System and method for characterizing aged fuel for engine cold start

Abstract

The present disclosure provides "Systems and methods for characterizing aged fuel for engine cold starts". Methods and systems for characterizing aged fuel that loses volatility over time are provided. In one example, a method may include: using a predetermined fuel distillation curve to estimate a fuel vapor pressure during an engine cold start; and adjusting one or more combustion parameters based on the estimated fuel vapor pressure. Because the fuel vapor pressure is directly related to the fuel volatility, adjusting the one or more combustion parameters based on the estimated fuel vapor pressure can reduce engine performance degradation associated with aged fuel, such as lag and emissions during cold starts.

Description

Technical Field

[0001] The present description generally relates to methods and systems for controlling a vehicle engine during a cold start. Background Art

[0002] Fuel volatility may affect the starting performance of an engine that may be included in a vehicle. As an example, lower molecular weight hydrocarbons (also referred to herein as "light oils," such as one carbon methane to four carbon butane) may evaporate as the fuel ages, leaving a higher percentage of less volatile higher molecular weight hydrocarbons (also referred to herein as "heavy oils," such as seven carbon heptanes and higher carbon alkanes) in the fuel. In hybrid electric vehicle (HEV) systems, fuel aging may be exacerbated because the engine may be used intermittently and the fuel may therefore be consumed more slowly. Aged less volatile fuels (also referred to as "hysteresis fuels") may cause engine hysteresis during cold starts, resulting in vehicle emissions and customer dissatisfaction during cold starts. Therefore, various methods for adjusting combustion during cold starts to compensate for aged fuel may be used.

[0003] Huber et al. in U.S. Pat. No. 9,581,101 B2 show an example of a fuel injection control method for engine start-up that compensates for fuel age. Therein, an adaptation factor representing fuel age is determined based on a model of the fuel, the mass of fuel evaporated through the fuel tank vent, and various system temperatures (e.g., ambient temperature, engine temperature, and manifold air temperature). The adaptation factor is used to adjust the fuel injection amount and / or timing.

[0004] However, the inventors herein have recognized potential problems with such approaches, primarily due to the fact that the approaches do not take into account the chemical properties of the fuel. As an example, the amount of fuel evaporated may not be an accurate indication of the volatility of the remaining fuel. As a result, adjustments to the fuel injection amount and / or timing may not be accurate. As a result, engine lag and vehicle emissions during engine starting may not be adequately mitigated. Summary of the invention

[0005] In one example, the problem described above may be solved by a method comprising: during a cold start of an engine burning fuel, estimating a vapor pressure of fuel stored in a fuel tank via a predetermined fuel distillation curve; and adjusting combustion parameters based on the estimated vapor pressure. In this way, the fuel vapor pressure and thus the fuel volatility may be accurately estimated.

[0006] As an example, the predetermined distillation curve is selected from a plurality of predetermined fuel distillation curves included in a physics-based model. For example, the predetermined fuel distillation curve may be selected based on one or more of alcohol content, octane number, and age of the fuel. The controller may input fuel temperature and fuel tank pressure into the physics-based model to determine an estimated fuel vapor pressure, which may then be used to adjust combustion parameters, for example. In some examples, the fuel temperature is estimated based on ambient temperature, and the fuel tank pressure is estimated based on ambient pressure. The combustion parameters may include one or more of fuel injection amount, fuel injection timing, fraction of port fuel injection relative to direct fuel injection, commanded air-fuel ratio, and ignition timing. In this way, the combustion parameters may be optimized for the estimated fuel vapor pressure (and thus the reduced fuel volatility as the fuel ages), thereby reducing engine lag and vehicle emissions during engine starting.

[0007] The inventors herein have further recognized that, for example, depending on ambient conditions and the amount of time the engine has been off, ambient temperature and ambient pressure may not accurately represent fuel temperature and fuel tank pressure, respectively. Therefore, using ambient temperature and ambient pressure to estimate fuel vapor pressure may not fully optimize combustion parameters. For example, if combustion parameters are over-adjusted or under-adjusted, engine lag may still occur and / or fuel economy may be reduced, for example, depending on the specific combustion parameters and adjustments made.

[0008] Thus, as another example, a method includes: in response to an engine start request during a cold start condition, estimating volatility of fuel stored in a fuel tank using a physics-based model; determining a confidence level of the estimated volatility based on an engine inactivity duration; and adjusting an injection amount and injection timing of fuel delivered from the fuel tank to an engine based on the estimated volatility and the determined confidence level. By adjusting the injection amount and injection timing based on the determined confidence level, over-adjustment and under-adjustment may be reduced, thereby further reducing engine lag and increasing fuel economy.

[0009] It should be understood that the above summary is provided to introduce in simplified form a series of concepts that are further described in the detailed description. This is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address any disadvantages described above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 An exemplary vehicle propulsion system is schematically illustrated.

[0011] Figure 2 A schematic depiction of a fuel system and an evaporative emissions system coupled to an engine system is shown.

[0012] Figure 3 is a flow chart of an exemplary method for estimating fuel properties during an engine cold start and optimizing one or more combustion parameters based on the estimated fuel properties.

[0013] Figure 4 A block diagram illustrating a physics-based model that may be used to optimize one or more combustion parameters based on fuel volatility during an engine cold start.

[0014] Figure 5 The relationship between engine shut-off time, confidence in the estimated vapor pressure, and the degree of adjustment to the combustion parameters is shown.

[0015] Figure 6 Exemplary relationships between engine shut-off time, estimated fuel temperature range, estimated fuel vapor pressure range, and fuel injection amount are shown. DETAILED DESCRIPTION

[0016] The following description relates to systems and methods for reducing engine lag and vehicle emissions during engine cold starts. Specifically, a method for estimating vehicle systems (e.g., regarding Figure 1 and Figure 2 The system and method for determining fuel volatility in an exemplary hybrid electric vehicle system described in the specification and the like. The fuel volatility is represented by the estimated fuel vapor pressure, and a physics-based model (e.g., in Figure 4 The estimated fuel vapor pressure can be used, for example, to determine the estimated fuel vapor pressure based on the physics-based model shown in FIG. Figure 3 An exemplary method is provided for optimizing one or more combustion parameters. Figure 5 The graph illustrates how combustion parameters may be adjusted more when confidence in the estimated fuel vapor pressure is higher, as a function of the amount of time the engine has been shut down prior to an engine cold start. Figure 6 A graphical illustration of how a fuel injection amount may be determined based on an estimated fuel temperature range that decreases as the amount of time the engine has been shut down prior to an engine cold start increases.

[0017] Figure 1An exemplary vehicle system 100 is described. The vehicle system 100 includes an engine 110 and a motor 120 that burn fuel. As a non-limiting example, the engine 110 includes an internal combustion engine and the motor 120 includes an electric motor. The motor 120 can be configured to utilize or consume energy sources different from the engine 110. For example, the engine 110 can consume liquid fuel (e.g., gasoline) to produce an engine output, and the motor 120 can consume electrical energy to produce a motor output. Therefore, a vehicle having the propulsion system 100 can be referred to as a hybrid electric vehicle (HEV).

[0018] The vehicle system 100 can utilize a variety of different operating modes depending on the operating conditions encountered by the vehicle propulsion system. Some of these modes can enable the engine 110 to be maintained in an off state (e.g., set to an unactivated state) in which the combustion of fuel at the engine is suspended. For example, under selected operating conditions, when the engine 110 is deactivated, the motor 120 can propel the vehicle via the drive wheels 130, as indicated by arrow 122.

[0019] During other operating conditions, the engine 110 can be set to a deactivated state (as described above), and the motor 120 can be operated to charge the energy storage device 150. For example, the motor 120 can receive wheel torque from the drive wheel 130, as indicated by arrow 122, and can convert the kinetic energy of the vehicle into electrical energy for storage at the energy storage device 150, as indicated by arrow 124. This operation can be referred to as regenerative braking of the vehicle. Therefore, the motor 120 can act as a generator in some examples. However, in other examples, the generator 160 can alternatively receive wheel torque from the drive wheel 130, and can convert the kinetic energy of the vehicle into electrical energy for storage at the energy storage device 150, as indicated by arrow 162. As an additional example, the motor 120 can use the energy stored at the energy storage device 150 to start the engine 110 in a starting operation, as indicated by arrow 186.

[0020] During other operating conditions, the engine 110 can be operated by combusting fuel received from the fuel system 140, as indicated by arrow 142. For example, when the motor 120 is deactivated, the engine 110 can be operated to propel the vehicle via the drive wheels 130, as indicated by arrow 112. During other operating conditions, the engine 110 and the motor 120 can each be operated to propel the vehicle via the drive wheels 130, as indicated by arrows 112 and 122, respectively. A configuration in which the engine and the motor can selectively propel the vehicle can be referred to as a parallel-type vehicle propulsion system. It should be noted that in some examples, the motor 120 can propel the vehicle via a first set of drive wheels, and the engine 110 can propel the vehicle via a second set of drive wheels.

[0021] In other examples, the vehicle system 100 can be configured as a series type vehicle propulsion system, whereby the engine does not directly propel the drive wheels. Instead, the engine 110 can be operated to supply power to the motor 120, which in turn can propel the vehicle via the drive wheels 130, as indicated by arrow 122. For example, during selected operating conditions, the engine 110 can drive the generator 160 as indicated by arrow 116, which in turn can supply electrical energy to one or more of the motors 120 as indicated by arrow 114 or to the energy storage device 150 as indicated by arrow 162. As another example, the engine 110 can be operated to drive the motor 120, which in turn can act as a generator to convert the engine output into electrical energy. The electrical energy can be stored at the energy storage device 150 (for example) for later use by the motor.

[0022] The fuel system 140 may include one or more fuel tanks 144 for storing fuel on the vehicle. For example, the fuel tank 144 may store one or more liquid fuels, including (but not limited to): gasoline, diesel, and ethanol fuel. In some examples, the fuel may be stored as a mixture of two or more different fuels on the vehicle. For example, the fuel tank 144 may be configured to store a mixture of gasoline and ethanol (e.g., E10, E85, etc.) or a mixture of gasoline and methanol (e.g., M10, M85, etc.), whereby these fuels or fuel mixtures may be delivered to the engine 110 as indicated by arrow 142. Other suitable fuels or fuel mixtures may be supplied to the engine 110, where they may be burned to produce an engine output (e.g., torque). The engine output may be used to propel the vehicle (as indicated by arrow 112), or to recharge the energy storage device 150 via the motor 120 or the generator 160.

[0023] In some examples, energy storage device 150 may be configured to store electrical energy that may be supplied to other electrical loads resident on the vehicle (in addition to the motor), including cabin heating and air conditioning, engine starting, headlights, cabin audio and video systems, etc. As non-limiting examples, energy storage device 150 may include one or more batteries and / or capacitors.

[0024] Control system 190 may communicate with one or more of engine 110, motor 120, fuel system 140, energy storage device 150, and generator 160. Control system 190 may receive sensory feedback information from one or more of engine 110, motor 120, fuel system 140, energy storage device 150, and generator 160. In addition, control system 190 may send control signals to one or more of engine 110, motor 120, fuel system 140, energy storage device 150, and generator 160 in response to this sensory feedback.

[0025] The control system 190 may receive an indication of an output of the vehicle propulsion system requested by the operator from the vehicle operator 102. For example, the control system 190 may receive sensory feedback regarding the position of a pedal 192 from a pedal position sensor 194. The pedal 192 may illustratively refer to a brake pedal and / or an accelerator pedal that the vehicle operator 102 may depress. Additionally, in some examples, the control system 190 may communicate with a remote engine start receiver 195 (or transceiver) that receives a wireless signal 106 from a key fob 104 having a remote start button 105. In other examples (not shown), a remote engine start may be initiated via a cellular phone or smartphone-based system, where the user's phone sends data to a server and the server communicates with the vehicle to start the engine.

