Internal combustion engine with secondary air or combustion gases injection

Abstract

An internal combustion engine, has: a body defining a cylinder; a head secured to the body; a piston received within the cylinder, a combustion chamber; a crankshaft engaged to the crankshaft; an injection system for injecting a mixture of air and fuel via an intake port; and a secondary injection system, having: a secondary valve fluidly connecting a gas source of one or more of combustion gases and air to the combustion chamber via at least one secondary intake port defined in one or more of the head and a wall of the at least one cylinder, the at least one secondary intake port distinct from the intake port, the secondary valve having a closed configuration fluidly disconnecting the gas source from the combustion chamber and an open configuration in fluidly connecting the gas source to the combustion chamber.

Description

INTERNAL COMBUSTION ENGINE WITH SECONDARY AIR OR COMBUSTION GASES INJECTIONCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority from United States patent application 63 / 608,846 filed on December 12, 2023, the entire contents of which are incorporated by reference herein.TECHNICAL FIELD

[0002] The application relates generally to internal combustion engines and, more particularly, to systems and methods used to recirculate exhaust gases into combustion chambers of such engines.BACKGROUND

[0003] Exhaust gas recirculation (EGR) is used in some internal combustion engines. Some of the combustion gases are recirculated back into a combustion chamber to be mixed with newly admitted air and fuel. EGR may be used to control the combustion process and enhance fuel economy. However, improvements are always sought.SUMMARY

[0004] In one aspect, there is provided an internal combustion engine, comprising: a body defining at least one cylinder; a head secured to the body; a piston slidingly received within the cylinder, a combustion chamber defined within the cylinder and extending from the piston to the head, the combustion chamber varying in volume with movements of the piston within the cylinder; a crankshaft rotatable about an axis, the piston drivingly engaged to the crankshaft; an injection system for injecting a mixture of air and fuel into the combustion chamber via an intake port in the head; and a secondary injection system, having: a secondary valve fluidly connecting a gas source of one or more of combustion gases and air to the combustion chamber via at least one secondary intake port defined in one or more of the head and a wall of the at least one cylinder, the at least one secondary intake port distinct from the intake port, the secondary valve having a closed configuration in which the gas source is fluidly disconnected from the combustion chamber by the secondary valve and an open configuration in which the gas source is fluidly connected to the combustion chamber through the secondary valve.

[0005] The internal combustion engine described above may include any of the following features, in any combinations.

[0006] In some embodiments, the secondary valve is fluidly connected to the combustion chamber via the secondary intake port defined through one or more of the head and the wall of the cylinder.

[0007] In some embodiments, the secondary valve includes a plurality of secondary valves and the secondary intake port includes a plurality of secondary intake ports, each of the plurality of secondary valves fluidly connected to a respective one of the plurality of secondary intake ports defined through the one or more of the head and the wall of the cylinder.

[0008] In some embodiments, the secondary intake port is defined through the head.

[0009] In some embodiments, a plurality of secondary intake ports are defined through the head and being offset from a center of the cylinder.

[0010] In some embodiments, secondary valves are each fluidly connected to a respective one of the plurality of secondary intake ports, the secondary valves configured to inject the one or more of combustion gases and air into the combustion chamber in a direction having an axial component relative to a central axis of the cylinder.

[0011] In some embodiments, an exit flow axis at which the gas is injected into the combustion chamber via the secondary intake ports extends perpendicularly to the wall of the cylinder.

[0012] In some embodiments, the secondary intake ports are located at a common circumferential position on the wall of the cylinder and are axially offset from one another relative to a central axis of the cylinder.

[0013] In some embodiments, an exit flow axis at which the gas is injected into the combustion chamber via the secondary intake ports extends along a direction having a circumferential component relative to a central axis of the cylinder.

[0014] In some embodiments, one of the secondary intake ports is located closer to the head than a remainder of the secondary intake ports, the exit flow axis of the one of the secondary intake ports has an axial component relative to the central axis.

[0015] In some embodiments, the gas is air.

[0016] In some embodiments, the engine includes a heat exchanger, the gas source fluidly connected to the combustion chamber through the heat exchanger, the heat exchanger providing heat exchange relationship between the air and a fluid having a greater temperature than the air.

[0017] In some embodiments, the fluid is a liquid coolant or the combustion gases.

[0018] In some embodiments, the gas is the combustion gases.

[0019] In some embodiments, the engine includes a heat exchanger, the gas source fluidly connected to the combustion chamber through the heat exchanger, the heat exchanger providing heat exchange relationship between the combustion gases and a fluid having a lowertemperature than the combustion gases.

[0020] In some embodiments, the engine includes a controller operatively connected to the secondary valve, the controller having a processing unit and a computer readable medium operatively connected to the processing unit and having instructions stored thereon executable by the processing unit for: controlling the injection system for permitting the mixture of air and fuel to enter the combustion chamber during an intake process, after the intake process, compressing the mixture of air and fuel during a compression process, after the compression process, igniting the mixture of air and fuel during a combustion process, and after the combustion process, expelling combustion gases during an exhaust process; and controlling the secondary injection system for one or more of: injecting one or more of air and combustion gases from the gas source into the combustion chamber during one or more of the intake process and the compression process, and injecting the air into the combustion chamber during the combustion process.

[0021] In another aspect, there is provided a method of operating an internal combustion engine having a piston riding within a combustion chamber defined by a cylinder, comprising: injecting a mixture of air and fuel into a combustion chamber during an intake process; after the intake process, compressing the mixture of air and fuel during a compression process; after the compression process, igniting the mixture of air and fuel during a combustion process; after the combustion process, expelling combustion gases out of the combustion chamber during an exhaust process; and one or more of: injecting one or more of air and combustion gases from a gas source into the combustion chamber during one or more of the intake process and the compression process, and injecting the air into the combustion chamber during the combustion process.

[0022] The method described above may include any of the following features, in any combinations.

[0023] In some embodiments, the injecting of the one or more of the air and the combustion gases includes injecting combustion gases at a plurality of locations through a head of the internal combustion engine.

[0024] In some embodiments, the injecting of the one or more of the air and the combustion gases includes injecting the one or more of the air and the combustion gases thereby stratifying a mixture contained within the combustion chamber.

[0025] In some embodiments, the method includes injecting the one or more of the air and the combustion gases at different time intervals as a function of a position of the piston.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Reference is now made to the accompanying figures in which:

[0027] Fig. 1 is a schematic cross-sectional view of an internal combustion engine in accordance with one embodiment;

[0028] Fig. 2A is a schematic diagram of the internal combustion engine illustrating an injection system and a control system thereof;

[0029] Fig. 2B is a three-dimensional view of a head of the internal combustion engine of Fig. 1 ;

[0030] Fig. 3 is a schematic cross-sectional view of the internal combustion engine illustrating a cylinder thereof in accordance with one embodiment;

[0031] Fig. 4 is a schematic cross-sectional view of the internal combustion engine of Fig. 1 in accordance with another variant;

[0032] Fig. 5 is a schematic cross-sectional view of the internal combustion engine illustrating a cylinder thereof in accordance with the variant of Fig. 4;

[0033] Fig. 6 is a chart illustrating an exemplary timing of different events during the operation of the internal combustion engine of Fig. 1 ;

[0034] Fig. 7 is a flowchart illustrating steps of a method of operating the internal combustion engine of Fig. 1 ;

[0035] Fig. 8 is a chart illustrating the EGR strategies and spark timing in relation to engine strokes;

[0036] Figs. 9A-9B are graphs illustrating impact of the EGR strategies on the coefficient of variation of the indicated mean effective pressure at two engine regimes: 2100 RPM (Fig. 9A) and 2500 RPM (Fig. 9B);

[0037] Figs. 10A-10B are graphs illustrating impact of EGR strategies on combustion duration fortwo engine regimes: 2100 RPM (Fig. 10A) and 2500 RPM (Fig. 10B) (symbols identify location of 50% mass fraction burned);

[0038] Figs. 11A-11 B are graphs illustrating impact of EGR strategies on cylinder maximum pressure rise for two engine regimes: 2100 RPM (Fig. 11 A) and 2500 RPM (Fig. 11 B);

[0039] Figs. 12A-12B are graphs illustrating impact of EGR strategies on specific fuel consumption for two engine regimes: 2100 RPM (Fig. 12A) and 2500 RPM (Fig. 12B);

[0040] Figs. 13A-13B are graphs illustrating impact of EGR strategies on NO emissions for two engine regimes: 2100 RPM (Fig. 13A) and 2500 RPM (Fig. 13B);

