A variable mixture control system is a fuel injection system in which the fuel/air ratio can be continuously varied depending on operating conditions and the oxygen content of the exhaust gases.
The control commands of the mixture formation device are received from the oxygen concentration sensor (lambda probe), which is installed before the catalytic converter or in the exhaust manifold and is blown by the exhaust gas flow, the lambda probe is an electric sensor that records the residual oxygen content in the exhaust gases and produces a corresponding electric signal. The signal value allows us to draw a conclusion about the composition of the working mixture. In a split second, the lambda probe can produce a corresponding signal to the electronic control unit, due to which the composition of the working mixture can be constantly adjusted. On the one hand, this is necessary, since the operating conditions are constantly changing (e.g. full throttle, idle), on the other hand, because optimal afterburning occurs in the catalytic converter only if the exhaust gases contain a sufficient number of carbon particles (unburned gasoline).
Thus, in order for afterburning to occur at all in the catalytic converter at a temperature of +300...+800°C, the exhaust gases must contain more fuel than is required for complete combustion in the engine cylinders. In this regard, when operating a car equipped with an engine with a catalytic converter, fuel consumption increases by approximately 5%. The catalytic converter is located in the engine compartment of the car in place of the front muffler. The catalytic converter consists of a ceramic honeycomb block coated with a noble metal catalyst: platinum or rhodium. An elastic heat-resistant wire mesh is used to attach the impact-sensitive ceramic block.
The catalytic converter used is a so-called 3-way catalyst. This means that the converter simultaneously oxidizes carbon monoxide (CO) and hydrocarbons (CH), and reduces nitrogen oxides (NOx).
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