[0026] In the case of an autonomous vehicle (AV), an autonomous vehicle control system 191 included within the control system 190 may replace the operator 102 prior to start or en route during a specified trip. The AV control system 191 may provide the control system 190 with instructions and / or requested outputs of the vehicle system 100. Based on requests from the AV control system 191, the control system 190 then actuates various vehicle actuators to propel the vehicle. In the case of an AV, the vehicle system 100 may include various devices for detecting the vehicle's surroundings, such as radar, laser, GPS, odometer, and computer vision sensors. A high-level control system as part of the AV control system may interpret the sensory information to identify appropriate navigation paths as well as obstacles and related signs (e.g., speed limits, traffic signals, etc.). The AV control system 191 may also include executable instructions capable of analyzing sensory data to distinguish between different vehicles on the road, which may assist in planning a path to a desired destination; and executable instructions for parking the vehicle in a designated or detected available parking lot in combination with sensory feedback. For example, the AV control system may include executable instructions for detecting the type of road (e.g., one-way street, freeway, divided highway, etc.) or available parking lots (e.g., empty spaces with sufficient clearance for vehicles that are not prohibited based on time of day or pick-up zones, etc.).

[0027] The energy storage device 150 may periodically receive electrical energy from a power source 180 residing outside the vehicle (e.g., an external stationary power grid that is not part of the vehicle), as indicated by arrow 184. As a non-limiting example, the vehicle system 100 may be configured as a plug-in HEV (PHEV), whereby electrical energy may be supplied to the energy storage device 150 from the power source 180 via an electrical energy transmission cable 182. During a recharging operation of the energy storage device 150 from the power source 180, the electrical transmission cable 182 may electrically couple the energy storage device 150 and the power source 180. When operating the vehicle propulsion system to propel the vehicle, the electrical transmission cable 182 may be disconnected between the power source 180 and the energy storage device 150. The control system 190 may identify and / or control the amount of electrical energy stored at the energy storage device, which may be referred to as a state of charge (SOC).

[0028] In other examples, electrical transmission cable 182 may be omitted, where electrical energy may be received wirelessly at energy storage device 150 from power source 180. For example, energy storage device 150 may receive electrical energy from power source 180 via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. Thus, it should be appreciated that any suitable method may be used for recharging energy storage device 150 from a power source that does not constitute part of the vehicle. In this manner, motor 120 may propel the vehicle by utilizing an energy source other than the fuel utilized by engine 110.

[0029] In other examples, the vehicle system 100 may include one or more solar cells 108 that operate to convert incident solar radiation into electrical energy. The solar cell 108 is electrically coupled to the solar cell 30 via the charge controller 32. The solar cell 108 and the charge controller 32 operate to supply current to charge the solar cell 30. In this example, the solar cell 30 is housed in and electrically coupled to the energy storage device 150, but in other configurations, the solar cell 30 may be electrically coupled to the energy storage device 150 while being housed separately. In other configurations, the solar cell 30 may be physically and electrically isolated from the energy storage device 150. The solar cell 30 may therefore be configured to provide charge or receive charge from the energy storage device 150 depending on engine operating conditions, charge state, and battery requirements. In some examples, the solar cell 30 may be configured to independently supply charge directly to vehicle actuators and devices. In addition, in some examples, the charge controller 32 may be used to directly supply power to vehicle actuators and devices without first storing the charge in the solar cell 30.

[0030] The solar cell 108 can be mounted on any convenient exterior surface of the vehicle, such as the roof, hood, trunk, etc. However, the solar cell 108 can be mounted on the interior of the vehicle in addition or alternatively, such as on the dashboard or other passenger compartment surface near a window or interior light bulb. In general, solar cells operate to convert solar radiation incident thereon into electrical energy. In some examples, the solar cell 108 can include a series of photovoltaic cells formed of an amorphous semiconductor material such as silicon. In addition, individual photovoltaic cells can be interconnected to provide a constant flow of electrical energy to a common output cable 188, which electrically couples the solar cell 108 to the charge controller 32 and the solar cell 30. In this way, the solar cell 108 can generate electrical energy for propelling the vehicle or supplying power to one or more additional vehicle actuators and devices.

[0031] The fuel system 140 may periodically receive fuel from a fuel source residing outside the vehicle. As a non-limiting example, the vehicle system 100 may be refueled by receiving fuel via the fuel distribution device 170, as indicated by arrow 172. In some examples, the fuel tank 144 may be configured to store the fuel received from the fuel distribution device 170 until the fuel is supplied to the engine 110 for combustion. In some examples, the control system 190 may receive an indication of the level of fuel stored in the fuel tank 144 via a fuel level sensor. The level of fuel stored in the fuel tank 144 (e.g., identified by the fuel level sensor) may be communicated to the vehicle operator, for example, via a fuel gauge or indication in a vehicle dashboard (e.g., a message center) 196.

[0032] The vehicle system 100 may also include an ambient temperature sensor 198 and roll stability control sensors (e.g., lateral and / or longitudinal and / or yaw rate sensors 199). The vehicle instrument panel 196 may include indicator lights and / or a text-based display in which messages are displayed to the operator. The vehicle instrument panel 196 may also include various input devices for receiving operator input, such as buttons, touch screens, voice input / recognition, etc. For example, the vehicle instrument panel 196 may include a fuel fill button 197 that the vehicle operator may manually actuate or press to initiate a fuel fill.

[0033] The control system 190 can be communicatively connected to other vehicles or infrastructure using appropriate communication technology. For example, the control system 190 can be connected to other vehicles or infrastructure via a wireless network 131, which may include Wi-Fi, Bluetooth, cellular service types, wireless data transfer protocols, etc. The control system 190 can broadcast (and receive) information about vehicle data, vehicle diagnostics, traffic conditions, vehicle location information, vehicle operating procedures, etc. via vehicle-to-vehicle (V2V), vehicle-to-infrastructure-to-vehicle (V2I2V) and / or vehicle-to-infrastructure (V2I or V2X) technology. The information exchanged between vehicles can be transmitted directly between vehicles or can be multi-hop. In some examples, longer-range communications (e.g., WiMax) can be used to replace V2V or V2I2V or in conjunction with V2V or V2I2V to extend the coverage area by several miles. In other examples, the vehicle control system 190 can be communicatively connected to other vehicles or infrastructure via a wireless network 131 and the Internet (e.g., cloud).

[0034] The vehicle system 100 may also include an onboard navigation system 132 (e.g., a global positioning system) with which the operator of the vehicle can interact. The navigation system 132 may include one or more position sensors for assisting in estimating vehicle speed, vehicle altitude, vehicle location / position, etc. This information may additionally be used to infer engine operating parameters, such as local barometric pressure. As discussed above, the control system 190 may be further configured to receive information via the Internet or other communication networks. The information received from the GPS may be cross-referenced with information available via the Internet to determine local weather conditions, local vehicle regulations, etc.

[0035] Figure 2 A schematic depiction of an engine system 208 that may be included in the vehicle system 100 is shown. Figure 1The same components introduced in the above are numbered the same and may not be introduced again. The engine system 208 is shown as including an engine 110 having a plurality of cylinders 230. The engine 110 may include an engine intake system 223 and an engine exhaust system 225. The engine intake system 223 may include an intake throttle 262 fluidly coupled to an intake manifold 244 via an intake passage 242. Air may be delivered to the intake throttle 262 after passing through an air filter 252 coupled to the intake passage 242 upstream of the intake throttle 262. The engine exhaust system 225 includes an exhaust manifold 248 leading to an exhaust passage 235, which delivers exhaust gas to the atmosphere. The engine exhaust system 225 may include one or more emission control devices 270 installed in a close coupling position. The one or more emission control devices may include a three-way catalyst, a lean NOx trap, a particulate filter (e.g., a diesel particulate filter or a gasoline particulate filter), an oxidation catalyst, etc. It will be appreciated that other components may be included in the engine, such as various valves and sensors, as further described herein. In some embodiments where the engine system 208 is a supercharged engine system, the engine system may also include a boosting device, such as a turbocharger (not shown).

[0036] Knock sensor 290 may be coupled to various locations in engine 110, including the engine block. The output of knock sensor 290 may be used to indicate abnormal combustion events in cylinder 230 and the remaining cylinders included in engine 110. In one example, based on the output of knock sensor 290 in one or more defined windows (e.g., crank angle timing windows), abnormal combustion due to one or more of knock and pre-ignition may be identified and distinguished. For example, knock may be identified in response to a knock sensor output obtained in a knock window being higher than a knock threshold, while pre-ignition may be identified in response to a knock sensor output obtained in a pre-ignition window being higher than a pre-ignition threshold. For example, the pre-ignition threshold may be higher than the knock threshold, and the pre-ignition window may be earlier than the knock window. In some examples, the knock sensor output may be combined with the output of a crankshaft acceleration sensor to identify one or more of knock and pre-ignition.

[0037] Each cylinder of the engine 110 may include a spark plug 292 for initiating combustion. The ignition system may provide an ignition spark to the cylinder 230 via the spark plug 292 in response to a spark advance signal SA from a controller 12 included in the control system 190 in a selected operating mode. The timing of the signal SA may be adjusted based on the engine operating conditions and the driver torque requirement. For example, a spark may be provided at a maximum brake torque (MBT) timing to maximize engine power and efficiency. The controller 12 may input engine operating conditions, including engine speed, engine load, and exhaust air-fuel ratio (AFR), into a lookup table and output a corresponding MBT timing for the input engine operating conditions. In other examples, the spark may be retarded relative to the MBT in order to accelerate catalyst warm-up during engine start-up or reduce the incidence of engine knock.

[0038] The engine system 208 is shown as being coupled to the fuel system 140 and the evaporative emission system 219. The fuel system 140 includes a fuel tank 144 coupled to a fuel pump 234, which supplies fuel to the engine 110 that propels the vehicle system 100. The evaporative emission system 219 includes a fuel vapor storage canister 222. During a fuel tank refueling event, fuel can be pumped into the fuel tank 144 from an external source through a fuel refueling port 284. The fuel tank 144 can hold a variety of fuel mixtures, including fuels with a certain range of ethanol concentrations, such as various gasoline-ethanol mixtures, including E10, E85, gasoline, etc., and combinations thereof. A fuel level sensor 282 located in the fuel tank 144 can provide an indication of the fuel level ("fuel level input") to the controller 12. As depicted, the fuel level sensor 282 can include a float connected to a variable resistor. Alternatively, other types of fuel level sensors can be used.

[0039] Fuel pump 234 is configured to deliver pressurized fuel to fuel injectors of engine 110, such as exemplary fuel injector 266. Although only a single fuel injector 266 is shown, additional fuel injectors may be provided for each cylinder. Figure 2In the example of , fuel injector 266 is shown as being directly coupled to one cylinder 230 so as to inject fuel directly therein. For example, the amount of fuel injected may be proportional to the pulse width of signal FPW received from controller 12 via an electronic driver. In this way, fuel injector 266 provides what is considered to be a fuel injector that directly injects fuel (hereinafter also referred to as "DI") into cylinder 230. In an alternative example, in one configuration, fuel injector 266 may be arranged in the intake passage rather than being directly coupled to cylinder 230, the configuration providing a configuration referred to as port injection of fuel (hereinafter also referred to as "PFI") into the intake passage upstream of cylinder 230. In other examples, cylinder 230 may include multiple injectors, which may be configured as direct fuel injectors, port fuel injectors, or a combination thereof. Therefore, it should be understood that the fuel system described herein should not be limited by the above description and in the following. Figure 2 The specific fuel injector configuration limitations shown by way of example in FIG.

