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 a fuel 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 the exhaust gases. The lambda probe is an electrical measuring sensor that determines the residual oxygen content in the exhaust gases, converts it into electrical voltage and thus allows the composition of the air-fuel mixture to be regulated. 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 a sufficient proportion of gasoline.
Thus, in order for the fuel to be able to burn out in the catalyst at temperatures of 300-800°C, its proportion in the air-fuel mixture must be higher than that required for clean combustion. Thus, when using a regulated catalyst, one should expect an increase in fuel consumption by approximately 5 percent.
The catalytic converter is located in the place of the preliminary muffler under the bottom of the car. The catalytic converter consists of a honeycomb ceramic monolith coated with platinum or rhodium. To preserve the shock-sensitive body of the catalytic converter, 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).
Operation of vehicles with a catalytic converter
To avoid damage to the lambda probe and catalytic converter, it is essential to follow these instructions:
- Use unleaded petrol only.
- Before installing the catalytic converter, fill up with unleaded fuel at least twice. In addition, on engines that require super gasoline, the ignition should be set to a later time, since unleaded super gasoline has an octane rating of only 95. How many degrees to set the ignition depends on the model.
- It is forbidden to start the engine by towing or "push starting". Unburned fuel will cause the catalytic converter to overheat when ignited. If the battery is discharged, do not start the engine from the battery of another car.
- Avoid frequent cold engine starts in a row. In this case, unburned fuel accumulates in the catalytic converter, and when heated, it undergoes shock combustion and the catalytic converter fails.
- If you have difficulty starting the engine, do not turn on the starter for a long time unless necessary. When the starter is running, fuel is constantly injected. Determine and eliminate the source of the malfunction.
- If ignition malfunctions occur, remove the fuel pump relay connector until the cause is determined. This prevents fuel injection when starting the engine. The fuel pump relay is located at the front passenger's feet in front of the front pillar under the side trim.
- Do not check for spark with the spark plug caps removed.
- Comparison of cylinders cannot be performed (balance test) by turning off the ignition of one of the cylinders. When turning off the ignition of one of the cylinders - even with the help of an engine tester - unburned fuel gets into the catalytic converter.
- If ignition failures occur, avoid running the engine at high speeds and immediately eliminate the malfunction.
- Install only spark plugs recommended for vehicles with a catalytic converter.