Abstract:
An aspect of the present disclosure relates to a method and system for reducing emissions and improving knock-tolerance in an engine. Air, including exhaust gas present at levels greater than 20% by total air mass, may be introduced into a combustion chamber having a volume including a piston and a cylinder head. A first amount of fuel and a second amount of fuel may be directly injected into the combustion chamber at various points during the cycle, wherein the ratio of the air, including the exhaust gas, to the first and second amounts of fuel is 14.0:1 to 15.0:1. The first and second amounts of fuel may then be ignited. An electronic control unit may be utilized to time the injections and control the introduction of exhaust gas.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     REFERENCE TO SEQUENTIAL LISTING, ETC. 
     None. 
     FIELD OF THE INVENTION 
     The present disclosure relates generally to the use of gasoline direct injection systems and, in particular, the use of a stratified charge to improve stability at relatively high exhaust gas recirculation levels. 
     BACKGROUND 
     In gasoline direct injection (GDI) systems fuel may be injected at relatively higher pressures over a common rail system directly into the combustion chamber of an engine. Gasoline direct injection allows for stratified charge, wherein the air/fuel mixture may be layered. A rich portion of the air to fuel mixture may be directed around the spark plug and fresh air or a mix having a relatively lower air to fuel ratio may be present around the richer portion. In addition, GDI systems may be run at relatively lean conditions, where air to fuel ratios may be 50:1 or higher. However, running GDI systems at lean conditions may require relatively costly after treatment systems or may fail in attaining various emissions standards. 
     Exhaust gas recirculation may provide benefits in terms of reducing certain emissions and improved fuel consumption at moderate loads, including those greater than 5 bar and up to 8 bar. Such benefits may include improvements in fuel consumption, carbon monoxide emissions and nitrous oxide emissions. For example, improvements in fuel consumption for a given engine may be in the range of 1% to 3%, nitrous oxide emissions may be reduced by 10% to 80% and carbon monoxide emissions may be reduced by 5% to 20% upon the introduction of 5% to 20% EGR at 1500 rpm and 8 bar. In addition, the coefficient of variation of the indicated mean effective pressure (cov imep) may be less than 1.5%. At these conditions, some increase in hydrocarbons may be exhibited, in the range of under 5% to 45%. 
     However, this may not be true across all engine speeds and loads, such as low loads of 5 bar and less, as increased EGR amounts may lead to engine instability as reflected by an increase in cov imep. For example, the cov imep at an engine speed of 2,000 rpm and pressures of 2 bar and 5 bar may be greater than 1% and up to 6%. While some improvements in fuel consumption may be seen up to 3% some decreases may also be exhibited at loads of 5 bar. 
     SUMMARY OF THE INVENTION 
     An aspect of the present disclosure relates to a method of reducing emissions and improving knock-tolerance in an engine. The method may include providing air, including exhaust gas present at levels greater than 20% by total air mass, and introducing the air, including the exhaust gas, into a combustion chamber having a volume including a piston and a cylinder head. A first amount of fuel may be directly injected into the combustion chamber, when the piston is moving away from the cylinder head, and a second amount of fuel may be directly injected into the combustion chamber, when the piston is moving towards the cylinder head. The first and second amounts of fuel may then be ignited wherein the ratio of the air to the first and second amounts of fuel is 14.0:1 to 15.0:1. 
     Another aspect of the present disclosure relates to a system for reducing emissions and controlling knock. The system may include a combustion chamber having a volume including a piston and a cylinder head, a fuel injector, configured to directly inject fuel into the combustion chamber and an electronic control system in electrical communication with the fuel injector. The system may also include a high pressure exhaust gas recirculation valve in electrical communication with the electronic control system and a low pressure exhaust gas recirculation valve in electrical communication with the electronic control system. The electronic control system may be configured to introduce air, including exhaust gas present at levels greater than 20% by total air mass, into the combustion chamber, inject a first amount of fuel directly into the combustion chamber, when said piston is moving away from the cylinder head, inject a second amount of fuel directly into the combustion chamber, when the piston is moving towards the cylinder head, and ignite the first and second amounts of fuel, wherein the ratio of the air to the first and second amounts of fuel is 14.0:1 to 15.0:1. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features of this disclosure, and the manner of attaining them, will become more apparent and better understood by reference to the following description of embodiments described herein taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is schematic diagram of an example of a gasoline direct injection engine; 
         FIG. 2  is an illustration of a combustion chamber. 