[0040] It will be appreciated that the fuel system 140 may be a returnless fuel system, a return fuel system, or various other types of fuel systems. Vapors generated in the fuel tank 144 may be transported to a fuel vapor storage canister 222 via conduit 231 for storage before being purged to the engine intake system 223. The fuel vapor storage canister 222 is equipped with a suitable adsorbent 280 for temporarily capturing fuel vapors (including vaporized hydrocarbons), diurnal vapors, and running loss vapors generated during the fuel tank fueling operation. In one example, the adsorbent 280 is activated carbon (e.g., carbon). Although a single fuel vapor storage canister 222 is shown, it will be appreciated that the fuel system 140 and the evaporative emission system 219 may include any number of fuel vapor storage canisters. When a flushing condition is met, such as when the fuel vapor storage canister is saturated, the vapors stored in the fuel vapor storage canister 222 may be flushed to the engine intake system 223 by opening a canister flushing valve (CPV) 212 in the flushing line 228, which may be a normally closed valve. In some examples, canister purge valve 212 may be a solenoid valve where opening or closing of the valve is performed via actuation of a canister purge solenoid.

[0041] The fuel vapor storage canister 222 may include a buffer 222a (or buffer zone), each of which includes an adsorbent. For example, the buffer 222a is shown as being filled with adsorbent 280a. As shown, the volume of the buffer 222a may be less than the volume of the fuel vapor storage canister 222 (e.g., a fraction of the volume of the fuel vapor storage canister). The adsorbent 280a in the buffer 222a may be the same as or different from the adsorbent 280 in the fuel vapor storage canister (e.g., both may include charcoal). The buffer 222a may be positioned within the fuel vapor storage canister 222 such that during fuel vapor storage canister loading, fuel tank vapors are first absorbed within the buffer, and then other fuel tank vapors are absorbed in the fuel vapor storage canister when the buffer is saturated. In contrast, during fuel vapor storage canister purging, fuel vapors are first desorbed from the fuel vapor storage canister (e.g., to a threshold amount) and then desorbed from the buffer. In other words, the loading and unloading of the buffer is not consistent with the loading and unloading of the fuel vapor storage canister. Therefore, the effect of the fuel vapor storage canister buffer is to inhibit any fuel vapor peak from flowing from the fuel tank to the fuel vapor storage canister, thereby reducing the likelihood of any fuel vapor peak going to the engine.

[0042] Fuel vapor storage canister 222 includes a vent 227 for conveying gas from fuel vapor storage canister 222 to the atmosphere when storing fuel vapor from fuel tank 144. Vent 227 may also allow fresh air to be drawn into fuel vapor storage canister 222 when the stored fuel vapor is flushed to engine intake 223 via flush line 228 and canister flush valve 212. While this example shows vent 227 in communication with fresh, unheated air, various modifications may also be used. Vent 227 may include a canister ventilation valve (CVV) 214 to adjust the flow of air and vapor between fuel vapor storage canister 222 and the atmosphere. When a vent valve is included, the vent valve may be a normally open valve so that air that has been stripped of fuel vapor after having passed through the fuel vapor storage canister may be pushed out to the atmosphere (e.g., during refueling when the engine is off). Likewise, during a purge operation (e.g., during regeneration of a fuel vapor storage canister and while the engine is running), a fuel vapor storage canister ventilation valve may be opened to allow fresh air flow to remove fuel vapors stored in the fuel vapor storage canister. In some examples, canister ventilation valve 214 may be a solenoid valve, wherein opening or closing of the valve is performed via actuation of a canister vent solenoid. Specifically, the canister ventilation valve may be in an open position, which is closed when the canister ventilation solenoid is actuated.

[0043] The evaporative emission system 219 may further include a bleed air fuel vapor storage canister 211. Hydrocarbons desorbed from a fuel vapor storage canister 222 (hereinafter also referred to as a "primary fuel vapor storage canister") may be absorbed within the bleed air fuel vapor storage canister. The bleed air fuel vapor storage canister 211 may include an adsorbent 280b that is different from the adsorbent 280 included in the primary fuel vapor storage canister 222. Alternatively, the adsorbent material in the bleed air fuel vapor storage canister 211 may be the same as the adsorbent material included in the primary fuel vapor storage canister 222.

[0044] A hydrocarbon (HC) sensor 213 may be present in the evaporative emission system 219 to indicate the concentration of hydrocarbons in the vent 227. As illustrated, the HC sensor 213 is positioned between the main fuel vapor storage canister 222 and the bleed fuel vapor storage canister 211. A probe (e.g., a sensing element) of the HC sensor 213 is exposed to the fluid flow in the vent 227 and senses the hydrocarbon concentration of the fluid flow. In one example, the control system 190 may use the HC sensor 213 to determine the penetration of hydrocarbon vapors from the main fuel vapor storage canister 222.

[0045] One or more temperature sensors 215 may be coupled to the fuel vapor storage canister 222 and / or coupled within the fuel vapor storage canister. When fuel vapor is absorbed by the adsorbent in the fuel vapor storage canister, heat is generated (absorption heat). Similarly, when fuel vapor is desorbed by the adsorbent in the fuel vapor storage canister, heat is consumed. In this way, the absorption and desorption of fuel vapor by the fuel vapor storage canister may be monitored and estimated based on temperature changes within the fuel vapor storage canister. In addition, one or more canister heating elements 216 may be coupled to the fuel vapor storage canister 222 and / or located within the fuel vapor storage canister. The canister heating element 216 may be used to selectively heat the fuel vapor storage canister (and the adsorbent contained therein), for example, to increase the desorption of fuel vapor before performing a flushing operation. The canister heating element 216 may include an electrical heating element, such as a conductive metal, ceramic, or an electrically heatable carbon element. In some examples, the canister heating element 216 may include a source of microwave energy or may include a fuel vapor storage canister jacket coupled to a source of hot air or hot water. The canister heating element 216 may be coupled to one or more heat exchangers that may facilitate transfer of heat (e.g., from hot exhaust) to the fuel vapor storage canister 222. The canister heating element 216 may be configured to heat the air within the fuel vapor storage canister 222 and / or directly heat the adsorbent located within the fuel vapor storage canister 222. In some embodiments, the canister heating element 216 may be included in a heater compartment coupled to the interior or exterior of the fuel vapor storage canister 222. In some embodiments, the fuel vapor storage canister 222 may be coupled to one or more cooling circuits and / or cooling fans. In this way, the fuel vapor storage canister 222 may be selectively cooled to increase absorption of fuel vapors (e.g., prior to a refueling event). In some examples, the canister heating element 216 may include one or more Peltier elements that may be configured to selectively heat or cool the fuel vapor storage canister 222.

[0046] Since the vehicle system 100 is powered by the engine system 208 during some conditions and is not powered by the engine system 208 during other conditions (e.g., Figure 1The vehicle may have reduced engine operating time due to the fact that the vehicle is powered by an energy storage device or because the engine is turned off when the vehicle is started and stationary (e.g., when the vehicle system 100 is included in a stop / start vehicle). Although reduced engine operating time reduces the vehicle's overall carbon emissions, they may also result in insufficient flushing of fuel vapors from the evaporative emissions system 219. To at least partially address this issue, a fuel tank isolation valve (FTIV) 236 may be optionally included in conduit 231 so that the fuel tank 144 is coupled to the fuel vapor storage canister 222 via the valve. In some examples, the FTIV 236 may be a solenoid valve, wherein the opening or closing of the valve is performed via actuation of a canister ventilation solenoid. Specifically, the FTIV may be in an open position, which is closed when the canister ventilation solenoid is actuated. For example, when the engine is off, the FTIV 236 may be opened so that the fuel tank 144 is vented to the atmosphere through the evaporative emissions system 219 (e.g., via the vent 227 and the open CVV 214). In another example, while the engine is on and burning fuel, FTIV 236 may remain closed to limit the amount of diurnal vapor or “running loss” vapors directed from fuel tank 144 to fuel vapor storage canister 222. During selected purge conditions, FTIV 236 may be temporarily opened, such as for a certain duration, to direct fuel vapors from fuel tank 144 to fuel vapor storage canister 222. While the depicted example shows FTIV 236 positioned along conduit 231, in alternative embodiments, FTIV 236 may be mounted on fuel tank 144.

[0047] In some examples, one or more pressure sensors may be coupled to fuel system 140 and evaporative emissions system 219 for providing estimates of fuel system pressure and evaporative emissions system pressure, respectively. Figure 2In the example illustrated in FIG. 1 , first pressure sensor 217 is coupled directly to fuel tank 144, and second pressure sensor 238 is coupled to conduit 231 between FTIV 236 and fuel vapor storage canister 222. For example, first pressure sensor 217 may be a fuel tank pressure transducer (FTPT) coupled to fuel tank 144 for measuring the pressure of fuel tank 144, and second pressure sensor 238 may measure the pressure of evaporative emission system 219. In an alternative example, first pressure sensor 217 may be coupled between fuel tank 144 and fuel vapor storage canister 222, specifically, between the fuel tank and FTIV 236. In other examples, such as when FTIV 236 is turned on or omitted, a single pressure sensor may be included for measuring the fuel system pressure and the evaporative system pressure. In other examples, both first pressure sensor 217 and second pressure sensor 238 may be omitted, and the fuel tank pressure may be estimated based on ambient pressure, as further described herein.

[0048] In some examples, one or more temperature sensors 221 may also be coupled to fuel system 140 for providing an estimate of fuel system temperature. In one example, the fuel system temperature is a fuel tank temperature, where temperature sensor 221 is a fuel tank temperature sensor coupled to fuel tank 144. While the depicted example shows temperature sensor 221 coupled directly to fuel tank 144, in alternative examples, the temperature sensor may be coupled between the fuel tank and fuel vapor storage canister 222. In other examples, temperature sensor 221 may be provided, and the fuel tank temperature may be estimated based on ambient temperature, as further described herein.

[0049] Control system 190 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81 (various examples of which are described herein). As one example, sensors 16 may include exhaust gas sensor 226 located upstream of emission control device 270, exhaust temperature sensor 232 coupled to exhaust passage 235, manifold absolute pressure (MAP) sensor 240 coupled to intake passage, mass airflow (MAF) sensor 246, ambient pressure sensor 250 coupled to intake passage 242, ambient humidity sensor 256 coupled to intake passage 242, ambient temperature sensor 198 coupled to intake passage, engine coolant temperature sensor 254 coupled to a cooling jacket of the engine, knock sensor 290, FTPT 217, second pressure sensor 238, hydrocarbon sensor 213, temperature sensor 221, and exhaust pressure sensor 229 located downstream of emission control device 270. Other sensors, such as additional pressure sensors, temperature sensors, air / fuel ratio sensors, and composition sensors, may be coupled to various locations in vehicle system 100. As another example, actuators 81 may include fuel injectors 266, FTIV 236, CPV 212, CVV 214, fuel pump 234, spark plugs 292, and throttle 262.

[0050] As mentioned above Figure 1 As described, the control system 190 may further receive information about the location of the vehicle from an onboard GPS. The information received from the GPS may include vehicle speed, vehicle altitude, vehicle location, etc. This information may be used to infer engine operating parameters, such as local air pressure. The control system 190 may further be configured to receive information via the Internet or other communication networks. The information received from the GPS may be cross-referenced with information available via the Internet to determine local weather conditions, local vehicle regulations, etc. The control system 190 may also use the Internet to obtain updated software modules, which may be stored in non-transitory memory.