[0041] Figs. 14A-14B are graphs illustrating impact of EGR strategies on THC emissions for two engine regimes: 2100 RPM (Fig. 14A) and 2500 RPM (Fig. 14B);

[0042] Figs. 15A-15B are graphs illustrating impact of EGR strategies on CO emissions for two engine regimes: 2100 RPM (Fig. 15A) and 2500 RPM (Fig. 15B); and

[0043] Fig. 16 is a schematic representation of a controller for the internal combustion engine of Fig. 1.DETAILED DESCRIPTIONIntroduction

[0044] Exhaust gas recirculation may be used to decrease nitrogen oxides emissions or to increase thermal engine efficiency at part load in internal combustion engines. The exhaust gas is homogeneously mixed with air in the intake manifold before entering the engine’s cylinders. Inspark-ignition engines, the amount of gas recirculated is limited due to combustion deterioration. In the present disclosure, a system is proposed to achieve stratified EGR. The system is based on the direct injection of EGR through the cylinder head. The proposed concept is experimentally tested using a modified single cylinder engine with which three different EGR timings are evaluated and compared to a homogeneous EGR. The results suggested that EGR timing is a function of engine speed and EGR level. Moreover, the results indicate that with the proposed approach, it is possible to enhance the combustion process as quantify by a shorter combustion duration and increase in in-cylinder maximum pressure rise. Finally, for certain EGR timing, specific fuel consumption was improved while at the highest EGR level, NOx emissions were similar to homogeneous EGR.

[0045] Gasoline spark-ignition engines are submitted to stringent pollutant emissions and fuel economy regulations and exhaust gas recirculation (EGR) is one of the technologies that may allow decreasing the environmental impact of the internal combustion engine through different aspects. For example, EGR influences the combustion process in three different ways: 1) EGR may increase the heat capacity of the mixture (named thermal effect) lowering the combustion temperature and thus decreases nitrogen oxides (NOx) emissions; 2) EGR may result in a dilution effect as it decreases the oxygen concentration in the mixture; 3) EGR may have a chemical effect on soot formation by suppressing large aromatic sheet formation. Moreover, the use of hot EGR is said to decrease particulate emissions in both port fuel and direct injection engines due to an increase in temperature of the mixture that favors fuel evaporation and the fuel-air mixing process. EGR may also improve fuel economy by reducing pumping loss at part load while it may also be used to suppress end-gas auto-ignition and as a knock mitigation approach if cooled. Overall, EGR may help achieve high-efficiency spark-ignition engines.

[0046] In EGR system, exhaust gas is taken from the exhaust system and brought to the intake manifold, after the throttle body, so as to create a homogeneous air - exhaust gas (EG) mixture. In that configuration, the pressure difference between the exhaust and intake is the driving force to recirculate the hot gas while a valve allows controlling the amount of exhaust gases recirculated. Contrary to homogeneous EGR, the stratification approach tries to separate the exhaust gas from the air within the cylinder as to achieve an EG gradient within the mixture. One possibility to achieve stratification is to create an asymmetrical EG supply in the intake ports of the engine in such a way that both intake ports do not have the same concentration of EGR.

[0047] In general, the aim with the some techniques to achieve EGR stratification is to increase the amount of EG within the cylinder without the inconvenience encountered with a homogeneous high EGR level, such as increase of local heterogeneity in the fuel-to-air mixture, combustion instabilities, lower fuel efficiency and in some cases, misfire. Moreover, as the engine approach wide-open throttle (WOT) condition, homogeneous EGR decrease engine power as it is detrimental to the intake air density entering the cylinder.

[0048] In this disclosure, an approach is proposed and is experimentally tested to achieve EGR stratification. Instead of modifying the intake port or valve timing during the intake stroke, EG is directly injected in the cylinder allowing timing the EGR injection during the intake and compression stroke at will. Experiments are then conducted with a modified single cylinder engine to illustrate how the system performs.Internal combustion engine

[0049] Referring to Fig. 1 , an internal combustion engine, depicted as a piston engine, is shown at 10. Although the engine 10 is a piston engine, the principles of the present disclosure may be applied to other combustion engines, such as rotary engines and so on. The engine 10 has a body 1 1 defining a cylinder 12. A piston 13 is slidably received within the cylinder 12 and is engaged to a crankshaft 14 that drivingly engages an output of the engine 10. The piston 13 is sealingly engaged to a wall of the cylinder 12. The cylinder 12 and the piston 13 may include more than one cylinder and more than one piston 13 each received within a respective cylinder. For instance, the engine 10 may be a 4-cylinder engine, a 6-cylinder engine, and so on without departing from the scope of the present disclosure. The body 11 may thus define a plurality of cylinders each receiving a respective one of a plurality of pistons. For the sake of clarity, the below description uses the singular form when referring to the cylinder 12 and to the piston 13, but the below description may apply to all of the cylinders 12 and the pistons 13 of the engine 10. The piston 13 is engaged to the crankshaft 14 via a connecting rod 15 that translates a reciprocating motion of the piston 13 within the cylinder 12 into a rotational motion of the crankshaft 14. The crankshaft 14 may thus transmit a rotational input to a load, such as wheels of a vehicle, a generator, a propeller, a helicopter rotor, and so on.

[0050] The engine may have a displacement volume of 389 cubic centimeters, a stroke of 88 millimetres, a bore of 64 millimetres, a compression ratio of 8, and a speed varying from 2100 to2500 RPM. Understandably, these values may vary from engine to engine and the scope of the present disclosure is not limited by these values.

[0051] The engine 10 includes a head 16 secured to the body 11. The head 16 defines an inlet port 17 for receiving a mixture of air and fuel and an outlet port 18 for expelling combustion gases. A combustion chamber 19 is located within the cylinder 12 and extends from the head 16 to the piston 13. A volume of the combustion chamber 19 varies with movements of the piston 13. The volume of the combustion chamber 19 varies from a minimum volume where a distance between the piston 13 and the head 16 is minimal to a maximum volume where the distance between the piston 13 and the head 16 is maximal. The piston 13 is thus movable between an upper-most position, also referred to as a top dead center position TDC, that corresponds to the minimum volume of the combustion chamber 19 to a bottom-most position, also referred to as a bottom dead center position BDC, that corresponds to the maximum volume of the combustion chamber 19.Injection System

[0052] With an EGR system, the exhaust gas is routed from the exhaust system to the intake manifold using an electronic controlled valve. The EGR valve allows controlling the quantity of exhaust gas recirculated as a function of engine speed and load. In this disclosure, it is proposed to inject the EG directly into the cylinder through the head 16. Hence, the EG may be injected along a direction having an axial component relative to the central axis A1 of the cylinder. To do so, three solenoid valves (e.g., Festo MHA4 with a nominal flow rate of 6.67L / S having a 3.5 ms opening and closing delay) supply the head 16 and are controlled by the ECU. More or less than three EGR valves may be used in some embodiments. These valves may allow adjusting the EGR injection timing and duration. Due to temperature constraints, the valves were connected by pipes to check valves mounted directly on the cylinder head. That configuration also prevents the high-pressure gas of the cylinder to return into the EGR system.

[0053] Referring to Figs. 1 , and 2A, an injection system 20 is used to supply the combustion chamber 19 with a mixture of air and fuel and to expel the combustion gases out of the combustion chamber 19. The injection system 20 includes an intake valve 21 , which is herein a poppet valve, fluidly connected to the inlet port 17 and an exhaust valve 22, which is also a poppet valve, fluidly connected to the outlet port 18. The intake valve 21 has an open configuration in which an air source S1 and a fuel source S2 are fluidly connected the combustion chamber 19 through theintake valve 21 and a closed configuration in which the air source S1 and the fuel source S2 are fluidly disconnected from the combustion chamber 19 by the intake valve 21 . The exhaust valve 22 has an open configuration in which the combustion chamber 19 is fluidly connected to an environment outside thereof through the exhaust valve 22 and a closed configuration in which the combustion chamber 19 is fluidly disconnected from the environment by the exhaust valve 22. It will be appreciated that any suitable valves may be used to admit the fuel and air and to expel the combustion gases without departing from the scope of the present disclosure. In the present embodiment, the intake valve 21 and the exhaust valve 22 are mechanically controlled by a cam that is drivingly engaged to the crankshaft 14 via a timing belt or chain. It will be appreciated that the intake valve 21 and the exhaust valve 22 may alternatively be electronically-controlled valves (e.g., solenoid valves). As will be discussed further below, the opening and closing of the intake valve 21 and the exhaust valve 22 is timely controlled for proper operation of the engine 10.

