°C or less, about 150°C or less, or about 100°C or less. Combinations of IVC temperature and / or intake temperature for the transitions to HCCI referenced above (e.g., at least about 50°C and about 500°C or less or at least about 100°C and about 400°C or less) are also possible, including all values and ranges therebetween. In some embodiments, the engine may transition to HCCI when the IVC temperature and / or the intake temperature reaches about 50°C, about 100°C, about 150°C, about 200°C, about 250°C, about 300°C, about 350°C, about 400°C, about 450°C, or about 500°C.

[0063]

[0068] In some embodiments, the engine can transition to steady-state MCCI operation at an IVC temperature and / or intake temperature of at least about 500°C, at least about 520°C, at least about 540°C, at least about 560°C, at least about 580°C, at least about 600°C, at least about 620°C, at least about 640°C, at least about 660°C, at least about 680°C, at least about 700°C, at least about 780°C, at least about 800°C, at least about 820°C, at least about 840°C, at least about 860°C, at least about 880°C, at least about 900°C, at least about 920°C, at least about 940°C, at least about 960°C, or at least about 980°C. In some embodiments, the engine can transition to steady-state MCCI operation at an IVC temperature and / or intake temperature of about 1,000°C or less, about 980°C or less, about 960°C or less, about 940°C or less, about 920°C or less, about 900°C or less, about 880°C or less, about 860°C or less, about 840°C or less, about 820°C or less, about 800°C or less, about 780°C or less, about 760°C or less, about 740°C or less, about 720°C or less, about 700°C or less, about 680°C or less, about 660°C or less, about 640°C or less, about 620°C or less, about 600°C or less, about 580°C or less, about 540°C or less, or about 520°C or less.

[0064]

[0069] Combinations of IVC temperatures and / or intake temperatures for the transitions to steady-state MCCI referred to above (e.g., at least about 500°C and about 1,000°C or less or at least about 600°C and about 800°C or less) are also possible, including all values and ranges therebetween. In some embodiments, the engine can transition to steady-state MCCI operation at an IVC temperature and / or intake temperature of about 500°C, about 520°C, about 540°C, about 560°C, about 580°C, about 600°C, about 620°C, about 640°C, about 660°C, about 680°C, about 700°C, about 720°C, about 740°C, about 760°C, about 780°C, about 800°C, about 820°C, about 840°C, about 860°C, about 880°C, about 900°C, about 920°C, about 940°C, about 960°C, about 980°C, or about 1,000°C.

[0065]

[0070] In some embodiments, the engine can transition from a cold start to HCCI and then from HCCI to steady-state MCCI. In some embodiments, the engine can transition directly from a cold start to steady-state MCCI.

[0066]

[0071] Figure 6 depicts a VVT scheme that may be associated with the transition of engine operation from a cold start operation to an HCCI operation and ultimately to a steady state MCCI operation, according to some embodiments. In each of the aforementioned cold start strategies, there are various ways to switch from the cold start operation to the steady state operation as quickly and efficiently as possible while reducing knock. When moving from the cold start combustion mode to the steady state MCCI combustion, VVT can facilitate this transition. Figure 6 is an example of a cam phasing approach for implementing VVT, where only the cam timing of valve opening and closing is changing. In some embodiments, the valve opening period and valve lift (i.e., valve profile) of the valve remain constant. In some embodiments, the cam timing may be adjusted with respect to the engine position, and both the intake valve profile and the exhaust valve profile are effectively shifted in the same direction by an equal amount of time. In some embodiments, the basic exhaust timing profile 601 may be the valve profile of the exhaust valve during the first cold start operation and during the steady state MCCI operation, while the basic intake timing profile 602 may be the valve profile of the intake valve during the first cold start operation and during the steady state MCCI operation. In some embodiments, the timing of the exhaust valve can be adjusted from the basic exhaust timing profile 601 to the intermediate exhaust timing profile 603 and then to the advanced exhaust timing profile 605 during the transition from cold start to HCCI or spark assisted operation. In some embodiments, the timing of the exhaust valve can be adjusted from the advanced exhaust timing profile 605 to the intermediate exhaust timing profile 603 and then to the basic exhaust timing profile 601 during the transition from spark assisted or HCCI operation to steady state MCCI operation. In some embodiments, the timing of the intake valve can be adjusted from the basic intake timing profile 602 to the intermediate intake timing profile 604 and then to the advanced intake timing profile 606 during the transition from cold start to ignition assisted or HCCI operation.In some embodiments, the intake valve timing can be adjusted from the advanced intake timing profile 606 to the intermediate intake timing profile 604 and to the base intake timing profile 602 during the transition from ignition assist to HCCI operation and to steady state MCCI operation.

[0067]

[0072] Some of the benefits of the transition from cold start to HCCI can be realized when the valve timing changes to an advanced state. First, as the intake valve closes earlier during the intake stroke, the effective compression ratio changes. This limits the amount of air drawn into the cylinder, thereby reducing the amount of piston stroke available for compression. This can reduce the amount of energy available to facilitate out-of-time auto-ignition events, or increase the energy available to shorten the ignition delay when combustion transitions back to the MCCI mode. This same effect is possible by retarding the valve timing (i.e., by closing the intake valve later), in which case compression is limited because it cannot start before the valve closes.

[0068]

[0073] In the glow plug assist mode, SACI mode, spark assist MCCI mode, and plasma ignition cold start mode, there are advantages associated with having a high initial effective compression ratio (approximately 17:1, the baseline ratio) via a valve timing profile. When the engine has warmed up to a temperature above ambient but is still below the temperature desirable for steady state operation, the aforementioned cold start methods are still practical. However, at a compression ratio near 17:1, the likelihood of knock becomes more significant with glow plug or spark assist (when there is substantial fuel air mixing and homogeneity). To mitigate this likelihood, the valve timing can be advanced in accordance with the advanced exhaust timing profile 605 and the advanced intake timing profile 606 to reduce the effective compression ratio to a value of approximately 12:1 (where higher octane fuels utilize higher compression ratios, based on the octane rating of this fuel). As the engine continues to warm, combustion can transition towards the steady state MCCI combustion mode by retarding the valve timing towards the base value. However, before reaching steady state MCCI combustion, the engine can first utilize the HCCI combustion strategy at a compression ratio from approximately 13:1 to approximately 15:1 while the valve timing is making the transition back to the base value. Using HCCI during this time window is advantageous for reducing knock and for taking advantage of the small temperature window where the efficient operation of HCCI is most practical. Finally, when the engine reaches a temperature sufficient for steady state MCCI operation, the valve profile reaches the base timing scheme and can achieve a compression ratio of approximately 17:1, which is important for steady state MCCI operation. At this point, the cold start assist method can be stopped.

