A System and Method for Controlled Combustion in a Direct Injection Engine

FIELD OF THE INVENTION

[001] The present invention relates to a system and method for controlled combustion in a direct injection engine.

BACKGROUND OF THE INVENTION

[002] A direct injection engine is a system where fuel is injected directly into the engine’s combustion chamber. The direct injection helps increase engine efficiency, power output and also reduces exhaust emissions. Maximizing engine efficiency depends on how the fuel is distributed inside the combustion chamber after injection - this is termed as a ‘charge mode’. Broadly, there are two types of charge mode, homogenous charge mode and stratified charge mode. Utilizing the direct injection engine to its full potential to maximize its benefits depends on how effectively the engine can be operated and switched between the stratified charge mode and homogeneous charge mode of operation.

[003] In the homogeneous charge mode, the engine operates on an air/ fuel mixture of A = 1, meaning, that there is a homogenous mixture of the fuel and air in the combustion chamber. The fuel is injected at intake stroke in order to give the injected fuel maximum time to mix with the air, so that homogeneous air/fuel mixture is formed. The stratified charge mode creates a small zone of fuel/air mixture around the spark plug, which is surrounded by air in the rest of the combustion chamber. This results in less fuel being injected into the cylinder, leading to very lean air- fuel ratios of X > 2. The stratified charge mode is used at low loads in order to reduce fuel consumption and exhaust emissions. [004] In order to achieve optimum fuel consumption, higher engine efficiency, maximum power output, and lower exhaust emissions, there must be an easy switch between the homogenous mode and the stratified mode. However, in practicality, switching between the stratified mode and the homogeneous mode in the same engine operation becomes difficult. Several factors that affect a successful switching between the homogenous and the stratified modes are, air motion inside cylinder, spray pattern, air fuel mixing, evaporation, local air-fuel ratio (AFR) distribution with time etc. Hence, there have been various attempts to achieve a seamless switching between the homogenous mode and the stratified mode however, they still have persisting problems.

[005] One such attempt relates to a spark ignition stratified charge combustion internal combustion engine. In this, charge stratification is achieved by having two intake valves and two exhaust valves in a pent roof type combustion chamber recessed in a cylinder head, and having an ignition plug in the center of the cylinder. However, even though such arrangement helps to achieve a stratified mode of combustion, the fuel injected would have less time to mix with the air. Further, wall wetting may increase since the fuel is directly injected into bowl of the piston. This results in an incomplete combustion causing soot formation, reduced spark plug life and carbon deposits.

[006] Another attempt relates to stratified charge internal combustion engine with fuel injection and dual injection. In this, a piston having a concave recess is made. This concave recess is narrow near the injector and gets wider as it moves away from the injector. Although there is a low knock tendency, smooth combustion, lower emissions and better fuel economy, however, because of very late main injection followed by immediate combustion, fuel air mixing is a challenge which may lead to higher coefficient of variation (COV) of combustion and possible soot formation. Further, use of two spark plugs in small engines poses geometrical constraints, increases complexity and adds up cost. [007] Yet another attempt relates to stratified charge engines with two spark plugs. As per the method, engine stratification is achieved based on the octane rating. Thus, stratification is achieved through the introduction of two types of fuels (with different octane ratings) through two intake manifolds. Even though low load efficiency and high load anti knock is possible to achieve by this method, it requires the engine to operate on two separate fuel characteristic fuels and two spark plugs. Correspondingly there is an implicit requirement of two fuel storage systems. Thus this system is hard to adapt in practicality and more over availability of different octane rating fuels is itself a challenging requirement.

[008] Thus, there is a need in the art for a system which not only effectively achieves stratified charge combustion but also offers easy switchability to homogeneous combustion and thus addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION

[009] The present invention, in one aspect, is directed to a system for controlled combustion in a direct injection engine. The system has a piston disposed inside a combustion chamber of the direct injection engine, the piston has a crown portion and a body portion. The crown portion has an axial outer end surface configured to create at least two zones inside the combustion chamber during compression stroke of the piston, and the body portion extending from the crown portion. The system further has an Electronic Control Unit (ECU) coupled with a fuel injector. The ECU is configured to generate fuel injector control signal at a predetermined time, and the fuel injector configured to inject fuel into the combustion chamber in response to the fuel injector control signal such that the injected fuel mixes in at least one zone so formed in order to achieve stratified charge combustion. [010] In an embodiment of the invention, the ECU is configured to generate fuel injector control signals at predetermined time intervals, and the fuel injector is configured to inject fuel into the combustion chamber in response to the fuel injector control signals such that the injected fuel mixes in both the zones in order to achieve a homogenous charge combustion.

