Hydrogen opposed piston engine

Abstract

The opposed piston engine is configured to use hydrogen fuel. The opposed piston engine has at least one cylinder and a pair of pistons arranged for counter movement within the bore of the cylinder. Hydrogen fuel is side injected directly into the cylinder during the compression stroke of the opposed piston engine, mixed with charge air in the cylinder, and auto-ignited in a combustion chamber formed in the cylinder between the pistons during the compression stroke. A method of operating a hydrogen opposed piston engine includes switching between a first ignition mode that uses an externally generated ignition impulse to ignite the hydrogen fuel and charge air mixture and a second ignition mode that uses compression to ignite the mixture.

Description

[Technical field]

[0001] The field includes opposed-piston engines, and more particularly, the field includes opposed-piston engines configured to burn hydrogen fuel. [Background technology]

[0002] Two-stroke cycle opposed-piston engines have advantages that allow for greater efficiency than conventional four-stroke engines. For example, opposed-piston engines have a lower surface area to volume ratio, which results in less heat loss than four-stroke engines. In addition, the two-stroke operation of the engine inherently reduces the mean effective cylinder pressure, thereby allowing for faster combustion without creating excessive mechanical stresses. Furthermore, the air handling system of the opposed-piston system allows for complete control of the air intake by a pumping device that is decoupled from the base engine operation. Opposed-piston engines of this type are disclosed, for example, in U.S. Pat. No. 5,393,431, U.S. Pat. No. 5,493,431 and U.S. Pat. No. 5,523,636.

[0003] Opposed-piston engines of the above type typically operate by burning diesel fuel injected directly through the side of the cylinder into the combustion chamber, where it is ignited by the compression of an air-fuel mixture. The compressed mixture reaches a temperature at which the fuel ignites spontaneously without a flame or spark. Spontaneous ignition is called "autoignition" and the process of compression ignition is called "compression ignition" (CI). Such engines are sometimes referred to as direct injection compression ignition (DICI) opposed-piston engines.

[0004] Diesel combustion presents challenges with regard to emissions, particularly due to the production of greenhouse gases and soot. These challenges are mitigated in opposed piston engine technology by the fundamental advantages of the engine, adaptation of exhaust aftertreatment strategies, and advances in combustion technology. Nevertheless, opposed piston engine design and development add layers of technical complexity and cost issues before these solutions can be effective. Alternative combustion technologies may provide simpler and cheaper solutions to the emissions challenges without compromising the opposed piston performance advantages. For example, internal combustion engines have been adapted to run on natural gas and propane. However, these fuels contain carbon and produce undesirable emissions when burned, thereby requiring complex and costly mitigation measures. However, hydrogen is carbon-free if produced from renewable resources. It has been our key insight that the combustion of hydrogen under lean burn conditions, which are easily achieved in opposed piston engines operating by a two-stroke cycle, has the potential to significantly reduce undesirable NOx emissions. Furthermore, by using CI-initiated combustion at mid- and high-load points, hydrogen opposed-piston engines can reach levels of thermal efficiency comparable to that of fuel cells.

[0005] Compared to conventional four-stroke engines, the above type of opposed-piston engine has the ability to trap hotter exhaust products by keeping a preset amount of exhaust residue inside the cylinder. This results in the ability to autoignite the fuel at a relatively high autoignition temperature due to compression, allowing for higher compression ratios and higher thermal efficiency of opposed-piston engines. Furthermore, the lower heat loss from the lower area-to-volume ratio of opposed-piston engines also preserves more heat in the compression stroke to further raise the temperature of the trapped residue in the cylinder when both ports are closed, when the fuel-air mixture needs to be ignited. Also, the two-stroke operation of opposed-piston engines at a lower Break Mean Effective Pressure (BMEP) supports faster combustion without creating excessive mechanical stress.

[0006] There have been few proposals to date regarding the use of hydrogen fuel in opposed-piston engines. One such proposal is in U.S. Patent No. 5,399,363, entitled "Hydrogen-Powered Opposed-Piston Engine," which is commonly assigned herewith. Furthermore, little attention has been paid to optimizing hydrogen combustion for the operating conditions of the opposed-piston engine. Summary of the Invention

[0007] Hydrogen's flame speed is faster than that of other fuels, allowing faster combustion to be achieved, resulting in higher efficiency. Opposed piston engines, with their lower BMEP requirements and lower heat losses, can take advantage of hydrogen's fast combustion. The present invention is an opposed piston engine configured to run on hydrogen fuel ignited in-cylinder by temperatures above the hydrogen auto-ignition temperature. At higher load conditions, the in-cylinder temperatures of the opposed piston engine are high enough for hydrogen to auto-ignite, and the higher the temperature, the shorter the ignition delay. It is an object of the present invention to realize these advantages by compression ignition of hydrogen fuel in an opposed piston engine.

[0008] The present invention is an opposed-piston engine operating by compression ignition of hydrogen fuel in a two-stroke cycle, the engine including one or more ported cylinders, each ported cylinder being provided with one or more fuel injectors for injecting hydrogen fuel directly into a combustion chamber formed near the end of the compression stroke between opposed end faces of a pair of pistons disposed within the cylinders.

