Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1994-05-17
1997-03-11
Hart, Douglas
Power plants
Internal combustion engine with treatment or handling of...
Methods
60285, 60286, 60289, F01N 320
Patent
active
056090218
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of operating an internal combustion engine burning a fuel, such as petrol, diesel fuel or alcohol, containing carbon and hydrogen.
BACKGROUND OF THE INVENTION
As is known, an exhaust catalytic converter only performs its task of reducing the unburnt hydrocarbons, carbon monoxide and oxides of nitrogen content of the exhaust gases after it has reached a critical temperature, termed the light-off temperature, which is between 300.degree. C. and 400.degree. C. In the case of an internal combustion engine in which very lean mixtures are burnt under light load conditions, the excess air tends to cool the catalytic converter making it difficult for the latter to remain above the light-off temperature under certain conditions, notably during idling. To some extent, this problem can be counteracted by placing the converter nearer to the engine (close coupling) but the converter may then not be able to withstand the temperature at full load. Ideally therefore, the converter should be kept sufficiently far away from the engine to allow safe full load operation, but means should be provided for heating the catalyst when it risks dropping below its light-off temperature.
Diesel engines tend to produce soot in their exhaust gases and are required to have a filter trap in order to meet regulations for reducing toxic emissions from engines. Such filter traps tend to be blocked by the soot particles after some time and various proposals have been made for regenerating the filter trap. One way is to burn off the soot and it is known that if burning is started by an external heat source at the front face of the filter trap, the exothermic reaction will itself spread along the length of the trap in a manner similar to the burning of a cigarette when air is drawn through it.
OBJECT OF THE INVENTION
Thus, in both diesel and petrol engines, it is desirable to be able at certain times to generate heat within the exhaust system and the present invention seeks to provide a method of operating the engine to create such a heat source under selected conditions.
SUMMARY OF THE INVENTION
The present invention provides a method of operating an internal combustion engine burning a fuel, such as petrol, diesel fuel or alcohol, containing carbon and hydrogen, which method comprises the steps of determining when the engine is operating in a deceleration mode, reducing the throttle opening of the air intake to the engine only during deceleration modes below the throttle opening for steady speed idling to reduce the mass of air in each combustion charge when the engine is overrunning while continuing to admit fuel into the combustion chamber to result in excessively rich combustion in at least a region of the combustion charge and thereby create a proportion of combustible gases in the exhaust gas stream, ensuring the presence in the exhaust gas stream of additional air from an external source or unused air from the engine to mix with the combustible gases to achieve during deceleration modes an exhaust mixture having sufficiently high concentrations of combustible gases and oxygen to be ignitable, and igniting the mixture to burn as a flame within an afterburner chamber arranged upstream of an element of the exhaust system, such as a catalytic converter or a filter trap, in order to heat the element during deceleration modes.
To ensure reliable ignition of the exhaust mixture, the engine in the present invention is run with more severe throttling than during steady speed idling in order to produce a very rich mixture even with a small quantity of fuel admitted into the combustion chamber during deceleration modes and this mixture undergoes incomplete combustion resulting in the exhaust gases having a sufficiently high concentration of combustible gases, especially hydrogen and carbon monoxide, to be easily ignitable.
The invention can be applied to different types of engines. The charge preparation may be homogeneous or stratified, ignition may be by spark or by compr
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patent: 4391095 (1983-07-01), Virk
patent: 4614184 (1986-09-01), Hansen
patent: 5085049 (1992-02-01), Rim
patent: 5090200 (1992-02-01), Arai
patent: 5133184 (1992-07-01), Geiger
Drouillard Jerome R.
Ford Motor Company
Hart Douglas
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