[Oi l] In another embodiment of the invention, the ECU is configured to generate the fuel injector control signal during an early intake stroke of the piston to achieve the stratified charge combustion.

[012] In yet another embodiment of the invention, the ECU is configured to generate a first fuel injector control signal during an early intake stroke of the piston; a second fuel injector control signal during a mid-intake stroke of the piston; and a third fuel injector control signal during a late intake stroke of the piston.

[013] In a further embodiment of the invention, the axial outer end surface of the crown is configured to form a conic-sectioned bridge extending diametrically between a first end and a second end with height of the bridge being maximum at center of the crown.

[014] In another embodiment of the invention, the center of the bridge comprises a flat surface; and a pair of opposing sides extending from the flat surface, the pair of opposing sides being substantially flat with respect to the flat surface.

[015] In an embodiment of the invention the axial outer end surface of the crown is configured to form a recess on each side of the bridge, each recess forms the at least one zone. In an embodiment of the invention, the recess is a concave depression formed on each side of the bridge.

[016] In another aspect, the present invention is directed to a method for controlled combustion in a direct injection engine, wherein the method comprising the steps of: forming at least two zones inside a combustion chamber of the engine by a piston disposed inside therein; generating a fuel injector control signal by an Electric Control Unit (ECU) at predetermined time; and injecting fuel into the combustion chamber in response to the fuel injector control signal such that the injected fuel mixes in at least one zone so formed in order to achieve a stratified charge combustion.

[017] In an embodiment of the invention, the method comprises the steps of: generating fuel injector control signals at predetermined time intervals; and injecting fuel into the combustion chamber in response to the fuel injector control signals such that the injected fuel mixes in both the zones in order to achieve a homogenous charge combustion.

[018] In another embodiment of the invention, the method comprises the step of estimating engine speed and engine load by the ECU in order to generate the fuel injector control signal.

[019] In yet another embodiment of the invention, the ECU generates the fuel injection control signal when the engine load is lesser than 50% of maximum engine load and the engine speed is lesser than 70% of maximum engine speed.

[020] In a further embodiment of the invention, the fuel injection control signal is generated by the ECU during an early intake stroke of the piston such that the injected fuel mixes in at least one zone so formed in order to achieve the stratified charge combustion.

[021] In another embodiment of the invention, the ECU generates at least three fuel injection control signals when the engine load is greater than 30% of maximum engine load and the engine speed is greater than 50% of maximum engine speed.

[022] In yet an embodiment of the invention, the ECU generates a first fuel injector control signal during an early intake stroke of the piston; a second fuel injector control signal during a mid-intake stroke of the piston; and a third fuel injector control signal during a late intake stroke of the piston such that the injected fuel mixes in both the zones in order to achieve the homogenous charge combustion.

[023] In another aspect, the present invention is directed towards a piston for a direct injection engine. The piston has a crown portion and a body portion. The crown portion has an axial outer end surface configured to create at least two zones inside the combustion chamber during compression stroke of the piston, and the body portion extending from the crown portion.

[024] In an embodiment of the invention, the axial outer end surface of the crown is configured to form a conic-sectioned bridge extending diametrically between a first end and a second end with height of the bridge being maximum at center of the crown.

[025] In another embodiment of the invention, the center of the bridge comprises a flat surface; and a pair of opposing sides extending from the flat surface, the pair of opposing sides being substantially flat with respect to the flat surface.

[026] In an embodiment of the invention the axial outer end surface of the crown is configured to form a recess on each side of the bridge, each recess forms the at least one zone. In an embodiment of the invention, the recess is a concave depression formed on each side of the bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

[027] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Figure 1 shows a transverse section of a direct injection engine in accordance with an embodiment of the invention.

Figure 2a shows a top perspective view of crown portion of a piston in accordance with an embodiment of the invention.

