To reduce the content of toxic components in exhaust gases, diesel models are equipped with a special oxidizing catalytic converter. At the same time, the recirculation system (EGR), due to the metered mixing of a small amount of exhaust gases into the air sucked into the engine and, as a result, a decrease in the concentration of oxygen in the combustible mixture, provides a significant decrease in the content of nitrogen oxides (NOX) in the combustion products. Due to the operation of the EGR system, the ignition delay time is reduced and the combustion temperature is lowered, which ultimately leads to a decrease in the formation of NOX. An indispensable condition for organizing EGR is the accuracy of the mixing dosage, since otherwise the content of solid carbon particles (soot) in the exhaust gases increases. The amount of air sucked into the engine is determined by a special meter, the information from which allows the electronic control module to monitor the recirculation process.
Fuel is injected directly into the combustion chambers of the cylinders (CDI).
The engine operation is controlled by an electronic system, similar in structure and operating principle to the engine management system used in gasoline models. The commands generated by the control module are based on data received from a whole set of information sensors that continuously monitor the operating parameters of the engine and transmission line.
Information about the position of the crankshaft and engine speed is sent to the control unit from crankshaft position sensor (CKP). The inductive head of the sensor is located opposite the flywheel and constantly scans special reference marks applied to the surface of the latter. When a mark passes the sensitive element of the measuring head, the sensor generates a signal pulse sent to the control module. The marks are uniformly applied to the surface of the flywheel, with the exception of a single gap corresponding to the position 90° before the TDC of the piston of the first cylinder. When the flywheel passes this point, the signal pulse is not sent to the control module, which allows the latter to determine the TDC moment. Based on the length of the pause/pulse duty cycle, the module receives information about the crankshaft rotation frequency.
Information about the amount and temperature of air entering the engine comes from manifold absolute pressure (MAP) and intake air temperature (IAT) sensors. The MAP sensor is connected to the intake manifold by a vacuum hose and measures the depth of the vacuum inside the latter. Two IAT sensors are used to monitor the intake air temperature, one of which is installed in front turbocharger, the other one is behind Intercooler (intercooler). The readings taken by the sensors are used by the control module to calculate the exact amount of fuel that should be injected into the engine's combustion chambers.
The traditional coolant temperature sensor has been replaced with cylinder head temperature sensor, supplying the control module with information used to adjust the quality of the air-fuel mixture and calculate injection times. In addition, the data collected by the sensor are used to control the operation of the cold engine preheating system.
Brake Light/Brake Pedal Position Switch Sensor informs the control unit of the current position of the foot brake pedal. Upon receiving signals from these sensors, the control system immediately switches the engine to idle mode and maintains it until a signal is received from the gas pedal position sensor.
The fuel supply system is organized according to the direct injection scheme. The piston crowns are provided with vortex chambers, providing for the swirl of the fuel injected into the combustion chambers of the cylinders. To optimize the combustion process, the injectors are opened in two stages (for this purpose, two springs are placed inside each nozzle). When the injector's working valve opens, a small amount of fuel gets onto the injector's internal components, providing lubrication, and then returns to the fuel tank.
Preheating control is also carried out by the engine control module, which, when the engine is cold, provides a certain offset of the injection moment. In addition, the control module monitors the functioning of the glow plugs. Glow plugs are screwed into each cylinder, are activated before starting the engine and remain hot during the entire time the crankshaft is turned by the starter, as well as for some time after starting the engine. The use of glow plugs makes it much easier to start the engine in cold weather. A special indicator lamp mounted in the instrument cluster warns the driver about the activation of the spark plugs (see Chapter Controls and operating techniques), - as soon as the lamp goes out, you can start the engine. In particularly cold weather, the spark plugs continue to function for some time after starting, maintaining the stability of engine speed and ensuring a reduction in toxic components in combustion products.
Note: The design of modern diesel engines is characterized by increased starting efficiency, as a result of which the need to use glow plugs arises only at air temperatures below - 10°C.
(Material created based on the website mercedesman.ru)
The fuel pumped by the pre-fuel pump is passed through fuel filter, where it is cleaned from moisture impurities and other contaminants, try to conscientiously perform maintenance procedures, replacing the filter element in a timely manner.