[0051] The controller 12 of the control system 190 may be configured as a conventional microcomputer including a microprocessor unit, input / output ports, read-only memory, random access memory, keep-alive memory, a controller area network (CAN) bus, etc. The controller 12 may be configured as a powertrain control module (PCM). The controller may receive input data from various sensors, process the input data, and trigger actuators in response to the processed input data based on instructions or codes programmed therein corresponding to one or more routines, such as regarding Figure 3 An exemplary routine is described.

[0052] In some examples, the controller can be placed in a power reduction mode or sleep mode, in which the controller maintains only necessary functions and operates with lower battery consumption than in a corresponding wake-up mode. For example, the controller can be placed in sleep mode after a vehicle shutdown event (e.g., a human driver removes the key from the vehicle and / or the remote control key is out of the vehicle's proximity, at which time the engine can be stopped from rotating and the electric propulsion device (if present) can be disabled). The controller can have a wake-up input that allows the controller to return to the wake-up mode based on input received from one or more sensors. For example, opening the vehicle's door before a vehicle key event (e.g., a key-on event, in which the vehicle's ignition is switched to the "on" position) can trigger a return to the wake-up mode. As another example, via the remote control key 104 ( Figure 1 ) unlocking the vehicle can trigger a return to wake mode. Thus, controller 12 is "powered up" prior to an engine start request.

[0053] Next, Figure 3 An exemplary method 300 is shown for adjusting one or more combustion parameters during an engine cold start based on estimated fuel characteristics. For example, fuel may be stored in a fuel tank (e.g., Figure 1 and Figure 2 As the fuel ages (e.g., the duration that the fuel has been stored in the fuel tank increases), the volatility of the fuel may decrease, resulting in engine lag during cold starts and increased vehicle emissions. For example, when in an HEV system (e.g., in Figure 1 and Figure 2When an engine is included in a vehicle system 100 (shown in FIG. 1 ), the duration that fuel has been stored in the fuel tank may be relatively long (e.g., months to years). In addition, when the vehicle is an AV, refueling may be less controlled than when the vehicle is non-autonomous (e.g., operated by a human). For example, the frequency of refueling and the location of refueling may be different when the vehicle is an AV relative to a non-autonomous vehicle. For AVs and non-AVs, the frequency and location of refueling may affect the fuel composition, which may vary with the region and season and various additives added to the fuel mixture to change the volatility of the fuel. For example, fuel sold in an area with a warm climate may have a lower volatility than fuel sold in an area with a colder climate, so that the difference in climate corresponds to the difference in fuel volatility. Similarly, fuel volatility may vary throughout the year in the same area based on the climate of the area. For example, fuel dispensed at a fuel pump may have a lower fuel volatility during warmer months than fuel dispensed during colder months. Additionally, commercial fuel distributors may offer fuels that include blends of gasoline and ethanol (e.g., E10, E25, E85, etc.) to reduce carbon emissions. Furthermore, a fuel tank may be filled with a fuel of a particular composition while still containing a certain amount of fuel that may have a different composition. Thus, a typical fuel tank may contain a variety of different fuel blends, which may be further affected by the age of the fuel. Specifically, as the fuel ages, the fraction of higher volatility light oil may decrease as the light oil evaporates, leaving a higher fraction of lower volatility heavy oil (e.g., hysteresis fuel). Therefore, a controller (e.g., Figure 1 and Figure 2 The controller 12 of the embodiment of the present invention can estimate the fuel volatility and adjust the combustion parameters accordingly to reduce engine lag and vehicle emissions during cold start, as described below. Instructions for carrying out method 300 and the remainder of the methods included herein can be executed by the controller based on instructions stored on a memory of the controller and in combination with sensors of the engine system (e.g., as described above in reference to Figure 1 and Figure 2 The described sensors (e.g. Figure 1 and Figure 2 Ambient temperature sensor 198, Figure 2 The ambient humidity sensor 256 and Figure 2 The controller may use the engine actuator of the engine system (e.g., Figure 2 Fuel injector 266 shown in FIG. 2 is used to adjust engine operation.

[0054] Method 300 begins at 301 and includes estimating and / or measuring operating conditions. The operating conditions can include (but are not limited to) vehicle operating modes (e.g., an electric mode in which torque from an electric motor is used to propel the vehicle, or an engine mode in which torque from an engine is at least partially used to propel the vehicle), driver-requested torque, engine speed and load, engine temperature, ambient temperature, ambient (e.g., barometric) pressure, and ambient humidity. The operating conditions can be measured by one or more sensors communicatively coupled to a controller, or can be inferred based on available data. For example, the engine temperature can be estimated from the engine coolant temperature measured by an engine coolant temperature sensor. The ambient conditions (e.g., ambient humidity, temperature, and pressure) can be measured by corresponding sensors, as further described below, or can be inferred based on information downloaded from the Internet and / or information from a GPS (e.g., local weather conditions).

[0055] At 302, method 300 includes determining whether an engine cold start condition exists. A cold start condition can be confirmed in response to an engine start request after a long period of engine inactivity (e.g., when the engine has been inactive for more than a first threshold duration) when starting the engine (e.g., rotating the engine from zero speed to a non-zero speed while providing fuel and spark to initiate combustion). For example, the first threshold duration can refer to the amount of time expected for the engine to cool to ambient temperature. In one example, the first threshold duration can be a fixed duration. In another example, the first threshold duration can be adjusted based on one or more of the engine temperature and ambient temperature at the previous engine shutdown. Additionally or alternatively, a cold start condition can be confirmed when the engine temperature is below a threshold temperature (e.g., below the light-off temperature of an emission control device) at engine start. As another example, a cold start condition can be confirmed when the engine temperature is substantially equal to the ambient temperature (e.g., within a threshold of the ambient temperature (e.g., within 10 degrees of the ambient temperature)) at engine start. The engine start can be requested by a vehicle operator, e.g., via a vehicle turn-on event, or by a controller (e.g., based on torque demand).

[0056] If an engine cold start condition does not exist, then method 300 proceeds to 304 and includes not performing an engine cold start adjustment. For example, if an engine start is not requested, the engine can continue to operate according to the current operating conditions when the engine is already on, or the engine can remain off (e.g., stationary with no combustion occurring in the engine cylinders). As another example, if an engine start is requested, but the engine is not cold (e.g., a hot start condition exists), the engine can be started according to a nominal start procedure for the given operating conditions. After 304, method 300 ends.

[0057] If an engine cold start condition exists at 302, method 300 proceeds to 306 and includes estimating and / or measuring fuel characteristics. Fuel characteristics may include one or more of fuel temperature, fuel tank pressure, fuel vapor pressure, and fuel octane rating. Fuel characteristics may also include fuel type, such as a fuel blend. Fuel characteristics may be estimated (e.g., based on operating conditions), measured (e.g., via sensors), or inferred based on available data, as further described below. For example, fuel characteristics may be estimated after a fuel tank refill event based on an exhaust gas oxygen sensor (e.g., at Figure 2 The fuel type is determined based on the concentration of oxygen in the exhaust gas measured by an exhaust gas sensor 226 shown in FIG. 1 and the pulse width of a control signal sent to a fuel injector of the engine. For example, the controller may input the concentration and the pulse width into a lookup table and output the fuel type. Alternatively, a flexible fuel ethanol sensor may be used to directly determine the fuel type.

[0058] Estimating and / or measuring the fuel property may include estimating the fuel temperature based on the measured ambient temperature, as indicated at 308. For example, during a cold start, when the engine has cooled to or about ambient temperature, it may be assumed that the fuel has also cooled to or about ambient temperature, as described below. Thus, the measured ambient temperature value may be used as the estimated fuel temperature value. Alternatively, the fuel temperature may be estimated based on, for example, a fuel tank temperature sensor (e.g., Figure 2 The fuel temperature is estimated by using the fuel tank temperature measured by the temperature sensor 221 (when included in the fuel system).

[0059] Estimating and / or measuring fuel characteristics may include estimating fuel tank pressure based on the measured gas pressure, as indicated at 310. For example, in a fuel tank, such as via an open FTIV (e.g., Figure 2 FTIV 236) and evaporative emission systems connected to the atmosphere (e.g. Figure 2 When the fuel tank is vented to the atmosphere by an evaporative emission system 219 (e.g., an evaporative emission system 219), the fuel tank pressure may be estimated based on the measured air pressure. In the case where the fuel tank is connected to the atmosphere via an evaporative emission system, the measured air pressure value may be used as the estimated fuel tank pressure value. Alternatively, the fuel tank pressure may be estimated based on the measured air pressure value. Figure 2 A first pressure sensor 217 (when included in the fuel system) is used to directly measure the fuel tank pressure.

[0060] Estimating and / or measuring fuel characteristics may also include estimating the fuel vapor pressure using a physics-based model based on the estimated fuel temperature and the estimated fuel tank pressure, as indicated at 312. For example, the physics-based model may utilize a fuel distillation curve stored in a memory of the controller, such as Figure 4 Further description. Fuel vapor pressure is directly related to fuel volatility; as fuel vapor pressure increases, fuel volatility increases. Therefore, fuel vapor pressure can be used as a measure of fuel volatility.

[0061] Estimating and / or measuring fuel characteristics may also include estimating a fuel octane number via a knock adaptation module, as indicated at 314. For example, the controller may retrieve a recent fuel octane number estimate that may be stored in a memory of the controller. For example, a recent fuel octane number may have been determined during a previous engine operation, where the controller may estimate the fuel octane number using a knock adaptation module. The knock adaptation module may use a global correction factor to adjust the fuel octane number (e.g., determined from the fuel type), which in turn may adjust the boundary spark value to achieve increased engine torque output. The global correction factor may be learned by the knock adaptation module based on knock detection (e.g., using a knock sensor) by integrating a rapid cycle spark knock correction value over a knock window. Additionally or alternatively, the fuel octane number may be estimated based on the fuel type and ambient humidity. For example, the controller may input the fuel type and ambient humidity into a lookup table and output the estimated fuel octane number.

[0062] At 316, method 300 includes determining a confidence level in the estimated fuel vapor pressure based on an engine inactivity duration. The engine inactivity duration may refer to an amount of time that has elapsed since the engine was last operated (e.g., since combustion last occurred in the engine). For example, the engine inactivity duration may be compared to a second threshold duration. For example, the second threshold duration may refer to an amount of time during which fuel in the fuel tank is expected to cool to ambient temperature. The second threshold duration may be the same as or different from the first threshold duration. In one example, the second threshold duration may be a fixed duration. In another example, the confidence level of the estimated fuel vapor pressure may be determined based on an engine run time (e.g., an amount of time the engine was operated) prior to a previous (e.g., most recent) engine shutdown, a fuel level (e.g., as determined by a fuel level sensor (e.g., Figure 2The second threshold duration may be adjusted based on one or more of the ambient temperature at a previous engine shutdown, the current engine temperature, and the current ambient temperature. The controller may compare the engine inactivity duration to the second threshold duration to determine a confidence level using a probability model (e.g., a Gaussian probability distribution). For example, as the engine inactivity duration increases to exceed the second threshold duration, the confidence that the estimated fuel temperature is accurate increases until a maximum confidence level is reached, and as the engine inactivity duration decreases to below the second threshold, the confidence that the estimated fuel temperature is accurate decreases. Although the fuel tank pressure may also deviate from the barometric pressure, in the case where the fuel tank is open to the atmosphere, it may take a relatively short amount of time for the fuel tank pressure to balance with the barometric pressure, such as less than the amount of time required for the engine to achieve a cold start condition (e.g., less than the first threshold duration described at 302). Therefore, it may be assumed that the difference in fuel temperature relative to ambient temperature is the primary source of potential inaccuracy in the fuel vapor pressure estimate.