[0054] The injection system 20 includes a fuel injector 23, only one shown, but more than one may be used, in fluid communication with the combustion chamber 19 through the intake valve 21 . The fuel injector 23 may be a Denso four-hole injector coupled with a low-pressure fuel pump, fuel filter, and pressure regulator that held the injection pressure at 3.1 bar. These values are exemplary and othertypes of injectors may be used. The fuel injector23 may be fluidly connected to a conduit that fluidly connects the fuel source S2 to the intake valve 21 . Alternatively, the fuel injector 23 may be directly fluidly connected to the combustion chamber 19 via the head 16 to provide direct fuel injection. In other words, the fuel injector 23 may be a GDI injector. The GDI injector may be located at a position denoted by 23’ in Fig. 2. The injection system 20 further includes an igniter 24 operatively connected to the combustion chamber 19 for igniting the mixture of air and fuel received into the combustion chamber 19 via the intake valve 21 . The combustion chamber 19 is fluidly connected to the air source S1 , via an air valve 25 (e.g., throttle), which has an open configuration to fluidly connect the air source S1 to the inlet port 17 and a closed configuration to fluidly disconnect the air source S1 from the inlet port 17. The air valve 25 has a closed configuration to block fluid communication between the air source S1 and the combustion chamber 19 and a plurality of open configurations to permit fluid communication between the air source S1 and the combustion chamber 19. A mass flow rate that may flow through the air valve 25 varies from one of the open configurations of the other. Each of the open configurations of the air valve 25 may define a respective flow circulating area. A flow meter 26 may be fluidly connected between the air source S1 and the inlet port 17 to measure a mass flow rate of air that flows through the inlet port 17. Once the fuel injected into the combustion chamber 19 iscombusted, the exhaust valve 22 opens to allow the combustion gases to exit the combustion chamber 19. The combustion gases may then flow through a catalyzer 27 before being expelled into the environment. Referring to Fig. 2B, the cylinder head 16 is shown with the spark plug hole between the intake port 21 and exhaust port 22, and the three (3) EGR inlet ports 32.

[0055] A stratification of the mixture of air and fuel into the combustion chamber 19 prior to ignition may improve efficiency of the engine 10. A stratification of the mixture implies that the mixture received into the combustion chamber 19 is non-homogeneous. A property of said mixture varies along one or more directions within the combustion chamber 19. This property may be, for instance, a ratio of a mass of airto a mass of fuel contained within a unit volume of the combustion chamber 19. This stratification may be obtained by flowing a gas, such as air and combustion gases, into the combustion chamber 19 alongside newly admitted fuel and air. In some cases, this stratification may be obtained by recirculating a portion of the combustion gases back into the combustion chamber 19 with newly admitted fuel and air. This may provide efficiency gains.

[0056] As shown in Fig. 2B, the engine 10 thus includes a secondary injection system 30 for injecting a gas, such as one or more of combustion gases and air, into the combustion chamber 19. The secondary injection system 30 injects the gas from a gas source S3 into the combustion chamber 19. The gas source S3 may correspond to an exhaust of the engine 10. In other words, a conduit may fluidly connect the exhaust of the engine 10 to the secondary injection system 30 for injecting a portion of the combustion gases that are bleed out of the exhaust upstream of the catalyzer 27.

[0057] The secondary injection system 30 injects the gas in such a way as to provide a stratification of a mixture of air, fuel, and of the gas (e.g., air, combustion gases) received into the combustion chamber 19. As will be discussed below, the stratification may be in a radial direction relative to a central axis A1 (Fig. 1) of the cylinder 12, in an axial direction relative to the central axis A1 of the cylinder 12, or in any direction. Put differently, the secondary injection system 30 is used to create an anisotropy within the combustion chamber 19. A property of the mixture in the combustion chamber 19 may thus vary along a given direction (e.g., axial, radial, circumferential, any combinations thereof).

[0058] As shown in Fig. 2A, the secondary injection system 30 includes secondary valves 31 , three secondary valves 31 are illustrated, but more or less than three may be used, each being in fluid communication with the gas source S3 and a respective secondary intake port 32 fluidlyconnected to the combustion chamber 19. As illustrated, these secondary intake ports 32 are offset from a center of the cylinder (i.e., radially offset from the central axis A1). The secondary valves 31 are operable to inject the gas into the combustion chamber 19 independently of the intake port 17. Put differently, the secondary intake ports 32 are distinct from the intake port 17. Herein, the expression “distinct” implies that the intake port 17 and the secondary intake ports 32 are separated from one another. The secondary intake ports 32 may be defined in one or more of the head 16 and the wall of the cylinder 12, but they define an alternative passage via which a fluid, such as air and combustion gases, may be injected into the combustion chamber 19. This alternative passage does not rely on a position of the intake valve 21 for fluidly connecting the gas source S3 to the combustion chamber 19. The injection of the air and the combustion gases into the combustion chamber 19 via the secondary intake ports 32 may be performed independently of the injection of air and fuel into the combustion chamber 19 via the intake port 17. The expression “independently” implies that the injection of the one or more of the air and the combustion gases into the combustion chamber 19 does not require the intake valve 21 to be opened. Stated differently, the one or more of the air and the combustion chamber may be injected into the combustion chamber 19 regardless of a position of the intake valve 21. In some embodiments, one or more of the secondary intake ports 32 may intersect the intake port 17, but downstream of the intake valve 21 .

[0059] The secondary valves 31 may be Festo™ valves, but any suitable valves, such as electronically-controlled valves (e.g., solenoid valves), may be used. The secondary valves 31 each has a closed configuration in which the gas source S3 is fluidly disconnected from the combustion chamber 19 by the secondary valve 31 and an open configuration in which the secondary valve 31 fluidly connects the gas source S3 to the combustion chamber 19. Secondary injectors 33 (Fig. 1) are provided and are used to inject the gas into the combustion chamber 19. Check valves 34 may be fluidly connected between the secondary valves 31 and the secondary intake ports 32 to prevent combustion gases from flowing out of the combustion chamber 19 via the secondary intake ports 32. A pressure regulator 35 is fluidly connected upstream of the secondary valves 31 and downstream of the gas source S3. The pressure regulator 35 is configured to ensure that a pressure of the gas reaching the combustion chamber 19 is within a desired range. The pressure regulator 35 may be any suitable regulators known in the art. In some embodiments, the secondary valves 31 and the check valves 34 may be integrated into the secondary injectors 33. The secondary injectors 33 may thus correspond to electronically-controlled injectors or any suitable types of injectors used, for instance, natural gas direct injection (GDI).

[0060] Referring to Figs. 1 and 3, in some embodiments, the secondary injectors 33, three being illustrated but more or less may be used, are vertically stacked one above the other along the central axis A1 of the combustion chamber 19. This configuration may thus allow the creation of a vertical or axial stratification of the different fluids contained in the combustion chamber 19. The secondary injectors 33 inject the gas directly into the combustion chamber 19 through a wall of the cylinder 12. As shown in Fig. 3, an injector exit flow axis A2 of the secondary injectors 33 extend in a direction having a radial component. In this case, the direction of the injector exit flow axis A2 is solely radial relative to the central axis A1 of the combustion chamber 19. The head 16 of the engine 10 may thus be devoid of any secondary injector and all of the secondary injectors 33 may be secured to the cylinder 12.

[0061] All of the secondary injectors 33 are located at a common circumferential position relative to the central axis A1 of the combustion chamber 19. Alternatively, the secondary injectors 33 may be divided in two or more sets; the secondary injectors 33 of each set being located at a respective circumferential positions. The secondary injectors 33 of the second set are shown in dashed lines in Figs. 1 and 3. The circumferential position of each set of the secondary injectors 33 is offset from the circumferential position of the other sets of the secondary injectors 33. In this embodiment, two sets of the secondary injectors 33 are provided. The two sets of the secondary injectors 33 are located at diametrically opposed circumferential positions. In other words, the two sets of secondary injectors 33 may thus face one another. The secondary injectors 33 may thus be symmetrically distributed on opposite sides of the cylinder 12. However, this need not be the case and they may be offset from one another by any suitable circumferential offset (e.g., 45 degrees, 90, degrees, etc). In another alternate embodiment, the secondary injectors 33 may be circumferentially distributed about the central axis A1 . The secondary injectors 33 may be located at a common axial position and be circumferentially offset from one another. Or, they may be both circumferentially and axially offset from one another relative to the central axis A1 .

