Contents: Emission Control System ↡ Crankcase ventilation system (PCV) ↡ Reducing toxicity of exhaust gases ↡ Exhaust Gas Recirculation (EGR)…↡ Fuel Evaporative Emissions (EVAP)…↡ Continuous crankcase ventilation…↡ Catalytic converter ↡ Exhaust Gas Recirculation (EGR)…↡
The exhaust system of a gasoline engine consists of an exhaust manifold, an intake pipe, a catalytic converter(s), a central muffler, a connecting pipe, an additional muffler and an exhaust pipe(s). The exhaust system of a 6-cylinder engine in the section between the exhaust manifolds and the central muffler has a dual-flow design. Diesel engines are also equipped with two catalytic converters, the first of which is located near the engine.
As part of a restoration repair, each section can be replaced separately.
Emission Control System
Petrol models
All petrol models must use unleaded petrol in their fuel systems. The engine management system is designed to provide maximum engine performance with minimum fuel consumption and emissions. The fuel vapor recovery system prevents fuel from escaping from the fuel tank into the atmosphere. An exhaust gas recirculation system is installed.
Crankcase ventilation system (PCV)
To eliminate leaks of unburned hydrocarbons into the atmosphere, the engine is completely sealed. Gases and oil vapors formed in the crankcase enter the intake manifold through a mesh filter and burn in the cylinders together with the fuel.
Gases are removed from the crankcase due to the pressure difference in the crankcase and the intake manifold (crankcase pressure is higher).
Reducing toxicity of exhaust gases
To reduce harmful emissions into the atmosphere, all petrol models have a three-function catalytic converter built into the exhaust system. The fuel injection control system has a feedback loop that includes an oxygen sensor. This sensor, installed in the exhaust system, constantly informs the control unit about the composition of the exhaust gases. Depending on the data received, the control unit adjusts the quality of the mixture supplied to the combustion chambers and thus optimizes fuel combustion.
The lambda probe has a built-in heating element, which is switched on by the control unit via a special relay. The working surface of the lambda probe is sensitive to changes in the oxygen content in the gases. Depending on the oxygen concentration, the sensor sends signals of different voltages. If the mixture is over-enriched - the oxygen content in the exhaust gases is very low, the sensor sends signals with low voltage. The voltage increases as the mixture becomes leaner and the oxygen content in the gases increases. The converter works most effectively with an optimal composition of the combustible mixture (14.7 parts air to 1 part fuel). At the optimum concentration of oxygen in the exhaust gases, a jump in voltage occurs on the sensor. This jump is the starting point for the control unit when adjusting the mixture quality.
Two sensors are installed: one before and one after the catalytic converter assembly. This allows for more accurate monitoring of the exhaust gas composition.
Exhaust Gas Recirculation (EGR) system - models equipped with 112 and 113 series engines
The exhaust gas recirculation system reduces the amount of NOX in the exhaust gases. To do this, a small portion of the exhaust gases is fed into the intake manifold through a special valve. The recirculation system valve is controlled by the control unit.
Fuel Evaporative Emissions (EVAP) System
To reduce the emission of unburned hydrocarbons into the atmosphere, all petrol models are equipped with a fuel recovery system. The fuel filler neck of the fuel tank is hermetically sealed with a lid, and a carbon adsorber is installed under the fuel tank. It collects fuel vapors that form in the tank when the car is parked and stores them there until the control unit signals the filter to start purging. Then the fuel vapors begin to be supplied through the purging valve(s) into the intake manifold, where they mix with the working mixture and then burn in the usual way in the combustion chambers.
To ensure normal engine operation at idle speed and during warm-up, the control unit keeps the valve closed. This prevents unburned fuel from entering the converter (at high idle speed the mixture is too rich). After the engine warms up, the valve begins to open and close, supplying fuel vapors into the intake tract.
Diesel models
[Material borrowed from an online resource: MercedesMan.ru]
The engine management system operates in such a way as to obtain maximum output from the engine with minimum fuel consumption and toxicity of exhaust gases. To further reduce toxicity of gases, several additional systems are installed on the car. The crankcase ventilation system reduces gas leaks into the atmosphere from the engine lubrication system. The catalytic converter reduces toxicity of exhaust gases. An exhaust gas recirculation system is installed.
Continuous crankcase ventilation (PCV) system
To eliminate leaks of unburned hydrocarbons into the atmosphere, the engine is completely sealed. Gases and oil vapors formed in the engine crankcase are passed through a mesh filter, directed into the intake manifold and burned in the cylinders during normal engine operation
The removal of crankcase gases is achieved due to the difference in pressure in the crankcase and the intake manifold.
Catalytic converter
To reduce the amount of harmful emissions into the atmosphere, all diesel models have a catalytic converter built into the exhaust system. It neutralizes most of the gaseous hydrocarbons, carbon monoxide (CO) and other toxic impurities contained in the combustion products of the air-fuel mixture.
Exhaust Gas Recirculation (EGR) System
All diesel models are also equipped with an exhaust gas recirculation system, the main task of which is to reduce the percentage of nitrogen oxides (NOX) in the engine combustion products. To accomplish this task, a small portion of the exhaust gases from the exhaust system tract is redirected through a special valve to the intake manifold. The operation of the EGR valve is controlled by the control unit.