Patent Publication Number: US-7720593-B2

Title: Fuel injection strategy for gasoline direct injection engine during high speed/load operation

Description:
BACKGROUND 
   1. Technical Field 
   The present disclosure relates to a system and method for fuel injection in a gasoline direct injection engine during high speed/load operation. 
   2. Background Art 
   Direct-injection spark-ignition (DISI) internal combustion engines have been developed to reduce fuel consumption and feedgas emissions of gasoline engines. DISI engines may operate in a stratified charge mode with layers or strata of richer air/fuel ratio near the spark plug and progressively leaner layers below under certain operating conditions, such as low to medium loads and engine speeds and during starting, for example. At higher engine loads and speeds, a stoichiometric or slightly rich homogeneous charge is provided where the air-fuel mixture of the charge is generally well-mixed and homogeneous throughout the combustion chamber. 
   DISI engines have traditionally used a low-pressure fuel pump in combination with an auxiliary or high-pressure fuel pump to produce injection pressures that provide desired torque while meeting combustion efficiency and emissions targets. More recently, as disclosed in U.S. Pat. No. 6,712,037 for example, gasoline direct injection engines have been developed that rely solely on a low-pressure fuel pump, which provides advantages in terms of lower cost and complexity, but may have reduced cold start performance and reduced maximum torque output at higher engine speeds/loads. 
   A fuel injection strategy to improve performance during engine startup is disclosed in U.S. Pat. No. 7,234,440, which uses two or more fuel injections for a single combustion event or cycle. During start-up some fuel may be injected during the exhaust stroke with the remaining fuel injected during the intake and/or compression strokes. That strategy includes transitioning to a single injection for normal operation after some number of combustion events have occurred. Similarly, U.S. Pat. No. 7,089,908 discloses modifying valve timing to increase residual exhaust gases and injecting some fuel during the exhaust stroke under partial loading conditions, but transitions to a reference mode with a single injection during the intake stroke at higher speeds/loads. 
   Under high speed, high load conditions, particularly in applications that rely solely on a low-pressure fuel pump with a side-mounted fuel injector, the injected fuel spray may be deformed by the incoming air stream, which prevents fuel from penetrating across the cylinder and mixing properly to form a homogeneous charge. One method to improve mixture homogeneity, as disclosed in U.S. Pat. No. 6,378,488, uses an intake air deflector in the cylinder head to reduce the influence of the intake air on the injected fuel spray. While this approach may be suitable for many applications, it affects operation across the entire operating range and requires increased complexity in the cylinder head to form the deflectors, which may also impact the cost of the system. 
   SUMMARY 
   A system and method for controlling operation of a multiple cylinder direct injection internal combustion engine include injecting a fraction of total fuel injected per engine cycle directly into the combustion chamber during the exhaust stroke at high engine speeds and loads to reduce the effect of intake airflow on the injection spray and improve fuel-air mixture homogeneity. 
   In one embodiment a direct injection multiple cylinder internal combustion engine includes a fuel injector associated with each cylinder and configured to inject fuel directly into the cylinder in response to control signals during operation of the engine. A controller in communication with each fuel injector and configured to generate control signals to control fuel injection generates a fuel injection signal for the injector to start and end a first fuel injection during an exhaust stroke when the engine is operating at high speed and high load. The first fuel injection mixes with inducted air and fuel from at least a second fuel injection that starts during the subsequent intake stroke and/or a compression stroke of the same cycle to form a mixture for combustion. An ignition source, such as a spark plug, ignites the mixture to initiate combustion. The system and method are particularly suited for use with low-pressure direct injection engines that have a single fuel pump to provide fuel at a pressure of less than about 40 bar for example. 
   The present disclosure includes embodiments having various advantages. For example, the systems and methods of the present disclosure provide increased torque at high engine speeds and loads using a single, low-pressure fuel pump. Embodiments of the present disclosure provide fuel-air mixing homogeneity at high engine speeds and loads resulting in reduced soot. Separation between a first fuel injection and subsequent fuel injection(s) according to the present disclosure increases mixing time and may reduce piston wetting to reduce smoke. Embodiments of the present disclosure facilitate elimination of an auxiliary high-pressure fuel pump reducing cost and complexity of the engine. 