         FIG. 3  is an example where a rich mixture of air and fuel positioned proximate to a spark plug; 
         FIGS. 4   a - 4   d  illustrate an example of piston motion and dual injection during a four stroke cycle; and 
         FIG. 5  illustrates an example of an electronic control unit and a knock sensor. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that this disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The embodiments herein are capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
       FIG. 1  illustrates an example of a gasoline direction injection system  100  including a dual loop exhaust gas recirculation system (EGR). The gasoline direct injection engine, as illustrated, may be a four stroke engine. However, it may be appreciated that gasoline direct injection engines may be two strokes or higher, including two strokes to twelve strokes, including all values and increments therein. The system may include an internal combustion engine  101 , e.g., a spark ignition engine, with a dual-loop EGR system. The engine  101  may include four cylinders  102   a ,  102   b ,  102   c ,  102   d , however it may be appreciated that one or more cylinders in a given engine application. 
     In one embodiment, each cylinder  102   a ,  102   b ,  102   c  and  102   d , may further have an associated fuel injector  104   a ,  104   b ,  104   c , and  104   d , respectively. Each fuel injector  104   a ,  104   b ,  104   c , and  104   d  may be operatively connected to a common rail  106 . The common rail  106  may be connected to a fuel supply (not shown) and may supply fuel relatively continuously to each injector  104   a ,  104   b ,  104   c ,  104   d . Each injector  104   a ,  104   b ,  104   c ,  104   d  may then individually regulate the fuel provided to each cylinder  102   a ,  102   b ,  102   c  and  102   d.    
     The engine  101  may receive air via intake manifold  110 . The intake manifold  110  may be connected to each cylinder  102   a ,  102   b ,  102   c  and  102   d  through an associated valve or valves (not shown). The intake manifold  110  may be further connected to a dual loop EGR system, including a high pressure loop  112  and a low pressure loop  114 . Exhaust manifold  116  may receive exhaust gas from the engine  101  and may provide this exhaust gas to a turbocharger or supercharger  118  and/or the high pressure EGR system  112 . 
     A turbocharger may be understood to mean a turbine and a compressor that may be coupled by a shaft. The flow of the exhaust gas may cause the turbine to rotate which may then activate the compressor. Incoming air and/or EGR gas to the compressor may then be compressed and forced out of the compressor into, e.g., an intake manifold, and thereby into one or more cylinders. It may be appreciated that a variable geometry turbocharger may allow one or more parameters of the turbocharger, e.g., turbine vane angle, to be varied. This variable geometry may then allow relatively more uniform compressor output over a range of engine speeds. This relatively more uniform output may be accomplished by maintaining a relatively uniform turbine, shaft and compressor rotational speed. A super charger may also compress the intake air but may be driven by the crank shaft. 
     The high pressure EGR system  112  may include the exhaust manifold  116  that may be coupled to a high pressure EGR channel (HP-EGR)  120 . A bypass valve (not illustrated) may couple the HP-EGR channel  120  to an alternate channel  122  at a first location. An alternate channel may bypass the HP-EGR cooler  124  and may be further coupled to HP-EGR channel  120  at a second location. A HP-EGR valve  126  may regulate the flow of exhaust gas delivered to the intake manifold  110  from HP-EGR channel  120 . 
     The low pressure EGR system  114  may include the exhaust manifold  116 , which may be coupled to a low pressure EGR channel (LP-EGR)  130 . The exhaust manifold  116  may be coupled to turbine channel (not illustrated), which may be coupled to turbine  118 . The turbine  118  may be coupled to exhaust catalyst channel  132 . The exhaust catalyst channel  132  may include a three-way catalytic converter system  134 . A three-way catalytic converter may be understood as a system which may reduce nitrous oxides (NO x ) into N 2  and xO 2 ; oxidize carbon monoxide (CO) into (CO 2 ); and oxidize unburned hydrocarbons (HC) into carbon dioxide (CO 2 ) and water (H 2 O). 
     A portion of the exhaust may be diverted into the LP-EGR channel  130  and a portion may leave the system  100  through the exhaust channel  132 . The LP-EGR channel  130  may include a LP-EGR cooler  136 , which may reduce the temperature of the LP-EGR gas. In addition, the LP-EGR channel  130  may include a LP-EGR valve  138  regulating the amount of low pressure exhaust passing back into the intake channel  108 . It may be appreciated that while, as illustrated, the HP-EGR channel  120  connects with the intake channel  108  prior to the intake valve  109  and the low pressure (LP-EGR) channel  130  may connect with the intake channel  108  prior to air entering the turbocharger  118 , various other arrangements may be provided as well. 
     In one embodiment, the air and/or EGR gases provided to the intake manifold  110  by the HP-EGR system  112  and LP-EGR system  114  may be quite different. For example, the HP-EGR loop receives EGR gas directly from the exhaust manifold  116 . Accordingly, this EGR gas may contain relatively hot unburned air and/or relatively hot unfiltered EGR gas that may include NO x , CO and/or HC. This air and/or EGR gas may or may not pass through an HP EGR cooler  124  prior to being provided to the intake manifold  110 . 
