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 there is no 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 in the front of the catalytic converter or in the exhaust manifold, where it is flown around by the 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 part, information about the oxygen content is transmitted from the lambda probe to the control unit of the mixture preparation device, which provides for constant regulation of its composition. This is necessary, on the one hand, because the modes are constantly changing (idle, full throttle), and on the other hand also because the combustion of fuel in the catalytic converter only occurs when the exhaust gases contain enough gasoline. Thus, in order for the combustion of fuel in the catalytic converter to occur at all at temperatures of 300°C, the proportion of fuel in the air-fuel mixture must be higher than that required for clean combustion. Thus, when using a regulated catalytic converter, an increase in fuel consumption of approximately 5 percent can be expected.
The catalyst for conventional use is a so-called triple 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).
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