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How does a catalyst work in a car?
The combustion of fuel with the aid of atmospheric oxygen produces water and Co² in the engine. Since the combustion does not take place completely, however, further combustion products are produced, which we call exhaust gas. The exhaust air of petrol engines mainly contains pollutants such as:
- carbon monoxide (CO)
- hydrocarbon(HC)
- nitric oxide (NOX)
In diesel engines, on the other hand, sulphur dioxide (SO²) and soot particles (PM) are added. The vehicle catalytic converter now cleans the exhaust gases and filters the pollutants or helps to convert them into harmless gases such as water, nitrogen and CO². Since a car catalytic converter in petrol vehicles can render 3 pollutants harmless, it is also called a three-way catalytic converter.
In diesel vehicles, an oxidation catalytic converter is predominantly used and at least one soot particle filter is added. This converts carbon monoxide and hydrocarbons into harmless gases. Modern diesel engines also have a nitrogen oxide storage catalytic converter. This means that the third pollutant can also be effectively reduced.
In order for the vehicle catalytic converter to unfold its full effect, it requires a specific exhaust gas composition and an engine temperature of at least 500° Celsius. In order to achieve the required mixture, the lambda sensor placed between the engine and the vehicle catalytic converter measures the residual oxygen content in the exhaust gas. The engine control system processes the measurement result and provides the control impulses for perfect mixture formation.
How can catalytic converters be defective?
Like many other vehicle components, the catalytic converter in a car is subject to a natural ageing process. Constantly high temperatures of over 500°C and the mechanical loads caused by vibration contribute to the loss of the precious metal-containing coating (platinum, rhodium or palladium) of the carrier over time. Likewise, additives can deposit in the catalytic converter and clog it if the engine burns too much oil. The exhaust gases then no longer reach the precious metals and the catalytic converter loses its function, which leads to a fault in the board computer.
This error also occurs when a vehicle is used exclusively for short distances. Since the engine takes 3-5 minutes to reach operating temperature, the vehicle catalytic converter can only then work effectively. In shorter journeys, pollutant residues remain in the catalytic converter and lead to clogging in the long run. The same happens if you fill up with leaded fuel instead of unleaded petrol. Therefore you should always pay attention to the right fuel when refuelling, especially abroad.
In the event of a blockage, the catalyst in the car can be regenerated again by driving on the motorway for a longer period of time; this is also referred to as "free-running". Of course, an error in the ignition or mixture preparation system can also lead to an unburned fuel-air mixture getting into the catalytic converter and burning inside. Therefore, malfunctions in the ignition or mixture preparation should be rectified immediately in a specialist workshop.
High-quality catalysts in cars are not only important to protect the environment, but also to pass the TÜV test. Therefore, high quality should always be a priority here. But it does not always have to be the original part. Many leading spare part manufacturers offer identical catalytic converters that fully meet the requirements of the original parts. Branded identical parts represent a good price alternative without having to compromise on quality. We will be happy to advise you on the choice of the right catalyst for your vehicle.
