5.4.1. Operation of the catalytic converter
All engines are equipped with one or several catalytic converters for purification of exhaust gases.The catalytic converter has the central ceramic part of a cellular design –3– covered with a carrier layer. On a layer of the carrier there are salts of precious metals operating as converters. The catalytic converter is fixed in the case-1-by means of the insulating basic layer –2– compensating at the same time thermal expansions of the catalytic converter.
Catalytic converter
| 1 case 2 consolidation |
3 honeycombs of the catalytic converter |
Petrol engines
To reduce harmful emissions by means of the catalytic converter, systems of injection has to dose precisely amount of the injectable fuel necessary for combustion. The sensor of oxygen is in a reception pipe in front of the catalytic converter and is washed by a stream of the fulfilled gases. The sensor of oxygen represents the electronic sensor measuring the content of oxygen in final gases and representing its type of fluctuations of tension. Information from the sensor of oxygen is transferred to the control unit of system of injection. The received value allows to regulate composition of air-petrol mix. On the one hand it is necessary as service conditions constantly change (idling, full gas), on the other hand, as optimum reburning of fuel in the catalyst happens only in this case if final gases contain enough fuel.
That in the catalyst there was a fuel reburning, it is necessary to have temperature of 300 - 800 °C. For this purpose the bigger content of fuel in mix, than is necessary for pure burning.
The used catalytic converters of petrol engines represent so-called three-functional devices. In adjustable process of transformation oxidation of carbon monoxide (SO) and hydrocarbon (NANOSECOND), and also reduction of concentration of nitrogen oxides (NOx) is carried out.
Gases on an entrance of the catalytic converter and products at its exit
The catalytic converter and system of recirculation of the fulfilled gases of the diesel engine
The fulfilled gases of the diesel engine are also purified in the catalytic converter. At the same time it is about the unregulated oxidizing catalytic converter. Such catalytic converter turns the carbon oxides and hydrocarbonic connections which are contained in the fulfilled gases into CO2 and H2O.
Decrease in concentration in the fulfilled gases of the diesel engine of nitrogen oxides (NOx) is reached thanks to existence of additional system of regeneration of the fulfilled gases (EGR system).
On a final collector of the engine the valve of system of recirculation operated by vacuum is located. Its task is the direction of a part of the fulfilled gases in engine combustion chambers that promotes decrease in temperature of the fulfilled gases and by that to decrease in concentration of harmful substances.