Method of operating an internal combustion engine

Details Method of operating an internal combustion engine Method of operating an internal combustion engine

1995-06-06

1997-08-12

Argenbright, Tony M.

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

123 73C, 123305, F01N 336, F01N 338, F02D 4106, F02P 515

Patent

active

056553650

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a method of operating an internal combustion engine in order to produce high exhaust gas temperatures and is particularly useful for internal combustion engines incorporating a catalytic treatment means in the exhaust system for treatment of the exhaust gases to reduce undesirable contaminants therein.
Although catalytic treatment of gases to reduce the level of undesirable emissions therein is effective, the catalytic material or catalyst of the catalytic treatment means has a minimum operating temperature (generally referred to as the "light off" temperature and conventionally taken as the temperature at which the catalyst is 50% efficient), and is relatively ineffective until this required operating temperature has been reached, Thus, during such periods, increased levels of undesirable emissions are likely to issue from the exhaust system. Normally, at engine startup, particularly after a period of non-operation, the catalytic material is below its light-off temperature and in order to reduce the time, and therefore the amount of emissions output until light-off of the catalyst, it may be desirable to raise the temperature of the exhaust gases delivered from the combustion chamber(s) of the engine to the exhaust system. However, at startup the engine typically will operate at a relatively low load and speed, such as is termed "engine idle", and therefore the amount of fuel being delivered to the engine is comparatively small and hence, only a relatively small amount of heat is available for raising the temperature of the exhaust gases and hence the temperature of the catalytic material to its "light-off" temperature.
Further, after catalyst light-off, when the engine is allowed to idle or operate at a low load condition for a significant period of time, particularly in low ambient temperature conditions, the exhaust gas temperature may drop to a value that is insufficient to maintain the catalytic material in the light-off condition and thus it will become ineffective in the treatment of contaminants and undesirable emissions in the exhaust gas.
There have been proposals to heat the catalytic material by means of an afterburner device placed upstream of the catalytic treatment means. In such an arrangement, the afterburner device ignites the remaining combustible mixture within the exhaust gases to raise the temperature of the catalytic material. This arrangement does however add significantly to the cost and complexity of the engine installation.
It is therefore the object of the present invention to provide a method of operating an internal combustion engine which will assist in maintaining high exhaust gas temperatures and thus, where appropriate, achieve rapid light-off of the catalytic material in the exhaust system and maintain such a light-off condition whilst the engine is operating.
With this object in view, there is provided a method of operating an internal combustion engine comprising retarding the ignition of a gas/fuel mixture within at least one cylinder of the engine to after top dead centre (ATDC) in respect of the combustion cycle of said at least one cylinder of the engine. While said ignition is so retarded, the fuelling rate of said at least one cylinder is preferably increased to a level higher than that required when the engine is operating normally.
Conveniently, ignition can be retarded up to about -30.degree. BTDC (i.e 30.degree. ATDC) and is preferably of the order of -20.degree. BTDC (i.e 20.degree. ATDC). The ignition retardation may alternatively be variable, preferably between 15.degree. ATDC to 30.degree. ATDC in the case of a multi cylinder engine such as a three cylinder engine. Preferably, the fuelling rate (measured in mg/cylinder/cycle) is greater than 50% of the fuelling rate at maximum load, and more preferably is up to about 80% of the fuelling rate at maximum load. However, if desired, the fuelling rate can be in excess of 100% of the fuelling rate at maximum engine load. However, the selected fuelling rate is conveniently the minimum r

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