Table of contents: Petrol engines ↓ Catalytic converter on diesel… ↓ Servicing cars with a catalytic… ↓
All vehicles are equipped with one or more catalytic converters to reduce emissions of harmful substances along with exhaust gases.
The catalyst consists of a ceramic monolith with a honeycomb structure, covered with a protective layer. The protective layer contains salts of noble metals, which ensure the process of cleaning the exhaust gases. In the catalyst body there is a support insulator, which compensates for thermal expansion.
Petrol engines
Thanks to the electronic control of the fuel injection system in combination with information from the lambda probe, fuel injection into the combustion chambers occurs in doses so that the catalyst can reduce the level of harmful substances in the exhaust gases. The lambda probe is an electric sensor that reacts to the content of residual oxygen in the exhaust gases by fluctuating electrical voltage, which ultimately allows the control unit to assess the composition of the fuel-air mixture. The injection system control unit can change the fuel-air ratio in a fraction of a second. On the one hand, this is necessary because the operating conditions are constantly changing ("full throttle", idle), and on the other hand, because afterburning in the catalyst occurs only when the exhaust gases contain a sufficient proportion of gasoline.
In order for afterburning processes to occur in the catalyst at temperatures from +300° to +800°C, the fuel-air mixture must have a greater proportion of fuel than is necessary for simple combustion.
Catalytic converter on diesel vehicles
Unlike catalytic converters installed on gasoline engines, diesel vehicles use non-regulated oxidation catalysts. Regulation of harmful substance content using a lambda probe is not required in this case.
This catalyst converts carbon monoxide and hydrocarbon compounds contained in the exhaust gases into carbon dioxide (CO₂) and water (H₂ O). In addition, it neutralizes the characteristic smell of burnt fuel in a diesel engine.
The high content of nitrogen oxides (NOx) in the exhaust gases is reduced by 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 reduce the ignition temperature of the fuel-air mixture and thereby reduce the content of harmful substances in the exhaust gases.
The Motronic fuel injection system provides for the afterburning of unburned particles, etc., by supplying fresh air to the exhaust valves via a separate air pump.
Servicing cars with a catalytic converter
To avoid damage to the catalytic converter, it is necessary to strictly follow the following recommendations:
Cars with gasoline engines
Use unleaded petrol only.
It is not recommended to force start the engine by pushing or towing. If necessary, only one attempt is allowed at a distance of no more than 50 meters. In this case, it is best to use an auxiliary battery. Unburned fuel, when ignited, can cause overheating and destruction of the catalytic converter.
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, it is necessary to find and eliminate the cause of the malfunction.
Monitor the amount of fuel in the tank and do not allow it to run dry.
If misfires are observed, avoid high engine speeds and eliminate the malfunction immediately. If a defect is detected, 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 spark plug types recommended by the vehicle manufacturer.
Do not test the new formation with the spark plug tip removed.
Don't compare cylinders (balance test) by disabling the ignition in the combustion chamber of one cylinder. With such a disabling, including with the help of a stand for checking the engine operation, unburned fuel gets into the catalyst.
Cars with petrol and diesel engines
Do not park the 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 is turned off.
Do not apply underbody anti-corrosion protection to exhaust system components.
Do not modify the exhaust system heat shields.
When filling and topping up engine oil, pay special attention to not exceeding the maximum oil level mark on the dipstick. Excess oil gets into the catalyst due to incomplete combustion and can damage the noble metal or completely destroy the catalyst.
[The article was copied from the website audimanual.ru]