Contents: Exhaust emission control system ↡ Crankcase ventilation system ↡ Catalytic converter on petrol engine…↡ Catalytic converter on diesel models ↡ Fuel vapor recovery system on models…↡ Exhaust system ↡
Exhaust emission control system
All models with petrol engines can use unleaded petrol. Engine management systems select the optimal mode to combine the vehicle's dynamic characteristics, minimum fuel consumption and reduction of harmful substances in exhaust gases.
In order to reduce atmospheric pollution from incompletely burned hydrocarbons and evaporating gases and to create optimal conditions for engine operation, the following exhaust gas toxicity reduction systems are used:
- crankcase ventilation system that reduces emissions of pollutants from the engine lubrication system (installed on all models);
- a catalyst that neutralizes harmful substances in exhaust gases (installed on most models);
- fuel vapor recovery system that reduces the release of gaseous hydrocarbons and fuel tank (installed on all models).
In addition, some models are equipped with an exhaust gas recirculation (EGR) system and a forced air injection system, which reduces the amount of unburned fuel in the exhaust gases.
All diesel engines are also equipped with a crankcase ventilation system. Some models also have a catalytic converter and an exhaust gas re-burning system (EGR).
Crankcase ventilation system
To reduce the emission of unburned hydrocarbons from the crankcase into the atmosphere, with a sealed engine, crankcase gases and oil vapor are drawn from the crankcase into the air supply tract to the engine and are burned by the engine.
Catalytic converter on petrol engine models
To reduce emissions of harmful substances with exhaust gases, a catalytic converter is installed on most models. On all models with a catalytic converter, the fuel supply system is of a closed type, i.e. based on the signal from the Lambda sensor installed in the exhaust pipe, the ECU constantly optimizes the composition of the fuel-air mixture.
For normal operation of the Lambda sensor, it has a heater, which is controlled by the ECU and through the Lambda sensor relay maintains a constant temperature of the Lambda sensor. Depending on the oxygen content in the exhaust gases, the Lambda sensor induces a voltage of 0.1 V (high oxygen, lean mixture) up to 0.9 V (low oxygen, rich mixture). Based on this data, the engine control unit changes the opening time of the fuel injectors and changes the ratio of fuel in the fuel mixture. The stoichiometric ratio of the fuel mixture, at which its complete combustion occurs and there are no harmful substances in the exhaust, is 14.7 parts by weight of air to 1 part of fuel.
Additional air supply to the exhaust system reduces emissions of harmful substances and CO. An air pump, driven by an auxiliary drive belt, pumps air under pressure into the exhaust manifold, where fresh air mixes with incompletely burned fuel particles. Fresh air performs the final oxidation of unburned substances, converting them into carbon dioxide and water vapor.
To reduce the emission of nitrogen oxide into the atmosphere along with the exhaust gases, part of the exhaust gases enters the intake manifold through the EGR valve and is re-burned.
Catalytic converter on diesel models
On models with diesel engines, an oxidizing catalyst is installed in the exhaust system, which neutralizes gaseous hydrocarbons and CO in the exhaust gases. On some models, a special filter is installed in the exhaust system, which captures solid hydrocarbon particles.
Some models are equipped with an exhaust gas re-burning system. When this system is operating, to reduce nitrogen oxide emissions into the atmosphere along with the exhaust gases, part of the exhaust gases enter the intake manifold through the exhaust gas re-burning system valve and are re-burned. The electro-pneumatic exhaust gas re-burning system is controlled by the ECU.
Fuel vapor recovery system on models with gasoline engines
To prevent fuel vapors from entering the atmosphere, a fuel vapor recovery system with a canister filled with charcoal is used. Fuel vapors from the fuel tank and the carburetor float chamber are collected in a canister with charcoal located under the left wing. Fuel vapors from the canister with charcoal are drawn into the throttle body due to the pressure difference and are burned in the engine cylinders. The process of drawing fuel vapors from the canister with charcoal through the cleaning valve is regulated by a thermal valve, which opens the cleaning valve only after the engine has warmed up to a certain temperature. This is necessary to prevent over-enrichment of the mixture when the engine is cold.
Exhaust system
The exhaust system consists of an exhaust manifold, an exhaust pipe, mufflers and connecting pipes, a catalytic converter and brackets and rubber hangers.
Article was borrowed from the website: Mercedesman.ru
The turbocharger installed on models with diesel engines is oil-cooled and has a pressure control valve. If the control valve fails, the engine overload protection valve is activated and, via the actuator, reduces the fuel supply by the high-pressure fuel pump to the level of a diesel engine without turbocharging.