Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Patent
1994-01-10
1995-10-24
Warden, Robert J.
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
422171, 60289, 60284, 60307, 123564, 1235591, F01N 322
Patent
active
054607841
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an apparatus for injecting air into an exhaust system including a catalytic converter for a supercharged 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 quantities 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 in 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 fact the principal exhaust emission for cars with a catalytic exhaust cleaner takes place during the first or the very first minutes after the cold start, i.e. before the engine is operating at lambda =1. The length of this introductory high emission phase should in practice be of the order of 60-100 seconds. A supply of oxidizing additional air to the exhaust gases, particularly during this introductory high emission phase, can therefore drastically reduce the emission of exhaust gases.
After the cold start there is generally no longer any requirement for supplying extra air to the catalytic converter. During certain transient processes (full throttle/full load), a certain fuel enrichment may take place, and air may then be supplied to the exhaust gases for oxidation to a limited extent. However, this effect is very limited and is generally negligible compared with cold start emissions.
In such an initial operating stage, immediately after start
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Abstract of JP 63-18122, publ 1988-01-26 vol. 12, No. 222, M 71.
Gillbrand Per
Larsson Per-Inge
Saab Automobile Aktiebolag
Tran Hien
Warden Robert J.
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