[0069]

[0074] In some embodiments, when plasma ignition or an SACI device or method is employed during cold start, the IVC can be advanced (i.e., made earlier). In some embodiments, when plasma ignition or an SACI device or method is employed during cold start, the IVC can be retarded (i.e., made later). In some embodiments, when a glow plug is used to induce surface ignition during cold start, the basic valve timing (e.g., basic intake timing profile 602 and basic exhaust timing profile 601) can be used. In some embodiments, when a glow plug is used to induce surface ignition during cold start, the closing of the exhaust valve can be advanced. In some embodiments, when a glow plug is used to produce a heating effect during cold start, the basic valve timing (e.g., basic intake timing profile 602 and basic exhaust timing profile 601) can be used. In some embodiments, when a glow plug is used to produce a heating effect during cold start, the closing of the exhaust valve can be advanced. In some embodiments, when an internal or external cartridge heater is used to produce a heating effect during cold start, the basic valve timing (e.g., basic intake timing profile 602 and basic exhaust timing profile 601) can be used. In some embodiments, when an internal or external cartridge heater is used to produce a heating effect during cold start, the closing of the exhaust valve can be advanced.

[0070]

[0075] The VVT strategy can also be used to stabilize combustion over the duration of low engine load (i.e., low intake and combustion), although the thermal energy may be insufficient to sustain MCCI operation. In some embodiments, a more complex or asymmetric VVT scheme may assist in achieving the desired performance characteristics of a particular engine. Such VVT scheme strategies can function in conjunction with a spark plug, glow plug, plasma ignition, intake heater, pilot injection, or in concert with any combination of the aforementioned strategies.

[0071]

[0076] Also, the adoption of a VVT strategy can potentially regulate the energy remaining in the exhaust and the amount of exhaust available for retention and reintroduction to the intake valve. As the exhaust valve opening timing is advanced, the expulsion of exhaust through the exhaust valve occurs at an earlier stage of the expansion stroke and thus at a higher temperature (since the combustion gases experience less expansion during the expansion stroke). This higher temperature exhaust will remain available for reintroduction into the combustion chamber at the exhaust port. Applying both an advancement of the exhaust valve opening and a retardation of the exhaust valve closing (i.e., a longer valve opening period, an asymmetric VVT) can assist in reintroduction such that there is an overlap between the opening of the exhaust valve and the opening of the intake valve. Conversely, if the exhaust valve closing is advanced instead of being retarded to enable introduction, the exhaust can be trapped within the cylinder or transmitted to the intake port if the intake valve opening is also advanced. The latter enables backflow of the intake (inflow such that the trapped exhaust returns to the intake port), in which case this exhaust energy will remain in the intake until a major triggering event. Put another way, a modified valve timing can be used to utilize the additional thermal energy provided by the high temperature exhaust to assist in the ignition of subsequent engine cycles. This thermal energy can be important for HCCI combustion mode and for MCCI combustion operation at a moderate load where exhaust thermal energy is required to sustain a high temperature to facilitate steady state operation. In some embodiments, an asymmetric VVT can be employed such that, during HCCI, the exhaust valve is closed early and the intake valve is opened late.

[0072]

[0077] Further exemplary operating modes can be used for combustion phasing and valve timing. In some embodiments, the cold start strategy may start with a very late combustion phase due to the low energy in the combustion chamber. This late combustion phase can reduce the reaction rate of combustion. Also, in the case of SI combustion, the late combustion phase can reduce the time for flame propagation across the large bore engine (to avoid knocking). This can be achieved by a very early injection of fuel (direct or port) to create a premixed ignitable mixture of air and fuel that can be ignited using a spark plug.

[0073]

[0078] As the engine warms up, a transition to an auto-ignition combustion mode such as HCCI can result in a faster combustion phase and a faster and more rapid pressure rise near TDC. The homogeneity or semi-homogeneity of the air-fuel mixture allows for more rapid simultaneous combustion throughout the cylinder. The more rapid combustion results in a higher rate of pressure increase over a shorter period (as opposed to a larger spread over time, which often results in a late phase, especially during cold start). This higher rate of pressure increase can be achieved through early injection timing to create an ignitable mixture of air and fuel. The rate of pressure rise can be moderated by gradually shifting the injection timing of the direct injection device to a later stage of the compression stroke. This shift in injection timing can create stratification and a less homogeneous mixture, resulting in a larger spread of the combustion process over time, as a very high rate of pressure rise (greater than 15 bar per crank angle) can lead to undesirable engine noise.

[0074]

[0079] As the engine continues to warm up, the auto-ignition combustion can become too rapid or too early throughout the cylinder, resulting in a poor combustion phase (too early) or an unacceptable high rate of pressure increase. The high rate of pressure increase can cause NVH from the engine and may cause engine damage. Once the engine is sufficiently warm, these potential problems can be mitigated by shifting the injection timing to a later stage of the compression stroke. This shift can reduce the amount of pre-mixing before auto-ignition and allow combustion to proceed as the fuel is injected into the cylinder. Eventually, the pre-mixed fraction can become low enough, and the injection timing can become late enough to reach an injection timing and engine temperature where combustion is mixture-controlled and steady-state MCCI can be sustained. In some embodiments, a basic valve timing profile can be used during steady-state MCCI. In some embodiments, an early exhaust valve closing can be used at low load points during MCCI.