   The above advantages and other advantages and features will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 

   
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of illustrating operation of a system or method for controlling a direct injection internal combustion engine according to one embodiment of the present disclosure; 
       FIG. 2  is a graph illustrating the relationship between smoke emission and injection timing in a low-pressure direct injection engine at high speed/load according to one embodiment of the present disclosure; 
       FIG. 3  is a diagram illustrating a split fuel injection strategy at high speed/load conditions with a first fuel injection during the exhaust stroke and a second fuel injection during the immediately following intake stroke according to one embodiment of the present disclosure; 
       FIGS. 4A-4F  are graphics illustrating computer simulated fuel vapor evolution during the late exhaust and early intake stroke for a fuel injection strategy according to one embodiment of the present disclosure; 
       FIG. 5  is a graph comparing a single injection to a split injection using dynamometer measured smoke emission as a function of injection timing of the end of the injection occurring during the intake stroke of one embodiment of the present disclosure; 
       FIG. 6  is a graph comparing a single injection to a split injection using dynamometer measured NMEP as a function of the end of injection for the injection occurring during the intake stroke of one embodiment of the present disclosure; 
       FIG. 7  is a graph comparing a single injection to a split injection using dynamometer measured engine-out (feedgas) oxygen as a function of the end of injection timing for the injection occurring during the intake stroke of one embodiment of the present disclosure; 
       FIG. 8  is a graph comparing a single injection to a split injection using dynamometer measured engine-out (feedgas) hydrocarbon emissions as a function of the end of injection timing for the injection occurring during the intake stroke of one embodiment of the present disclosure; and 
       FIG. 9  is a flow chart illustrating operation of a system or method for controlling a direct injection internal combustion engine according to one embodiment of the present disclosure. 
   

   DETAILED DESCRIPTION OF EMBODIMENT(S) 
   As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. The representative embodiments used in the illustrations relate generally to a four-stroke, multi-cylinder, internal combustion engine with direct or in-cylinder injection. Those of ordinary skill in the art may recognize similar applications or implementations with other engine/vehicle technologies. 
   System  10  includes an internal combustion engine having a plurality of cylinders, represented by cylinder  12 , with corresponding combustion chambers  14 . As one of ordinary skill in the art will appreciate, system  10  includes various sensors and actuators to effect control of the engine. A single sensor or actuator may be provided for the engine, or one or more sensors or actuators may be provided for each cylinder  12 , with a representative actuator or sensor illustrated and described. For example, each cylinder  12  may include four actuators that operate intake valves  16  and exhaust valves  18  for each cylinder in a multiple cylinder engine. However, the engine may include only a single engine coolant temperature sensor  20 . 
   Controller  22  has a microprocessor  24 , which is part of a central processing unit (CPU), in communication with memory management unit (MMU)  25 . MMU  25  controls the movement of data among various computer readable storage media and communicates data to and from CPU  24 . The computer readable storage media preferably include volatile and nonvolatile storage in read-only memory (ROM)  26 , random-access memory (RAM)  28 , and keep-alive memory (KAM)  30 , for example. KAM  30  may be used to store various operating variables while CPU  24  is powered down. The computer-readable storage media may be implemented using any of a number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory devices capable of storing data, some of which represent executable instructions, used by CPU  24  in controlling the engine or vehicle into which the engine is mounted. The computer-readable storage media may also include floppy disks, CD-ROMs, hard disks, and the like. 
   CPU  24  communicates with various sensors and actuators via an input/output (I/O) interface  32 . Interface  32  may be implemented as a single integrated interface that provides various raw data or signal conditioning, processing, and/or conversion, short-circuit protection, and the like. Alternatively, one or more dedicated hardware or firmware chips may be used to condition and process particular signals before being supplied to CPU  24 . Examples of items that are actuated under control by CPU  24 , through I/O interface  32 , are fuel injection timing, fuel injection rate, fuel injection duration, throttle valve position, spark plug ignition timing (in the event that engine  10  is a spark-ignition engine), and others. Sensors communicating input through I/O interface  32  may be indicating piston position, engine rotational speed, vehicle speed, coolant temperature, intake manifold pressure, accelerator pedal position, throttle valve position, air temperature, exhaust temperature, exhaust air to fuel ratio, exhaust component concentration, and air flow, for example. Some controller architectures do not contain an MMU  25 . If no MMU  25  is employed, CPU  24  manages data and connects directly to ROM  26 , RAM  28 , and KAM  30 . Of course, the present invention could utilize more than one CPU  24  to provide engine control and controller  22  may contain multiple ROM  26 , RAM  28 , and KAM  30  coupled to MMU  25  or CPU  24  depending upon the particular application. 