     On the other hand, the LP-EGR loop may receive EGR gas that has passed through the turbine  118  (and done work), and that has been filtered by three-way catalytic converter  134 . The filtered EGR gas may then pass through EGR cooler  136  and may mix with ambient air in compressor input channel  105 . The mix of ambient air and filtered EGR gas may then be compressed in the compressor  118 . The compressed air and/or filtered EGR gas may then pass through intercooler  107 . The compressed and cooled air and/or filtered EGR gas may be regulated by intake throttle  109  and may then be provided to the intake manifold  110 . Accordingly, this air and/or filtered EGR gas may contain a relatively larger fraction of ambient air and a relatively smaller fraction of exhaust gas than the EGR gas provided by the HP-EGR system. 
     The engine displacement may be 1 liter or greater, including all values and increments in the range of 1 L to 10 L. Engine displacement may be understood as the total volume of air or air/fuel mixture an engine can draw in during one cycle by all of the cylinders, or may be understood as the volume swept by the pistons as the head of the piston  202  is moved from top dead center TDC, i.e., to the top of the cylinder, to bottom dead center BDC, i.e., to the bottom of the cylinder, as illustrated in  FIG. 2 . Furthermore, the engine may have a compression ratio of 7:1 to 13:1, where the compression ratio may be understood as the change volume of the combustion chamber when the piston is at the top dead center V TDC  and the bottom dead center V BDC . 
     In addition to the above, gasoline direct injection systems may also provide for a stratified charge, wherein the air/fuel mixture may be layered. As illustrated in  FIG. 3 , a rich charge  310  may be directed around the spark plug  312  and fresh air or a mix having a relatively lower air to fuel ratio  314  may be present around the rich charge  310 . The flame front may propagate through the rich charge and into the remaining area. A stratified charge may be developed by varying the physical geometry of the piston bowl and/or cylinder head and placement of the injection nozzle or intake valve. For example, the system may include a wall directed combustion system, where fuel may be injected into the combustion chamber from the side and deflected by a recess in the piston bowl towards the spark plug. In another example, the system may include an air-directed combustion system wherein a charge cloud moves on a cushion of air. In a further example, the system may include a jet-directed combustion process wherein the injector is installed at the very top of the cylinder, injecting into the combustion chamber and the fuel may be ignited directly after injection. 
     In addition to these mechanisms, a dual injection strategy may also be used herein to develop a stratified charge. A dual injection strategy may be understood as an injection strategy wherein the fuel charge may be injected in at least two stages.  FIGS. 4   a  through  4   d  illustrate the motion of a piston  402  within the cylinder  404  during an example of a four-stroke cycle incorporating a dual injection strategy. The piston  402 , cylinder  404 , and cylinder head  408  may form the combustion chamber, which may be understood as the location where combustion occurs in the engine. Therefore, it may be appreciated that the combustion chamber volume may vary throughout the cycle as the piston extends and retracts in the cylinder. 
     In  FIG. 4   a , air may be introduced into one of the engine cylinders  404 , through a runner  410  connecting the cylinder  404  to air intake manifold ( 110  of  FIG. 1 ) as the piston  402  retracts within the cylinder and moves away from the cylinder head  408 . Motion of the piston in the cylinder may be quantified in terms of crank angle, i.e., the angle of the crank shaft. The piston may be connected to the crankshaft, either directly or indirectly, such that as the piston moves up and down in the cylinder, the crankshaft turns. As referenced to herein, when the piston is fully extended in the cylinder at the top dead center point, the crank angle may be understood to be at 0°. 
     A first portion of fuel, in the range of 60% to 95% of the total fuel mass injected for a given stoichiometric charge (see below), including all values and increments therein, such as 80% to 90%, may be injected during the first stage by an injector  412 . As noted above, the injector may be a high pressure injector  412 , wherein the fuel may be at a pressure of 5 MPa or greater, including all values and increments in the range of 5 MPa to 15 MPa. The first portion of fuel may mix with the incoming charge of air as the piston retracts and begins to extend again in the cylinder. 