[0063] As an alternative example, the controller may use an algorithm to determine the expected amount of time for the fuel temperature to reach the ambient temperature, and then the engine inactivity duration may be compared to the expected amount of time. For example, the algorithm may use a temperature decay function, such as an exponential decay function, to determine the expected amount of time for the fuel temperature to reach the ambient temperature. The exponential decay function may utilize a time constant determined based on an empirical fuel cooling curve. The time constant may be stored in a memory of the controller (e.g., in a lookup table with the ambient temperature at the previous engine shutdown as input). In addition, the exponential decay function may be multiplied by a fuel level normalizer to account for the effect of the fuel level on the cooling rate of the fuel, because more fuel (e.g., a higher fuel level) cools slower than less fuel (e.g., a lower fuel level). In some examples, the expected amount of time may be determined at the previous engine shutdown and stored in the controller's memory for use at a subsequent engine start. The controller may compare the engine inactivity duration to the expected amount of time to determine a confidence level, for example, using a probability model. For example, as the engine inactivity duration increases above the expected amount of time, the confidence that the estimated fuel temperature is accurate increases until a maximum confidence is reached, and as the engine inactivity duration decreases below the expected amount of time, the confidence that the estimated fuel temperature is accurate decreases.

[0064] As another alternative example, the controller may determine the estimated fuel temperature range by reference to a model using a temperature decay function, engine inactivity duration, and ambient temperature, such as Figure 5Described. For example, it can be assumed with high (e.g., 95%) confidence that the actual fuel temperature is within the estimated fuel temperature range. The physics-based model can use the estimated fuel temperature range to determine the estimated fuel vapor pressure range. It can be assumed with (e.g.,) high confidence that the actual fuel vapor pressure is within the estimated fuel vapor pressure range. As the engine inactivity duration decreases, the estimated fuel temperature range can increase, and the resulting estimated fuel vapor pressure range can increase.

[0065] As another example, the confidence level may be determined based on a logic rule that varies with the duration of engine inactivity without comparing the duration of engine inactivity to a second threshold duration or the amount of time expected for the fuel temperature to reach ambient temperature. As another example, when a fuel tank pressure sensor and a fuel temperature sensor are included in the fuel system, the estimated fuel vapor pressure may be determined to be accurate with a high (e.g., maximum) confidence level without comparing the duration of engine inactivity to a second threshold duration or the amount of time expected for the fuel temperature to reach ambient temperature.

[0066] At 318, method 300 includes optimizing one or more combustion parameters based on the estimated fuel octane number, the estimated fuel vapor pressure (eg, volatility), and the determined confidence level. Figure 4 To further illustrate, the controller may input the estimated fuel octane number, the estimated fuel vapor pressure (and / or a correction factor determined directly from the estimated fuel vapor pressure), and the determined confidence level into a plurality of lookup tables, algorithms, and / or maps, and output one or more combustion parameters optimized for the input fuel characteristics to reduce engine lag during cold start. Furthermore, by optimizing the one or more combustion parameters based on the determined confidence level, more aggressive adjustments may be made when the determined confidence level is higher, and more conservative adjustments may be made when the determined confidence level is lower, such as adjusting the engine lag during cold start to reduce engine lag during cold start. Figure 5 Alternatively, when using the estimated fuel vapor pressure range, the most conservative combustion parameter adjustment can be made for a given range, such as Figure 6 Further explanation: By incorporating confidence levels, over-adjustment and under-adjustment can be minimized.

[0067] Optimizing one or more combustion parameters may include adjusting fuel injection timing, as indicated at 320. For example, as fuel vapor pressure decreases (e.g., as fuel age increases), fuel injection timing (e.g., start of injection) may be advanced. Additionally, as the determined confidence increases, the degree to which the fuel injection timing is advanced relative to a previous fuel injection timing setting for a given fuel type may be increased. For example, the previous fuel injection timing setting may be a nominal, pre-calibrated value for an engine cold start, or may be a previously updated value stored in a memory of the controller, such as an adjusted fuel injection timing determined during a previous engine cold start (e.g., determined during a previous execution according to method 300).

[0068] Optimizing one or more combustion parameters may include adjusting the fuel injection amount, as indicated at 322. For example, as the fuel vapor pressure decreases, the fuel injection amount may be increased. In addition, as the determined confidence increases, the degree to which the fuel injection amount is adjusted relative to a previous fuel injection amount for a given fuel type may be increased. For example, the previous fuel injection amount may be a nominal pre-calibrated value for an engine cold start, or may be a previously updated value stored in a memory of the controller, such as an adjusted fuel injection amount determined during a previous engine cold start (e.g., determined during a previous execution according to method 300). As an illustrative example, if the fuel is not as volatile as estimated (e.g., the estimated fuel vapor pressure is higher than the actual fuel vapor pressure) and the confidence of the fuel vapor pressure estimate is not considered, then a fuel injection amount that is smaller than the optimal fuel injection amount may be set, resulting in engine hysteresis still occurring. However, if the confidence is used to account for the inaccuracy of the fuel vapor pressure estimate, then the fuel injection amount may be reduced to a lesser extent (e.g., more conservatively), and engine hysteresis may be reduced. Similarly, if the fuel is more volatile than estimated (e.g., the estimated fuel vapor pressure is lower than the actual fuel vapor pressure) and the confidence level of the fuel vapor pressure estimate is not taken into account, then a fuel injection amount that is larger than the optimal fuel injection amount may be set, thereby reducing fuel economy and increasing hydrocarbon emissions during cold starts. However, if the confidence level is used to account for the inaccuracy of the fuel vapor pressure estimate, then the fuel injection amount may be increased to a lesser extent (e.g., more conservatively), and hydrocarbon emissions may be reduced while improving fuel economy. The controller may determine a control signal to be sent to the fuel injector having a pulse width corresponding to the adjusted fuel injection amount.

[0069] Optimizing one or more combustion parameters may include adjusting the fraction of fuel injected via PFI relative to DI when the engine includes both port fuel injectors and direct fuel injectors, as indicated at 324. For example, as the fuel vapor pressure decreases, the fraction of fuel injected via PFI relative to DI may be increased because it is more likely to be heavy-end hydrocarbons if injected in DI mode, thereby increasing particulate matter emissions. In addition, as the determined confidence increases, the degree to which the fraction of fuel injected via PFI relative to DI is adjusted for a given fuel type relative to a previous fraction setting may be increased. For example, the previous fraction setting may be a nominal pre-calibrated value for an engine cold start, or may be a previously updated value stored in a memory of the controller, such as an adjusted fraction of fuel injected via PFI relative to DI determined during a previous engine cold start (e.g., determined during a previous execution according to method 300). The controller may determine a first control signal to be sent to the port fuel injector having a first pulse width corresponding to the fraction of fuel to be injected via PFI, and a second control signal to be sent to the direct fuel injector having a second (different) pulse width corresponding to the fraction of fuel to be injected via DI.

[0070] Optimizing one or more combustion parameters may include adjusting a commanded air-fuel ratio (AFR), as indicated at 326. For example, as the fuel vapor pressure decreases (and the fuel age increases), the richness of the commanded AFR (relative to stoichiometry) may be increased. Additionally, as the determined confidence increases, the degree to which the commanded AFR is adjusted relative to a previous AFR setting for a given fuel type may be increased. For example, the previous AFR setting may be a nominal, pre-calibrated value for an engine cold start, or may be a previously updated value stored in a memory of the controller, such as an adjusted commanded AFR determined during a previous engine cold start (e.g., determined during a previous execution according to method 300). The adjusted commanded AFR may also affect the amount (e.g., mass) of fuel injection, as the controller may adjust the amount of fuel injection based on a given air charge in order to achieve the commanded AFR, and further adjust based on feedback from an exhaust oxygen sensor related to the actual (e.g., achieved) AFR.

[0071] Optimizing one or more combustion parameters may include adjusting spark timing, as indicated at 328. For example, as the fuel vapor pressure decreases (e.g., the fuel volatility decreases), the spark timing may be further advanced (e.g., less retarded) to compensate for the retarded burn rate of the lower volatility fuel. Additionally, as the determined confidence increases, the degree to which the spark timing is adjusted relative to a previous spark timing setting for a given fuel type may be increased. For example, the previous spark timing setting may be a nominal, pre-calibrated value for an engine cold start, or may be a previously updated setting stored in a memory of the controller, such as an adjusted spark timing determined during a previous engine cold start (e.g., determined during a previous execution according to method 300). As an illustrative example, if the fuel is less volatile than estimated (e.g., the estimated fuel vapor pressure is higher than the actual fuel vapor pressure) and the confidence of the fuel vapor pressure estimate is not considered, the spark timing may be further retarded than the optimal spark timing, thereby reducing fuel economy. However, if a confidence level is used to account for the inaccuracy of the fuel vapor pressure estimate, the spark timing can be retarded to a lesser extent (e.g., more conservatively) and fuel economy can be increased. Similarly, if the fuel is more volatile than estimated (e.g., the estimated fuel vapor pressure is lower than the actual fuel vapor pressure) and the confidence level of the fuel vapor pressure estimate is not considered, the spark timing may be further advanced (e.g., less retarded) than the optimal spark timing, resulting in a higher incidence of knock. However, if a confidence level is used to account for the inaccuracy of the fuel vapor pressure estimate, the spark timing can be advanced to a lesser extent (e.g., more conservatively) and the incidence of knock can be reduced while increasing fuel economy. The controller can determine a control signal, such as a spark advance signal, to be sent to the ignition system to actuate a spark plug connected to each engine cylinder according to the adjusted spark timing.

[0072] At 330, method 300 includes starting the engine using the optimized combustion parameters. For example, the engine may be cranked at a non-zero speed (e.g., via a starter motor or electric machine), an adjusted mass of fuel may be provided at an adjusted fuel injection timing (and an adjusted PFI to DI fuel fraction) to achieve an adjusted commanded AFR, and spark may be provided at an adjusted spark timing, such as by sending the control signal determined above. By starting the engine using one or more combustion parameters optimized for fuel volatility, engine lag may be reduced, vehicle emissions may be reduced, and fuel performance may be increased. After 330, method 300 ends.

[0073] Next, Figure 4A block diagram 400 is shown utilizing an exemplary physics-based model 402 during an engine cold start to determine fuel vapor pressure and a plurality of combustion parameters according to the model. The physics-based model 402 may be stored in a memory of a controller included in a vehicle control system and may be used according to a routine (e.g., Figure 3 Method 300) for access, the controller is, for example, Figure 2 Controller 12.

[0074] During an engine cold start, the fuel temperature (which may be estimated to be equal to the ambient temperature) and the fuel tank pressure (which may be estimated to be equal to the barometric pressure) may be input into the physics-based model 402. The physics-based model 402 includes (or references) a plurality of fuel distillation curves 404, each of which is empirically determined (e.g., in a laboratory environment) and stored in a memory of the controller. The plurality of fuel distillation curves 404 include separate distillation curves for different fuel types (e.g., different blends of fuel). In addition, the plurality of fuel distillation curves 404 include separate distillation curves determined for each fuel type at different fuel ages (e.g., new fuel, 30-day aged fuel, 60-day aged fuel, 90-day aged fuel, etc.). In some examples, the plurality of fuel distillation curves 404 may include separate distillation curves determined at different pressures. Alternatively, the stored fuel distillation curves may be adjusted based on the fuel tank pressure according to a known pressure-temperature relationship. Individual distillation curves included in plurality of fuel distillation curves 404 are graphically represented by different line types (eg, solid line, dashed line, dotted line, etc.).