[0062] With the configuration depicted in Figs. 1 and 3, a vertical or axial stratification of the gas injected (e.g., air, combustion gases) is obtained. Put differently, a quantity of the gas per unit of volume (e.g., kg / m3) fluctuates in an axial direction relative to the central axis A1 of the combustion chamber 19. The proposed configuration may allow to stratify a concentration of the combustion products. Thus, the combustion gases, which include carbon dioxide, water vapor,carbon monoxide, nitrogen, and so on, are injected and their concentration is stratified since they are injected within a mixture of air and fuel. A gradient of the concentration of all the fluids injected in the combustion chamber may be obtained. If air is injected, a stratification of the air concentration may be obtained if the fuel has been previously injected. This may create a zone where a concentration of the fuel is less than neighboring zones because of a dilution created by the injected air.

[0063] Referring now to Figs. 4 and 5, another configuration of the secondary injectors 33 is illustrated. The secondary injectors 33 are axially stacked one above the other relative to the central axis A1 of the combustion chamber 19. A top one of the secondary injectors 33 has a first injector exit flow axis A3 that extends in a first direction having both of a circumferential and a radial component relative to the central axis A1 . The first direction of the first injector exit flow axis A3 may be devoid of an axial component relative to the central axis A1 . The other two secondary injectors 33, which are located further away from the head 16 have second exit flow axes A4 that have a circumferential, radial, and axial components relative to the central axis A1. In this embodiment, the second exit flow axes A4 extend upwardly towards the head 16 of the engine 10. The circumferential component of the second exit flow axes A4 extends in the same direction (e.g., clockwise, counter clockwise) as the circumferential component of the first exit flow axis A3. The circumferential components of the first and second exit flow axes A3, A4 may differ from one another even if they extend in the same circumferential direction.

[0064] With the configuration depicted in Figs. 4 and 5, a radial stratification of the gas injected (e.g., air, combustion gases) is obtained. Put differently, a concentration or mass fraction of the combustion gas varies in a radial direction relative to the central axis A1 of the combustion chamber 19. This configuration of the secondary injectors 33 may create a tumble flow to create the radial stratification. More specifically, the configuration of Fig. 4 may generate a tumble flow whereas the configuration of Fig. 5 may generate a swirl flow. For the tumble flow, the axis of rotation is parallel to a top face of the piston whereas, for the swirl flow, the axis of rotation is perpendicular to the top face of the piston.

[0065] All of the secondary injectors 33 are located at a common circumferential position relative to the central axis A1 of the combustion chamber 19. Alternatively, the secondary injectors 33 may be divided in two or more sets; the secondary injectors 33 of each set being located at a respective circumferential positions. The secondary injectors 33 of the second set are shown in dashed lines in Figs. 4 and 5. The circumferential position of each set of the secondary injectors33 is offset from the circumferential position of the other sets of the secondary injectors 33. In this embodiment, two sets of the secondary injectors 33 are provided. The two sets of the secondary injectors 33 are located at diametrically opposed circumferential positions. The secondary injectors 33 may be symmetrically distributed on opposite sides of the cylinder 12. However, this need not be the case and they may be offset from one another by any suitable circumferential offset (e.g., 45 degrees, 90, degrees, etc). In another alternate embodiment, the secondary injectors 33 may be circumferentially distributed about the central axis A1. The secondary injectors 33 may be located at a common axial position and be circumferentially offset from one another. Or, they may be both circumferentially and axially offset from one another relative to the central axis A1 .

[0066] In the embodiment shown, a top one of the secondary injectors 33 of the second set has a third injector exit flow axis A5 that extends in a third direction having both of a circumferential and a radial component relative to the central axis A1 . The other two secondary injectors 33 of the second set, which are located further away from the head 16, have fourth exit flow axes A6 that have a circumferential, a radial, and an axial components relative to the central axis A1 . In this embodiment, the fourth exit flow axes A6 extend downwardly away from the head 16 of the engine 10. The circumferential component of the fourth exit flow axes A6 extends in the same direction (e.g., clockwise, counter clockwise) as the circumferential component of the third exit flow axis A5. The circumferential components of the third and fourth exit flow axes A5, A6 may differ from one another even if they extend in the same circumferential direction. Having the second set of secondary injectors 33 may help creating a stronger tumble or swirl flow. This, in turn, may increase a stratification that may further improve the efficiency of the engine 10. Also, the second set of the secondary injectors 33 may increase an intensity of the swirl in the combustion chamber 19.

[0067] In Figs. 1-5, the secondary injectors 33 are axially offset from one another. In some cases, the piston 13 may overlap one or more of these secondary injectors 33. Thus, a controller of the engine 10 may adequately control the secondary valves 31 to trigger their opening in a sequential manner such that the secondary valves 31 located closer to the piston 13 open first. The order in which the secondary valves 31 open may thus follow a movement of the piston 13.

[0068] Referring to Figs. 1-5, for all configurations, one or more of combustion gases and air may be injected into the combustion chamber 19, either through the wall of the cylinder 12, through the head 16, or a combination of the wall of the cylinder 12 and the head 16. In somecases, it may be desired to increase a pressure of the air or the combustion gases. Thus, a compressor 36 (Fig. 2) may be fluidly connected to the gas source S3 and upstream of the combustion chamber 19. The compressor 36 may be driven by an electric motor. Alternatively, the compressor 36 may be driven by a turbine powered by the combustion gases. The compressor 36 is operable to increase a pressure of the combustion gases and / or the air being injected in to the combustion chamber 19. In an alternate embodiment, the gas source S3 may be pressurized. For instance, the gas source S3 may be a tank containing pressurized air. The pressure regulator 35 may be used to ensure that the pressure of the air reaching the combustion chamber 19 remains within a given threshold.

[0069] In some embodiments, it may be desired to pre-heat the air before injecting the air into the combustion chamber 19 via the secondary injectors 33. Thus, the secondary injection system 30 may include a heat exchanger 37 (Fig. 2), which is depicted as being located upstream of the compressor 36, but which may alternatively be located downstream of the compressor 36. The heat exchanger 37 may be used to heat the air if said is injected during the power stroke of the piston. The heat exchanger 37 may be used to cool the air if said air is injected during the compression stroke of the piston. The heat exchanger 37 may have at least one first conduit in fluid communication with the gas source S3 and at least one second conduit in fluid communication with another fluid. The at least one first conduit and the at least one second conduit are in heat exchange relationship with one another. The other fluid may be, for instance, the combustion gases generated in the combustion chamber 19. The other fluid may be a liquid coolant of the engine 10. Such a liquid coolant may flow within coolant passages defined within the body 11 of the engine 10 to pick up heat from the body 11 . This coolant may thus flow through the heat exchanger 37 to transfer at least a portion of its heat to the air before the liquid coolant flows through another heat exchanger, such as a radiator of a vehicle.

[0070] In an alternate embodiment, the heat exchanger 37 may be used to cool down the combustion gases before these combustion gases are injected into the combustion chamber 19 via the secondary injectors 33. In such a case, the combustion gases are expected to be at a higher temperature than the liquid coolant of the engine 10. Thus, heat may be transferred from the combustion gases to the liquid coolant. In another embodiment, the heat exchanger 37 may be an air-cooled heat exchanger in which the combustion gases transfer a portion of their heat to ambient air.

[0071] Referring back to Fig. 2, the engine 10 further has a controller 40 for controlling operation of the engine 10. The controller 40 is used for triggering the injection of air and fuel into the combustion chamber 19, the igniting of the mixture, the injection of the air and / or combustion gases back into the combustion chamber 19, and so on.

[0072] The controller 40 is operatively connected to the air valve 25 (e.g., throttle) for controlling a mass flow rate of air admitted into the combustion chamber 19, to the flow meter 26 operable to send a signal to the controller 40 indicative of the mass flow rate of the air flowing through the air valve 25, to a sensor 41 operable to send a signal to the controller 40 about a parameter of the air injected into the combustion chamber 19 (e.g., pressure, temperature, etc), to the fuel injector 23 to control an amount of fuel injected into the combustion chamber 19, and to the secondary valves 31 to control and amount of air and / or combustion gases injected into the combustion chamber 19 for generating the stratification of the fluids into the combustion chamber 19.

[0073] Referring now to Fig. 6, a chart illustrating the timing of different events during the up and down motions of the piston 13 is shown. These events may occur successively one after the other very quickly. The controller40 is operable to trigger these different events in a timely manner for proper operation of the engine 10.

