Fuel is sucked by the high-pressure fuel pump (HPFP) directly from the tank. In the HPFP, the fuel is compressed to the pressure required for injection. Injection is carried out in a manner similar to the ignition order in a gasoline engine.
To reduce the proportion of harmful substances in the exhaust gases, diesel engines have a diesel oxidation catalytic converter. At the same time, the recirculation system ensures a significant reduction in the content of nitrogen oxides in the exhaust gases. This is achieved by feeding the exhaust gases to the air sucked in by the engine, which reduces the oxygen concentration in the air entering the engine cylinders. This leads to a delay in ignition and a lower combustion temperature, which ultimately reduces the formation of NOx. The process of recirculation of exhaust gases must, however, be precisely dosed, since otherwise the emission of carbon deposits increases. For this purpose, the amount of sucked air is determined by a meter, which allows the electronic device to control the recirculation process.
When the engine is cold, the air compression temperature is insufficient to ignite the fuel. In this case, preheating is required. For this purpose, an electric glow plug is installed in each engine cylinder.
The duration of the glow depends on the outside air temperature and is regulated by a special relay.
Fuel injection into the cylinders can be carried out in three ways: through a pre-chamber, a swirl chamber or directly into the combustion chamber.
At pre-chamber injection diesel fuel is injected into the pre-chamber of the corresponding cylinder. The hot fuel mixture immediately ignites. However, the volume of oxygen contained in the pre-chamber is sufficient to burn only part of the injected fuel. The remaining unburned portion of the fuel, under the action of combustion pressure, is thrown into the main combustion chamber, where complete combustion of the fuel occurs.
At swirl chamber injection fuel is injected into a chamber separated from the main combustion chamber. The difference from pre-chamber injection is the different execution of the connecting channel between the swirl and main chambers. Here, during compression in the swirl chamber, a strong air swirl occurs, which contributes to good mixing of air with the injected fuel.
(This article was copied from the website AUDImanual.ru)