Internal-combustion engines – Combustion chamber means having fuel injection only – Having a particular relationship between injection and...
Reexamination Certificate
1999-10-27
2001-04-03
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Having a particular relationship between injection and...
C123S0780BA, C123S090150
Reexamination Certificate
active
06209516
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a control system for a diesel engine having a combustion mode for low engine loads whereby fuel injection is carried out in the first half of the compression stroke.
Generally in diesel engines, fuel injection is carried out at around top dead center of the compression stroke and combustion is effected substantially simultaneously with fuel injection. This is known as a diffusion combustion. In practice, the injected fuel front mixes with air and forms a gas mixture, and thus the diffusion combustion and a slight premix combustion both occur. When the proportion of diffusion combustion is large, the emission of uncombusted fuel particles (particulate gas) increases, and when the proportion of premix combustion is large, the emission of No
x
gases increases. Consequently, it has been difficult to reduce No
x
and particulate gas emissions at the same time.
To reduce No
x
and particulate gas emissions simultaneously, various proposals have been made for combustion wherein fuel and air are mixed uniformly inside the cylinder before a compression ignition (uniform highly diffuse premix combustion). In the uniform highly diffuse premix combustion, the fuel injection timing is advanced to around bottom dead center of the compression stroke so that the fuel and air mix uniformly before compression ignition occurs. With the uniform highly diffuse premix combustion, because the fuel and air are mixed uniformly, it is possible to reduce particulate gas emissions, and because there are fewer local hot spots, it is also possible to reduce No
x
emissions.
However, because diesel engines use a compression ignition, and the ignition occurs as soon as the pressure inside the cylinder has risen sufficiently after the fuel is injected, with the uniform highly diffuse premix combustion, the ignition timing has not been stable and ignition timing control has been impossible. Consequently, in an engine set to a high compression ratio, there has been a risk of ignition occurring early, before compression top dead center is reached.
And when, in order to stabilize ignition, a low compression ratio is set, thermal efficiency drops and it becomes impossible to develop sufficient power for high speeds and high loads; fuel consumption deteriorates; and there is also a risk of a deterioration in cold-starting performance.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a control system for a diesel engine capable of realizing a uniform highly diffuse premix combustion by making possible a combustion mode wherein fuel injection is carried out in the first half of the compression stroke.
To achieve this and other objects, in a first provision of the invention, a control system for a compression ignition type diesel engine comprises operating state detecting means for detecting the operating state of the diesel engine; combustion mode selecting means for selecting, in correspondence with the output of the operating state detecting means, a first combustion mode, wherein fuel injection is carried out in the first half of the compression stroke, or a second combustion mode, wherein fuel injection is carried out at around compression top dead center; effective compression ratio varying means for varying the effective compression ratio of the diesel engine; and control means for controlling the effective compression ratio varying means to lower the effective compression ratio when the first combustion mode is selected by the combustion mode selecting means compared to when the second combustion mode is selected.
By this means, when the first combustion mode is selected by the combustion mode selecting means, by fuel injection being carried out in the first half of the compression stroke and the effective compression ratio being lowered so that compression ignition occurs at around compression top dead center, uniform highly diffuse premix combustion can be realized.
When the second combustion mode is selected by the combustion mode selecting means, by fuel injection being carried out at around compression top dead center and ignition occurring at around compression top dead center substantially simultaneously with fuel injection, diffusion combustion can be realized without the effective compression ratio being lowered.
Thus, even in a diesel engine having a high compression ratio, a combustion mode, wherein fuel injection is carried out in the first half of the compression stroke, can be provided and a uniform highly diffuse premix combustion with stable ignition timing can be realized. As a result, exhaust gas quality improvement and noise reduction can be realized without loss of starting performance or power output capacity.
REFERENCES:
patent: 4883032 (1989-11-01), Hunter et al.
patent: 5373816 (1994-12-01), Asai et al.
patent: 5697332 (1997-12-01), Asai et al.
patent: 771279 (1995-03-01), None
patent: 9-324631 (1997-12-01), None
Argenbright Tony M.
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
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