In technology, an adjustable mixture preparation device means a carburetor or an injection system, where the proportion of air and fuel can be constantly changed depending on the driving parameters and the oxygen content in the exhaust gases. A conventional carburetor does not provide this, since it does not have a corresponding 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 the lambda probe, located at the front of the catalytic converter or in the exhaust manifold, where it is flown around by exhaust gases. The lambda probe is an electrical measuring sensor that determines the residual oxygen content in the exhaust gases and converts it into electrical voltage, thus allowing the composition of the air-fuel mixture to be influenced. In a fraction of a second, information about the oxygen content is transmitted from the lambda probe to the mixture preparation device control unit, 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 catalyst is located instead of the preliminary muffler under the bottom of the car. The catalyst consists of a honeycomb ceramic monolith coated with platinum or rhodium. To preserve the shock-sensitive body of the catalyst, elastic and heat-resistant wire fabric is used.
The catalyst for conventional use 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 oxides (Nox).