[0009] The control unit controls the operation of the engine by injecting hydrogen fuel directly into the cylinder during the compression stroke. In some examples, the direct injection may include a pilot injection of hydrogen fuel early in the compression stroke, followed by a main injection of hydrogen fuel later in the compression stroke. Here, the terms "pilot injection" and "main injection" are used in their ordinary sense to indicate an injection of a small amount of hydrogen fuel ("pilot injection") before an injection of a larger amount of hydrogen fuel ("main injection"). Stated differently, the pilot injection occurs before the combustion chamber reaches its minimum volume, and the main injection begins near the time when the combustion chamber reaches its minimum volume. In either case, the pilot injection is said to lead the main injection in that it occurs earlier in the compression stroke, as may be measured, for example, by crank angle.

[0010] The leading pilot injection can control and minimize the amount of fuel participating in the compression ignition of the main charge. The limited combustion caused by auto-ignition of the pilot charge ("pilot burn") can increase the in-cylinder temperature, thereby reducing the ignition delay of the main injection, which ignites almost instantly upon injection and burns in a diffusion flame manner during injection. The amount and timing of the pilot and main injections can be calibrated to achieve an optimal level of engine efficiency.

[0011] The duration of the pilot burn may last well into the main injection or may end before the main injection. The purpose of the pilot injection is to create an in-cylinder thermal environment that best matches the compression ignition of the hydrogen fuel main charge.

[0012] When the engine operates at low loads or when the in-cylinder temperature is insufficient to achieve auto-ignition (such as during cold start), the engine may be operated by supplying an ignition impulse from an external source ("external ignition"). In such cases, the main charge of hydrogen fuel is injected earlier in the compression cycle so that it has more time to be distributed and ignited by the externally supplied ignition impulse. To accommodate such cases, one or more igniters may be positioned against the cylinder wall to deliver an ignition impulse to the combustion chamber that ignites the hydrogen fuel. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a preferred embodiment of a hydrogen opposed piston engine of the present invention.

[0014] [Figure 2A] 4 is a graph showing the timing of hydrogen injection, external ignition, and combustion according to a first operating mode of the hydrogen opposed piston engine of the present invention.

[0015] [Figure 2B] 4 is a graph showing the timing of hydrogen injection, external ignition, and combustion according to a second operating mode of the hydrogen opposed piston engine of the present invention.

[0016] [Diagram 3] 4 is a flow chart showing an algorithm for controlling the hydrogen opposed piston engine of the present invention.

[0017] [Figure 4] FIG. 2 is a schematic diagram showing a second embodiment of a hydrogen opposed piston engine of the present invention.

[0018] [Figure 5A] FIG. 5B shows in-cylinder temperature mapped versus engine speed and engine load for a conventional four-stroke engine (FIG. 5A). [Figure 5B]1 shows in-cylinder temperatures mapped with respect to engine speed and engine load for a two-stroke cycle opposed-piston engine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The terms "hydrogen" and "hydrogen fuel" as used herein and in the appended claims are not intended to refer solely to a fuel composition consisting of pure hydrogen (H2). Rather, given that means of producing fuel-grade hydrogen and tolerating additives are currently available and evolving, hydrogen fuel may contain H2 as well as various impurities and / or additives. Thus, the terms "hydrogen" and "hydrogen fuel" are used interchangeably herein to mean a fuel that may contain 100% H2 or less than 100% H2, for example, hydrogen fuel may contain 95%-100% H2.

[0020] An opposed-piston engine cylinder has ports through its sidewall for the flow of gases into and out of the cylinder's bore. Such a cylinder is a "ported cylinder." An opposed-piston engine ported cylinder typically includes intake and exhaust ports cast, machined, or otherwise formed in the respective exhaust and intake portions of its sidewall. A ported cylinder may be configured as an element of a parent bore engine structure or as a liner (sometimes called a "sleeve") that is received within an engine block to form a cylinder. One or more fuel injectors are disposed between the intake and exhaust ports and inject one or more jets of hydrogen fuel directly through the sidewall and into the cylinder along a path transverse to the cylinder's longitudinal axis ("direct side injection").

[0021] One embodiment of a hydrogen fueled opposed piston engine according to the present invention is shown in FIG. 1. A preferred embodiment includes a two-stroke cycle, uniflow scavenged opposed piston engine 10 configured to burn hydrogen fuel. The engine 10 includes a ported cylinder 12 having a bore 13 and two ports for the flow of gases. For example, the opposed piston 10 may include one ported cylinder, two ported cylinders, or three or more ported cylinders. The ported cylinder 12 takes in air through an intake port 14 formed in an intake section including one end and exhausts exhaust gases through an exhaust port 16 formed in an exhaust section including the other end. The intake port 14 includes a circumferential array of port openings 14i in the intake section of the cylinder 12. The intake port openings 14i may be of a conventional shape to swirl air entering the cylinder within the bore. The exhaust port 16 includes a circumferential array of port openings 16e in the exhaust section of the cylinder 12. The exhaust port openings 16e may be conventionally sized and positioned to provide a sufficient amount of blowdown time to begin purging the exhaust gases from the cylinder before the intake ports open.