Figure 2b shows a top view of the crown portion of the piston in accordance with an embodiment of the invention. Figure 2c shows a side view of the crown portion of the piston in accordance with an embodiment of the invention.

Figure 2d shows a front view of the crown portion of the piston in accordance with an embodiment of the invention.

Figure 3 shows a top perspective view of the crown portion of the piston in accordance with an embodiment of the invention.

Figure 4a shows a side view of the crown portion of the piston in accordance with an embodiment of the invention.

Figure 4b shows a cross section of the side view of the crown portion of the piston in accordance with an embodiment of the invention.

Figure 4c shows a top view of the crown portion of the piston in accordance with an embodiment of the invention.

Figure 4d shows a cross section of the side view of the crown portion of the piston in accordance with an embodiment of the invention.

Figure 5 shows velocity vectors of charge motion and formation of separate zones in the combustion chamber in accordance with an embodiment of the invention.

Figure 6a shows distribution of stratified charge in the separate zones formed in the combustion chamber in stratified mode of operation in accordance with an embodiment of the invention.

Figure 6b shows distribution of homogenous charge in the separate zones formed in the combustion chamber in homogenous mode of operation in accordance with an embodiment of the invention.

Figure 7 shows a graph of operation between stratified mode and homogenous mode of operation in accordance with an embodiment of the invention. Figure 8 shows a method for controlled combustion in a direct injection engine in accordance with an embodiment of the invention.

Figure 9 shows a flowchart of ECU configuration in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[028] The present invention relates to a system and method for controlled combustion in a direct injection engine.

[029] Figure 1 depicts a direct injection (DI) engine 100 of a motor vehicle in accordance with an embodiment of the present invention. The DI engine 100 typically has a cylinder block 110 and a cylinder head 120. The cylinder block 110 has a plurality of cooling fins 140 around its periphery. The cylinder head 120 sits above the cylinder block 110 forming a combustion chamber 130, wherein combustion of fuel occurs in order for the motor vehicle to move. A piston 200 is disposed inside the combustion chamber 130. Further, the cylinder block 110 also has an intake valve 150a and an exhaust valve 150b.

[030] The combustion chamber 130 receives air through the intake valve 150a. Further, the combustion chamber 130 lets out combusted mixture through the exhaust valve 150b. The axially movable piston 200 inside the cylinder block 110 is connected to a crankshaft by a connecting rod. The piston 200 has a crown portion 300 and a body portion 250, whereby the body portion 250 extends from the crown portion 300 of the piston 200. The crown portion 300 of the piston 200 has an axial outer end surface 310.

[031] One aspect of the present invention relates to a system for controlled combustion in the DI engine. The controlled combustion relates to a stratified mode of combustion of air fuel mixture and a homogenous mode of combustion of the air fuel mixture inside the combustion chamber. Thus, according to the invention, in order to achieve the controlled combustion, formation of at least two zones inside the combustion chamber 130 is required. Accordingly, the outer end surface 310 of the crown portion 300 of the piston 200 is so configured that at least two zones are created during compression stroke of the piston 200. Further, an Electric Control Unit (ECU) is coupled with a fuel injector. The ECU is configured to generate fuel injector control signal at a predetermined time and at predetermined time intervals depending on the stratified or the homogeneous mode respectively. In response to the fuel injector control signal the fuel injector is configured to inject a predetermined quantity of fuel at predetermined time into the combustion chamber 130 such that the injected fuel mixes in at least one zone so formed (explained hereinbelow) in order to achieve the controlled combustion of the air fuel mixture.

[032] As shown in the embodiment depicted in Figures 2a, 2b, 2c and 2d, the outer end surface 310 of the crown portion 300 of the piston 200 is configured to form a conic-sectioned bridge 320. Since the outer end surface 310 is circular in shape, the conic-sectioned bridge 320 is configured to extend diametrically over the outer end surface 310, thus extending between a first end 320a and a second end 320b of the bridge 320. Further, the conic-sectioned bridge 320 is configured such that height of the bridge 320 is maximum at center 312 of the crown 300. In the present embodiment, the axial outer end surface 310 of the crown 300 is configured to form a recess on each side 322a, 322b of the bridge 320. In yet another embodiment, the recess comprises a concave depression thus formed on each side 322a, 322b of the bridge 320. Thus, when the piston 200 linearly moves inside the combustion chamber 130, the configuration of the crown portion 300 of the piston 200 described hereinabove, more specifically the recesses on each side 322a and 322b of the bridge 320, result in formation of at least two zones, as shown in Figure 5, inside the combustion chamber 130.