   In operation, air passes through intake  34  and is distributed to the plurality of cylinders via an intake manifold, indicated generally by reference numeral  36 . System  10  preferably includes a mass airflow sensor  38  that provides a corresponding signal (MAF) to controller  22  indicative of the mass airflow. A throttle valve  40  may be used to modulate the airflow through intake  34 . Throttle valve  40  is preferably electronically controlled by an appropriate actuator  42  based on a corresponding throttle position signal generated by controller  22 . The throttle position signal may be generated in response to a corresponding engine output or demanded torque indicated by an operator via accelerator pedal  46 . A throttle position sensor  48  provides a feedback signal (TP) to controller  22  indicative of the actual position of throttle valve  40  to implement closed loop control of throttle valve  40 . 
   A manifold absolute pressure sensor  50  is used to provide a signal (MAP) indicative of the manifold pressure to controller  22 . Air passing through intake manifold  36  enters combustion chamber  14  through appropriate control of one or more intake valves  16 . Intake valves  16  and exhaust valves  18  may be controlled using a conventional camshaft arrangement, indicated generally by reference numeral  52 . Camshaft arrangement  52  includes a camshaft  54  that completes one revolution per combustion or engine cycle, which requires two revolutions of crankshaft  56  for a four-stroke engine, such that camshaft  54  rotates at half the speed of crankshaft  56 . Rotation of camshaft  54  (or controller  22  in a variable cam timing or camless engine application) controls one or more exhaust valves  18  to exhaust the combusted air/fuel mixture through an exhaust manifold. A cylinder identification sensor  58  provides a signal (CID) once each revolution of the camshaft or equivalently once each combustion cycle from which the rotational position of the camshaft can be determined. In one embodiment, cylinder identification sensor  58  includes a sensor wheel  60  that rotates with camshaft  54  and includes a single protrusion or tooth whose rotation is detected by a Hall effect or variable reluctance sensor  62 . Cylinder identification sensor  58  may be used to identify with certainty the position of a designated piston  64  within cylinder  12 . The particular cylinder number and piston position may vary depending upon the particular application and implementation. 
   Additional rotational position information for controlling the engine is provided by a crankshaft position sensor  66  that includes a toothed wheel  68  and an associated sensor  70 . In one embodiment, toothed wheel  68  includes thirty-five teeth equally spaced at ten-degree (10°) intervals with a single twenty-degree gap or space referred to as a missing tooth. In one embodiment for a four-cylinder engine, the missing tooth is positioned to identify ninety degrees (90°) before top center (BTC) of cylinder # 1  and cylinder # 4 . In combination with cylinder identification sensor  58 , the missing tooth of crankshaft position sensor  66  may be used to generate a signal (PIP) used by controller  22  for fuel injection and ignition timing as explained in greater detail herein. In one embodiment, a dedicated integrated circuit chip (EDIS) within controller  22  is used to condition/process the raw rotational position signal generated by position sensor  66  and outputs a signal (PIP) once per cylinder per combustion cycle, i.e. for a four-cylinder engine, four PIP signals per combustion cycle are generated for use by the control logic. Depending upon the particular application, control logic within CPU  24  may have additional position information provided by sensor  66  to generate a PIP signal or equivalent, for example. Crankshaft position sensor  66  may also be used to determine engine rotational speed and to identify cylinder combustion based on an absolute, relative, or differential engine rotation speed where desired. 
   An exhaust gas oxygen sensor  62  provides a signal (EGO) to controller  22  indicative of whether the exhaust gasses are lean or rich of stoichiometry. Depending upon the particular application, sensor  62  may provide a two-state signal corresponding to a rich or lean condition, or alternatively a signal that is proportional to the stoichiometry of the exhaust feedgas. This signal may be used to adjust the air/fuel ratio, or control the operating mode of one or more cylinders, for example. The exhaust gas is passed through the exhaust manifold and one or more emission control or treatment devices  90  before being exhausted to atmosphere. 