[0022] As shown in FIG. 1, the opposed piston engine 10 includes first and second pistons 20, 22 that are arranged for counter movement within the bore 13 with their end faces 20e, 22e facing each other. The pistons 20, 22 are so oriented so that they can reciprocate in opposite directions along the longitudinal axis of the cylinder bore 13. For convenience, the first piston 20 may be referred to as the "intake" piston since it is proximate the intake port 14. Similarly, the second piston 22 may be referred to as the "exhaust" piston since it is proximate the exhaust port 16. The intake port 14 is opened and closed in response to the intake piston 20 moving back and forth as it reciprocates through the bore between its top dead center (TC) and bottom dead center (BC) positions. The exhaust port 16 is opened and closed in response to the exhaust piston 22 moving back and forth as it reciprocates through the bore between its top dead center (TC) and bottom dead center (BC) positions.

[0023] The pistons of an opposed piston engine are coupled to at least one crankshaft. In some cases, the pistons are connected to a single crankshaft by a rocker arm linkage. Preferably, as in FIG. 1, a hydrogen fueled opposed piston engine 10 includes two crankshafts 30 and 32, with the intake piston 20 connected to the crankshaft 30 by a linkage 21 and the exhaust piston 22 connected to the crankshaft 32 by a linkage 23. Often, the crankshafts are connected by a gear train or equivalent means so that they rotate together in synchronism. In some other cases, the crankshafts may not be mechanically connected, but may synchronize their rotation by other means.

[0024] The operation of the hydrogen opposed piston engine 10 is based on a two-stroke cycle, where the engine completes one cycle of operation with one complete revolution of the crankshaft and two strokes of the pistons connected to the crankshaft. The two strokes are shown as the power stroke and the compression stroke. Each of the opposed pistons 20, 22 moves between a respective BC (bottom dead center) position in the cylinder 12 closest to one end of the cylinder and a respective TC (top dead center) position in the cylinder furthest from the end. During the power stroke, the pistons are driven from their TC positions toward their BC positions by the combustion of fuel between their end faces. During the compression stroke, the pistons are pushed from their BC positions toward their TC regions by the rotation of the crankshaft to which they are attached. The intake and exhaust ports 14, 16 are located near the respective BC positions of the intake and exhaust pistons. Each of the opposed pistons 20, 22 controls a respective one of the ports 14, 16, opening the port as it approaches its BC position and closing the port as it moves away from its BC position.

[0025] There may be a phase offset between the rotation of the crankshaft 30 and the rotation of the crankshaft 32. For example, the crankshaft 32 may lead the crankshaft 30. Such a phase offset causes the movement of the exhaust piston 22 to lead the movement of the intake piston 20 during each two-stroke cycle of the engine. Thus, near the end of the power stroke, the movement of the exhaust piston 22 opens the exhaust port 16 before the movement of the intake piston 20 opens the intake port 14. This causes the exhaust gases to begin to flow out of the cylinder 12 before the air begins to flow into the cylinder 12. This initial discharge of the exhaust gases is called "blowdown". For a short time, after blowdown, both ports are open and air enters the intake port 14 at a higher intake pressure than the exhaust pressure felt at the exhaust port 16. This pressure difference causes the exhaust gases to continue to flow out of the exhaust port. This discharge of the exhaust gases by the air is called "scavenging" or "gas exchange". Gases flow through the cylinder in one direction ("uniflow") from the intake port to the exhaust port, and this displacement of exhaust gases by air is referred to as "uniflow scavenging." Shortly after the start of the compression stroke, the intake port 14 and exhaust port 16 close, trapping air within the ported cylinder 12 for the remainder of the compression stroke.

[0026] As the pistons 20, 22 move together and apart during an engine operating cycle, maximum and minimum volumes occur between their end faces. Maximum volume is defined as the cylinder volume contained between the piston end faces 20e, 22e as the pistons move (simultaneously or sequentially) from BC, which occurs when the pistons are furthest apart. Minimum volume is defined as the cylinder volume contained between the end faces 20e, 22e when the pistons are closest to each other. A representative minimum volume zone of bore 13 is represented by shading in FIG. 1.

[0027] As shown in FIG. 1, the engine 10 is provided with an intake channel 40 that carries intake air to the intake port 14 and an exhaust channel 42 that receives exhaust gases discharged through the exhaust port 16. A compressor 44 is disposed in the intake channel 40 upstream of the intake port 14, and a turbine 45 is disposed in the exhaust channel 42 downstream of the exhaust port 16. The compressor 44 and the turbine 45 are mechanically coupled by a rotatable shaft 47. The compressor 44, the turbine 45 and the rotatable shaft 47 together form a turbocharger arrangement 48. The turbocharger arrangement 48 operates in response to exhaust gases flowing from the exhaust port 16 through the exhaust channel 42 to rotate the turbine 45, which in turn rotates the compressor 44 via the rotatable shaft 47. As the compressor 44 rotates, atmospheric air entering the compressor 44 is pressurized and supplied to the intake channel 40. The pressurized air flowing through the intake channel 40 to the intake port 14 is referred to as "charge air," and in some cases, the charge air may include a portion of the exhaust gases produced by the engine. A preferred turbocharger arrangement 48 for a hydrogen fueled opposed-piston engine is a turbocharger with an auxiliary device in which an auxiliary device 49 connected to a rotatable shaft 47 provides power to the rotatable shaft 47. The auxiliary device enables the turbocharger arrangement 48 to augment the supply of charge air in response to torque demands to speed up the response of the turbine. The auxiliary device 49 may include any turbocharger auxiliary mechanism. For example, the power may be provided to the rotatable shaft 47 via an electric motor, a hydraulic motor, a multi-speed device with a clutch connected to the crankshaft, or the like.