[0074] The piston 13 moves upwardly from a first intermediate position P1 towards a topdead center position TDC. The intake valve 21 moves from its closed position to its opened position when the piston is at the first intermediate position P1 . The first intermediate position P1 is labelled IVO in Fig. 6 for “intake valve open”. An intake process therefore starts at the first intermediate position P1 where air and fuel is admitted in to the combustion chamber 19 via the intake valve 21 . Air and fuel are admitted in the combustion chamber 19 via the intake valve 21 for a spark ignition engine. For a GDI or diesel engine, the intake valve 21 is used to admit air only since the fuel is directly injected in the combustion chamber 19. The piston 13 then moves downwardly from the top-dead center position TDC and reaches a bottom-dead position BDC before starting to move back upwardly towards the top-dead center position TDC. During its travel towards the top-dead center positon TDC, the piston 13 reaches a second intermediate position P2. The intake valve 21 moves from its open configuration to its closed configuration at the second intermediate position P2. At which point, admission of air and fuel in to the combustion chamber 19 stops. An intake process therefore extends while the piston 13 moves from the firstintermediate position P1 to the second intermediate position P2. The second intermediate positionP2 is labeled IVC for “intake valve closed”.

[0075] A compression process then starts after the intake process ends. During the compression process, the piston 13 moves upwardly from the second intermediate position P2 back to the top-dead center position TDC, where the compression process ends since the volume of the combustion chamber 19 is minimal at the top-dead center position TDC. A pressure of the fuel and air increases within the combustion chamber 19 during the compression process.

[0076] A combustion process may then start after or near the end of the compression process. However, for a spark ignition engine, the combustion process starts when the mixture is ignited by the igniter 24 and before the end of the compression stroke. The combustion process occurs while the piston 13 moves from the top-dead center position TDC to a third intermediate position P3, which is located between the top-dead center position TDC and the bottom-dead center position BDC. The third intermediate position P3 is, in the present embodiment, closer to the bottom-dead center position BDC than the top-dead center position TDC. The gas is combusted within the combustion chamber 19 during the combustion process. The exhaust valve 22 moves from its closed configuration to its open configuration at the third intermediate position P3, which is labelled EVO for “exhaust valve open” in Fig. 6.

[0077] An exhaust process then starts afterthe combustion process ends. During the exhaust process, the combustion gases generated in the combustion chamber 19 are expelled out of the combustion chamber 19. The exhaust process occurs while the piston 13 moves from the third intermediate position P3 where the exhaust valve 22 opens to a fourth intermediate position P4 where the exhaust valve 22 moves from its open configuration to its closed configuration. During the exhaust process, the piston 13 moves from the third intermediate position P3 to the bottomdead center position BDC, upwardly to the top-dead center position TDC, and downwardly to the fourth intermediate position P4, which is labelled EVC for “exhaust valve close” in Fig. 6. The different cycles then repeat continuously as long as the engine 10 is operating.

[0078] The engine 10 of the present disclosure may include two additional processes: a late air injection process and a stratification process. These two processes are carried over by the controller 40 and by the secondary injection system 30 described herein above and are described successively herein below.

[0079] During the late air injection process, further air may be injected directly into the combustion chamber 19, either through the head 16 or through the wall of the cylinder 12 via the secondary injectors 33. The late air injection process may occur during the combustion process. Put differently, the late air injection process may occur concurrently with the combustion process, which starts after the ignition of the air and fuel mixture. The late air injection process may start when the piston 13 reaches a fifth intermediary position P5 while the piston 13 moves downwardly from the top-dead center position where the combustion process starts. The late air injection process may end when the piston reaches the third intermediate positon P3 where the exhaust valve 22 opens.

[0080] This may generate a power gain without requiring any additional fuel. As aforementioned, this air may be pre-heated using the heat exchanger 37, either with combustion gases, the liquid coolant, or both. If the later air injection occurs during the exhaust stroke, which occurs as the piston 13 moves upwardly from the third intermediate position P3 to the fourth intermediate position P4, the mixture of the combustion gases and their oxidation may be favored. The air injected before the piston 13 reaches the third intermediate position P3 may favor the oxidation of the combustion gases.

[0081] During the stratification process, air and / or combustion gases may be injected directly into the combustion chamber 19, either through the head 16 or through the wall of the cylinder 12 via the secondary injectors 33. The stratification process may occur during both of the intake process and the compressor process. The stratification process may thus overlap with a portion of the intake process and with a portion of the compression process. The stratification process may start when the piston 13 reaches a sixth intermediate position P6 while the piston moves downwardly towards the bottom-dead center position BDC and while the intake valve 21 is open. The stratification process may end when the piston 13 reaches a seventh intermediate position P7 while the piston moves upwardly towards the top-dead center position TDC and afterthe intake valve 21 is closed. In this embodiment, the stratification process ends before ignition of the mixture of air and fuel.

[0082] The stratification process may occur during the intake process only, during the compression process only, or, as shown in Fig. 6, may span a portion of the intake process and a portion of the compression process. This may allow to obtain a stratification of the gas as a function of the axial position of injection of the gas via the different secondary injectors 33 (Fig. 1) when the secondary injectors 33 are oriented perpendicularly to the wall of the cylinder 12, and / ora stratification of the gas in the vicinity of the wall of the cylinder 12 (Fig. 4) when the secondary injectors 33 are oriented with a circumferential component.

[0083] The stratification process may permit the use of a greater quantity of combustion gases before deterioration of the combustion compared to a classical configuration in which the combustion gases are mixed with air and fuel upstream of the combustion chamber 19, and may reduce NOx emission and soot creation compared to the classical configuration. A maximal power curve of the engine is obtained for a plurality of rotational speeds (i.e., operating points) of the engine without EGR. Homogeneous EGR is typically not used when the air valve 25 is opened at or close to its maximum position. The homogeneous EGR is minimized or stopped proximate near a maximum power of a diesel engine. The homogeneous EGR is reduced or stopped proximate the maximum power because it reduces the amount of air admitted in the combustion chamber. Since less air is admitted, less fuel may be burned, which may in turn decrease the power. The closer an engine is to its maximal power, the less EGR is used.

[0084] Injecting air via the secondary intake ports 32 during the admission of air via the intake port 17 before the injection of fuel may allow to create turbulence in the combustion chamber to favor homogeneity of the mixture of air and fuel once the fuel is injected. In other words, the air that creates turbulence may help in distributing the fuel within the combustion chamber. The turbulence may favor the combustion since the mixture of air and fuel burns at a greater speed.

[0085] If fuel is present within the air in the combustion chamber while air is injected via the secondary intake ports 32, a stratification of the fuel and an increase of the turbulence (e.g., swirl or tumble) may occur. This may further accelerate the combustion process. However, a ratio of fuel to air may change, which may increase a speed of the combustion process. For a diesel engine, the air injection via the secondary intake ports 32 towards the end of the compression process may increase an intensity of the swirl flow, which may be beneficial to the formation of the mixture of air and fuel. For a diesel engine, a factor limiting power is the lack of contact between fuel and air. In this case, injecting the air, which favors turbulence, may help the combustion process and increase power.

[0086] The controller 40 is therefore able to control the injection of air and fuel, the ignition, the injection of air and / or combustion gases, and so on following the chart presented in Fig. 6. It will be appreciated that modifications to that chart may be contemplated by the person skilled in the art without departing from the scope of the present disclosure.

[0087] Referring now to Fig. 7, a method of operating the engine 10 is shown at 700. The method 700 includes injecting the mixture of air and fuel into the combustion chamber 19 during the intake process at 702; after the intake process, compressing the mixture of air and fuel during the compression process at 704; after the compression process, igniting the mixture of air and fuel during the combustion process at 706; after the combustion process, expelling combustion gases out of the combustion chamber 19 during the exhaust process at 708; and one or more of: injecting one or more of air and combustion gases from the gas source S3 into the combustion chamber 19 during one or more of the intake process and the compression process, and injecting the air into the combustion chamber 19 during the combustion process at 710.

[0088] As described above, many ways to inject the gas, such as air and / or combustion gases into the combustion chamber 19 are possible. The gas may be injected perpendicularly to the wall of the cylinder 12. The gas may be injected with a circumferential component. Any combinations of the above is possible. The gas may be injected through the head 16 ofthe engine 10. The gas may be compressed before being injected in to the combustion chamber 19. The gas may be either heated, forthe air, or cooled down, forthe combustion gases, before being injected into the combustion chamber 19.