[0075] The physics-based model 402 may identify one or more of the plurality of fuel distillation curves 404 to reference based on the fuel type, fuel age, and / or fuel tank pressure. The fuel age may be estimated by the duration since the fuel refill event and the fraction of new fuel added relative to the fuel remaining at the refill event. For example, the weighted average age may be determined at the fuel refill event, such as by the controller inputting the fraction of new fuel and the fraction of remaining fuel (and the estimated age of the remaining fuel) into a lookup table, algorithm, or model and outputting the weighted average age. The controller may update the estimated fuel age based on the weighted average age and the duration since the fuel refill event, which may be stored in the memory of the controller.

[0076] The horizontal axis of each of the plurality of fuel distillation curves represents a percentage of fuel evaporation, while the vertical axis represents a corresponding temperature at a given percentage of fuel evaporation. However, in other examples, the vertical axis may represent a percentage of fuel evaporation and the horizontal axis may represent a temperature. The physics-based model 402 references the fuel temperature relative to one or more of the identified fuel distillation curves to output an estimated fuel vapor pressure at a given fuel tank pressure, fuel type, and fuel age. In this way, the physics-based model 402 takes into account the vapor pressure of heavy-end hydrocarbons (which are less volatile and may comprise a larger fraction of the fuel as the fuel age increases) relative to light-end hydrocarbons (which are more volatile and may comprise a smaller fraction of the fuel as the fuel age increases).

[0077] Once the fuel vapor pressure is determined using multiple distillation curves 404, the fuel vapor pressure can be used directly to determine correction factors, which are then output from the physics-based model 402 and input into the fuel logic 405 of the controller. For example, the physics-based model 402 may include a lookup table that relates the determined fuel vapor pressure to the corresponding correction factor. As another example, the controller may make a logical determination of the correction factor based on a logic rule that varies with the determined fuel vapor pressure. Alternatively, the estimated fuel vapor pressure may be input directly into the fuel logic 405. The fuel logic 405 references multiple lookup tables, algorithms, or graphs 406 to determine multiple combustion parameters. For example, the correction factor, along with the confidence level and the estimated octane number, may be input into multiple lookup tables 406 to determine the corresponding combustion parameters for the input parameters. As described with respect to Figure 3 As described, in some examples, a confidence level may be determined based on the probability that the engine shutoff time is accurate based on the engine shutoff time and the fuel tank pressure and fuel temperature, for example using probability model 408 to determine the probability, which may be a Gaussian probability distribution. However, in other examples, a confidence level may not be included as an input to fuel logic 405. Also as described with respect to Figure 3As described, in some examples, the estimated octane number can be determined using a knock adaptation module 410. In other examples, the estimated octane number can be determined based on the fuel type, and the estimated octane number can be further adjusted based on the ambient humidity. In other examples, the fuel octane number can be considered in the referenced fuel distillation curve (e.g., input into the physics-based model 402) and the fuel octane number can not be input into the fuel logic 405. Multiple combustion parameters can be output from the fuel logic 405 and multiple lookup tables 406, including fuel injection timing, fuel quality, PFI relative to DI fuel fraction, AFR and spark timing. In some examples, a separate lookup table can be referenced for each of the multiple combustion parameters. In other examples, a subset of multiple combustion parameters can be referenced in a single lookup table. The controller can then use the multiple combustion parameters to control fuel filling and ignition during the cold start of the engine. Vehicle emissions can be reduced in the case of taking into account the fuel composition (e.g., light oil relative to heavy oil) and thus volatility.

[0078] Next, Figure 5 A set of graphs 500 and 510 are shown illustrating exemplary relationships between engine off time during an engine cold start, confidence in the estimated fuel vapor pressure, and the extent of adjustments made to combustion parameters (e.g., fuel injection timing, fuel injection amount, PFI to DI fuel fraction, commanded AFR, or spark timing). As described above with respect to Figure 3 and Figure 4 As described above, the fuel vapor pressure may be estimated based on the estimated fuel temperature and the estimated fuel tank pressure. Figure 1 and Figure 2 The ambient temperature sensor 198 of the engine may be used as the estimated fuel temperature. Depending on the engine off time (e.g., engine inactivity duration), for example, when a cold engine start is requested when the fuel system has not yet reached thermal equilibrium with the environment, the fuel temperature may not have reached the ambient temperature.

[0079] Graph 500 shows an exemplary graph 502 of the relationship between engine off time and confidence in the fuel vapor pressure estimate. The horizontal axis represents the engine off time, where the engine off time increases from left to right along the horizontal axis. The vertical axis represents the confidence in the fuel vapor pressure estimate, where the confidence increases from bottom to top along the vertical axis until a maximum confidence is reached. In addition, a threshold engine off time is indicated by dashed line 504. The threshold engine off time refers to the engine off time at which the fuel system can be assumed to be in thermal equilibrium with the environment with the maximum confidence. For example, the threshold engine off time can be about Figure 3 The second threshold duration described by 316 .

[0080] Graph 510 shows an exemplary graph 512 of the relationship between the confidence in the fuel vapor pressure estimate and the degree of adjustment made to the combustion parameters. The horizontal axis represents the confidence in the fuel vapor pressure estimate, where the confidence increases from left to right along the horizontal axis. The vertical axis represents the degree of adjustment made to the combustion parameters, where the degree of adjustment increases from bottom to top along the vertical axis until a maximum degree of adjustment is reached. For example, the maximum degree of adjustment may refer to an adjustment made at the maximum confidence. The degree of adjustment refers to an adjustment made relative to a previous setting, such as with respect to Figure 3 Furthermore, depending on the combustion parameters and the estimated fuel vapor pressure, the adjustment may be in an increasing direction or a decreasing direction.

[0081] As illustrated by graph 502 of diagram 500, as the engine shut-off time increases, the confidence increases until a maximum confidence (dashed line 504) is reached at a threshold engine shut-off time. Therefore, at an engine shut-off time greater than the threshold engine shut-off time, the confidence does not continue to increase. Graph 502 shows a nonlinear relationship between engine shut-off time and confidence. However, other curve shapes are also possible, such as linear and other nonlinear curves, in which the confidence generally increases as the engine shut-off time increases. In addition, for example, the shape of graph 502 can vary based on the amount of fuel, the ambient temperature when the engine is shut down, the current engine temperature, and the fuel temperature when the engine is shut down. Similarly, as illustrated by graph 512 of diagram 510, as the confidence increases, the adjustment degree increases until a maximum adjustment degree is reached. Graph 512 shows a linear relationship between confidence and adjustment degree. However, other curve shapes are also possible, such as nonlinear curves, in which the adjustment degree generally increases as the confidence increases. In addition, the shape of graph 512 can vary based on combustion parameters. As a non-limiting example, the degree of fuel injection amount adjustment may increase linearly with the confidence level, while the degree of spark timing adjustment may increase stepwise with the confidence level.

[0082] As an illustrative example, referring first to graph 500, an engine off time t1 less than a threshold engine off time (dashed line 504) corresponds to a confidence level c1 less than a maximum confidence level. An engine off time t2 less than a threshold engine off time (dashed line 504) and greater than engine off time t1 corresponds to a confidence level c2. Confidence level c2 is greater than confidence level c1 and less than the maximum confidence level. Referring next to graph 510, confidence level c1 corresponds to adjustment level d1, and confidence level c2 corresponds to adjustment level d2. Adjustment level d1 is less than adjustment level d2, and both adjustment levels are less than the maximum adjustment level. Therefore, as illustrated by graphs 500 and 510, when the engine off time is less than a threshold time (dashed line 504), the combustion parameters are adjusted to a greater extent (e.g., more aggressively) relative to previous settings when the engine idle time is longer (e.g., engine off time t2) and the confidence in the fuel vapor pressure estimate is higher (e.g., confidence c2) than when the engine idle time is shorter (e.g., engine off time t1).

[0083] Figure 6 A set of exemplary graphs 600, 610, and 620 are shown that illustrate how the estimated fuel vapor pressure range may be used to adjust combustion parameters during an engine cold start. As an illustrative example, the fuel injection amount is used as Figure 6 The graph 600 illustrates the relationship between fuel temperature and engine off time. The horizontal axis represents engine off time, where the engine off time increases from left to right along the horizontal axis. The vertical axis represents fuel temperature, where the fuel temperature increases from bottom to top along the vertical axis. The dashed line 602 indicates the relationship between fuel temperature and engine off time. Figure 6 610 illustrates the relationship between fuel vapor pressure and fuel temperature. The horizontal axis represents fuel temperature, where fuel temperature increases from left to right along the horizontal axis. The vertical axis represents fuel vapor pressure, where fuel vapor pressure increases from bottom to top along the vertical axis. Graph 620 illustrates the relationship between fuel vapor pressure and fuel quantity. The horizontal axis represents fuel vapor pressure, where fuel vapor pressure increases from left to right along the horizontal axis. The vertical axis represents fuel injection quantity, where fuel injection quantity increases from bottom to top along the vertical axis.

[0084] Referring first to diagram 600, graph 604 shows a temperature decay curve starting from a starting fuel temperature when the engine is shut down (e.g., at engine shut-down time t0). The shape of graph 604 may be determined based in part on ambient temperature and the starting fuel temperature, for example, the starting fuel temperature may be estimated based on the operating conditions at t0. Graph 606 shows an inverse of the temperature decay curve, which may be used with graph 604 to determine an estimated fuel temperature range (δ) for a given engine shut-down time. As the engine shut-down time increases, graphs 604 and 606 approach the ambient temperature (dashed line 602) and the span of the temperature range decreases until the temperature range equals a single value (e.g., ambient temperature). For example, at an engine shut-down time greater than engine shut-down time t3, the fuel temperature is balanced with the ambient temperature, and the ambient temperature is used alone to represent the estimated fuel temperature. The time value of engine shut-down time t3 varies based on the ambient temperature and the shapes of graphs 604 and 606. At an engine shutdown time that is less than the engine shutdown time t3, the temperature range can be determined using graphs 604 and 606. In addition, it can be assumed with a high (e.g., 95%) confidence that the actual fuel temperature is within the temperature range. For example, at the engine shutdown time t1, the graph 604 defines an upper bound and the graph 606 defines a lower bound of the temperature range δ1. Similarly, at an engine shutdown time t2 that is longer than the engine idle time t1, the graph 604 defines an upper bound and the graph 606 defines a lower bound of the temperature range δ2, which is less than the temperature range δ1. Therefore, as demonstrated by graph 600, as the engine shutdown time increases, the span of the estimated fuel temperature range decreases, which corresponds to an increase in the confidence that the fuel temperature is equal to the ambient temperature. As demonstrated by graph 600, each of the temperature ranges δ1 and δ2 is centered on the ambient temperature (dashed line 602).

[0085] Referring to Figure 610, graph 611 shows the relationship between fuel temperature and fuel vapor pressure. For example, graph 611 can be obtained from a distillation curve. As shown in Figure 600, dashed line 602 refers to the ambient temperature, which corresponds to fuel vapor pressure 612. Small dashed line 604a indicates the upper limit of the temperature range δ1 corresponding to fuel vapor pressure 614a, and small dashed line 606a indicates the lower limit of the temperature range δ1 corresponding to fuel vapor pressure 616a. 614a and 616a together define the upper and lower limits of the estimated fuel vapor pressure range α1 corresponding to engine shutdown time t1. Similarly, dotted line 604b indicates the upper limit of the temperature range δ2 corresponding to fuel vapor pressure 614b, and dotted line 606b indicates the lower limit of the temperature range δ2 corresponding to fuel vapor pressure 616b. 614b and 616b together define the upper and lower limits of the estimated fuel vapor pressure range α2 corresponding to engine shutdown time t2. The estimated fuel vapor pressure range α2 is smaller than the estimated fuel vapor pressure range α1 because the confidence that the actual fuel vapor pressure is equal to the fuel vapor pressure estimated from the ambient temperature increases.