[0028] The amount of charge air supplied to the cylinder for scavenging and combustion is adjusted by varying the amount of power connected by the auxiliary device 49 to the turbocharger device 48. A change in the power supplied by the auxiliary device 49 changes the speed of the compressor 44, which changes the mass flow rate of charge air supplied to the intake ports 14 through the intake channel 40. The pressure of the mass flow rate of charge air to the intake ports 14 is referred to as the "intake pressure". The mass flow rate of exhaust gases leaving the ported cylinder 12 through the exhaust channel 42 can be controlled by varying the opening of an exhaust backpressure valve 50 located in the exhaust channel 42 downstream of the outlet of the turbine 45. The exhaust backpressure valve 50 is opened and closed by an exhaust valve actuator 51.

[0029] As shown in FIG. 1, at least one fuel injector 60 is supported or mounted on a side wall of the ported cylinder 12 and configured to inject hydrogen fuel directly into the ported cylinder 12, radially of the cylinder, between the end faces 20e and 22e. The number of fuel injectors provided for injection of hydrogen fuel in the opposed piston engine of the present invention is a matter of design choice and may call for one, two, three or more fuel injectors. At least one ignition device 62, external to the ported cylinder, is supported or mounted on a wall of the ported cylinder 12 for delivering an ignition impulse into a combustion chamber defined in the cylinder bore 13 between the piston end faces 20e, 22e. The ignition impulse ignites the mixture of charge air and hydrogen fuel in the combustion chamber. The number of ignition devices provided for igniting the mixture of charge air and hydrogen fuel in the opposed piston engine of the present invention is a matter of design choice and may call for one, two, three or more ignition devices. 1, a second fuel injector 60a and / or a second ignition device 62b is provided. The fuel injector may comprise a hydrogen injector or a poppet valve. The ignition device may comprise an electric or electronic device such as a spark plug, laser or glow plug.

[0030] An electronic engine control unit (ECU) 70 controls the operation of the auxiliary devices 49, the exhaust valve actuator 51, the fuel injector device 60, and the ignition device 62. The ECU 70 comprises a programmable device programmed to execute fueling algorithms, air and exhaust control algorithms, and ignition algorithms under various engine operating conditions. Such algorithms are embodied in control modules and maps that are part of the engine system control program executed by the ECU 70 while the hydrogen fueled opposed piston engine is operating. The ECU is programmed to determine the total charge air mass and total hydrogen fuel mass required to meet the current engine conditions (i.e., cold start, restart, idle, acceleration, deceleration). The ECU 70 achieves the determined total charge air mass by controlling the auxiliary devices 49 to adjust the speed of the compressor 44. The ECU 70 controls the injection pattern and duration of one or more fuel injectors 60 to obtain the required amount of hydrogen fuel. The amount of intake air and hydrogen fuel may be constrained by the ECU 70 to maintain the intake air / hydrogen fuel balance within a particular lambda (λ) range that ensures an optimal mix of air and hydrogen fuel under most engine operating conditions.

[0031] The ECU 70 is electrically connected to a crankshaft position sensor that provides a signal indicative of the rotation angle of one of the crankshafts 30, 32 of the hydrogen fueled opposed piston engine 10. For example, as shown in FIG. 1, the ECU 70 receives a signal from a crankshaft position sensor 72 that is indicative of the rotation angle of the crankshaft 30. Other sensors electrically connected to the ECU 70 can be used to detect various engine operating parameters. For example, an exhaust temperature sensor 73 may be provided and used to calculate or calibrate in-cylinder temperature. Using the rotation angle and other parameter values, the ECU 70 can calculate engine speed, track engine operating cycles, and perform injection and ignition operations by controlling at least one fuel injector 60 and at least one ignition device 62. For example, the ECU 70 controls the fuel injectors 60, 60a and ignition devices 62, 62a.

[0032] The hydrogen fueled opposed piston engine 10 may be provided with means that function to manage the charge components retained (trapped) in the cylinder by closing both ports. In these cases, the ECU 70 is further configured to control the trapped temperature of the cylinder, which is the average charge / gas temperature in the cylinder when the ports are closed. According to the exhaust gas retention method, exhaust gases that may be purged during scavenging are retained in the cylinder 12. The ECU 70 determines, from engine operating conditions, the amount of exhaust gases to be retained and controls the auxiliary device 49 to reduce turbocharger speed and / or operate the backpressure valve actuator 51 to adjust the position of the backpressure valve 50 to achieve the determined amount.

[0033] According to an exhaust gas recirculation (EGR) method, exhaust gas may be transferred from the exhaust channel to mix with the charge air delivered to the intake port of the cylinder. If EGR is provided, the exact EGR configuration is a matter of design choice. The EGR configuration may comprise a low pressure EGR system, a high pressure EGR system, or a hybrid EGR system. FIG. 1 shows a preferred EGR system embodiment comprising a high pressure EGR channel 65 that recirculates an adjustable portion of exhaust gas from the exhaust channel 42 to mix with the charge air in the intake channel 40. An EGR pump 66 is disposed in the high pressure EGR channel 65 to regulate the amount of exhaust gas recirculated. The ECU 70 determines the amount of exhaust gas to be recirculated from engine operating conditions and controls the EGR pump 66 to obtain the determined amount.