[0075]

[0080] In some embodiments, the level of pre-mixing of fuel and air just prior to ignition can vary depending on whether the engine is operating in a cold start mode, in HCCI mode, or in steady-state MCCI mode. In some embodiments, the level of pre-mixing of fuel and air just prior to ignition can vary during cold start depending on which type of ignition assist device or method is used.

[0076]

[0081] In some embodiments, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, or at least about 60% of the fuel can be pre-mixed with air just prior to ignition, including all values and ranges therebetween.

[0077]

[0082] In some embodiments, when a plasma ignition or spark-assisted compression ignition device or method is used during cold start, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, or at least about 85% of the fuel can be premixed with air immediately prior to ignition, including all values and ranges therebetween. In some embodiments, when a glow plug is used during cold start and is located in a location that induces surface ignition, at least about 40%, at least about 45%, at least about 50%, at least about 55%, or at least about 60% of the fuel can be premixed with air immediately prior to ignition, including all values and ranges therebetween. In some embodiments, when a glow plug or in-cylinder cartridge heater is used to produce a heating effect during cold start, at least about 10%, at least about 15%, at least about 20%, at least about 25%, or at least about 30% of the fuel can be premixed with air immediately prior to ignition, including all values and ranges therebetween.

[0078]

[0083] In some embodiments, during HCCI, at least about 40%, at least about 45%, at least about 50%, at least about 55%, or at least about 60% of the fuel can be premixed with air immediately prior to ignition, including all values and ranges therebetween. In some embodiments, during steady-state MCCI, 60% or less, 55% or less, 50% or less, 45% or less, or 40% or less of the fuel can be premixed with air immediately prior to ignition.

[0079]

[0084] Regarding valve timing, this additional exemplary mode can also be understood with reference to FIG. 6. In this case, combustion begins towards the right of the figure (at a late combustion phase) and rapidly shifts towards the left of the figure as autoignition begins. After autoignition has started, the phase remains near the left of the figure (the most desirable phase for efficiency) and is maintained by varying the injection timing and stratification to control the ignition delay. Such injection modifications can offset the increasingly rapid combustion dynamics with less premixing.

[0080]

[0085] Throughout cold start, transition, and up to fully developed MCCI mode, the amount of exhaust gas that is suppressed or recirculated, the engine backpressure, or the level of engine throttle can be adjusted to stabilize combustion such that catalyst light-off is achieved in an acceptable short time frame after start while conforming to acceptable levels of stability and pressure rise, as described above.

[0081]

[0086] In some embodiments, the intake valve may be opened at an engine crank angle of at least about 660°, at least about 665°, at least about 670°, at least about 675°, at least about 680°, at least about 685°, at least about 690°, at least about 695°, or at least about 700° during cold start. In some embodiments, the intake valve may be opened at an engine crank angle of about 705° or less, about 700° or less, about 695° or less, about 690° or less, about 685° or less, about 680° or less, about 675° or less, about 670° or less, or about 665° or less during cold start. Combinations of the engine crank angles for intake valve opening during cold start referenced above (e.g., at least about 660° and about 705° or less or at least about 665° and about 700° or less) are also possible, including all values and ranges therebetween. In some embodiments, the intake valve may be opened at an engine crank angle of about 660°, about 665°, about 670°, about 675°, about 680°, about 685°, about 690°, about 695°, about 700°, or about 705° during cold start.

[0082]

[0087] In some embodiments, the intake valve can be opened at an engine crank angle of at least about 680°, at least about 685°, at least about 690°, at least about 695°, at least about 700°, at least about 705°, at least about 710°, at least about 715°, at least about 720° (0°, i.e., after the start of the intake stroke), at least about 5°, at least about 10°, at least about 15°, at least about 20°, at least about 25°, at least about 30°, at least about 35°, at least about 40°, at least about 45°, at least about 50°, or at least about 55° during HCCI operation. In some embodiments, the intake valve can be opened at an engine crank angle of about 60° or less, about 55° or less, about 50° or less, about 45° or less, about 40° or less, about 35° or less, about 30° or less, about 25° or less, about 20° or less, about 15° or less, about 10° or less, about 5° or less, about 720° or less, about 715° or less, about 710° or less, about 705° or less, about 700° or less, about 695° or less, about 690° or less, about 685° or less, about 680° or less, or about 675° or less during HCCI operation. Combinations of the engine crank angles for opening the intake valve during HCCI operation referred to above (e.g., at least about 680° and / or about 60° or less or at least about 685° and about 700° or less) are also possible, including all values and ranges therebetween. In some embodiments, the intake valve can be opened at an engine crank angle of about 680°, about 685°, about 690°, about 695°, about 700°, about 705°, about 710°, about 715°, about 720°, about 5°, about 10°, about 15°, about 20°, about 30°, about 40°, about 45°, about 50°, about 55°, or about 60° during HCCI operation.

[0083]

[0088] In some embodiments, the intake valve can be closed at an engine crank angle of at least about 160°, at least about 165°, at least about 170°, at least about 175°, at least about 180°, at least about 185°, at least about 190°, at least about 195°, at least about 200°, at least about 205°, at least about 210°, at least about 215°, at least about 220°, at least about 225°, at least about 230°, at least about 235°, at least about 240°, at least about 245°, at least about 250°, or at least about 255° during a cold start. In some embodiments, the intake valve can be closed at an engine crank angle of about 260° or less, about 255° or less, about 250° or less, about 245° or less, about 240° or less, about 235° or less, about 230° or less, about 225° or less, about 220° or less, about 215° or less, about 210° or less, about 205° or less, about 200° or less, about 195° or less, about 190° or less, about 185° or less, about 180° or less, about 175° or less, about 170° or less, or about 165° or less during a cold start. Combinations of the engine crank angles for closing the intake valve during a cold start referred to above (e.g., at least about 160° and about 260° or less or at least about 180° and about 200° or less) are also possible, including all values and ranges therebetween. In some embodiments, the intake valve can be closed at an engine crank angle of about 160°, about 165°, about 170°, about 175°, about 180°, about 185°, about 190°, about 195°, about 200°, about 205°, about 210°, about 215°, about 220°, about 225°, about 230°, about 235°, about 240°, about 245°, about 250°, about 255°, or about 260° during a cold start.