[0089] In the embodiment shown, the injecting of the one or more of the air and the combustion gases at 710 includes injecting the one or more of the air and the combustion gases thereby stratifying a mixture contained within the combustion chamber. The stratifying of the mixture includes creating a radial or a circumferential stratification ofthe mixture. The one or more of the air and the combustion gases may be injected at different time intervals as a function of a position of the piston.Engine Test Procedure

[0090] The experimental procedure ensures consistency between each test and is as follows. The engine 10 was started and was given enough time to warm up based on a K-type thermocouple measurement that is located against the side of the engine block between two cooling fins. Once the engine temperature reached 413K, the experiments begun. It is noted that the engine steady-state temperature of 413K varied by less than 20K on a day-to-day basis.

[0091] Once the steady-state temperature was reached, the engine was brought to its operating point with a brake mean effective pressure (BMEP) of 388 kPa at 2100 RPM or 2500 RPM. Under these conditions, engine throttle is near its wide-open position with an intake airpressure of 82 kPa measured in absence of EGR and values increasing to reach WOT under maximum homogeneous EGR. It is noted that with the proposed stratified EGR, a lower intake air pressure was measured than with the homogeneous approach. A stoichiometric gasoline-air mixture was set using the closed-loop control function of the OpenECU, while spark timing did not vary significantly between the different configuration. Unless stated otherwise, spark timing was set at 37 deg before top dead center (TDC). The engine settings allow a stable operation so as a constant RPM was held within a maximum +18 RPM.

[0092] Referring to Fig. 8, four different EGR operation modes were tested using the following nomenclature. Homogeneous EGR (H-EGR in what follows), involves that N2 is injected continuously in the intake manifold, similarly to the conventional approach, at a fixed mass flow rate. This configuration may enable comparison with the new proposed system. On the other hand, with stratified EGR, N2 injection begun with one of the three different timings evaluated: 215° (thus 35° before bottom dead center (BDC) intake stroke), 180° (thus at BDC of the intake stroke) and 50° before top dead center (TDC). They are named STR215, STR180 and STR50, respectively and are illustrated in Fig. 8 with respect to the intake and compression stroke where the spark timing (S.T.) is also identified. For STR215 and STR180, two EGR levels are tested, while with STR50, a single EGR level was studied as to explore a very late EGR injection strategy acknowledging that in-cylinder pressure becomes a constraint and limit the amount of EGR flowing due to the limitations of the solenoid valves. In all cases, the throttle was adjusted to maintain the engine torque constant at a given engine speed.

[0093] The EGR rate, in percent, is based on the equation below where nitrogen mass flow rate (mW2)wasobtained from a N2 flow meter while the air mass flow (mair) is computed using Equation 2 based on the lambda sensor measurement (A), using a stoichiometric A / F of 14.7, and the mass of gasoline injected. Herein, a low and a high level of EGR implies an average value of 14% and 20% of N2 respectively, while the exact EGR rate value is used when displaying the results.

[0094] 100

[0095] For STR50 the injection occurred during the in-cylinder pressure rise due to compression. This had the consequence to prevent part of the EGR from getting inside the cylinder and to be trapped in the injection pipe located between the check valve and the solenoid valve. Forthis reason, the mass injected in the cylinder for the STR50 configuration was estimated using the equation below which required the solenoid valve surface area (S) taken from the valve’smanufacturer and the nitrogen velocity entering the cylinder ( ^az(0)). The latter was computed with the equation below, where AP(0) is the pressure differential between the flowing nitrogen gas and the in-cylinder pressure as measured with the pressure transducer during the EGR injection process while the discharge coefficient (Cd) is taken from the valve’s manufacturer.

[0096] mgaz= S ^az(0) x S x pgazx dt

[0098] The in-cylinder pressure measurements allowed quantifying the combustion process. Hence, the data was used, to look at the repeatability of the combustion process as determined by the Coefficient of Variability of the Indicated Mean Effective Pressure (COV of IMEP) using equation below and where a is the standard deviation and IMEP is the average IMEP based on 250 consecutive cycles.(T

[0099] IMEP

[0100] The in-cylinder pressure was also used to determine the mass fraction burned (MFB) throuoh a net heat release analysis so as to quantify the early kernel growth expressed by 0-10% of MFB (MFB0-10) and the fully developed turbulent combustion defined by the interval between 10% and 90% of MFB (MFB10-90). The net heat release was determined, neglecting heat loss to the walls, based on the equation below, using the instantaneous in-cylinder pressure (P), incylinder volume (V) and their respective variation dP and dV. Finally, y is the heat capacity ratio and was taken as equal to 1 .3.[L0101

[0102] Pollutant species concentrations of NO, carbon monoxide (CO) and total unburnt hydrocarbons (THC) were measured using a Fast Transform InfraRed spectroscopy (California Analytical Instruments model FTIR600). The accuracy of the analyzer is 2% for NO, CO and THC, based on the manufacturer manual. From the FTIR molar concentrations ((), the emission index (El) and specific emissions (SE) were computed using equations below. In these equationsis the molar weight of the specie i, a is the number of carbon atoms in a molecule of gasoline, taken herein as CsHis, and Mfis its molar weight, while mfand W are the fuel mass flow rate and engine power, respectively.

[0104] Results and Discussion

[0105] In this section, a distinction is made when using the stratified EGR system proposed herein. Tests have been conducted with two EGR timings that end before intake valve closure. They are considered as early EGR injection in the analysis of the results based on the in-cylinder pressure. The other approach of stratified EGR involved a late EGR injection which begins 90 deg before TDC and ends at spark timing because the in-cylinder pressure has reached the EGR injection pressure. Due to this limitation, a lower level of EGR was reached with this latter configuration and in-cylinder pressure analysis is done separately to prevent confusion.

[0106] The analysis begins by looking at the engine stability based on the COV of IMEP which shows that the engine, while stable with respect to RPM, can be considered as having an inherent high Coefficient of Variability (COV) of indicated mean effective pressure (IMEP), in part due to the experimental setup (friction clutch to interface the engine and the dyno). Figs. 9A-9B show the COV of IMEP for H-EGR, STR215 and STR180 as a function of the EGR rate and for the two engine speeds studied herein. It is observed that in the absence of EGR, a COV of 8,8% and 9,5% is found at 2100 and 2500 RPM, respectively. For both engine speeds, the addition of homogeneous EGR increased the COV of IMEP while acknowledging that a cold EGR is used, which inherently increase the COV of IMEP. Moreover, the highest EGR rate tested with H-EGR can be considered nearthe EGR limit of the engine. Figs. 9A-9B also illustrate that stratified EGR can make the engine less sensitive to EGR than H-EGR as a decrease of COV of IMEP is observed depending of the engine speed and amount of EG injected. For example, at a 14% level of EGR, STR180 resulted in a lower COV of IMEP than H-EGR at 2100 RPM, while an earlier injection (STR215) was less advantageous even if a retarded spark timing was needed to obtain the data shown in Fig. 9A. On the other hand, at 2500 RPM STR215 offered lower values of COV of IMEP than H-EGR for both EGR levels. Finally, at 2500 RPM, STR180 offered a similar trend and values to H-EGR with an increase of COV of IMEP with increasing EGR rates, albeit that at the highest EGR level, STR180 is less stable.

[0107] As stated previously a test was conducted to see how a very late EGR injection would impact the engine performance knowing that the in-cylinder pressure being higher than during the intake stroke, the amount of EGR injected would be less due to the maximum operating pressure of the nitrogen valves. Therefore, with STR50, N2 addition was exploratory as to see how such a late EG injection would impact the combustion process. With STR50, the end of the injection wasreached when in-cylinder pressure reaches 8 bars (which is near spark timing). The consequence of using such a late injection is that the configuration of the experimental set-up would trap a residual amount of N2 in the pipe located between the electronic valve and the cylinder head where a check valve was added to prevent gas return from the cylinder. However, the configuration makes it possible for the residual nitrogen in the pipe to leak into the cylinder once the in-cylinder pressure felt under approximately 5 or 6 bar. From in-cylinder pressure measurements, this late N2 addition was nearly synchronized with the exhaust valve opening. So, the main impact of such a late nitrogen addition would be to enhance the dilution as it is estimated that less than 5% of the total in-cylinder mass was injected during that late period and thus making the total EGR level (including late dilution) similar to the lowest EGR cases studied herein.

[0108] Thus, due to the lower level of EGR achieved with STR50, the comparison is made without EGR and with the case 14% H-EGR, only. The results are shown in the table below. It is observed that at 2500 RPM, STR50 offered a lower COV of IMEP than in the absence of EGR, suggesting that a late injection might increase turbulence, which benefits the combustion process, which will be verified in a latter section, and lower the COV of IMEP.