[0086] Next, referring to Figure 620, an example graph 621 shows the relationship between fuel vapor pressure and fuel injection amount. As the fuel vapor pressure and therefore the fuel volatility increase, the fuel injection amount decreases. Graph 621 shows a nonlinear relationship between fuel vapor pressure and fuel injection amount. However, other curve shapes are also possible, such as linear and other nonlinear curves, in which the fuel injection amount generally decreases as the fuel vapor pressure increases. As shown in Figure 610, the dotted line 612 refers to the fuel vapor pressure determined according to the ambient temperature, and the fuel vapor pressure corresponds to the fuel injection amount 622 using the relationship shown in the graph 621. Similarly, the upper and lower limits of the estimated fuel vapor pressure range α1 (indicated by small dotted lines 614a and 616a, respectively) correspond to fuel injection amounts 624a and 626a, respectively. The upper and lower limits of the estimated fuel vapor pressure range α2 (indicated by small dotted lines 614b and 616b, respectively) correspond to fuel injection amounts 624b and 626b, respectively. Because the estimated fuel vapor pressure range α1 is greater than the estimated fuel vapor pressure range α2, the difference between the fuel injection amounts 626a and 624a is greater than the difference between the fuel injection amounts 626b and 624b. To mitigate engine hysteresis during engine cold start, for example, a controller (e.g., Figure 2The controller 12 of the embodiment of the present invention can select the most conservative fuel injection amount for each estimated fuel vapor pressure range. For example, the fuel injection amount 626a can be selected for the estimated fuel vapor pressure range α1, and the fuel injection amount 626b can be selected for the estimated fuel vapor pressure range α2. The fuel injection amount 626a and the fuel injection amount 262b are greater than the fuel injection amount 622 corresponding to the ambient temperature 612. Therefore, by ensuring that the fuel vapor pressure (and therefore the fuel volatility) is not overestimated by using the ambient temperature as an estimate of the fuel temperature, the engine lag during the cold start of the engine can be reduced.

[0087] In this way, the physics-based model can determine the vapor pressure (and therefore volatility) of the aged fuel with a high degree of accuracy, thereby enabling the optimization of combustion parameters such as fuel injection timing, fuel injection amount, fuel fraction of PFI relative to DI, spark timing, and AFR for the determined vapor pressure. Thus, the reduced fuel volatility as the fuel ages is taken into account, thereby reducing engine lag and emissions during cold starts and increasing fuel performance. In addition, the combustion parameters can be further adjusted based on additional fuel characteristics (e.g., octane number, fuel type, etc.) and the confidence in the accuracy of the determined vapor pressure. Therefore, over-adjustment and under-adjustment of combustion parameters can be avoided, thereby further reducing engine lag, vehicle emissions, and operator dissatisfaction caused by aged fuel during cold starts.

[0088] A technical effect of adjusting one or more combustion parameters based on estimated fuel vapor pressure during engine starting is that engine lag and vehicle emissions may be reduced.

[0089] As an example, a method includes: during a cold start of an engine burning fuel, estimating a vapor pressure of fuel stored in a fuel tank via a predetermined fuel distillation curve; and adjusting a combustion parameter based on the estimated vapor pressure. In the foregoing examples, additionally or optionally, the predetermined distillation curve is selected from a plurality of predetermined fuel distillation curves based on one or more fuel characteristics. In any or all of the foregoing examples, additionally or optionally, the one or more fuel characteristics include alcohol content and fuel octane number. In any or all of the foregoing examples, additionally or optionally, the fuel octane number is determined in part based on an output of a knock sensor coupled to the engine. In any or all of the foregoing examples, additionally or optionally, estimating the fuel vapor pressure via the predetermined fuel distillation curve includes inputting a temperature of the fuel and a pressure of the fuel into a physics-based model that references the predetermined fuel distillation curve. In any or all of the foregoing examples, additionally or optionally, the fuel tank is open to atmosphere, the temperature of the fuel is assumed to be ambient temperature, and the fuel tank pressure is assumed to be atmospheric pressure. In any or all of the foregoing examples, additionally or optionally, the engine that burns the fuel includes an internal combustion engine having a plurality of cylinders, each cylinder receiving fuel directly into the cylinder from a direct injector and each cylinder receiving fuel from a port injector through an intake port, and wherein the combustion parameters include one or more of the following: a fuel injection amount from the direct injector and / or the port injector, a fuel injection timing of the port injector and / or the direct injector, a fuel fraction of port fuel injection relative to direct fuel injection, a commanded air-fuel ratio, and ignition timing. In any or all of the foregoing examples, additionally or optionally, adjusting the combustion parameters based on the estimated vapor pressure includes updating the settings of each combustion parameter relative to a previous setting and initiating a starting operation of the engine according to each updated setting.

[0090] As another example, a method includes: in response to an engine start request during a cold start condition, estimating volatility of fuel stored in a fuel tank using a physics-based model; determining a confidence level in the estimated volatility based on a duration of engine inactivity; and adjusting an injection amount and injection timing of fuel delivered from the fuel tank to an engine based on the estimated volatility and the determined confidence level. In the foregoing examples, additionally or optionally, the physics-based model includes a plurality of empirically determined fuel distillation curves, and estimating volatility of fuel stored in the fuel tank using the physics-based model includes selecting a fuel distillation curve from the plurality of empirically determined fuel distillation curves based on at least one of an octane rating, an age, and a type of the fuel stored in the fuel tank. In any or all of the foregoing examples, additionally or optionally, estimating volatility of fuel stored in the fuel tank using the physics-based model also includes estimating fuel vapor pressure via the selected fuel distillation curve based on a current fuel temperature and a current fuel tank pressure. In any or all of the foregoing examples, additionally or optionally, the current fuel temperature is estimated as an ambient temperature measured by an ambient temperature sensor, and the current fuel tank pressure is estimated as an air pressure measured by an ambient pressure sensor. In any or all of the foregoing examples, additionally or optionally, the determined confidence of the estimated fuel volatility increases as the engine inactivity duration increases until a maximum confidence is reached at a threshold engine inactivity duration. In any or all of the foregoing examples, additionally or optionally, adjusting the injection amount and the injection timing based on the estimated volatility and the determined confidence includes: increasing the injection amount relative to a previous injection amount setting as the estimated volatility decreases, wherein the injection amount is increased to a greater extent as the determined confidence increases, and the injection amount is increased to a lesser extent as the determined confidence decreases; decreasing the injection amount relative to the previous injection amount as the estimated volatility increases, wherein the injection amount is decreased to a greater extent as the determined confidence increases, and the injection amount is decreased to a lesser extent as the determined confidence decreases. The method further comprises: reducing the injection amount to a lesser extent as the determined confidence decreases; advancing the injection timing relative to a previous injection timing setting as the estimated volatility decreases, wherein the injection timing is advanced to a greater extent as the determined confidence increases and is advanced to a lesser extent as the determined confidence decreases; and retarding the injection timing relative to the previous injection timing setting as the estimated volatility increases, wherein the injection timing is retarded to a greater extent as the determined confidence increases and is retarded to a lesser extent as the determined confidence decreases.

[0091] As another example, a system for a vehicle, the system for a vehicle comprising: an engine, the engine comprising a plurality of cylinders, each cylinder comprising a spark plug and a fuel injector for delivering fuel; a fuel system, the fuel system comprising a fuel tank for storing the fuel; an evaporative emission system, the evaporative emission system being in fluid communication with the fuel system, the evaporative emission system being coupled to the atmosphere via a vent; an ambient temperature sensor, the ambient temperature sensor being coupled to an intake passage of the engine; an ambient pressure sensor, the ambient pressure sensor being coupled to the intake passage of the engine; an engine coolant temperature sensor A sensor, the engine coolant temperature sensor coupled to a cooling sleeve of the engine; and a controller, the controller maintaining executable instructions in a non-transitory memory, the executable instructions, when executed, causing the controller to: determine an engine cold start condition based on the output of the engine coolant temperature sensor and an engine start request; estimate the vapor pressure of the fuel using a physics-based model in response to the determination of the engine cold start condition; and adjust the pulse width and / or timing of the signal sent to the fuel injector and the spark plug based on the estimated vapor pressure and engine shutdown time. In the foregoing examples, the system additionally or optionally includes a fuel tank isolation valve coupled between the fuel system and the evaporative emissions system, and wherein the fuel tank isolation valve is a normally open valve. In any or all of the foregoing examples, the system additionally or optionally also includes an autonomous vehicle control system, wherein the autonomous vehicle control system stores executable instructions in a non-transitory memory, the executable instructions enabling the vehicle to be operated without input from an operator. In any or all of the foregoing examples, additionally or optionally, the estimated vapor pressure is a range of vapor pressure values ​​determined based on an ambient temperature measured by the ambient pressure sensor, a temperature decay function, and the engine shutdown time, the span of the range decreasing as the engine shutdown time increases. In any or all of the foregoing examples, additionally or optionally, adjusting the pulse width and / or timing of the signal sent to the fuel injector and the spark plug includes selecting the most conservative adjustment for the range of vapor pressure values.In any or all of the foregoing examples, additionally or optionally, estimating the vapor pressure based on the ambient temperature and the ambient pressure, and adjusting the pulse width and / or timing of the signal sent to the fuel injector and the spark plug based on the estimated vapor pressure and the engine shutdown time also includes: determining a confidence level in the estimated fuel vapor pressure based on the engine shutdown time; increasing the pulse width of the signal sent to the fuel injector relative to a previously determined pulse width as the estimated vapor pressure decreases, increasing the pulse width of the signal to a greater extent as the confidence level increases; and advancing the timing of the signal sent to the spark plug relative to a previously determined timing as the estimated vapor pressure decreases, advancing the timing of the signal to a greater extent as the confidence level increases.

[0092] In another representation, a method for a hybrid electric vehicle includes: estimating a vapor pressure of fuel stored in a fuel tank via a predetermined fuel distillation curve prior to transitioning from an electric mode to an engine operating mode; and adjusting a combustion parameter based on the estimated vapor pressure. In the foregoing examples, additionally or optionally, the method also includes determining a confidence level for the estimated fuel vapor pressure based on an engine inactivity duration; and further adjusting the combustion parameter based on the determined confidence level. In any or all of the foregoing examples, additionally or optionally, estimating the fuel vapor pressure via the predetermined fuel distillation curve includes inputting a temperature of the fuel and a pressure of the fuel into a physics-based model that references the predetermined fuel distillation curve. In any or all of the foregoing examples, additionally or optionally, the fuel tank is vented to atmosphere via a fuel vapor storage canister, assuming that the temperature of the fuel is ambient temperature, and assuming that the fuel tank pressure is atmospheric pressure. In any or all of the foregoing examples, additionally or optionally, the estimated fuel vapor pressure is further adjusted based on a purge compensation factor determined during a previous purge event of the fuel vapor storage canister. In any or all of the foregoing examples, additionally or optionally, the method further comprises starting the engine according to the adjusted combustion parameters.

[0093] It should be noted that the exemplary control and estimation routines included herein can be used for various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non-transitory memory and can be executed by a control system including a combination of a controller and various sensors, actuators and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. Therefore, the various actions, operations and / or functions described can be omitted in the described sequence, in parallel, or in some cases. Similarly, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for the ease of description and description. One or more of the described actions, operations and / or functions can be repeatedly performed according to the specific strategy used. In addition, the described actions, operations and / or functions can clearly represent the code in the non-transitory memory of the computer-readable storage medium to be programmed into the engine control system, wherein the described actions are implemented by executing instructions in a system including a combination of various engine hardware components and an electronic controller.

[0094] It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments should not be viewed in a limiting sense, as numerous variations are possible. For example, the above techniques can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or properties disclosed herein.

