Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Patent
1994-01-10
1995-10-17
Warden, Robert J.
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
422171, 60289, 60307, 1235591, 123564, F01N 322
Patent
active
054588553
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an arrangement for injecting air into an exhaust system including a catalytic cleaner for a super charged Otto engine.
STATE OF THE ART
In recent years increasingly tighter requirements have been imposed on the motor industry, out of environmental considerations, among other things, to develop engines and exhaust systems with such characteristics that the quantroes of the substances in the exhaust gases most harmful to the environment can be reduced to much lower values than was previously possible.
Major advances have been made in this effort to achieve cleaner, less harmful vehicle exhaust gases, thanks mainly to the development of engines with more efficient ignition and combustion, combined with exhaust systems fitted with efficient catalytic converters or cleaners (catalytic exhaust cleaners), which reduce the content of harmful components in the exhaust gases. The harmful exhaust components referred to here include mainly carbon monoxide, hydrocarbons and nitrogen oxides, which must be converted by means of the catalytic cleaner to the harmless components carbon dioxide, water and nitrogen, respectively.
To ensure that the catalytic converter operates perfectly, however, the exhaust gases fed into the catalytic converter are required to have a certain minimum temperature and a certain composition.
However, if the exhaust gases contain a certain excess of oxygen, for example, the catalytic material (platinum or rhodium) in the catalytic converter is in most cases only able to bring about efficient combustion of carbon monoxide and hydrocarbons, together with combustible particles, whilst an oxygen deficit will instead result in a reduction in nitrogen oxides. On the other hand, the catalytic converter is obviously also required to provide an effective reduction in all three types of harmful exhaust components mentioned. To ensure that this can be achieved the fuel/air mixture supplied to the engine must be controlled so that an exact stoichiometric mixture is obtained.
The catalytic converter is therefore supplied by an oxygen measuring unit (e.g. lambda probe) in the exhaust pipe and an electronic feedback to the fuel system for continuous fine adjustment of the fuel supply. In this connection the term "lambda" denotes the ratio of the available oxygen to the oxygen required for complete combustion.
Exhaust systems so far developed, with catalytic cleaners, have shown to operate highly satisfactorily as soon as the engine and catalytic converter have reached their intended operating conditions in terms of the operating temperature if particular.
However, when a cold engine, and hence also a cold catalytic converter, is started, particularly in cold weather, a certain time must be allowed for the engine and catalytic converter to reach the intended operating temperature. Before this happens neither the engine nor the catalytic converter are operating under optimum conditions, therefore, which means that there are worse conditions for combustion in the engine and reduced efficiency of the catalytic cleaner in the exhaust system.
In such an initial operating stage, immediately after starting the engine, the latter has not yet reached a stable idling speed, and the fuel/air mixture is not optimum but "rich", i.e. there is an oxygen deficit both in the fuel/air mixture which is supplied to the cylinders for combustion and in the exhaust gases which are supplied to the catalytic cleaner. In this case the engine is not operating at the required lambda value 1 either. Obviously there may also be reasons other than that mentioned above (cold start) why the fuel/air mixture is too rich and/or lambda deviates from the ideal value of 1.
However, the result will be an increased content of harmful substances in the vehicle exhaust gases under these non-ideal operating conditions. In the case of a 4-cylinder, 2 litre engine, for example, the requirement for additional air to the catalytic converter on cold starting may be estimated at approximately 120 litres/min.
One way of tackling th
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Abstract of JP 63-18122, publ 1988 Jan. 26 vol. 12, No. 222, M 71.
Saab Automobile Aktiebolag
Tran Hien
Warden Robert J.
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