[0084]

[0089] In some embodiments, the intake valve may close at an engine crank angle of at least about 140°, at least about 145°, at least about 150°, at least about 155°, at least about 160°, at least about 165°, at least about 170°, at least about 175°, at least about 180°, at least about 185°, at least about 190°, at least about 195°, at least about 200°, at least about 205°, at least about 210°, at least about 215°, at least about 220°, at least about 225°, at least about 230°, at least about 235°, at least about 240°, at least about 245°, at least about 250°, at least about 255°, at least about 260°, at least about 265°, at least about 270°, or at least about 275° during HCCI operation. In some embodiments, the intake valve may close at an engine crank angle of about 280° or less, about 275° or less, about 270° or less, about 265° or less, about 260° or less, about 255° or less, about 250° or less, about 245° or less, about 240° or less, about 235° or less, about 230° or less, about 225° or less, about 220° or less, about 215° or less, about 210° or less, about 205° or less, about 200° or less, about 195° or less, about 190° or less, about 185° or less, about 180° or less, about 175° or less, about 170° or less, about 165° or less, about 160° or less, about 155° or less, about 150° or less, about 145° or less during HCCI operation. Combinations of the engine crank angles for closing the intake valve during HCCI operation referred to above (e.g., at least about 140° and about 280° or less or at least about 200° and about 220° or less), including all values and ranges therebetween, are also possible. In some embodiments, the intake valve may close at an engine crank angle of about 140°, about 145°, about 150°, about 155°, about 160°, about 165°, about 170°, about 175°, about 180°, about 185°, about 190°, about 195°, about 200°, about 205°, about 210°, about 215°, about 220°, about 225°, about 230°, about 235°, about 240°, about 245°, about 250°, about 255°, about 260°, about 265°, about 270°, about 275°, or about 280° during HCCI operation.

[0085]

[0090] In some embodiments, the exhaust valve may be opened at an engine crank angle of at least about 460°, at least about 465°, at least about 470°, at least about 475°, at least about 480°, at least about 485°, at least about 490°, at least about 495°, at least about 500°, or at least about 505° during a cold start. In some embodiments, the exhaust valve may be opened at an engine crank angle of about 510° or less, about 505° or less, about 500° or less, about 495° or less, about 490° or less, about 485° or less, about 480° or less, about 475° or less, about 470° or less, or about 465° or less during a cold start. Combinations of the engine crank angles for opening the exhaust valve during cold start referred to above (e.g., at least about 460° and about 510° or less or at least about 470° and about 490° or less) are also possible, including all values and ranges therebetween. In some embodiments, the exhaust valve may be opened at an engine crank angle of about 460°, about 465°, about 470°, about 475°, about 480°, about 485°, about 490°, about 495°, about 500°, about 505°, or about 510° during a cold start.

[0086]

[0091] In some embodiments, the exhaust valve may open at an engine crank angle of at least about 470°, at least about 475°, at least about 480°, at least about 485°, at least about 490°, at least about 495°, at least about 500°, at least about 505°, at least about 510°, or at least about 515° during HCCI operation. In some embodiments, the exhaust valve may open at an engine crank angle of about 520° or less, about 515° or less, about 510° or less, about 505° or less, about 500° or less, about 495° or less, about 490° or less, about 485° or less, about 480° or less, or about 475° or less during HCCI operation. Combinations of engine crank angles for opening the exhaust valve during HCCI operation as referenced above (e.g., at least about 470° and about 520° or less or at least about 490° and about 510° or less) are also possible, including all values and ranges therebetween. In some embodiments, the exhaust valve may open at an engine crank angle of about 470°, about 475°, about 480°, about 485°, about 490°, about 495°, about 500°, about 505°, about 510°, about 515°, or about 520° during HCCI operation.

[0087]

[0092] In some embodiments, the exhaust valve can be closed at an engine crank angle of at least about 700°, at least about 705°, at least about 710°, at least about 715°, at least about 0°, at least about 5°, or at least about 10° during a cold start. In some embodiments, the exhaust valve can be closed at an engine crank angle of about 15° or less, about 10° or less, about 5° or less, about 720° or less, about 715° or less, about 710° or less, or about 705° or less during a cold start. Combinations of the engine crank angles for closing the exhaust valve during a cold start referred to above (e.g., at least about 700° and / or about 15° or less or at least about 700° and about 710° or less) are also possible, including all values and ranges therebetween. In some embodiments, the exhaust valve can be closed at an engine crank angle of about 700°, about 705°, about 710°, about 715°, about 720°, about 5°, about 10°, about 15°, about 20°, about 25°, about 30°, or about 35° during a cold start.

[0088]