[0095] The appended claims particularly point out certain combinations and subcombinations regarded as novel and non-obvious. The claims may refer to "an" element or a "first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are also deemed to be included in the subject matter of the present disclosure.

[0096] According to the present invention, a method is provided having: during a cold start of an engine burning the fuel, estimating the vapor pressure of fuel stored in a fuel tank via a predetermined fuel distillation curve; and adjusting combustion parameters based on the estimated vapor pressure.

[0097] According to an embodiment, the predetermined distillation curve is selected from a plurality of predetermined fuel distillation curves based on one or more fuel characteristics.

[0098] According to an embodiment, the one or more fuel characteristics include alcohol content and fuel octane rating.

[0099] According to an embodiment, the fuel octane rating is determined based in part on an output of a knock sensor coupled to the engine.

[0100] According to an embodiment, estimating the fuel vapor pressure via the predetermined fuel distillation curve comprises inputting the temperature of the fuel and the pressure of the fuel into a physics-based model that references the predetermined fuel distillation curve.

[0101] According to an embodiment, the fuel tank is vented to atmosphere, the temperature of the fuel is assumed to be ambient temperature, and the fuel tank pressure is assumed to be atmospheric pressure.

[0102] According to an embodiment, the fuel-burning engine includes an internal combustion engine having a plurality of cylinders, each cylinder receiving fuel directly into the cylinder from a direct injector and each cylinder receiving fuel from an intake port injector through an intake port, and wherein the combustion parameters include one or more of the following: a fuel injection amount from the direct injector and / or the intake port injector, a fuel injection timing of the intake port injector and / or the direct injector, a fuel fraction of intake port fuel injection relative to direct fuel injection, a commanded air-fuel ratio, and an ignition timing.

[0103] According to an embodiment, adjusting the combustion parameters based on the estimated vapor pressure comprises updating a setting of each combustion parameter relative to a previous setting and initiating a starting operation of the engine according to each updated setting.

[0104] According to the present invention, a method is provided, the method having: in response to an engine start request during a cold start condition, estimating volatility of fuel stored in a fuel tank using a physics-based model; determining a confidence level in the estimated volatility based on an engine inactivity duration; and adjusting an injection amount and injection timing of fuel delivered from the fuel tank to an engine based on the estimated volatility and the determined confidence level.

[0105] According to an embodiment, the physics-based model includes a plurality of empirically determined fuel distillation curves, and using the physics-based model to estimate the volatility of the fuel stored in the fuel tank includes selecting a fuel distillation curve from the plurality of empirically determined fuel distillation curves based on at least one of an octane rating, an age, and a type of the fuel stored in the fuel tank.

[0106] According to an embodiment, estimating the volatility of the fuel stored in the fuel tank using the physics-based model further comprises estimating a fuel vapor pressure via the selected fuel distillation curve based on a current fuel temperature and a current fuel tank pressure.

[0107] According to an embodiment, the current fuel temperature is estimated as the ambient temperature measured by an ambient temperature sensor, and the current fuel tank pressure is estimated as the air pressure measured by an ambient pressure sensor.

[0108] According to an implementation, the determined confidence level of the estimated fuel volatility increases as the engine inactivity duration increases until a maximum confidence level is reached at a threshold engine inactivity duration.

[0109] According to an embodiment, adjusting the injection amount and the injection timing based on the estimated volatility and the determined confidence level includes: increasing the injection amount relative to a previous injection amount setting as the estimated volatility decreases, wherein the injection amount is increased to a greater extent as the determined confidence level increases, and the injection amount is increased to a lesser extent as the determined confidence level decreases; decreasing the injection amount relative to the previous injection amount as the estimated volatility increases, wherein the injection amount is decreased to a greater extent as the determined confidence level increases, and the injection amount is increased to a lesser extent as the determined confidence level decreases; The method further comprises: determining an injection amount as the estimated volatility decreases and an injection quantity as the injection amount decreases; advancing the injection timing relative to a previous injection timing setting as the estimated volatility decreases, wherein the injection timing is advanced to a greater extent as the determined confidence increases and the injection timing is advanced to a lesser extent as the determined confidence decreases; and retarding the injection timing relative to the previous injection timing setting as the estimated volatility increases, wherein the injection timing is retarded to a greater extent as the determined confidence increases and the injection timing is retarded to a lesser extent as the determined confidence decreases.

[0110] According to the present invention, a system for a vehicle is provided, the system for the vehicle having: an engine, the engine including a plurality of cylinders, each cylinder including a spark plug and a fuel injector for delivering fuel; a fuel system, the fuel system including a fuel tank for storing the fuel; an evaporative emission system, the evaporative emission system being in fluid communication with the fuel system, the evaporative emission system being coupled to the atmosphere via a vent; an ambient temperature sensor, the ambient temperature sensor being coupled to an intake passage of the engine; an ambient pressure sensor, the ambient pressure sensor being coupled to the intake passage of the engine; an engine coolant temperature sensor, the engine coolant temperature sensor being coupled to a cooling sleeve of the engine; and a controller, the controller retaining executable instructions in a non-transitory memory, the executable instructions when executed causing the controller to: determine an engine cold start condition based on an output of the engine coolant temperature sensor and an engine start request; estimate a vapor pressure of the fuel using a physics-based model in response to the determination of the engine cold start condition; and adjust a pulse width and / or timing of a signal sent to the fuel injector and the spark plug based on the estimated vapor pressure and an engine shutdown time.

[0111] According to an embodiment, the invention also features a fuel tank isolation valve coupled between the fuel system and the evaporative emissions system, and wherein the fuel tank isolation valve is a normally open valve.

[0112] According to an embodiment, the invention also features an autonomous vehicle control system wherein the autonomous vehicle control system stores executable instructions in a non-transitory memory that enable operation of the vehicle without input from an operator.

[0113] According to an embodiment, the estimated vapor pressure is a range of vapor pressure values ​​determined based on the ambient temperature measured by the ambient pressure sensor, a temperature decay function and the engine shut-off time, and the span of the range decreases as the engine shut-off time increases.

[0114] According to an embodiment, adjusting the pulse width and / or timing of the signals sent to the fuel injector and the spark plug comprises selecting the most conservative adjustment for the range of vapor pressure values.

[0115] According to the implementation scheme, estimating the vapor pressure based on the ambient temperature and the ambient pressure, and adjusting the pulse width and / or timing of the signal sent to the fuel injector and the spark plug based on the estimated vapor pressure and the engine shutdown time also includes: determining a confidence level of the estimated fuel vapor pressure based on the engine shutdown time; increasing the pulse width of the signal sent to the fuel injector relative to a previously determined pulse width as the estimated vapor pressure decreases, and increasing the pulse width of the signal to a greater extent as the confidence level increases; and advancing the timing of the signal sent to the spark plug relative to a previously determined timing as the estimated vapor pressure decreases, and advancing the timing of the signal to a greater extent as the confidence level increases.

Claims

1. A method, the method include: During a cold start of a fuel-burning engine, estimating a vapor pressure of fuel stored in a fuel tank based on a temperature of the fuel using a predetermined fuel distillation curve that relates the temperature of the fuel to a percentage of the fuel that evaporates, the predetermined fuel distillation curve being selected from a plurality of predetermined fuel distillation curves; and Combustion parameters are adjusted based on the estimated vapor pressure. 2 . The method of claim 1 , wherein the predetermined distillation curve is selected from the plurality of predetermined fuel distillation curves based on one or more characteristics of the fuel stored in the fuel tank. 3 . The method of claim 2 , wherein the one or more characteristics of the fuel stored in the fuel tank include alcohol content, fuel age, pressure in the fuel tank, and fuel octane rating. 4 . The method of claim 3 , wherein the fuel octane rating is determined based in part on an output of a knock sensor coupled to the engine.

5. The method of claim 1 , wherein estimating the vapor pressure of the fuel stored in the fuel tank based on the temperature of the fuel using the predetermined fuel distillation curve comprises inputting the temperature of the fuel and the pressure of the fuel into a physics-based model that references the predetermined fuel distillation curve.

6. The method of claim 5, wherein the fuel tank is vented to atmosphere, the temperature of the fuel is assumed to be ambient temperature, and the fuel tank pressure is assumed to be atmospheric pressure.

7. The method of claim 1 , wherein the engine that burns the fuel comprises an internal combustion engine having a plurality of cylinders, each cylinder receiving fuel directly into the cylinder from a direct injector and each cylinder receiving fuel from a port injector via an intake port, and wherein the combustion parameters comprise one or more of: a fuel injection amount from the direct injector and / or the port injector, a fuel injection timing of the port injector and / or the direct injector, a fuel fraction of port fuel injection relative to direct fuel injection, a commanded air-fuel ratio, and ignition timing.

8. The method of claim 7, wherein adjusting the combustion parameters based on the estimated vapor pressure comprises updating a setting for each combustion parameter relative to a previous setting and initiating a starting operation of the engine according to each updated setting.

9. The method of claim 1 wherein said adjusting said combustion parameter is further based on a confidence level of said estimated vapor pressure, said confidence level of said estimated vapor pressure being determined based on a duration of engine inactivity prior to said cold start.

10. A system for a vehicle, the system for a vehicle include: an engine comprising a plurality of cylinders, each cylinder including a spark plug and a fuel injector for delivering fuel; a fuel system, the fuel system comprising a fuel tank for storing the fuel; an evaporative emissions system in fluid communication with the fuel system, the evaporative emissions system coupled to the atmosphere via a vent; an ambient temperature sensor coupled to an intake duct of the engine; an ambient pressure sensor coupled to the intake passage of the engine; an engine coolant temperature sensor coupled to a cooling jacket of the engine; as well as a controller that retains executable instructions in a non-transitory memory that, when executed, cause the controller to: determining an engine cold start condition based on an output of the engine coolant temperature sensor and an engine start request; estimating a vapor pressure of the fuel using a physics-based model in response to the determination of the engine cold start condition, the physics-based model relating a temperature of the fuel to a percentage of vaporization of the fuel via an empirically determined fuel distillation curve selected from a plurality of empirically determined fuel distillation curves stored in the non-transitory memory; as well as Pulse widths and / or timings of signals sent to the fuel injectors and the spark plugs are adjusted based on the estimated vapor pressure and engine shut-off time.

11. The system of claim 10, further comprising a fuel tank isolation valve coupled between the fuel system and the evaporative emissions system, and wherein the fuel tank isolation valve is a normally open valve.

12. The system of claim 10, further comprising an autonomous vehicle control system, wherein the autonomous vehicle control system stores executable instructions in a non-transitory memory, the executable instructions enabling operation of the vehicle without input from an operator.

13. The system of claim 10, wherein the temperature of the fuel is an ambient temperature measured by the ambient temperature sensor, and the estimated vapor pressure is a range of vapor pressure values ​​determined based on the ambient temperature, a temperature decay function, and the engine shutdown time, the span of the range decreasing as the engine shutdown time increases.

14. The system of claim 13 wherein adjusting the pulse width and / or timing of the signals sent to the fuel injector and the spark plug comprises selecting the most conservative adjustment for the range of vapor pressure values.

15. The system of claim 10, wherein the pulse width and / or timing of the signal sent to the fuel injector and the spark plug is adjusted based on the estimated vapor pressure and the engine shut-off time. include: determining a confidence level of the estimated fuel vapor pressure based on the engine off time; increasing the pulse width of the signal sent to the fuel injector relative to a previously determined pulse width as the estimated vapor pressure decreases, increasing the pulse width of the signal to a greater extent as the confidence level increases; as well as The timing of the signal sent to the spark plug is advanced relative to a previously determined timing as the estimated vapor pressure decreases and the timing of the signal is advanced to a greater extent as the confidence increases.

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