[0034] The hydrogen-fueled opposed-piston engine 10 uses hydrogen as fuel. Means and methods for supplying this type of fuel to the combustion chamber formed between the end faces 20e, 22e in the bore 13 are shown in FIG. 1 and will be described in detail. At least one fuel injector 60 as described above is used to inject hydrogen fuel directly into the bore 13 of the ported cylinder 12 through a side wall of the ported cylinder 12. The hydrogen fuel is supplied to the one or more fuel injectors 60 from a hydrogen fuel supply 80 through a fuel channel 82. The hydrogen fuel supply 80 is configured to supply hydrogen fuel at high pressure, for example, 700 bar or more. The supply 80 may include a fuel pressure regulator in communication with a fuel tank to deliver compressed hydrogen gas to the at least one fuel injector 60 within a regulated pressure range that is much higher than the internal pressure of the ported cylinder during the compression stroke. It may be useful to provide a device for pumping hydrogen fuel to the one or more injectors 60.

[0035] 2A includes a graph 200 illustrating an external ignition mode ("SI mode") of engine operation. Graph 200 illustrates how ECU 70 controls the timing of injection by at least one fuel injector 60, the timing of external ignition of hydrogen fuel by at least one ignition device 62, and the timing of combustion of hydrogen fuel with respect to the operation of the intake and exhaust ports of the hydrogen opposed piston engine of the present invention. The horizontal axis of the graph represents crank angle (CA) in degrees of rotation of crankshaft 30 as sensed by sensing device 72. When crankshaft 32 leads crankshaft 30 by a certain crank angle, the movement of exhaust piston 22 to BC near the end of the power stroke leads the movement of intake piston 20 to BC, and exhaust port 16 opens before intake port 14. The ECU 70 initiates fuel injection by at least one fuel injector 60 during the compression stroke of the engine operating cycle when the gas exchange process occurring early in the compression stroke is complete or near completion when both the intake port 14 and the exhaust port 16 are closed, or shortly thereafter. For timing purposes, the closure of one port may be designated as an indication of the closure of both ports. Assuming that the closure of the intake port 14 indicates the closure of both ports, following maximum volume, the internal pressure of the cylinder is low and the ECU 70 causes fuel to be directly injected by one or more fuel injectors at or shortly thereafter when both ports are closed. The injected hydrogen fuel mixes with the trapped charge air as the compression stroke continues. Near the end of the compression stroke, the hydrogen fuel is well mixed with the charge air and the ECU ignites the air / fuel mixture by initiating an ignition impulse generated by at least one ignition device 62. For example, the ignition device 62 may be controlled by the ECU 70 to generate an ignition impulse just prior to the minimum volume for combustion phasing, which corresponds to approximately 2-4 degrees CA after the minimum volume for 50% mass fraction burned for optimal efficiency.

[0036] The injection / ignition / combustion example shown in FIG. 2A can be adapted for the specific application of a hydrogen opposed piston engine. Injection need not be limited to starting only at port closure, but can start just before port closure, for example, if at least one injector device 62 is located in or on the cylinder sidewall near the shaded minimum zone of the bore 13 seen in FIG. 1. This location provides each port with sufficient distance to ensure that both ports are closed before the injected hydrogen fuel reaches them. Thus, in the broadest sense, the ECU 70 can be programmed to base injection of hydrogen fuel at port closure under conditions that allow injection to occur just before, at, or just after port closure. The injection duration is a design choice. It depends on the current speed-load point of engine operation, the injection pressure, the number and flow rate of injectors, and the cylinder pressure. In a sample case of rated power in a heavy vehicle application, the duration is 60 CA degrees.

[0037] 2B includes a graph 210 illustrating a compression ignition mode ("CI") of engine operation. The graph 210 illustrates how the ECU 70 controls the timing of hydrogen injection by at least one fuel injector 60, the timing of the autoignition of the injected hydrogen, and the timing of the combustion of hydrogen with respect to the operation of the intake and exhaust ports of the hydrogen opposed piston engine of the present invention. The horizontal axis of the graph 210 represents the crank angle (CA) in degrees of rotation of the crankshaft 30 as detected by the detection device 72. When the crankshaft 32 leads the crankshaft 30 by a certain crank angle, the movement of the piston 22 to BC will precede the movement of the piston 20 to BC, and the exhaust port 16 will open before the intake port 14. The ECU 70 causes the at least one fuel injector 60 to inject fuel during the compression stroke of the engine operation cycle, after the gas exchange process that occurs at or during maximum volume is completed, or just after the point at which both the intake port 14 and the exhaust port 16 are closed. During the compression stroke, before the in-cylinder temperature reaches the auto-ignition temperature of the hydrogen fuel, the ECU 70 initiates a pilot injection ("Pilot") of hydrogen fuel through one or more injector devices 60. As the compression stroke continues, the injected pilot mass is mixed with the charge air, typically by swirl generated by the intake port. The air / pilot fuel mixture self-ignites when the cylinder temperature reaches the auto-ignition level. Near or during the minimum volume, the ECU 70 initiates a main injection ("Main") of hydrogen fuel through one or more injector devices 60, which results in near-instantaneous ignition. The use of a pilot injection injected early during the compression stroke after port closure can control and minimize the amount of fuel involved in auto-ignition. The small burn of the pilot injection raises the in-cylinder temperature to ignite almost instantly, further reducing the ignition delay of the main injection, which burns in a diffusion flame-like manner during injection. The amount and timing of both injections may be calibrated to obtain optimal efficiency. The compression ignition mode requires sufficient hydrogen injection pressure to inject the fuel long enough to create an air-fuel mixture that will self-ignite to achieve high speed combustion.