[0093] In some embodiments, the exhaust valve may be closed at an engine crank angle of at least about 600°, at least about 605°, at least about 610°, at least about 615°, at least about 620°, at least about 625°, at least about 630°, at least about 635°, at least about 640°, at least about 645°, at least about 650°, at least about 655°, at least about 660°, at least about 665°, at least about 670°, at least about 675°, at least about 680°, at least about 685°, at least about 690°, at least about 695°, at least about 700°, at least about 705°, at least about 710°, at least about 715°, at least about 0° (720°), at least about 5°, at least about 10°, at least about 15°, at least about 20°, at least about 25°, at least about 30°, at least about 35°, at least about 40°, at least about 45°, at least about 50°, at least about 55°, at least about 60°, at least about 65°, at least about 70°, at least about 75°, at least about 80°, at least about 85°, at least about 90°, at least about 95°, at least about 100°, at least about 105°, or at least about 110° during a cold start. In some embodiments, the exhaust valve may be closed at an engine crank angle of about 115° or less, about 110° or less, about 105° or less, about 100° or less, about 95° or less, about 90° or less, about 85° or less, about 80° or less, about 75° or less, about 70° or less, about 65° or less, about 60° or less, about 55° or less, about 50° or less, about 45° or less, about 40° or less, about 35° or less, about 30° or less, about 25° or less, about 20° or less, about 15° or less, about 10° or less, about 5° or less, about 720° or less, about 715° or less, about 710° or less, about 705° or less, about 700° or less, about 695° or less, about 690° or less, about 685° or less, about 680° or less, about 675° or less, about 670° or less, about 665° or less, about 660° or less, about 655° or less, about 650° or less, about 645° or less, about 640° or less, about 635° or less, about 630° or less, about 625° or less, about 620° or less, about 615° or less, about 610° or less, or about 605° or less during a cold start.The combinations of engine crank angles for closing the exhaust valve during cold start referred to above (e.g., at least about 600° and / or about 115° or less or at least about 0° to about 10° or less) are also possible, including all values and ranges therebetween. In some embodiments, the exhaust valve may be closed at an engine crank angle of about 700°, about 705°, about 710°, about 715°, about 720°, about 725°, about 730°, about 735°, about 740°, about 745°, about 750°, about 755°, about 760°, about 765°, about 770°, about 775°, about 780°, about 785°, about 790°, about 795°, about 705°, about 710°, about 715°, about 0°, about 5°, about 10°, about 15°, about 20°, about 25°, about 30°, about 35°, about 40°, about 45°, about 50°, about 55°, about 60°, about 65°, about 70°, about 75°, about 80°, about 85°, about 90°, about 95°, about 100°, about 105°, about 110°, or about 115° during cold start.

[0089]

[0094] Shifting the timing of the exhaust valve closing during operation, or the exhaust valve closing relative to the intake valve opening, can assist in confining the exhaust in the combustion chamber or re - inhaling the exhaust into the combustion chamber. In some embodiments, the exhaust valve closing time can shift a short time after the engine starts. In some embodiments, the exhaust valve closing time can shift during cold start. In some embodiments, the exhaust valve closing time can shift during the transition from cold start to HCCI operation. In some embodiments, the exhaust valve closing time can shift during HCCI operation. In some embodiments, the exhaust valve closing time can shift during the transition from HCCI operation to steady - state MCCI operation.

[0090]

[0095] Shifting the timing of the intake valve closing during operation (i.e., where the second engine cycle occurs later than the first engine cycle, shifting the intake valve closing time between the first engine cycle and the second engine cycle) can affect the amount of air introduced into the combustion chamber and the level of compression the gas experiences after the intake valve closes. In some embodiments, the shift in the intake valve closing time can be an advance (i.e., earlier closing). In some embodiments, the advance can be at least about 20 degrees of crank angle, at least about 25 degrees of crank angle, at least about 30 degrees of crank angle, at least about 35 degrees of crank angle, at least about 40 degrees of crank angle, at least about 45 degrees of crank angle, at least about 50 degrees of crank angle, or at least about 55 degrees of crank angle. In some embodiments, the advance can be a crank angle of about 60 degrees or less, about 55 degrees or less, about 50 degrees or less, about 45 degrees or less, about 40 degrees or less, about 35 degrees or less, about 30 degrees or less, or about 25 degrees or less. Combinations of the intake valve closing advances referred to above (e.g., at least about 20 degrees of crank angle and about 60 degrees or less of crank angle or at least about 30 degrees of crank angle and about 50 degrees or less of crank angle) are also possible, including all values and ranges therebetween. In some embodiments, the intake valve advance can be about 20 degrees of crank angle, about 25 degrees of crank angle, about 30 degrees of crank angle, about 35 degrees of crank angle, about 40 degrees of crank angle, about 45 degrees of crank angle, about 50 degrees of crank angle, about 55 degrees of crank angle, or about 60 degrees of crank angle.

[0091]

[0096] In some embodiments, the shift in the intake valve closing timing can be retarded (i.e., later closing). In some embodiments, the retard can be at least about 20 degrees of crank angle, at least about 25 degrees of crank angle, at least about 30 degrees of crank angle, at least about 35 degrees of crank angle, at least about 40 degrees of crank angle, at least about 45 degrees of crank angle, at least about 50 degrees of crank angle, or at least about 55 degrees of crank angle. In some embodiments, the retard can be a crank angle of about 60 degrees or less, about 55 degrees or less, about 50 degrees or less, about 45 degrees or less, about 40 degrees or less, about 35 degrees or less, about 30 degrees or less, or about 25 degrees or less. Combinations of the intake valve closing retard angles referred to above (e.g., at least about 20 degrees of crank angle and about 60 degrees or less of crank angle or at least about 30 degrees of crank angle and about 50 degrees or less of crank angle), including all values and ranges therebetween, are also possible. In some embodiments, the intake valve retard angle can be about 20 degrees of crank angle, about 25 degrees of crank angle, about 30 degrees of crank angle, about 35 degrees of crank angle, about 40 degrees of crank angle, about 45 degrees of crank angle, about 50 degrees of crank angle, about 55 degrees of crank angle, or about 60 degrees of crank angle.

[0092]

[0097] In some embodiments, the exhaust valve closing timing can shift a short time after the engine starts. In some embodiments, the exhaust valve closing timing can shift during a cold start. In some embodiments, the exhaust valve closing timing can shift during the transition from a cold start to HCCI operation. In some embodiments, the exhaust valve closing timing can shift during HCCI operation. In some embodiments, the exhaust valve closing timing can shift during the transition from HCCI operation to steady state MCCI operation.

