Vehicles with catalytic converter

BMW cars are necessarily equipped with adjustable catalysts. In the presence of a catalyst, the vehicle must be operated only on unleaded gasoline. If a variable catalyst is installed, a variable mixing device must also be provided.

Under the adjustable mixture preparation device in technology is meant a carburetor or injection system, where the proportion of air and fuel can constantly change depending on the parameters of movement and the oxygen content in the exhaust gases. A conventional carburetor does not provide this, since it does not have an appropriate control unit. For this reason, either a carburetor with an electronic control system or an injection system is installed.

The mixture preparation device receives control commands from a lambda probe located in front of the catalyst or in the exhaust manifold, 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 device preparation of the mixture, 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 catalytic converter is located under the bottom of the vehicle instead of the pre-muffler. The catalyst consists of a honeycomb ceramic monolith plated with platinum or rhodium. Elastic and heat-resistant wire cloth is used to retain the shock-sensitive body of the catalyst.

The catalyst for conventional use 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 nitrogen oxides (Nox).