   A fuel delivery system includes a fuel tank  100  with a fuel pump  110  for supplying fuel to a common fuel rail  112  that supplies injectors  80  with pressurized fuel. In one embodiment, the fuel delivery system includes only one fuel pump  110 , which is a low-pressure fuel pump that provides pressurized fuel with a maximum pressure of less than about 35-40 bar (3.5-4.0 MPa) and typically between 30 bar-35 bar during normal operation. Fuel pressure may be controlled within a predetermined operating range of fuel pump  110  by a corresponding signal from controller  22 . The injection strategy of the present disclosure was developed for use at high engine speeds/loads in low-pressure direct injection engines that rely solely on a low-pressure fuel pump such that an auxiliary or high-pressure pump (operating in the range of 150 bar) could be eliminated to reduce complexity and cost of the fuel system. However, the strategy is not necessarily limited to such applications and could be used in high-pressure fuel injection applications, although may not have the same advantages or result in the same degree of performance improvement. 
   In the representative embodiment illustrated in  FIG. 1 , fuel injector  80  is side-mounted on the intake side of combustion chamber  14 , typically between intake valves  16 . Fuel injector  80  injects a quantity of fuel directly into combustion chamber  14  in one or more injection events for a single engine cycle based on the current operating mode in response to a signal (fpw) generated by controller  22  and processed by driver  82 . At the appropriate time during the combustion cycle, controller  22  generates a signal (SA) processed by ignition system  84  to control spark plug  86  and initiate combustion within chamber  14 . 
   The present inventors have recognized that low-pressure direct injection applications often produce lower engine torque at high engine speeds relative to high-pressure systems. This is believed to be due to insufficient fuel-air mixing homogeneity. Lower fuel injection pressures may result in low penetration of the fuel spray droplets. Combined with strong intake airflow motion, the fuel spray is prevented from sufficient penetration through the airflow to the exhaust side of the combustion chamber. The injection strategy described herein improves high speed engine torque in low-pressure direct injection systems and may also provide benefits in high-pressure systems. 
   Controller  22  includes software and/or hardware implementing control logic to control the engine. In one embodiment, controller  22  controls injector  80  at high engine speed/load to inject fuel from fuel rail  112  directly into cylinder  14  in a first fuel injection during an exhaust stroke that mixes with air inducted through intake  36  and fuel from at least a second fuel injection starting during a subsequent intake stroke and/or compression stroke of the same engine cycle to form a mixture for combustion. Fuel is provided to common fuel rail  112  by pump  110 , which may be a low-pressure pump that supplies pressurized fuel at a pressure of less than about 35-40 bar (3.5-4.0 MPa), for example. Engine speed may be determined based on the signal from crankshaft sensor  70  with high speed corresponding to a calibratable threshold related to maximum engine speed, such as at least 80% or 90% or corresponding values, for example. High load may be determined based on one or more signals from sensors including pedal position sensor  46 , throttle position sensor  48 , mass airflow sensor  38 , and manifold pressure sensor  50 , for example, with high load corresponding to a calibratable threshold related to full load, maximum torque, or wide open throttle, such as at least 80% or 90% or corresponding values, for example. The beginning, duration, and/or end of fuel injection events may be designated relative to crankshaft rotational position or degrees of crankshaft rotation. As used herein, start-of-injection (SOI) and end-of-injection events are generally referenced relative to degrees before top-dead-center (BTDC) of compression, i.e. relative to the number of degrees of crankshaft rotation before a piston reaches its uppermost position within the cylinder during the compression stroke of the combustion cycle. In terms of crankshaft or crank angle, zero/720 degrees corresponds to TDC at the beginning of the power stroke with 360 degrees corresponding to TDC at the end of the exhaust stroke and beginning of the intake stroke. Of course, the control strategy of this disclosure is not limited to any particular reference system or notation and other methods for designating or measuring the beginning, ending, and/or duration of injection events may also be used. 
