Internal-combustion engines – Combustion chamber means having fuel injection only – Using multiple injectors or injections
Reexamination Certificate
2003-03-24
2004-04-27
Kwon, John (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Using multiple injectors or injections
C123S568210
Reexamination Certificate
active
06725829
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a combustion control apparatus of a direct-injection diesel engine, and in particular, belongs to a technical field relating to a transient control at a change of a combustion state of engine.
In general, a direct-injection diesel engine injects a fuel into a combustion chamber with high pressure and high temperature at around the top dead center of the compression stroke of cylinder, so that the fuel is burned by its self-ignition. Here, the fuel injected into the combustion chamber proceeds being divided (atomized) into minute liquid drops by a collision with air having high density, and forms substantially a cone-shape fuel spray. The fuel evaporates from surfaces of the fuel drops and forms a fuel mixture by involving air surrounding around mainly a front end and a periphery of the fuel spray. Then, the fuel mixture is self-ignited when it becomes a certain condition with its appropriate concentration and temperature necessary for an ignition, and begins to burn (pre-mixed combustion). Then, it is considered that the portion beginning to burn becomes a core and diffusion combustion is performed involving surrounding fuel vapor and air.
In such a normal combustion of the diesel engine (hereinafter, also referred to as diesel combustion, simply), the initial pre-mixed combustion may be followed by the diffusion combustion that burns most part of fuel. Here, nitrogen oxides (NOx) is produced at a portion, in which an air excessive ratio &lgr; is nearly 1 in the fuel spray (fuel mixture) having un-homogeneous concentration, due to a rapid generation of heat, and also smoke is produced at a portion, in which a fuel concentration is too high, due to a lack of air. Conventionally, some measures to reduce NOx or smoke are took, such as recirculating part of an exhaust gas into an intake air (Exhaust Gas Recirculation, hereinafter, referred to as EGR, simply) and increasing injection pressure of fuel.
Such recirculating the inert exhaust gas into the intake air system by EGR may suppress production of NOx by decreasing combustion temperature but, on the other hand, promote production of smoke with a large amount of EGR decreasing oxygen in the intake air. Further, increasing injection pressure of fuel may promote minute fuel spray and improve air utilization rate by increasing penetration of the fuel spray, resulting in suppression of smoke, but, on the other hand, it may make a condition where NOx is produced easily. In other words, the conventional combustion of diesel engine provided a trade-off relationship on NOx reduction and smoke reduction, so that it was difficult to reduce both NOx and smoke coincidently.
In contrast, new combustion modes have been recently proposed that provide a combustion sate consisting of pre-mixed combustion mainly by advancing the timing of fuel injection and thereby can reduce NOx and smoke coincidently and greatly. These are generally known as the name of diesel pre-mixed combustion or pre-mixed compression ignition combustion. This is, for example, a new combustion mode, in which a large amount of exhaust gas is recirculated by EGR and a fuel is injected at relatively early timing of the compression stroke of cylinder to mix with air sufficiently, so that the pre-mixed mixture is self-ignited at the end of the compression stroke of cylinder and burns (for example, as shown in Japanese Patent Laid-Open Publication No. 2000-110669).
It is preferable that the rate of recirculated exhaust gas into intake air by EGR (EGR ratio) at such combustion state is set at a much higher level than that at the above-described diesel combustion. That is, a rage amount of exhaust gas having larger thermal capacity than that of air is mixed and thereby density of fuel and oxygen in the pre-mixed mixture is reduced, and as a result, the timing of self-ignition of the pre-mixed mixture may be delayed until near the top dead center of compression of cylinder (TDC) by extending its delay time of ignition. Further, the inert exhaust gas disperses evenly around fuel and oxygen in the pre-mixed mixture and absorbs the heat by combustion, and thereby the production of NOx may be suppressed greatly.
However, because increasing the rate of recirculated exhaust gas in the intake air by EGR means decreasing the amount of air in return, it may be difficult to perform the above-described combustion at an engine operating area where the engine load is relatively high. Thus, conventionally, when the engine operation is at relatively low load, an early fuel injection like the above is performed and EGR ratio is controlled higher than a first predetermined value that is relatively high, resulting in pre-mixed compression ignition combustion. Whereas, when the engine operation is at relatively high load, fuel is injected at around the top dead center by changing fuel injection mode, resulting in diesel combustion. Here, EGR ratio is controlled lower than a second predetermined value that is lower than the first predetermined value in order to suppress an increase of smoke.
In the meantime, in a case where the engine combustion mode is changeable between the pre-mixed compression ignition combustion and the diesel combustion like the above, there exists some problems, such as a transient deterioration of exhaust gas condition at its changing and an occurrence of large noise. That is, when changed from the pre-mixed compression ignition combustion to the diesel combustion, the EGR ratio is changed from a state where it is higher than the first predetermined value to another state where it is lower than the second predetermined value, by reducing the amount of recirculated exhaust gas by EGR. Here, if only fuel injection mode is changed at once to its injection at around TDC for the diesel combustion, the combustion consisting of the diffusion combustion mainly is performed along with an excessive EGR ratio because adjusting controlling the amount of exhaust gas recirculation needs a certain time. As a result, smoke is produced greatly.
On the other hand, in changing from the diesel combustion to the pre-mixed compression ignition combustion, if only fuel injection mode is changed to its early injection when the EGR ratio is not sufficiently high, the fuel may be self-ignited at the too-early timing because adjusting the amount of exhaust gas recirculation needs a certain time as well. As a result, considerably large noise of combustion is produced and an increase of NOx is produced rapidly as well. In addition, a large amount of smoke is produced by combustion of fuel having an insufficient mixture with intake air.
In view of the above-described problems, the present invention has been devised and its object is to suppress a transient deterioration of exhaust gas condition and a production of large noise by applying an effective control to procedures of changing combustion of a diesel engine, in which its combustion is changeable between a first combustion state where its combustion consists of pre-mixed combustion mainly (for example, pre-mixed compression ignition combustion described above) and a second combustion state where its combustion consists of diffusion combustion mainly (for example, conventional diesel combustion).
SUMMARY OF THE INVENTION
In order to achieve the above-described object, the present invention provides solution means, in which a farther fuel is injected at a proper timing (latter-injection) after a main combustion begins at around the top dead center of compression of cylinder when a combustion state of diesel engine transfers between the above-described first combustion state and the second combustion state, and thereby smoke produced by the main combustion is burned again by the combustion of this latter-injected fuel.
Specifically, the first aspect of the present invention is premised on a combustion control apparatus of a diesel engine, comprising a fuel injector projecting into a combustion chamber of an engine cylinder, exhaust gas recirculation amount adjusting means for adjusting the amou
Kataoka Motoshi
Kobayashi Akihiro
Saito Tomoaki
Kwon John
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
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