[0038] A method of operating a hydrogen opposed piston engine in a dual mode manner by selectively switching between an external ignition mode of engine operation as in FIG. 2A and a compression ignition mode of engine operation as in FIG. 2B is shown in FIG. 3. Switching between these modes may be controlled according to the magnitude of the indicated engine load and the in-cylinder temperature. In this regard, under conditions where the indicated load is high and the in-cylinder temperature is insufficient to support compression ignition of hydrogen fuel at the indicated load, the injection and ignition devices are controlled to enable the external ignition mode of engine operation. Conversely, under conditions where the indicated load is low and the in-cylinder temperature is sufficient to support compression ignition of hydrogen fuel at the indicated load, the injectors are controlled to enable the compression ignition mode of engine operation. Given the anticipated difficulties in directly measuring in-cylinder temperature, an index such as exhaust manifold temperature may be useful to indicate in-cylinder temperature.

[0039] The method of Figure 3 is performed by an ECU 70 which determines the operating state of a hydrogen opposed piston engine and controls one or more injectors 60 and one or more ignition devices 62 to operate the engine in an external ignition mode (SI) as shown in Figure 2A, or a compression ignition mode (CI) as shown in Figure 2B, and switch between them depending on the engine operating conditions. The ECU 70 operates the engine according to the algorithm 300. First, the engine is started at step 310. As the start-up step 310 proceeds, the engine warms up and the ECU 70 transitions the engine to a predefined initial operating state 312, which preferably includes operating the engine in SI mode according to Figure 2A. From step 312, the ECU 70 determines the engine temperature (T E ) and checks the engine speed and load indicated in step 316. In step 318, the ECU 70 E is the calibrated engine temperature value (T C ) for the speeds and loads shown. E T CIf so, the ECU 70 operates the engine in CI mode (per FIG. 2B) in step 320. E For the speed and load indicated, C If so, the ECU 70 operates the engine in SI mode (per FIG. 2A) in step 322. From step 320 or step 322, the ECU proceeds to step 314. Thus, once the engine is started, the ECU 70 continuously loops through steps 314, 316, 318, 320 or 322 until engine operation stops.

[0040] A second embodiment of a hydrogen opposed-piston engine according to the invention is shown in Figure 4. The second embodiment comprises a two-stroke cycle uniflow scavenged opposed-piston engine 100 arranged to burn hydrogen fuel. The hydrogen fuelled opposed-piston engine 100 essentially corresponds in almost all respects to the hydrogen fuelled engine 10 of the first embodiment, differing only in the manner in which the intake air and exhaust gases are adjustably controlled.

[0041] As seen in FIG. 4, the ported cylinder 12 is provided with an intake channel 140 that carries air to the intake port 14 and an exhaust channel 142 that carries exhaust gases discharged through the exhaust port 16. A compressor 144 is disposed in the intake channel 140 upstream of the intake port 14, and a turbine 145 is disposed in the exhaust channel 142 downstream of the exhaust port 16. The compressor 144 and the turbine 145 are mechanically connected by a rotatable shaft 147. The compressor 144, the turbine 145 and the rotatable shaft 147 together form a turbocharger arrangement 148, in which exhaust gases flowing from the exhaust port 16 through the exhaust channel 142 rotate the turbine 145, which in turn rotates the compressor 144 via the rotatable shaft 147. As the compressor 144 rotates, atmospheric air entering the compressor 144 is pressurized and supplied to the intake channel 142. The compressed air flowing through the intake channel 142 is referred to as "charge air" and in some cases the charge air may include a portion of the exhaust gases generated by the engine. A preferred turbocharger arrangement 148 for a hydrogen-fueled opposed-piston engine 100 may include an adjustable turbine 145 having one or more integral devices that are actuated to vary the pressure across the turbine 145, thereby allowing some control of the turbocharger's speed and response. Such turbine pressure controls include variable geometry vanes and walls. Other adjustable turbine configurations may include a wastegate that is actuated to control the flow of exhaust gases to the turbine 144, which adjusts the rotational speed of the compressor. An adjustable supercharger arrangement 166 is positioned within the air channel 140 downstream of the compressor 144 and upstream of the intake port 14. A preferred configuration of the adjustable supercharger arrangement 166 may include an adjustable drive that is actuated to vary the speed of the supercharger arrangement, thereby allowing some control of the speed and response of the supercharger arrangement.The adjustable supercharger system 166 may also include a bypass valve that is actuated to control the flow of intake air through the supercharger system, allowing control of the pressure across the hydrogen fuel opposed piston 100, control of boost in response to torque demand, and control of the pressure for pumping EGR to the intake port 14.

