In combination with the electronic fuel injection system and the lambda probe, the combustible amount of fuel is precisely dosed, which ensures the reduction of the composition of harmful substances by the catalyst. The lambda probe is located in the front pipe of the muffler, where it is flown around by the exhaust gases. The lambda probe is an electric measuring sensor that determines the content of residual oxygen in the exhaust gases and converts it into electrical voltage, thus allowing you to influence the composition of the air-fuel mixture. In a split second, information about the oxygen content is transmitted from the lambda probe to the control unit of the mixture preparation device, which ensures constant regulation of its composition. This is necessary on the one hand, because the operating modes are constantly changing (idle, full throttle), and on the other hand, also because the combustion of fuel in the catalytic converter occurs only when the exhaust gases contain enough fuel for gasoline.
Thus, in order for the combustion of fuel to occur at all in the catalyst at temperatures from 300°C to 800°C, the proportion of fuel in the air-fuel mixture must be higher than that required for clean combustion.
The installed catalyst is a so-called 3-way catalyst. This means that in such a catalyst, with lambda control, the oxidation of carbon monoxide (CO) and hydrocarbons (PC) occurs simultaneously, as well as the reduction of nitrogen oxide (MOx).
Catalytic converter on a diesel engine
A catalytic converter is also installed in BMW production diesel vehicles. However, mixture regulation similar to lambda regulation on petrol engines is not possible here. However, the catalytic converter does reduce the content of environmentally harmful carbon dioxide and hydrocarbon compounds to a level lower than that provided by a system with a regulated catalytic converter on petrol engines. In addition, a diesel engine with a catalytic converter is distinguished by reduced smoke formation typical of diesel engines.
The catalyst is located under the bottom of the car in the exhaust tract in the area of the preliminary muffler. As in gasoline engines, the catalyst consists of honeycomb monoliths with a platinum-rhodium coating. An elastic and heat-resistant wire mesh is used as a support for the impact-sensitive ceramic monolith.