Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Patent
1997-08-13
1999-06-22
Tran, Hien
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
422174, 422177, 60297, B01D 5334
Patent
active
059140909
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to an apparatus for catalytic exhaust gas cleaning for an internal-combustion engine, comprising a first catalytic converter located downstream the engine, a hydrocarbon trap arranged at a certain distance from a point directly downstream the first three-way catalytic converter.
Current motor vehicles are often provided with catalytic converters for cleaning the exhaust gas of the vehicle. Normally, current catalytic converters are not able to function with their full cleaning capacity during a cold start of the vehicle. Therefore, such a converter may be supplemented with another electrically heated converter, a so called start converter or a start-up-converter which is located upstream the regular converter. By heating the start converter electrically during start of the engine, the period for warming the regular converter is reduced, which leads to an enhanced cleaning effect. An arrangement of this kind is described in the Swedish patent application 9100541-3.
Of the pollution (primarily HC-, NO.sub.x -, and CO-pollution) emitted by an engine, the emission of HC-pollution is especially high directly after engine start. Owing to this, it is known to use a so called "hydrocarbon-trap" which can be located in the exhaust system between the engine and the regular catalytic converter. The hydrocarbon-trap which may be manufactured from a zeolitic material, can adsorb, i.e. "collect", the HC-pollution emitted by the engine until the regular converter has reached its normal operating temperature, and also its full cleaning capacity.
When the temperature in the exhaust stream, and thus also in the hydrocarbon-trap, surpasses a certain limit, the hydrocarbon-trap will emit (desorb) the previously collected HC-compounds. In this way, hazardous HC-compound emissions can be reduced during the heating phase for the following converter, when its temperature is too low to obtain an optimal cleaning function. A conventional three-way catalytic converter may be arranged downstream the hydrocarbon-trap, for elimination of the desorbed HC-compounds.
The invention is especially aimed at a so called "tailpipe catalyst", i.e. an apparatus for catalytic conversion in connection with motor vehicles, which apparatus comprises a conventional three-way catalytic converter in combination with an electrically heated start converter and a hydrocarbon-trap. Such an apparatus is already disclosed in the patent document EP 485179, in which is shown (see FIG. 1(e), and page 5, lines 41-48) an arrangement with a three-way catalytic converter which has been located downstream the engine. The exhausts from the engine are conducted through the converter and further to an electrically heated start converter. Further along downstream in the exhaust system is another three-way catalytic converter arranged.
One drawback with the apparatus according to EP 485179 is that it does not pay regard to the fact that the hydrocarbon-trap must be located in an optimum position with relation to the ordinary catalytic converter, in order to achieve a satisfactory cleaning function in the exhaust system. If the distance between the regular catalytic converter and the hydrocarbon-trap is small, the latter will be heated too rapidly to the limit temperature where desorption starts. Thus, there is a risk of desorption in the hydrocarbon-trap starting before the regular converter has "ignited" (which normally takes about 100 seconds from start of the engine), which in its turn causes that the HC-compounds which thereafter are emitted neither are cleaned by the regular converter nor are adsorbed by the hydrocarbontrap.
If, on the other hand, the distance between the ordinary converter and the hydrocarbon-trap is large, the limit temperature of the hydrocarbon-trap will be reached very late. This can mean that desorption within the hydrocarbon-trap occurs under uncontrollable conditions.
The object of the present invention is to achieve an enhanced cleaning capacity for the exhausts from a motor vehicle, especially in connection with
REFERENCES:
patent: 5271906 (1993-12-01), Yuuki et al.
AB Volvo
Tran Hien
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