   During development of the fuel injection strategy of the present disclosure, it was recognized that mixture homogeneity can be improved by advancing fuel injection timing, which improves evaporation of fuel contacting the piston and increases time for the mixing process prior to ignition. However, the fuel injection timing is constrained by limits on smoke production. Line  200  in the graph of  FIG. 2  illustrates dynamometer measured smoke emission as a function of injection timing for a low-pressure direct injection engine at 5000 rpm, wide-open throttle (WOT). This graph illustrates that smoke increases if injection timing is too early as indicated by reference numeral  202 , which is believed to be caused by increased piston wetting. Similarly, smoke increases if fuel injection timing is too late as indicated by reference numeral  204 , which is believed to be due to the lack of time for mixing. As such, embodiments of the present disclosure advance fuel injection timing with a portion of the total amount of fuel to attain a desired torque injected during the late exhaust stroke and the remaining fuel injected during the immediately following intake and/or compression stroke of the same engine cycle. 
     FIG. 3  is a graphical representation of one embodiment of a fuel injection strategy according to the present disclosure. Reference numeral  250  represents top dead center (TDC) for the piston between the exhaust stroke and intake stroke. As shown in  FIG. 3 , a first fuel injection  260  begins and ends during the late exhaust stroke while the intake valves are still closed or only partially open where intake air flow momentum is not present or insignificant. This allows the fuel spray to penetrate the combustion chamber toward the exhaust side without being affected by the intake airflow. The low fuel penetration rate associated with the lower fuel injection pressure keeps substantially all of the fuel injected during the exhaust stroke within the combustion chamber for mixing with intake airflow and fuel injected during the subsequent fuel injection(s). This prevents any significant amount of fuel from escaping through the open exhaust valve(s), which could increase hydrocarbon emissions and/or adversely impact emissions treatment devices. A second fuel injection  262  begins during the immediately following intake stroke as the piston moves downward in the cylinder away from TDC and away from the fuel spray. Depending upon the particular application and implementation, the second fuel injection may extend into the compression stroke. Alternatively, the second fuel injection may end during the intake stroke as illustrated, with one or more additional fuel injections during the compression stroke, or the second injection may start and end during the compression stroke in some operating modes. 
   As illustrated in the embodiment of  FIG. 3 , the first injection is separated from the second injection to provide mixing and dispersion time for the first injection. Neither the end of the first fuel injection nor the beginning of the second fuel injection is performed immediately surrounding the TDC position of the piston to reduce piston wetting and the resulting smoke emissions. In this embodiment, the first injection starts at about 390 degrees BTDC of compression or, equivalently, at about 30 degrees before TDC of the intake, and has a duration of about 13 crank angle degrees. The second injection begins at about 300 degrees BTDC compression and has a duration of about 110 degrees. In another embodiment with an engine at 5000 rpm and wide-open throttle (WOT), the first injection begins at about 391 degrees BTDC compression and ends at TDC intake or, equivalently, 360 degrees BTDC compression. A second injection is separated by 36 crank angle degrees beginning at 324 degrees BTDC compression and ending at 200 degrees BTDC compression and resulting in a torque improvement of 1.5% relative to a single low-pressure injection. 
     FIGS. 4A-4F  are diagrams representing computer simulated operation of a fuel injection strategy for a low-pressure direct injection engine according to one embodiment of the present disclosure. The diagrams of  FIG. 4  illustrate fuel vapor evolution at 20 degree crank angle increments along the central cross section of the cylinder around TDC between the exhaust and intake stroke. As shown in  FIG. 4A  representing a crank angle of 320 degrees during the late exhaust stroke, the exhaust port  280  is open and fuel  290  is injected from a side-mounted fuel injector mounted on the intake side of the cylinder. As shown in  FIG. 4B  representing a crank angle of 340 degrees, the fuel vapor and liquid fuel  290  penetrate into the cylinder toward the exhaust side as the intake port  282  begins to open and the exhaust port  280  begins to close. At this stage, the in-cylinder pressure is generally higher than the intake port pressure and the fuel vapor and liquid fuel  290  continue to travel toward the exhaust side of the cylinder.  FIG. 4C , representing TDC or a crank angle of 360 degrees, the exhaust port  280  is closed and the intake airflow begins to deflect the fuel-vapor cloud  290 . As the piston moves away from TDC at a crank angle of about 380 degrees, the fuel-vapor cloud  290  has moved to the exhaust port region as shown in  FIG. 4D . The intake airflow continues to push the fuel vapor cloud  290  toward the exhaust side at crank angles of about 400 degrees and 420 degrees as shown in  FIGS. 4E and 4F , respectively. Enriching the fuel-air mixture around the exhaust port improved the overall mixing homogeneity of the fuel-air mixture. 