[0109] To further quantify the impact of the direct EGR injection, the analysis is pursued using the mass fraction burned (MFB). The idea of using a stratified EGR as proposed herein is to try to confine the EGR away from the spark plug while to also increase turbulence in the cylinder as to speed up the combustion process. Both effects shall translate into faster flame propagation. Figs. 10A-10B show the mass fraction burned duration (0-10MFB and 10-90MFB) for H-EGR, STR215 and STR180. As stated previously, STR215 at 2100 RPM required a retarded spark timing. Fig. 10A shows the results at 2100 RPM where the 0-10MFB is nearly constant irrespective of the EGR strategy employed. However, once the fully turbulent combustion phase (10-90MFB) is reached, stratified EGR is always fasterthan H-EGR, suggesting that an increase of turbulence and / or the stratification of EGR within the cylinder as both might be responsible for this decrease in burn duration.

[0110] The above conclusion is reached based on the following: 1) homogeneous cooled EGR increase the 10-90MFB duration in spark-ignition engines; 2) Data for the 10-50MFB and 50-90MFB, shows that STR180 and STR215 decreased 50-90MFB at both engine speeds when the highest level of EGR was used but that the 10-50MFB remained relatively constant and similar to that of H-EGR. This result suggests an N2 stratification that is located near the center of the cylinder (in concordance with the orientation of the N2 direct injection inlet ports); 3) At 2100 RPM, STR215 and STR180 with the highest level of EGR offered shorter 50-90MFB than in absence of EGR, suggesting not only the stratification of nitrogen but also a possible increase of turbulence (particularly with STR180) due to the direct N2 injection.

[0111] The mass fraction burned results above provided some insight into the consequence of using a stratified EGR. It is assumed that the injection of nitrogen directly in the cylinder through three different ports will increase the turbulence and thus favors the combustion process. Based on EGR mass flow rate measurement, the average velocity of the N2 flowing in the cylinder was estimated considering the three ports size area. Injected N2 could reach an average velocity of between 43 m / s and 63m / s at 2100 RPM depending on the EGR rate while an N2 jet velocity between 38 m / s and 59 m / s is estimated at 2500 RPM. Such a velocity can thus generate an increase of turbulence during the intake and compression strokes, resulting in a faster combustion process. To further quantify this effect, the maximum pressure rise rate during combustion P \d0 max has been calculated. It is noted that the increase in turbulence resulted into higherP \dM0 max when studying the effect of the tumble ratio in presence of EGR. Figs. 11 A-1 1 B show the maximum pressure rise rate in the cylinder for both engine speeds. It is observed that (— ) is, in general, greater with a stratified approach, for a given level of EGR, than for an H-EGR. Overall, Figs. 11 A-1 1 B support the hypothesis of the turbulence increase induced by the N2 injection.

[0112] The late EGR injection strategy, STR50, is now compared with the results obtained in the absence of EGR in the table below. One observes that at 2100 RPM, STR50 decreased the early flame kernel development duration but that this positive impact is not observed at 2500 RPM for which the 0-10MFB increased, probably due to the presence of EGR in the vicinity of the spark plug. However, at 2500 RPM, the benefit of using STR50 is seen on the 10-90MFB, which is fasterthan the case without EGR, suggesting that at higher engine speed, the turbulence increase by the injection of EGR is felt later in the cycle compared to the case at 2100 RPM. Therefore, by looking at the 50-90MFB, it appears that the late injection of EGR at 2500 is mostly felt during the latter part of the combustion process suggesting EG stratification located in the center of thecylinder and / or a possible increase of turbulence at the periphery of the cylinder. Therefore, the impact being felt late in the cycle, no impact on P \d0 max is observed with STR50 when compared to the results in the absence of EGR.

[0113] The impact of using stratified EGR of the specific fuel consumption (SFC) is presented in Figs. 12A-12B. The general behavior observed is a decrease of SFC at the lowest EGR level followed by its increase at the highest EGR level at 2100 RPM while at 2500 RPM SFC is increasing with EGR level. At the latter engine speed as with the highest EGR level at 2100 RPM, the throttle is nearly fully open, therefore the addition of N2 with homogeneous EGR decrease the volumetric efficiency. When compared to H-EGR, the advantage of using a stratified EGR on the SFC is observed at both engine speeds with the highest EGR level offering a decrease of SFC by 12.5% and 6.6% at 2100 RPM and 2500 RPM, respectively, with STR215. Overall, it is observed at both engine speeds that retarding the stratified EGR injection timing slightly increase SFC but that overall the values are lower or similar to the one obtained with H-EGR. This general trend is due to a slight decrease of volumetric efficiency as stratified EGR injection timing is retarded, because the throttle opening has to be decreased to lower the intake manifold pressure so as to keep the engine torque constant compared to H-EGR.

[0114] Brake specific nitrogen oxide (BSNO) emission are presented in Figs. 13A-13B. The results show that H-EGR offered a greater reduction of NO at both engine speeds when a 14% EGR rate was used with the exception of STR50 at 2100 RPM which provided a similar BSNO but with less EGR. At a higher EGR rate of 20%, STR180 matched H-EGR at both engine speeds, while STR215 also did the same at 2500 RPM, albeit at a slightly higher EGR level. It is observed that a very late EGR strategy (STR50) at 2500 RPM does not offer any benefit with respect to NO possibly because the added N2 might be confined to a smaller zone in the spark plug vicinity (based on MFB above) than at 2100 RPM due to a shorter time between N2 injection and spark timing. The consequence is that this configuration has no significant impact on the combustion temperature as the combustion process was the fastest among the different EGR configurations and that the different MFBs duration were closed to the reference point without EGR. Overall, the higher NO observed with respect to homogeneous EGR.

[0115] The observation made at 2500 RPM with STR50 in combination to the highest EGR rate is that the strategy did not offer a decrease in NO probably due to a lack of mixing between the added nitrogen and the fuel-air mixture. This hypothesis is supported by the THC emissions reported in Figs. 14A-14B where the STR50 configuration offered the lowest amount of THC at 2500 rpm. It is assumed that while time was lacking to mixed N2 to the air-fuel mixture, the late N2 addition might have increase in-cylinder turbulence which is known to be beneficial to homogenize the air-fuel mixture resulting in a decrease of THC. A similar observation is made for STR215 at 2100 RPM where higher NO are associated to the lowest THC and that EGR strategy also has the fastest MFB10-90 at that engine speed.

[0116] Figs. 15A-15B present the carbon monoxide (CO) emissions are similar at 2100 RPM irrespective of the EGR strategy employed. As CO is mainly dependent on air-fuel ratio, the results suggested that the air-fuel mixture did not change much at 2100 RPM. On the contrary, at 2500 RPM, increase of CO are observed with stratified EGR strategies that could be due to the EGR I mixture interface and thus the stratification of the EGR that impact locally the air-fuel mixture. Ongoing CFD results might help explain the observed trends.Conclusions

[0117] A novel approach to generate a stratified EGR has been proposed. To do so, the cylinder head of a single-cylinder engine has been modified to include the addition of 3 EGR inlet ports based on electronic controlled valves which were connected to an 8-bar nitrogen supply to emulate engine EGR. To illustrate the capability of the proof of concept, three different injection timings were evaluated. Experiments were conducted with two EGR levels at two different engine speeds and high loads while in-cylinder pressure and pollutant emissions were measured. From the experiments, the main findings are; direct injection of EGR with a stratification strategy provided faster burning rate than H-EGR and in some instance, nearly as fast as without EGR; at similar EGR rate, all stratified EGR strategies tend to improve specific fuel consumption when compared with a homogeneous EGR approach; depending of EGR level and engine operating point, it was possible to find an EGR stratified strategy that offered similar NOx and THC emissions to the one obtained with a homogeneous approach; and the preliminary results obtained herein suggest that the optimum stratified EGR strategy would be a function of engine speed and load, similarly to what is observed with stratified fuel injection. The above results suggested that based on the EGR injection timing, EGR stratification and turbulence enhancement were probably achieved.Controller

[0118] With reference to Fig. 16, an example of a computing device 1600 is illustrated. For simplicity only one computing device 1600 is shown but the system may include more computing devices 1600 operable to exchange data. The computing devices 1600 may be the same or different types of devices. The controller 40 may be implemented with one or more computing devices 1600.