     It may be appreciated that the air may include not only ambient air drawn in through the compressor input channel ( 105  of  FIG. 1 ), but also exhaust gas air directed through the high pressure exhaust gas system ( 112  of  FIG. 1 ) and/or the low pressure exhaust gas system ( 114  of  FIG. 1 ). Exhaust gas air may be present at levels greater than 20% by mass of the intake air. The exhaust gas may be low pressure exhaust gas, high pressure exhaust gas, or a mixture thereof, depending upon the load and temperature of the engine. For example, at low loads, e.g., less than 5 bar, or during cold start, e.g., when the coolant temperature is below 120° F., the exhaust gas may include mostly high pressure exhaust gas provided at a relatively high temperature. The high pressure exhaust gas may be present at greater than 50% by exhaust gas air mass, including all values and increments therein. At higher loads, e.g., 5 bar or greater, or higher temperatures, e.g., when the coolant temperature is above 120° F., the exhaust gas may include mostly low pressure exhaust gas. The low pressure exhaust bas may be present at greater than 50% by exhaust gas air mass. 
       FIG. 4   b  illustrates a second stage where compression of the air/fuel mixture takes place in the cylinder, by the extension of the piston  402  towards the cylinder head  408 . Mixing of fuel from the first injection event with air/exhaust gas may still occur. In addition, a second injection event may occur during this compression stroke and may form a locally rich region of fuel around the spark plug  414 . The second injection event may inject a second portion of fuel in the range of 5% to 40% of the total fuel mass injected for a given stoichiometric charge, including all values and increments therein, such as 10% to 20%. 
     The air to fuel ratio for the total fuel mass injected may be maintained at or near stoichiometric. The air to fuel ratio may be understood as the ratio of the air mass in the cylinder to the fuel mass in the cylinder. One example of a stoichiometric air to fuel ratio may be understood as the air to fuel ratio exhibiting ideal theoretical combustion, which may generally be understood to be around 14.6:1. It may also be appreciated however, that a stoichiometric air to fuel ratio, in the context of the present disclosure, may depend on factors such as fuel composition, intake air/exhaust composition, temperature, pressure, etc., and may range from 14.0:1 to 15.0:1. 
     The start of injection for the second injection event may be in the range of about 70 to 110 degrees, including all values and increments therein, before top dead center. In addition, further injection events may be added to the cycle. For example, a third injection event of a fourth injection event may occur to further stratify the charge in the cylinder. Such additional injection events may occur during the injection stage, compression stage or combustion stage of the cycle. 
       FIG. 4   c  illustrates a third stage where the spark plug may then ignite causing the fuel in the locally rich region to ignite and burn. Ignition of the fuel may occur between 50° to 0° before top dead center, including all values and increments therein. The flame may propagate from the rich region through the remainder of the fuel. Pressure developed during combustion may cause the piston  402  to move away from the cylinder head  408 . During the fourth stage, illustrated in  FIG. 4   d , the exhaust gases may then be forced out of the cylinder  404  through an exhaust runner  416  by the upward stroke of the piston  402 . The exhaust runner  416  may connect the cylinder  404  to the exhaust manifold ( 116  illustrate in  FIG. 1 ). 
     The above injection strategy and injection strategy may be controlled by an electronic control system as illustrated in  FIG. 5 . The electronic control system  500  may aid in timing of the injection of the fuel and the timing of ignition. The electronic control system  500  may include a processor  504 , which may be capable of evaluating various signals received by one or more sensors  502  by a signal evaluation circuit  506 . The processor  504  may be configured to electronically communicate with the injection valves  508 , intake valve  510 , high pressure exhaust gas recirculation valve  512  and/or low pressure exhaust recirculation valve  514  to execute the dual stage injection strategy discussed herein. In one embodiment, the sensor may be a knock sensor. The signals received by the knock sensor may be processed by the signal evaluation circuit. The processor may then control, for example, ignition valve timing, and retard ignition when knock is detected. 
     The strategies utilized herein may therefore allow for an increase in EGR levels, including at lower loads, to levels of greater than 20% by total air mass for a given stoichiometric charge, including all values and increments in the range of 20% to 30% by total air mass. Total air mass may be understood as the mass of the air and exhaust gas provided into the combustion chambers during a cycle. As alluded to above, adjustments in low vs. high pressure EGR may be made depending on the load or engine temperature. Thus, it may be appreciated that EGR levels may be consistently maintained, regardless of the load, temperature or speed of the engine. 
     In utilizing the dual injection strategy in combination with EGR levels of greater than 20% by total air mass, for a given stoichiometric charge, the peak torque may improve and/or the engine size may be reduced while obtaining the same power output. For example, the peak torque of the engine may be improved by 5% or greater, including all values and increments in the range of 5% to 50% as compared to a like engine running without a dual injection strategy. In addition, by providing the dual injection/EGR strategy described herein, the engine may perform in a sufficient manner in such that the size or capacity of the engine may be cut by 25% to 75%, including all values and increments therein, and capable of maintaining the same performance of a like engine running without a dual injection strategy. 
     The foregoing description of several methods and embodiments has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the claims to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.