[033] In another embodiment depicted in Figures 3, 4a, 4b, 4c and 4d, the center 312 of the bridge

320 has a flat surface 400. Further, the bridge 320 has a pair of opposing sides 410a, 410b extending from the flat surface 400. Shown in Figures 4c and 4d is a cross section S-S of the piston 200. As seen in the Figures, the opposing sides 410a, 410b are substantially flat with respect to the flat surface 400. In the same embodiment, as explained hereinabove, and as shown in Figures 4b, 4c, the axial outer end surface 310 of the crown portion 300 is configured to form a recess on each side 322a, 322b of the bridge 320. In yet another embodiment, and as shown in the Figures 4a and 4b which is a cross section T-T of the piston 200, the recess comprises a concave depression thus formed on the each side 322a, 322b of the bridge 320. Thus, when the piston 200 linearly moves inside the combustion chamber 130, the configuration of the crown portion 300 of the piston 200 described hereinabove, more specifically the recesses on each side 322a and 322b of the bridge 320, result in formation of at least two zones, as shown in Figure 5, inside the combustion chamber 130.

[034] To achieve the stratified mode of combustion in the system, the ECU is configured to generate the fuel injector control signal at a predetermined time. In response to the fuel injector control signal, the fuel injector is configured to inject a predetermined quantity of the fuel into the combustion chamber 130. In an embodiment of the invention, the ECU is configured to generate the fuel injector control signal during an early intake stroke of the piston 200. Shown in Figure 6a, there is a formation of two zones. As seen in the Figure, at a predetermined engine load and engine speed (explained hereinunder), the fuel injector injects the fuel inside the combustion chamber 130. Accordingly, one of the zones receives the fuel from the fuel injector. The fuel mixes with the air in the respective zone formed thus attaining locally homogeneous charge/air/fuel mixture in of the zones and an overall lean charge/air/fuel mixture. This stratified mixture undergoes completed combustion resulting in low emission and low soot formation. Combustion of this mixture occurs resultantly having a controlled combustion, i.e. the stratified mode of combustion.

[035] To achieve the homogenous mode of combustion in the system, the ECU is configured to generate the fuel injector control signals at a predetermined time and at predetermined time intervals. In response to the fuel injector control signal, the fuel injector is configured to inject predetermined quantities of the fuel into the combustion chamber 130. In an embodiment of the invention, the ECU is configured to generate a first fuel injector control signal during an early intake stroke of the piston 200; a second fuel injector control signal during a mid-intake stroke of the piston 200; and a third fuel injector control signal during a late intake stroke of the piston 200. Shown in Figure 6b, is a formation of two zones. As seen in the Figure, at a predetermined engine load and engine speed (explained hereinunder), the fuel injector injects the fuel at three time intervals, inside the combustion chamber 130. Accordingly, one of the zones receives the fuel from the fuel injector. Further, although one of the zones receives the fuel from the fuel injector, since the fuel is injected at least three times at different time intervals, the fuel is distributed and mixed in the second zone as well. Thus, combustion of such air/ fuel ratio occurs and resultantly, controlled combustion, i.e. the homogenous mode of combustion is achieved.

[036] Another aspect of the present invention relates to a method for controlled combustion in the DI engine as shown in Figure 8. The controlled combustion relates to a stratified mode of combustion of air fuel mixture and a homogenous mode of combustion of the air fuel mixture. In order to achieve the controlled combustion, according to the invention, at step 910, formation of at least two zones inside the combustion chamber 130 is required.

[037] Further, an Electric Control Unit (ECU) coupled with a fuel injector, is configured to generate fuel injector control signal at step 920, at a predetermined time and at predetermined time intervals depending on the stratified or the homogeneous mode. The ECU is also configured to estimate engine speed and engine load and thus generate fuel injector signals accordingly. Furthermore, in response to the fuel injector control signal, the fuel injector is configured to inject a predetermined quantity of fuel, at step 930, into the combustion chamber 130 at predetermined time and time intervals such that the injected fuel mixes in at least one zone so formed (explained hereinbelow) in order to achieve the controlled combustion of the air fuel mixture.