[0042] The amount of charge air provided to the ported cylinder 12 for scavenging and combustion is regulated by control of the adjustable turbine 145 and the adjustable supercharger 166. Changing the speed of the adjustable turbine 145 changes the speed of the compressor 144, thereby changing the mass flow rate of charge air provided to the supercharger 166. Changing the speed of the adjustable supercharger 166 adjusts the mass flow rate of charge air through the intake channel 140 and into the intake port 14. The pressure of the mass flow rate of charge air into the intake port 14 is referred to as the "intake pressure."

[0043] An electronic engine control unit (ECU) 170 controls the operation of the adjustable turbocharger, adjustable supercharger 166, exhaust valve actuator 51, fuel injector 60, and ignition system 62. The ECU 170 comprises a programmable device programmed to execute fueling algorithms, air and exhaust conditioning algorithms, and ignition algorithms under various engine operating conditions. Such algorithms are embodied in control modules and maps that are part of the engine system control program executed by the ECU 170 while the hydrogen fueled opposed piston engine is operating. The ECU 170 is programmed to determine the total charge air mass and total hydrogen fuel mass required to meet the current engine conditions (i.e., cold start, restart, idle, acceleration, deceleration). The ECU 170 controls the adjustable turbine 145 to adjust the speed of the compressor 144, thereby providing a mass flow rate of charge air to the adjustable supercharger 166. The ECU 170 controls the adjustable supercharger 166 to achieve the determined total charge air mass. The ECU 170 controls the injection pattern and duration of one or more fuel injectors 60 to obtain the required amount of hydrogen fuel. The amount of intake air and hydrogen fuel is constrained by the ECU 170 to maintain the intake air / hydrogen fuel balance within a particular lambda (λ) range, thereby ensuring a desired lean mixture of air and hydrogen fuel under most engine operating conditions. The ECU 170 operates the engine 100 according to the method shown in FIG. 3.

[0044] As will become apparent with reference to this specification, important advantages provided by the hydrogen opposed piston engine according to the present invention are illustrated in Figures 5A and 5B. Each figure shows the in-cylinder temperature mapped with respect to engine speed and engine load. With reference to Figure 5A, a conventional four-stroke engine typically expels all of the hot combustion gases of the cylinder and introduces a fresh cool air (or air + EGR) charge on the intake stroke. This process makes it difficult to control the trapping temperature required for hydrogen auto-ignition, since there is minimal internal residual of high temperature, unless complex air handling systems are used in the conventional engine. One possible way to increase the trapping temperature in a conventional four-stroke engine is to introduce a large amount of uncooled EGR. However, this significantly reduces the volumetric efficiency of the engine. As a result, as seen in Figure 5A, the in-cylinder temperature of a conventional four-stroke engine is rarely high enough for compression ignition of hydrogen (shown as H2CI). Thus, conventional engines typically cannot efficiently use compression ignition for difficult to self-ignite fuels such as hydrogen, because the trapping temperature is too low. Conventional engines burning hydrogen must use spark plugs or pre-combustion chambers or dual fuel solutions over almost the entire operating range, increasing cost and complexity or affecting the maximum efficiency of the engine. As can be seen in FIG. 5B, the opposed piston engine according to the present invention can control scavenging over a wide range of engine operation, thereby controlling the cylinder confinement temperature. This allows the opposed piston engine to operate in a targeted confinement state, making it possible to use hydrogen as a fuel, which is difficult to auto-ignite. As a result, for the opposed piston engine, most of the map in FIG. 5A is H2CI capable. In contrast, as the four-stroke map in FIG. 5A shows, most of the operating range is that of a conventional four-stroke engine, which is too low for hydrogen compression ignition, and only a small portion has suitable confinement conditions (at very high loads) for hydrogen compression ignition.

[0045] In the foregoing specification, the embodiments have been described with reference to numerous specific details that may vary from implementation to implementation. Certain adaptations and modifications of the described embodiments may be made. Other embodiments may be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the appended claims. [Prior art documents] [Patent documents]

[0046] [Patent Document 1] US Patent Application Publication No. 2016 / 0138499 [Patent Document 2] US Patent Application Publication No. 2016 / 0369686 [Patent Document 3] US Patent Application Publication No. 2017 / 0204801 [Patent Document 4] US Patent Application Publication No. 2017 / 0204790 [Patent Document 5] U.S. Provisional Patent Application No. 63 / 224,721

Claims

1. An opposed piston engine, at least one ported cylinder having a bore; a pair of pistons disposed for opposite movement within said bore; an intake channel configured to convey a flow of intake air to an intake port of the cylinder; an exhaust channel configured to receive a flow of exhaust gas through an exhaust port of the cylinder; a hydrogen fuel supply device for supplying hydrogen fuel; at least one fuel injector connected to the hydrogen fuel supply and configured to inject the supplied hydrogen fuel directly into the bore of the cylinder; at least one ignition device configured to ignite a mixture of charge air and injected hydrogen in a combustion chamber defined in the bore between end faces of the pair of pistons; a control unit connected to the at least one fuel injector and the at least one ignition device, operating the at least one fuel injector to cause injection of hydrogen fuel into a maximum volume defined within the bore when the first and second pistons are furthest apart; and a control unit configured to operate the at least one ignition device to cause ignition of the mixture after injection of the hydrogen fuel; and An opposed piston engine.