[0119] The computing device 1600 comprises a processing unit 1602 and a memory 1604 which has stored therein computer-executable instructions 1606. The processing unit 1602 may comprise any suitable devices configured to implement the method 700 such that instructions 1606, when executed by the computing device 1600 or other programmable apparatus, may cause the functions / acts / steps performed as part of the method 700 as described herein to be executed. The processing unit 1602 may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof.

[0120] The memory 1604 may comprise any suitable known or other machine-readable storage medium. The memory 1604 may comprise non-transitory computer readable storage medium, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory 1604 may include a suitable combination of any type of computer memory that is located either internally or externally to device, for example random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magnetooptical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. Memory 1604 may comprise any storage means (e.g., devices) suitable for retrievably storing machine- readable instructions 1606 executable by processing unit 1602.

[0121] The methods and systems for operating the engine 10 described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device 1600. Alternatively, the methods and systems for operating the engine 10 may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems foroperating the engine 10 may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computerwhen the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems for operating the engine 10 may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit 1602 of the computing device 1600, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method 700.

[0122] Computer-executable instructions may be in many forms, including program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0123] The embodiments described herein are implemented by physical computer hardware, including computing devices, servers, receivers, transmitters, processors, memory, displays, and networks. The embodiments described herein provide useful physical machines and particularly configured computer hardware arrangements. The embodiments described herein are directed to electronic machines and methods implemented by electronic machines adapted for processing and transforming electromagnetic signals which represent various types of information. The embodiments described herein pervasively and integrally relate to machines, and their uses; and the embodiments described herein have no meaning or practical applicability outside their use with computer hardware, machines, and various hardware components. Substituting the physical hardware particularly configured to implement various acts for non-physical hardware, using mental steps for example, may substantially affect the way the embodiments work. Such computer hardware limitations are clearly essential elements of the embodiments described herein, and they cannot be omitted or substituted for mental means without having a material effect on the operation and structure of the embodiments described herein. The computer hardware is essential to implement the various embodiments described herein and is not merely used to perform steps expeditiously and in an efficient manner.

[0124] The technical solution of embodiments may be in the form of a software product. The software product may be stored in a non-volatile or non-transitory storage medium, which can be a compact disk read-only memory (CD-ROM), a USB flash disk, or a removable hard disk. The software product includes a number of instructions that enable a computer device (personal computer, server, or network device) to execute the methods provided by the embodiments.

[0125] It is noted that various connections are set forth between elements in the preceding description and in the drawings. It is noted that these connections are general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. A coupling between two or more entities may refer to a direct connection or an indirect connection. An indirect connection may incorporate one or more intervening entities. The term “connected” or "coupled to" may therefore include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0126] It is further noted that various method or process steps for embodiments of the present disclosure are described in the following description and drawings. The description may present the method and / or process steps as a particular sequence. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the description should not be construed as a limitation.

[0127] Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0128] While various aspects of the present disclosure have been disclosed, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the present disclosure. For example, the present disclosure as described herein includes several aspects and embodiments that include particular features.Although these particular features may be described individually, it is within the scope of the present disclosure that some or all of these features may be combined with any one of the aspects and remain within the scope of the present disclosure. References to “various embodiments,” “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. The use of the indefinite article “a” as used herein with reference to a particular element is intended to encompass “one or more” such elements, and similarly the use of the definite article “the” in reference to a particular element is not intended to exclude the possibility that multiple of such elements may be present.

[0129] In the context of the present disclosure, the expression “about” implies variations of plus or minus 10%.

[0130] The embodiments described in this document accordingly provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.

Claims

CLAIMS1 . An internal combustion engine, comprising: a body defining at least one cylinder; a head secured to the body; a piston slidingly received within the cylinder, a combustion chamber defined within the cylinder and extending from the piston to the head, the combustion chamber varying in volume with movements of the piston within the cylinder; a crankshaft rotatable about an axis, the piston drivingly engaged to the crankshaft; an injection system for injecting a mixture of air and fuel into the combustion chamber via an intake port in the head; and a secondary injection system, having: a secondary valve fluidly connecting a gas source of one or more of combustion gases and air to the combustion chamber via at least one secondary intake port defined in one or more of the head and a wall of the at least one cylinder, the at least one secondary intake port distinct from the intake port, the secondary valve having a closed configuration in which the gas source is fluidly disconnected from the combustion chamber by the secondary valve and an open configuration in which the gas source is fluidly connected to the combustion chamber through the secondary valve.

2. The internal combustion engine of claim 1 , wherein the secondary valve is fluidly connected to the combustion chamber via the secondary intake port defined through one or more of the head and the wall of the cylinder.

3. The internal combustion engine of claim 2, wherein the secondary valve includes a plurality of secondary valves and the secondary intake port includes a plurality of secondary intake ports, each of the plurality of secondary valves fluidly connected to a respective one of the plurality of secondary intake ports defined through the one or more of the head and the wall of the cylinder.

4. The internal combustion engine of claim 2 or 3, wherein the secondary intake port is defined through the head.

5. The internal combustion engine of claim 1 , comprising a plurality of secondary intake ports defined through the head and being offset from a center of the cylinder.

6. The internal combustion engine of claim 5, comprising secondary valves each fluidly connected to a respective one of the plurality of secondary intake ports, the secondary valves configured to inject the one or more of combustion gases and air into the combustion chamber in a direction having an axial component relative to a central axis of the cylinder.

7. The internal combustion engine of claim 3, wherein an exit flow axis at which the gas is injected into the combustion chamber via the secondary intake ports extends perpendicularly to the wall of the cylinder.

8. The internal combustion engine of claim 7, wherein the secondary intake ports are located at a common circumferential position on the wall of the cylinder and are axially offset from one another relative to a central axis of the cylinder.

9. The internal combustion engine of claim 3, wherein an exit flow axis at which the gas is injected into the combustion chamber via the secondary intake ports extends along a direction having a circumferential component relative to a central axis of the cylinder.

10. The internal combustion engine of claim 9, wherein one of the secondary intake ports is located closer to the head than a remainder of the secondary intake ports, the exit flow axis of the one of the secondary intake ports has an axial component relative to the central axis.11 . The internal combustion engine of any one of claims 1 to 10, wherein the gas is air.

12. The internal combustion engine of claim 11 , comprising a heat exchanger, the gas source fluidly connected to the combustion chamber through the heat exchanger, the heat exchanger providing heat exchange relationship between the air and a fluid having a greater temperature than the air.

13. The internal combustion engine of claim 12, wherein the fluid is a liquid coolant or the combustion gases.

14. The internal combustion engine of any one of claims 1 to 10, wherein the gas is the combustion gases.

15. The internal combustion engine of claim 14, comprising a heat exchanger, the gas source fluidly connected to the combustion chamber through the heat exchanger, the heat exchanger providing heat exchange relationship between the combustion gases and a fluid having a lower temperature than the combustion gases.

16. The internal combustion engine of any one of claims 1 to 15, comprising a controller operatively connected to the secondary valve, the controller having a processing unit and a computer readable medium operatively connected to the processing unit and having instructions stored thereon executable by the processing unit for: controlling the injection system for permitting the mixture of air and fuel to enter the combustion chamber during an intake process, after the intake process, compressing the mixture of air and fuel during a compression process, after the compression process, igniting the mixture of air and fuel during a combustion process, and after the combustion process, expelling combustion gases during an exhaust process; and controlling the secondary injection system for one or more of: injecting one or more of air and combustion gases from the gas source into the combustion chamber during one or more of the intake process and the compression process, and injecting the air into the combustion chamber during the combustion process.

17. A method of operating an internal combustion engine having a piston riding within a combustion chamber defined by a cylinder, comprising: injecting a mixture of air and fuel into a combustion chamber during an intake process;after the intake process, compressing the mixture of air and fuel during a compression process; after the compression process, igniting the mixture of air and fuel during a combustion process; after the combustion process, expelling combustion gases out of the combustion chamber during an exhaust process; and one or more of: injecting one or more of air and combustion gases from a gas source into the combustion chamber during one or more of the intake process and the compression process, and injecting the air into the combustion chamber during the combustion process.

18. The method of claim 17, wherein the injecting of the one or more of the air and the combustion gases includes injecting combustion gases at a plurality of locations through a head of the internal combustion engine.

19. The method of claim 17, wherein the injecting of the one or more of the air and the combustion gases includes injecting the one or more of the air and the combustion gases thereby stratifying a mixture contained within the combustion chamber.

20. The method of claim 17, comprising injecting the one or more of the air and the combustion gases at different time intervals as a function of a position of the piston.

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