[038] Referring to Figures 7 and 9, in order to achieve the stratified mode of combustion in operation, the ECU estimates the engine speed and the engine load as stated hereinabove. In an embodiment of the invention, and as shown in Figure 9, when the engine load is lesser than 50% of maximum engine load and the engine speed is lesser than 70% of maximum engine speed the ECU generates a single fuel injection control signal. In response to the fuel injector control signal, the fuel injector injects a predetermined quantity of the fuel into the combustion chamber 130. In an embodiment of the invention, the fuel injector injects the fuel during an early intake stroke of the piston 200. Shown in Figure 6a, there is a formation of two zones. As seen in the Figure, at a predetermined engine load and engine speed (explained hereinabove), the fuel injector injects the fuel inside the combustion chamber 130. Accordingly, one of the zones receives the fuel from the fuel injector. The fuel mixes with the air in the respective zone formed thus attaining an optimum air/fuel mixture. Combustion of this mixture occurs resultantly having a controlled combustion, i.e. the stratified mode of combustion.

[039] Referring yet to Figures 7 and 9, in order to achieve the homogenous mode of combustion in operation, the ECU estimates the engine speed and the engine load as stated hereinabove. Based on the engine speed and the engine load, the ECU generates fuel injector control signals at predetermined times whereby the fuel injector injects fuel inside the combustion chamber in response to such fuel injector signals. In an embodiment of the invention, and as shown in Figure 9, when the engine load is greater than 30% of maximum engine load and the engine speed is greater than 50% of maximum engine speed, the ECU generates at least three fuel injection control signals. Thus, a first fuel injector control signal is generated during an early intake stroke of the piston 200; a second fuel injector control signal is generated during a mid-intake stroke of the piston 200; and a third fuel injector control signal is generated during a late intake stroke of the piston 200. In response to the fuel injection control signals, the fuel injector injects fuel into the combustion chamber 130 accordingly. Shown in Figure 6b, is a formation of two zones. As seen in the Figure, at a predetermined engine load and engine speed (explained hereinabove), the fuel injector injects the fuel at three time intervals, inside the combustion chamber 130. Accordingly, one of the zones receives the fuel from the fuel injector. Further, although one of the zones receives the fuel from the fuel injector, since the fuel is injected at least three times at different time intervals, the fuel is distributed and mixed in the second zone as well. Thus, combustion of such air/ fuel ratio occurs and resultantly, controlled combustion, i.e. the homogenous mode of combustion is achieved.

[040] Advantageously, the present invention provides an efficient way to achieve stratified charge combustion and also provides for switching efficiently between the stratified mode of combustion and the homogeneous mode of combustion. Thus, owing to the stratified mode of combustion, the motor vehicle has lower fuel consumption, reduced emissions and a higher thermal efficiency. On the other hand, owing to the homogenous mode of combustion offered by the present invention, there is a higher volumetric efficiency, an improved overall performance of the engine and lower combustion temperature. Further, achieving the stratified mode and the homogeneous mode of operation based on engine speed and load makes the engine versatile. The present invention thus solves the problem of improper air fuel mixing, especially during the stratified mode of combustion. The present invention also solves the problem of soot formation.

[041] Further, in lower engine load operation (stratified mode), due to ultra-lean mode operation and higher throttle opening, pumping losses are lower and thermal efficiency of the engine increases. Due to ultra-lean mode operation and higher thermal efficiency, fuel economy increases which leads to lower Carbon Dioxide Emission (CO2). Also, emissions of Carbon Monoxide (CO) and Hydrocarbons are reduced. Furthermore, Nitrogen Oxide emission reduces due to lower temperature of combustion. At higher engine loads, i.e. in homogeneous mode operation, due to direct injection of the fuel into the combustion chamber, volumetric efficiency and in turn engine output in terms of BMEP (Brake Mean Effective Pressure) increases. Due to evaporation of the fuel inside the combustion chamber, peak combustion temperature reduces which leads to reduced Nitrogen Oxide (NOx) emission and improved durability. Thus, the present invention improves performance, fuel economy and durability and reduces the harmful emissions from the engine. Further, the present invention is applicable for engines used in two, three, four wheeled vehicles, or any other engine applications.

[042] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.