2. The control unit causing a pilot injection of hydrogen fuel after the maximum volume is defined; and and further configured to cause a main charge injection of hydrogen fuel following the pilot injection of the hydrogen fuel when a minimum volume is defined between the first piston and the second piston; 2. The opposed-piston engine of claim 1, whereby said pilot and main injections auto-ignite in response to compression of the intake air.

3. 2. The opposed-piston engine of claim 1, wherein the ignition system comprises at least one spark plug positioned to ignite the mixture of charge air and injected hydrogen fuel in the combustion chamber.

4. 2. The opposed-piston engine of claim 1, wherein the control unit is configured to cause the at least one fuel injector to inject the supplied hydrogen fuel based on a closing of the intake port by the first piston.

5. 2. The opposed-piston engine of claim 1, further comprising means for diluting said mixture of charge air and injected hydrogen.

6. 5. The opposed-piston engine of claim 4, wherein the means for diluting the mixture comprises an EGR channel.

7. An opposed piston engine, at least one ported cylinder having a bore; a pair of pistons disposed for opposite movement within said bore; an intake channel for providing a flow of intake air through an intake port of the cylinder; an exhaust channel for receiving a flow of exhaust gases through an exhaust port of the cylinder; a hydrogen fuel supply device for supplying hydrogen fuel; at least one fuel injector connected to the hydrogen fuel supply and configured to inject the supplied hydrogen fuel directly into the bore of the cylinder; at least one ignition device configured to ignite a mixture of charge air and injected hydrogen in a combustion chamber defined in the bore between end faces of the pair of pistons; a control unit connected to the at least one fuel injector and the at least one ignition device, initiating injection of the supplied hydrogen fuel in response to closing of a designated one of the intake port and the exhaust port; and a control unit configured to initiate ignition of the mixture of charge air and injected hydrogen fuel using the at least one ignition device; An opposed piston engine.

8. 8. The opposed-piston engine of claim 7, wherein the control unit is further configured to initiate a pilot injection of hydrogen fuel and initiate injection of the main charge of hydrogen fuel following the pilot injection of hydrogen fuel, whereby the pilot and main injections auto-ignite in response to compression of the charge air.

9. 8. The opposed-piston engine of claim 7, wherein the at least one ignition device comprises a spark plug positioned to ignite the mixture of charge air and injected hydrogen fuel in the combustion chamber.

10. 8. The opposed-piston engine of claim 7, wherein the control unit is configured to cause the at least one fuel injector to inject the supplied hydrogen fuel based on closing of the intake port by the first piston.

11. 8. The opposed-piston engine of claim 7, further comprising means for diluting said mixture of charge air and injected hydrogen.

12. 12. The opposed-piston engine of claim 11, wherein the means for diluting the mixture comprises an EGR channel.

13. An opposed piston engine, at least one ported cylinder having a bore; a pair of pistons disposed for opposite movement within said bore; an air channel configured to provide a flow of intake air through the intake port in response to movement of a first piston of the pair of pistons through the intake port of the cylinder; an exhaust channel configured to receive a flow of exhaust gas through the exhaust port in response to movement of a second of the pair of pistons through the exhaust port of the cylinder; a fuel supply configured to supply hydrogen fuel; at least one fuel injector connected to the fuel supply and configured to inject the supplied hydrogen fuel directly into the bore of the cylinder; at least one ignition device configured to ignite a mixture of charge air and injected hydrogen in a combustion chamber defined in the bore between end faces of the pair of pistons; a control unit connected to the at least one fuel injector and to the means for regulating the intake air, using said at least one ignition device to cause external ignition of a mixture of hydrogen fuel and charge air to generate an ignition impulse within said bore; and using the at least one fuel injector to compression ignite the mixture of hydrogen fuel and charge air to provide a pilot charge injection of hydrogen fuel followed by a main charge injection of hydrogen fuel; and a control unit configured to selectively switch between a first mode of engine operation using external ignition and a second mode of engine operation using compression ignition based on engine temperature; An opposed piston engine.

14. 14. The opposed-piston engine of claim 13, wherein the exhaust channel includes an auxiliary turbocharger having a turbine disposed in the exhaust channel and a compressor disposed in the air channel.

15. 14. The opposed-piston engine of claim 13, further comprising means for diluting the mixture of charge air and injected hydrogen.

16. 14. The opposed-piston engine of claim 13, wherein the at least one ignition device comprises at least one spark plug positioned to ignite the mixture of charge air and injected hydrogen fuel in the combustion chamber.

17. 1. A method for operating an opposed-piston engine, comprising: providing a flow of intake air into a combustion chamber of the engine; injecting hydrogen fuel directly into the combustion chamber; forming a mixture of injected hydrogen fuel and intake air in the combustion chamber; igniting the mixture of injected hydrogen fuel and charge air by an externally generated ignition impulse; igniting the mixture of injected hydrogen fuel and charge air by compressing the mixture; A method comprising:

18. 20. The method of claim 17, further comprising selectively switching between a first mode of engine operation using the externally generated ignition impulse and a second mode of engine operation using compression of the air-fuel mixture based on engine temperature.

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