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Catalyst
Catalyst
| 1 - body,
2 - seal
3 - honeycomb catalyst |
Elements included in the catalyst and products exiting from the catalyst
All vehicles are installed catalysts to reduce the amount of harmful substances emitted into the atmosphere with the exhaust gases. Catalytic exhaust gas has a stainless steel, welded to which are attached the inlet and outlet cones to the nozzles and mounting flanges and also Heat Reflector holding the ceramic liner. The entire internal volume of the housing occupied by the porous ceramic monolith fixed rings or stainless steel mesh. The structure of the monolith is a conventional filter, but the entire inner and outer surface of pores in contact with the gases covered with very thin molecular layer of an alloy which contains platinum, rhodium and palladium. The porosity of the monolith has a greater surface area covered by this alloy from very expensive metals, which mainly determines a high price catalyst, see. Fig. In the catalyst reaction occurs, resulting in potentially harmful hydrocarbon and carbon monoxide in the exhaust gas are converted into harmless gases and water vapor. The engine emits the exhaust gases together with the products of complete (water vapor H 2 O 2 and nitrogen N m. P.) And incomplete (carbon monoxide CO and CnHm, nitrogen oxides NOx) combustion. The total number of components that are contained in these gases exceed a few hundred, and most of them are harmful to human health. Exhaust gases permeating through the porous monolith surface, firstly, heat it, and secondly, dookislyayutsya. Because CO is obtained CO 2, that is non-toxic carbon dioxide, CnHm in some stages passes into CO 2 and H 2 O, NOx is converted to molecular N 2 which is contained in normal air, and water. In short, the catalyst occur fairly complex chemical reactions due to the high temperature and the presence of a special covering from expensive metals. The main positive effect of the catalyst - full neutralization of three components - CO, CnHm, NOx, - which in the exhaust gases more than other harmful substances. And it is achieved not only due to the presence of platinum, rhodium and palladium. Plays an important role temperature, kept within the boundaries of 300-800 ?� C. If it is reduced to 250 ?� C, chemical neutralization of CO, CnHm, NOx, despite the presence of metal catalysts, do not occur. A temperature of about 900 ?� C begins to melt and break the catalyst film.
Gasoline engines
All models with the catalyst system of the fuel supply of the closed type, ie based on a signal from the oxygen sensor installed in the exhaust system control module constantly optimizes the composition of the fuel-air mixture. Depending on the content of oxygen in the exhaust gas oxygen sensor induces a voltage of 0.1 V (high content of oxygen, a poor mix) to 0.9 V (low oxygen content, rich mixture). Based on these data, the engine control unit changes the opening of the fuel injector and changes the ratio of fuel in the fuel-air mixture. Metric ratio of the fuel mixture in which it occurs, and complete combustion of the exhaust gases are no harmful substances - is 14.7 weight parts of air to 1 part of fuel, see. Fig. Elements included in the catalyst and products exiting the catalyst. The catalyst operates efficiently at temperatures of 300 ?� C - + 800 ?� C.
Diesel engines
On vehicles with diesel engine exhaust emission control is performed not controlled oxidation catalyst. Reducing the percentage of nitrogen oxides in the exhaust gas of the diesel engine is achieved by installing on the car system of repeated burning of the fulfilled gases (EGR). The EGR valve of exhaust gas recirculation is installed in the exhaust system and the knee is controlled by a vacuum controller. EGR valve in a warm engine directs a portion of the exhaust gases in the combustion chamber of the engine, resulting in reduced temperature and thus decreases the percentage of nitrogen oxides in exhaust gases.
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