[0093]

[0098] In some embodiments, the shift in the exhaust valve closing time can be an advance (i.e., earlier closing). In some embodiments, the advance can be at least about 20 degrees of crank angle, at least about 25 degrees of crank angle, at least about 30 degrees of crank angle, at least about 35 degrees of crank angle, at least about 40 degrees of crank angle, at least about 45 degrees of crank angle, at least about 50 degrees of crank angle, or at least about 55 degrees of crank angle. In some embodiments, the advance can be a crank angle of about 60 degrees or less, about 55 degrees or less, about 50 degrees or less, about 45 degrees or less, about 40 degrees or less, about 35 degrees or less, about 30 degrees or less, or about 25 degrees or less. Combinations of the exhaust valve closing advances referred to above (e.g., at least about 20 degrees of crank angle and about 60 degrees or less of crank angle or at least about 30 degrees of crank angle and about 50 degrees or less of crank angle), including all values and ranges therebetween, are also possible. In some embodiments, the exhaust valve advance can be about 20 degrees of crank angle, about 25 degrees of crank angle, about 30 degrees of crank angle, about 35 degrees of crank angle, about 40 degrees of crank angle, about 45 degrees of crank angle, about 50 degrees of crank angle, about 55 degrees of crank angle, or about 60 degrees of crank angle.

[0094]

[0099] In some embodiments, the shift in the exhaust valve closing time can be a retarded angle (i.e., a later closing). In some embodiments, the retarded angle can be at least about 20 degrees of crank angle, at least about 25 degrees of crank angle, at least about 30 degrees of crank angle, at least about 35 degrees of crank angle, at least about 40 degrees of crank angle, at least about 45 degrees of crank angle, at least about 50 degrees of crank angle, or at least about 55 degrees of crank angle. In some embodiments, the retarded angle can be a crank angle of about 60 degrees or less, about 55 degrees or less, about 50 degrees or less, about 45 degrees or less, about 40 degrees or less, about 35 degrees or less, about 30 degrees or less, or about 25 degrees or less. Combinations of the exhaust valve closing retard angles referred to above (e.g., at least about 20 degrees of crank angle and about 60 degrees or less of crank angle or at least about 30 degrees of crank angle and about 50 degrees or less of crank angle), including all values and ranges therebetween, are also possible. In some embodiments, the exhaust valve retard angle can be about 20 degrees of crank angle, about 25 degrees of crank angle, about 30 degrees of crank angle, about 35 degrees of crank angle, about 40 degrees of crank angle, about 45 degrees of crank angle, about 50 degrees of crank angle, about 55 degrees of crank angle, or about 60 degrees of crank angle.

[0095]

[0100] In some embodiments, the engine can employ the strategies described herein in parallel. While each of these methods can be used independently, combinations thereof are also within the scope of the present disclosure.

[0096]

[0101] Various concepts may be embodied in one or more ways, and at least one example of this is provided. The acts performed as part of the method may be arranged in any suitable order. Accordingly, embodiments may be constructed such that the acts are performed in an order different from that illustrated, which may include performing some acts simultaneously, even if they are shown as consecutive acts in the illustrated embodiments. Stated differently, such features may not necessarily be limited to a particular order of execution, but rather any number of threads, processes, services, servers, and / or the like may perform in a continuous, asynchronous, simultaneous, parallel, concurrent, synchronous, and / or the like manner consistent with the present disclosure. Thus, some of these features may be mutually contradictory in that they cannot exist simultaneously in a single embodiment. Similarly, some features may be applicable to an innovation in one aspect and not applicable to another aspect.

[0097]

[0102] Further, the present disclosure may include other innovations not currently described. The applicant retains all rights with respect to such innovations, including the right to embody such innovations and to file additional applications, continuations, continuation-in-parts, divisional applications, and / or the like. Thus, the advantages, embodiments, examples, functional features, logical, operational, organizational, structural, topological, and / or other aspects of the present disclosure should not be considered as limitations to the present disclosure as defined by the embodiments or limitations to the equivalents of the embodiments. Depending on the desires and / or characteristics of individual and / or corporate users, database configurations and / or relational models, data types, data transmission and / or network frameworks, syntax structures, and / or the like, various embodiments of the technologies disclosed herein may be implemented to allow for many of the flexibilities and customizations described herein.

[0098]

[0103] All definitions defined and used herein are to be understood as governing the dictionary definitions, definitions in incorporated by reference documents, and / or the ordinary meaning of the defined terms.

[0099]

[0104] As used herein, particularly in the embodiments, the term "about" or "approximately" when preceding a numerical value indicates a range of plus or minus 10% of that value. When a range of values is presented, each value from one tenth of the unit of the lower limit up to and including the upper and lower limits of the range, and any other defined value or intervening value within the defined range, is included in the present disclosure, unless the context clearly dictates otherwise. It is also included in the present disclosure that the upper and lower limits of these smaller ranges may be independently included in the smaller ranges, subject to any limitations specifically excluded within the defined range. If the defined range includes one or both of the limits, the range excluding either or both of the included limits is also included in the present disclosure.

[0100]

[0105] The phrase "and / or" as used in this specification and the embodiments is to be understood as meaning "either or both" of the elements so conjoined, i.e., elements that may be present conjunctively or disjunctively in some cases. A plurality of elements listed using "and / or" are likewise to be understood as meaning "one or more" of the elements so conjoined. Other elements may optionally be present, whether or not related to the specifically identified elements by the "and / or" clause. Thus, by way of non-limiting example, when used in connection with open-ended language such as "comprising", the phrase "A and / or B" may refer, in one embodiment, to A only (optionally including elements other than B), in another embodiment, to B only (optionally including elements other than A), and in yet another embodiment, to both A and B (optionally including other elements).

[0101]

[0106] As used in this specification and the embodiments, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating the listed items, "or" or "and / or" should be construed in an inclusive sense, i.e., as being at least one but more than one of several or the listed elements, and optionally including further unlisted items. Terms such as "only one of...", "merely one of...", or when used in the embodiments, "consisting of", etc., which are not otherwise explicitly stated, refer to including only one of several or the listed elements. Generally, the term "or" as used in this specification should be construed as indicating an exclusive alternative (i.e., "either one or the other but not both") only when there are prior exclusive terms such as "any one of", "one of...", "only one of...", or "merely one of...". When used in the embodiments, "consisting essentially of" should have its ordinary meaning as used in the field of patent law.

