8.4.3. Cars with the catalyst

Engines which are installed on the S-class are serially equipped with the adjustable catalyst. This catalyst demands that the petrol engine was essentially operated on unleaded fuel. Besides, cars with the adjustable catalyst have to have an adjustable carburetor.

The adjustable carburetor is understood as the carburetor or system of injection of fuel at which the fuel relation to air can constantly change depending on the modes of the movement and from the content of oxygen in exhaust gases. It cannot be carried out when using the traditional carburetor as it is not equipped with the corresponding control unit. For this reason come back or to the carburetor adjusted by means of electronics or to system of injection of fuel.

The carburetor receives commands of management from the oxygen sensor which is installed in the final pipeline in front of the catalyst or in a final collector and here is washed by a stream of final gases. The oxygen sensor is a sensitive element and signals about the residual content of oxygen in exhaust gases by means of fluctuation of tension and promotes issue of the conclusion about composition of fuel-air mix. To fractions of a second the oxygen sensor can transmit the corresponding electric signals to the control unit of the carburetor and, thanks to it, the ratio fuel-air constantly changes. It, on the one hand, is required as anyway service conditions constantly change (idling, full opening of a butterfly valve), and, on the other hand, as well because only in this case on the catalyst there is a reburning as in the fulfilled engine gases still there is a sufficient share of gasoline.

Therefore, in order that at a temperature from 300 to 800 °C on the catalyst in general there could be a reburning, gas mixture has to have bigger percent of fuel, than its would be required for pure combustion. Thus, at use of the catalyst it is necessary to reckon with the increased fuel consumption reaching from one five percent.

The catalyst is installed under the car body basis instead of the additional muffler. The catalyst consists of the porous ceramic monolith covered with a layer of platinum or rhodium. For installation of a ceramic body, sensitive to pushes, elastic and heat-resistant wire cloth is used.

In this case it is about the so-called three-functional catalyst. It means that on this catalyst, on the basis of the data obtained from the oxygen sensor oxidation of carbon monoxide (SO) and hydrocarbons (NANOSECONDS) to CO2 and H2O, and also simultaneous restoration of oxides of nitrogen (NOh) to nitrogen is carried out.

Care of the cars equipped with the catalyst

To avoid damage of the oxygen sensor and the catalyst, surely follow the following instructions:

 – Essentially fill the car only with unleaded gasoline. If you by mistake refueled ethylated gasoline, then it is necessary to replace an exhaust pipe in front of the catalyst, and also the catalyst. Before installation of new details of the catalyst it is necessary to train not less than two fuel tanks filled with unleaded gasoline. Start of the engine by means of pushing or towage can be made only in that case when the engine is at once started. Not burned down fuel at ignition can lead to a catalyst overheat and by that to its destruction. Use start of a starter from the auxiliary rechargeable battery.

 – It is necessary to avoid the frequent, following one after another launch of the cold engine. In this case not burned down fuel which at the subsequent heating suddenly ignites gathers on the catalyst, and at the same time harm is done to the catalyst.

 – At emergence of difficulties at start of the engine it is not necessary to press a long time a starter. During start fuel is continuously injected. Define and remove a cause of defect.

 – Apply only the spark plugs of Mercedes allowed for operation.

 – You do not carry out verification of the spark category on tips of wires to spark plugs.

 – If sparking interruptions are observed, avoid the high frequency of rotation of a shaft of the engine and urgently eliminate defect.

 – Do not stop the car over the dried foliage or a grass. The system of production of exhaust gases becomes very hot in a zone of the catalyst and radiates residual heat even after an engine stop.

 – During the filling or a dolivka of engine oil especially pay attention to that the maximum mark in the index of level of oil was not exceeded at all. Otherwise excess oil because of incomplete combustion gets on the catalyst and can damage precious metal or completely destroy the catalyst.