     FIGS. 5-8  are graphs illustrating improved performance of a split fuel injection strategy for low-pressure direct injection spark ignition engines according to the present disclosure relative to a single fuel injection. The graphs illustrate dynamometer data collected at 5000 rpm WOT conditions.  FIG. 5  is a graph illustrating the relationship between smoke and the end of fuel injection for the injection during the intake stroke. Line  300  represents the relationship for a single injection while line  302  represents the relationship for the second injection of a split injection with the first injection beginning during the late exhaust stroke. As shown by line  302 , the end of injection for the split injection can be as early as 230 degrees BTDC with smoke level remaining less than 1.0. In contrast, the single injection represented by line  300  is constrained to 220 degrees to keep the smoke level less than 1.0. 
     FIG. 6  is a graph of the net maximum effective pressure (NMEP), which corresponds to the maximum torque produced, as a function of the end of injection timing for the injection occurring during the intake stroke, i.e. a single injection as represented by line  310  or the second of multiple injections represented by line  312 . The plot of  FIG. 6  shows that NMEP increased across the range of injection times with the maximum value increasing from about 13.35 for a single injection to about 13.7 for a split injection—an increase of about 2.5%. 
     FIGS. 7 and 8  demonstrate reduction in oxygen and hydrocarbon emissions, respectively, for a split injection strategy according to the present disclosure relative to a single injection.  FIG. 7  is a graph of oxygen in exhaust as a function of injection timing for a single injection strategy represented by line  320  and the second injection of a split injection strategy represented by line  322 .  FIG. 8  is a graph of hydrocarbon emissions as a function of injection timing for a single injection strategy represented by line  330  and the second injection of a split injection strategy represented by line  332 . 
     FIG. 9  is a flow chart illustrating operation of a system or method for operating a direct injection spark ignition engine according to one embodiment of the present disclosure. The specific control logic illustrated may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or function illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the representative embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated steps may be repeatedly performed depending on the particular strategy being used whether or not explicitly illustrated or described. 
   Various engine operating parameters are monitored as indicated at block  400 . Operating parameters that may be used in determining whether the engine is operating in a high speed and/or high load region include engine speed (Ne), manifold pressure (MAP), accelerator pedal position (PPS) or demanded torque, mass airflow (MAF), and the like. Block  410  represents a determination of whether the engine is operating in a region above a threshold based on one or more of the monitored operating parameters. Block  410  may be implemented by a single-dimensional or multi-dimensional look-up table, for example. In one embodiment, the threshold represented by block  410  corresponds to maximum engine speed and wide-open throttle. Other representative values may be 80% or 90% of maximum engine speed, torque, and/or load, for example. 
   When the engine is operating in a high speed and/or load region as determined by block  410 , a split injection strategy is used with a first fuel injection occurring during the exhaust stroke as represented by block  420  and a second fuel injection occurring during the intake stroke as represented by block  430 . If the engine is not operating in a high speed/load region, a single fuel injection may be used as represented by block  430 . Of course, those of ordinary skill in the art will recognize that various engine and/or vehicle operating modes may also affect the selection of a particular fuel injection mode or strategy. As such, split injection may be used during these modes if desired. Conversely, a single injection may be indicated for some operating conditions that would otherwise trigger split injection using the illustrated logic. 
   As such, the present disclosure includes embodiments that provide increased torque at high engine speeds and loads using a single, low-pressure fuel pump by injecting a fraction of the total fuel injected per engine cycle during the exhaust stroke. Improved homogeneity of the fuel-air mixture at high engine speeds and loads results in reduced smoke and reduced feedgas emissions. 
   While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments discussed herein that are described as less desirable to other embodiments with respect to one or more characteristics are not outside the scope of the disclosure.