[0102]

[0107] As used in this specification and the embodiments, the phrase "at least one" referring to an enumeration of one or more elements means at least one element selected from any one or more of the elements in the enumeration of those elements, but does not necessarily include at least one of each of the elements specifically enumerated in the enumeration of those elements, and should be understood not to exclude any combination of the elements in the enumeration of those elements. This definition allows for the optional presence of elements other than those specifically identified in the enumeration of elements referred to by the phrase "at least one", whether or not related to the specifically identified elements. Thus, as a non-limiting example, "at least one of A and B" (or equivalently "at least one of A or B", or equivalently "at least one of A and / or B") may, in one embodiment, refer to at least one, optionally more than one, A without B (and optionally including elements other than B), in another embodiment, refer to at least one, optionally more than one, B without A (and optionally including elements other than A), and in yet another embodiment, refer to at least one, optionally more than one, A and at least one, optionally more than one, B (and optionally including other elements).

[0103]

[0108] As used in this specification, the numerical definition of "crank angle" or "engine crank angle" should be understood as the crank angle with respect to the TDC position between the exhaust stroke and the intake stroke (illustrated in FIG. 6). In other words, the engine crank angle is 0° (or 720°) when the piston is at the TDC position between the exhaust stroke and the intake stroke. The engine crank angle is 360° when the piston is at the TDC position between the compression stroke and the expansion stroke. The engine crank angle is 540° when the piston is at the BDC position between the expansion stroke and the exhaust stroke. The engine crank angle is 180° when the piston is at the BDC position between the intake stroke and the compression stroke.

[0104]

[0109] In some embodiments, the term "immediately before ignition" may refer to a point in time when the engine crank angle is about 300°, about 305°, about 310°, about 315°, about 320°, about 325°, about 330°, about 335°, about 340°, about 345°, about 350°, about 355°, about 360°, about 365°, about 370°, about 375°, or about 380°, including all intervening values and ranges.

[0105]

[0110] In some embodiments, the term "immediately before ignition" may refer to a point in time prior to the time at which 5% of fuel heat release is observed. In other words, when a measurable deviation in pressure is detected indicating that exothermic fuel oxidation is occurring, the fuel may be considered ignited.

[0106]

[0111] In some embodiments, the term "valve closed" (e.g., "intake valve closed" or "exhaust valve closed") may refer to the point in time when the valve is fully seated (i.e., 0 mm valve lift). In some embodiments, the term "valve open" (e.g., "intake valve open" or "exhaust valve open") may refer to the point in time when the valve is unseated (i.e., lift > 0 mm).

[0107]

[0112] In the embodiments and in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," etc. should be understood to be open-ended, i.e., to mean including but not limited to. As described in the United States Patent Examination Handbook 2111.03, only the transitional phrases "consisting of" and "consisting essentially of" are considered closed or semi-closed transitional phrases, respectively.

[0108]

[0113] While the specific embodiments of the present disclosure have been outlined above, many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the embodiments described herein are intended to be illustrative and not limiting. Various changes can be made without departing from the spirit and scope of the present disclosure. If the methods and steps described above indicate specific events occurring in a particular order, those skilled in the art who benefit from the present disclosure will recognize that the ordering of the specific steps may be modified, and such modifications will be in accordance with variations of the present invention. Also, certain of the steps may be carried out simultaneously in a parallel process if possible, or carried out sequentially as described above. Although the embodiments have been shown and described in detail individually, it will be understood that various changes in form and detail may be made.

Claims

1. A method of operating a compression ignition engine, wherein the compression ignition engine includes an engine cylinder having an inner surface, a head surface, a piston disposed and configured to move within the engine cylinder, an intake valve, an exhaust valve, and an ignition assist device, the inner surface of the engine cylinder, the piston, the head surface, the intake valve, and the exhaust valve define a combustion chamber, and the piston and the head surface define a bowl region of the combustion chamber, the method comprising: opening the intake valve to draw a quantity of air into the combustion chamber, the quantity of air having a mass average temperature of less than about 150° C. at the instant the quantity of air passes through the intake valve; moving the piston from a bottom dead center (BDC) position to a top dead center (TDC) position within the combustion chamber at a compression ratio between about 15 and about 25; injecting a quantity of fuel at an engine crank angle between 0 degrees and 360 degrees, the fuel having a cetane number of less than about 30, the quantity of fuel and the quantity of air forming an air-fuel mixture; closing the intake valve; substantially completely combusting substantially all of the quantity of fuel; and a method.

2. The method of claim 1, wherein the ignition assist device includes a glow plug, a spark plug, and / or a plasma ignition device.

3. wherein the fuel is a first fuel, the method of claim 1, further comprising injecting a second fuel into the combustion chamber, the second fuel having a cetane number greater than about 30.

4. closing the intake valve at a first engine crank angle in a first engine cycle, the method further comprising closing the intake valve at a second engine crank angle in a second engine cycle, the second engine crank angle being earlier than the first engine crank angle by an engine crank angle greater than 40 degrees or later than the first engine crank angle by an engine crank angle greater than 40 degrees, the second engine cycle occurring after the first engine cycle.

5. The method of claim 4, further comprising adjusting the closing of the exhaust valve so that the valve timings of the intake valve and the exhaust valve are asymmetric with respect to TDC.

6. The method of claim 5, further comprising operating the compression ignition engine over a period of time such that the air-fuel mixture has a mass average temperature higher than about 400 °C at an engine crank angle of 330 degrees.

7. Closing the exhaust valve is performed at a first engine crank angle in a first engine cycle, The method further comprises closing the exhaust valve at a second engine crank angle in a second engine cycle, The second engine crank angle is earlier by an engine crank angle greater than 40 degrees or later by an engine crank angle greater than 40 degrees than the first engine crank angle, The method of claim 6, wherein the second engine cycle occurs after the first engine cycle.

8. The method of claim 7, further comprising operating the internal combustion engine over a period of time such that the air-fuel mixture has a mass average temperature higher than about 500 °C at an engine crank angle of 330 degrees.

9. The method of claim 8, further comprising closing the intake valve at an engine crank angle between 175 degrees and 255 degrees.

10. The method of claim 1, further comprising recirculating a portion of the exhaust from the exhaust valve into the combustion chamber via the intake valve.

