The catalyst consists of a honeycomb ceramic monolith coated with a protective layer. On the protective layer there are salts of noble metals, which provide the process of cleaning the exhaust gas. In the catalyst housing there is a support insulator that compensates for thermal expansion.
Gasoline engines
Thanks to the electronic control of the fuel injection system, in combination with information from the lambda probe, fuel is injected into the combustion chambers in a dosed manner so that the catalyst can reduce the level of harmful substances in the exhaust gas. The lambda probe is an electrical sensor that reacts to the content of oxygen residues in the exhaust gases by fluctuations in electrical voltage, which ultimately allows the control unit to evaluate the composition of the fuel-air mixture. The injection system control unit can change the ratio of fuel and air in a fraction of a second. On the one hand, this is necessary because operating conditions are constantly changing («full throttle», idling), and on the other hand, because afterburning in the catalyst occurs only when the exhaust gases contain a sufficient proportion of gasoline.
In order to at a temperature of +300" up to +800°C, post-combustion processes generally took place in the catalyst, the air-fuel mixture should have a larger proportion of fuel than is necessary for simple combustion.
Catalyst on vehicles with a diesel engine
Unlike the catalysts installed on gasoline engines, vehicles with a diesel engine use unregulated oxidation-type catalysts. Regulation of the content of harmful substances using a lambda probe is not required in this case.
Such a catalyst converts carbon monoxide and hydrocarbon compounds contained in the exhaust gas into carbon dioxide (CO2) and water (H2O). In addition, it neutralizes the smell of burnt fuel characteristic of a diesel engine.
High content of nitrogen oxides (NOx) in the exhaust gases is reduced as a result of the operation of the exhaust gas recirculation system.
The EGR valve is located on the intake manifold and is actuated by low pressure (see illustration 2.0). Its task is to divert part of the exhaust gases back into the combustion chamber in order to lower the ignition temperature of the fuel-air mixture and thereby reduce the content of harmful substances in the exhaust gas.
The Motronic fuel injection system provides for the afterburning of unburned particles, etc., by supplying fresh air to the exhaust valves by a separate air pump.
Servicing vehicles with a catalyst
To avoid damage to the catalyst, the following recommendations must be strictly followed:
Cars with a gasoline engine
Refuel with unleaded gasoline only.
It is not recommended to perform a forced start of the engine with a push or towing. If necessary, only one attempt is allowed at a distance of not more than 50 meters. In this case, it is best to use an auxiliary battery. Unburned fuel, if ignited, can cause overheating and destruction of the catalyst.
If the engine is difficult to start, do not operate the starter for too long. When starting the engine, fuel is continuously injected. In such cases, you need to find and eliminate the cause of the malfunction.
Keep an eye on the amount of fuel in the tank and do not let it «devastation».
If misfires are observed, high engine speeds must be avoided and the fault repaired immediately. If a defect is found, do not allow fuel injection when the starter is turned on. To do this, remove the fuel injection system control relay or the fuel pump relay.
Install only the types of spark plugs recommended by the vehicle manufacturer.
Do not test for growths with the spark plug tip removed.
Do not compare cylinders (balance test) by turning off the ignition in the combustion chamber of one cylinder. With such a shutdown, including with the help of a stand to check the operation of the engine, unburned fuel enters the catalyst.
Vehicles with petrol and diesel engines
Do not park your vehicle over dry leaves or grass. The exhaust system in the area of the catalytic converter is very hot and emits heat even after the engine has been switched off.
Do not apply underbody corrosion protection to parts of the exhaust system.
Do not modify the heat shields of the exhaust system.
When refueling and adding engine oil, pay special attention to ensure that the maximum oil level mark on the dipstick is not exceeded. Excess oil due to incomplete combustion enters the catalyst and can damage the precious metal or completely destroy the catalyst.
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