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Exhaust system of a four-cylinder engine: 1 - front muffler, 2, 5, 20 and 24 - bolt 25 Nm, 3, 4, 14, 19 and 25 - suspension, 6 - nut 30 Nm, 7 and 12 - seal, 8 - exhaust manifold, 9 - catalytic converter, 10 and 11 - oxygen sensor 55 Nm, 13 - front exhaust pipe, 15 and 22 - adapter sleeve, 17 - clamp 25 Nm, 18 - muffler exhaust pipe, 20 - nut 25 Nm, 21 - additional muffler (when equipped by the manufacturer, together with the front muffler forms a single unit), 23 - nut 40 Nm.
In all cases, the manifold is followed by a catalytic converter, a front exhaust pipe, a middle silencer and an additional silencer. Parts of the system are connected to each other by means of bolted connections or clamps, they can be replaced individually. When fitted from the factory, the center and secondary silencers are installed in one continuous exhaust pipe. In the event of a repair, silencers can be replaced individually. To do this, the connecting pipe must be sawn in the designated place. After installation, both parts are connected using an adapter sleeve. In vehicles with all-wheel drive, exhaust systems of a different design are installed. In vehicles with gasoline direct injection with stratified charge (FSI) exhaust gases are also cleaned differently.
In all models, too much heat radiation on the lower parts of the body is prevented by means of heat shields. Once the seals and self-locking nuts have been removed, they must be replaced. If necessary, the circlips and rubber buffers should also be replaced.
Terminology
carbon monoxide (SO). The content of monoxide is measured when monitoring the toxicity of exhaust gases. A prerequisite for low CO content is the exact dosage of the amount of injected fuel, the adjustment of the ignition timing and the uniform swirling of the mixture in the combustion chamber. In enclosed spaces, carbon monoxide is toxic; when combined with atmospheric oxygen, it forms non-toxic carbon dioxide, which plays a significant role in the greenhouse effect.
hydrocarbons (CH). Hydrocarbons do not burn completely in cold places and at the corners of the combustion chamber. The proportion of hydrocarbons depends on the design of the engine (immutable parameter), however, the emission of hydrocarbons is also increased due to a too rich or too lean combustible mixture. Together with carbon oxides, hydrocarbons are responsible for the formation of smog.
nitrogen oxides (NOx). The content of nitrogen oxides in the exhaust gas rises at high combustion temperatures. This happens, for example, in engines that are designed to emit small amounts of CO and CH (it reduces fuel consumption). At high concentrations, nitrogen oxides can irritate the respiratory system. When combined with water, they form nitric acid (acid rain).
Sulfur. The efficiency of a NO* storage catalytic converter is significantly degraded due to the presence of sulfur in the fuel. The sulfur content in normal gasoline is 150 ppm. Low sulfur fuel will be required in the future (less than 10 ppm).
Special monitoring of exhaust gas toxicity. Special monitoring of toxic exhaust gases with variable catalytic converters has been mandatory since December 1993. For new vehicles, the results of the control are valid for three years, after which the control must be carried out every two years. When checking, the exhaust gas system must be in good order, no additional air must enter the intake system.
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