Catalytic converters in diesel -engine cars

Catalytic converters, commonly called “cats” were initially installed in petrol engines only but for some time now that exhaust system component can also be found in diesel engine cars. What is the role of a cat in diesel cars? What is the design of such a cat?

For around 30 years catalytic converters have been installed in exhaust systems of all petrol engines. In view of the latest exhaust gas emission standards the car manufacturers install them also in compression ignition engines – the popular diesel engines. All that is meant to reduce the air pollution as much as possible.

Catalytic converter, an important component of an exhaust system.

Catalytic converter is one of the essential components of an exhaust system. The main purpose of a catalytic converter is the reduction of the amount of harmful chemicals produced while the engine is running. With that less toxic exhaust gas which contributes to smog formation is emitted to the atmosphere. But to make it possible not only the catalytic converter but also the whole exhaust system should be in a sound condition. Both ceramic and metal core catalytic converters are installed in vehicles. The latter ones, though more expensive, are more durable.

What catalytic converters are installed in diesel engine cars?

Spark ignition petrol engines are equipped with 3-way converters also called 3-function converters. They have three tasks: reduction of nitrogen oxides, oxidation of hydrocarbons to water and carbon dioxide and oxidation of carbon monoxide to carbon dioxide. The design and tasks of converters installed in diesel engines are slightly different due to a different composition of exhaust gas produced during the operation. Diesel engines produce little carbon monoxide but they generate nitrogen oxides and particulate matter instead. Nitrogen oxides are partially reduced in the engine but still the manufacturers are obliged to install catalytic converters in diesel cars so that new vehicles which leave the production line meet all the exhaust gas cleanliness standards in force. Additionally, a catalytic converter of a diesel engine needs to be supported by a converter with an active substance e.g. urea.

Catalytic converter in a diesel engine vs. DPF

Catalytic converter in a diesel engine is installed downstream the particulate matter filter(DPF). With such a location the exhaust flows first through the DPF and then enters the converter. Sometimes both parts of the exhaust system are installed inside a single housing which resemble a metal can. Still the above mentioned sequence is always maintained which ensures effective exhaust cleaning.