In combination with an electronic fuel injection system and a lambda probe, an accurate dosing of the combustible amount of fuel is carried out, which ensures the reduction of the composition of harmful substances by the catalyst. The lambda probe is located in the front muffler pipe, where it flows around the exhaust gases. The lambda probe is an electrical measuring sensor that detects the content of residual oxygen in the exhaust gases and converts it into electrical voltage and thus allows you to influence the composition of the air-fuel mixture. In a fraction of a 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. On the one hand, this is necessary because the operating modes are constantly changing (idle, full throttle), and on the other hand, also because the afterburning of the fuel in the catalyst occurs only when the exhaust gases contain sufficient for gasoline.
Thus, in order for the afterburning of fuel to occur 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, under lambda control, carbon monoxide is simultaneously oxidized (SO) and hydrocarbons (PC), as well as a decrease in nitric oxide (Moss).
Diesel engine catalyst
A catalytic converter is also installed on BMW production vehicles with a diesel engine. However, here it is not possible to control the mixture like lambda control on gasoline engines. However, the catalyst still reduces the content of environmentally harmful carbon dioxide and hydrocarbon compounds at least to a level that is lower than that provided by a variable catalyst system on gasoline engines. In addition, the catalyzed diesel engine is characterized by reduced smoke generation typical of diesel engines.
The catalyst is located under the bottom of the car in the exhaust gas path near the pre-muffler. As with 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 shock-sensitive ceramic monolith.