11. The method of claim 1, wherein the ignition assist device is installed in the combustion chamber.

12. The method of claim 11, wherein the ignition assist device is installed in the ball region of the combustion chamber.

13. The method of claim 1, wherein the compression ignition engine further comprises a turbocharger, a supercharger, and / or a turbocompounding device.

14. The method of claim 13, further comprising passing the certain amount of air through the turbocharger, the supercharger, and / or the turbocompounding device before sucking the certain amount of air into the combustion chamber.

15. The method of claim 14, wherein injecting the certain amount of fuel is performed at an injection pressure of at least about 1,000 bar.

16. The method of claim 13, further comprising restricting at least a portion of a quantity of exhaust from exiting the combustion chamber.

17. The method of claim 1, further comprising operating the internal combustion engine over a period of time such that the air-fuel mixture has a mass average temperature higher than about 500°C at an engine crank angle of 330 degrees.

18. The method of claim 17, further comprising closing the intake valve at an engine crank angle between 175 degrees and 255 degrees.

19. A method of operating a compression ignition engine during cold start, wherein the compression ignition engine includes an engine cylinder having an inner surface, a head surface, a piston disposed and configured to move within the engine cylinder, an intake valve, an exhaust valve, and an ignition assist device, the inner surface of the engine cylinder, the piston, the head surface, the intake valve, and the exhaust valve define a combustion chamber, and the compression ignition engine further includes a turbocharger, a supercharger, and / or a turbocompounding device, the method comprising: passing a quantity of air through the turbocharger, the supercharger, and / or the turbocompounding device; opening the intake valve to draw the quantity of air into the combustion chamber; moving the piston from a bottom dead center (BDC) position to a top dead center (TDC) position within the combustion chamber at a compression ratio between about 15 and about 25; injecting no more than about 25% of a quantity of fuel into the combustion chamber while the intake valve is open, the fuel having a cetane number of less than about 30; closing the intake valve; injecting at least about 75% of the quantity of fuel into the combustion chamber at an injection pressure of at least about 1,000 bar while the intake valve is closed, the quantity of fuel and the quantity of air forming a fuel-air mixture; igniting a portion of the quantity of fuel; burning substantially all of the quantity of fuel; and including.

20. The method of claim 19, wherein the quantity of air has a mass average temperature of less than about 150°C at the moment the quantity of air passes through the intake valve.

21. The ignition assisting device includes a glow plug and / or a cartridge heater, the method according to claim 19.

22. The ignition assisting device contacts a part of the certain amount of fuel, the method according to claim 19.

23. The ignition assisting device includes a glow plug, a spark plug, and / or a plasma ignition device, the method according to claim 19.

24. The ignition assisting device is installed in the combustion chamber, the method according to claim 23.

25. The ignition assisting device is installed in the ball region of the combustion chamber, the method according to claim 24.

26. Further including injecting a second fuel into the combustion chamber, The second fuel has a cetane number greater than about 30, the method according to claim 19.

27. The fuel has a cetane number less than about 20, the method according to claim 19.

28. The fuel has a cetane number less than about 10, the method according to claim 27.

29. Further including recirculating a part of the exhaust from the exhaust valve into the combustion chamber through the intake valve, the method according to claim 19.

30. Further including restricting at least a part of a certain amount of exhaust from leaving the combustion chamber, the method according to claim 19.

31. A method for operating a compression ignition engine, The compression ignition engine includes an engine cylinder having an inner surface, a head surface, a piston disposed and configured to move within the engine cylinder, an intake valve, an exhaust valve, and an ignition assisting device, and the inner surface of the engine cylinder, the piston, the head surface, the intake valve, and the exhaust valve define a combustion chamber, The method includes: Opening the intake valve to suck a certain amount of air into the combustion chamber during a first period, wherein the certain amount of air has a mass average temperature of less than about 150 °C at the moment when the certain amount of air passes through the intake valve; Moving the piston from a bottom dead center (BDC) position to a top dead center (TDC) position within the combustion chamber at a compression ratio between about 15 and about 25; Injecting a certain amount of fuel into the combustion chamber, wherein the fuel has a cetane number less than about 20, and the certain amount of fuel and the certain amount of air form an air-fuel mixture; Closing the intake valve; Burning substantially all of the certain amount of fuel. A method in which at least 20% of the certain amount of fuel is premixed with the certain amount of air immediately before ignition.

32. The method according to claim 31, wherein the ignition assist device is installed in the spherical region of the combustion chamber.

33. The method according to claim 32, wherein the ignition assist device includes a glow plug, a spark plug, a plasma ignition device, and / or a cartridge heater.

34. The fuel is a first fuel, further comprising injecting a second fuel into the combustion chamber, The method according to claim 32, wherein the second fuel has a cetane number greater than about 30.

35. The method according to claim 31, wherein at least 50% of the certain amount of fuel is premixed with the certain amount of air immediately before ignition.

36. The method according to claim 35, wherein at least 75% of the certain amount of fuel is premixed with the certain amount of air immediately before ignition.

37. Closing the intake valve during the first period is performed at an engine crank angle between 175 degrees and 255 degrees, The method according to claim 31, further comprising closing the intake valve at an engine crank angle less than 175 degrees or greater than 255 degrees to suck air into the combustion chamber during a second period.

38. The method according to claim 37, further comprising closing the intake valve at an engine crank angle between about 175 degrees and about 255 degrees during a third period.

39. The method according to claim 31, wherein the fuel has a cetane number of less than about 10.

40. The method according to claim 31, wherein the compression ignition engine further comprises a turbocharger, a supercharger, and / or a turbocompounding device.

41. The method according to claim 40, further comprising passing the certain amount of air through the turbocharger, the supercharger, and / or the turbocompounding device before sucking the certain amount of air into the combustion chamber.

42. The method according to claim 41, wherein injecting the certain amount of fuel is performed at an injection pressure of at least about 1,000 bar.

43. The method according to claim 41, further comprising restricting at least a portion of a certain amount of exhaust gas from exiting the combustion chamber.

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