Location of diesel engine controls in the engine compartment
- 1 - pressure and temperature sensors of the air entering the engine. On vehicles manufactured before VIII.1997, the pressure sensor for air entering the engine is installed in the control unit of the diesel direct injection system;
- 2 - electrical connector of the engine crankshaft speed sensor;
- 3 - electrical connector of the needle movement sensor;
- 4 - valve of the exhaust gas re-supply system;
- 5 - coolant temperature sensor;
- 6 - electrical connector of the high pressure fuel pump. The ten-pin connector is designed for the fuel temperature sensor, volume regulator and spool displacement sensor, as well as for the fuel cut-off valve and injection timing valve;
- 7 - speed sensor;
- 8 - control device. The control sensor is only installed on diesel engines with direct fuel injection;
- 11 - electrical connector. 7-pin electrical connector for fuel cut-off valve and fuel injection timing valve;
- 12 - place for measuring the volumes of the high pressure fuel pump;
- 13 - fuel injector with needle displacement sensor;
- 14 - magnetic valve. The solenoid valve is designed to limit the turbo boost pressure;
- 15 - exhaust gas re-supply valve;
- 16 - air flow meter
Location of vacuum hoses in the diesel engine control system
- 1 - connecting air duct. Turbocharged air heat exchanger;
- 2 - vacuum connection. For adjusting the boost pressure of the air generated by the turbocharger on AFN engines;
- 3 - connection for a vacuum brake booster;
- 4 - vacuum connection. For adjusting the air boost generated by the turbocharger on AFN engines;
- 5 - vacuum pump;
- 6 - ventilation hose. For adjusting the air boost generated by the turbocharger on AFN engines;
- 7 - ventilation hose on the air filter;
- 8 - exhaust gas re-supply valve;
- 9 - modulating exhaust gas re-supply valve
This type of engine got its name from the German engineer Rudolf Diesel, who built the first self-ignition engine in 1897. Structurally, a diesel engine is similar to a gasoline engine: the same cylinders, pistons, camshaft, valves. But there are a number of differences, of which the main, one might even say fundamental, is that the ignition of the fuel in a diesel engine is not produced by a spark from a spark plug, but due to the high temperature that the air reaches as a result of its compression by the piston in the cylinder.
The second important point is the method of fuel supply. In a gasoline engine, the working fluid is a mixture of gasoline and air. The mixture is prepared in advance (in the carburetor) or directly at the moment of its supply to the cylinders (in injection systems) - the main thing is that the fuel is supplied together with air, and a relatively homogeneous air-fuel mixture is ignited and burned.
In a diesel engine, fuel and air are supplied separately. First, air is sucked into the cylinder, then it is compressed, and only after that fuel is injected, so there is no need to talk about a homogeneous air-fuel mixture. The injection is made at the end of the compression stroke, the fuel and air do not actually mix with each other, combustion occurs at the front of the fuel jet injected into the compressed air.
Self-ignition of fuel is accompanied by a sharp, spasmodic increase in pressure in the cylinder - this explains the usually noisy, harsh operation of a diesel engine. In low-speed diesel engines with large displacement, which are used on trucks, this disadvantage is less pronounced, and it is tolerated. In passenger car diesel engines, they try to get rid of it by using a swirl chamber, or prechamber, a small compartment of the combustion chamber into which fuel is injected. There it ignites, partially mixes with air, after which the burning mixture spreads through the main volume of the cylinder. This method somewhat reduces the rigidity of the engine, but reduces its thermal efficiency and fuel efficiency. For smoother fuel ignition, two-stage injection and a complex electronic control circuit are used.
A characteristic feature of diesel engines is the presence of particulate matter in the exhaust gases. Due to the heterogeneity of the combustion process, a certain lack of oxygen is always observed on the surface of individual fuel particles, as a result of which, instead of their oxidation, partial thermal decomposition occurs with the formation of solid products - soot. For good combustion of diesel fuel, a significant, even excessive amount of air is required.
Also, the compression ratio of a diesel engine is 2 times higher than that of a gasoline engine. High, not less than 14 (reaches 25), the compression ratio is necessary in order for the air temperature in the cylinder to rise to a value sufficient to ignite the fuel. Usually in diesel engines the compression ratio is 21–22 and is limited only by the strength characteristics of the engine.
Fuel supply devices in diesel engines are much more complicated than in gasoline engines. Their complexity is determined primarily by the fact that it is necessary to inject very small, only a few milligrams, portions of fuel into a high-pressure medium. These portions must be very accurately measured - it is the amount of fuel supplied that controls the operation of a diesel engine. This requires fast and accurate nozzles. A high compression ratio requires the use of appropriate fuel pumps - the pressure in the injector nozzle must reach several hundred bar. All this complicates and significantly increases the cost of the fuel supply system and, accordingly, the diesel engine itself.
Fuel is drawn from the fuel tank by the high pressure fuel pump and then delivered under high pressure to the fuel injectors.
To reduce the amount of harmful substances contained in the exhaust gases on vehicles with diesel engines, an oxidizing catalyst is installed. A system is also used to mix exhaust gases with fresh air entering the engine, as a result of which the percentage of oxygen in the air that will be burned in the engine cylinders is reduced. As a result, the combustion temperature of the fuel mixture decreases, resulting in a decrease in the amount of nitrogen oxides formed.
There are three methods for injecting diesel fuel into engine cylinders. Through the prechamber, through the vortex chamber and direct injection.
When diesel fuel is injected through the prechamber, the fuel is sprayed over the prechamber and instantly ignites. Due to the small amount of oxygen in the prechamber, only part of the fuel burns out, and the rest of the fuel is displaced from the prechamber into the engine cylinder, where it burns out completely.
When fuel is injected through a vortex chamber, the fuel combustion process is carried out in the same way as when fuel is injected through a prechamber. The difference lies in the shape and size of the channel connecting the vortex chamber with the combustion chamber. When fuel is injected into the swirl chamber, the fuel is mixed with air much better, and the combustion process is smoother.
Direct fuel injection
With direct fuel injection, fuel is injected directly into the combustion chamber. The fuel pump delivers fuel at a pressure of about 900 bar, and the fuel is injected in two stages.
The use of dual-channel fuel injectors makes it possible to make the initial injection of a small part of the fuel, as a result of which the combustion process of the fuel is improved, and the combustion process itself proceeds more smoothly. The amount of fuel injected is controlled by the electronic engine management system. The amount of fuel injected is controlled by the control system based on information from the following sensors:
- - the accelerator pedal position sensor transmits information to the engine control device about the position of the accelerator pedal at the present time;
- - engine crankshaft speed sensor;
- fuel injector needle movement sensor. Based on the information from this sensor, the moment of fuel injection is determined and the injection process is adjusted depending on the operating conditions and engine crankshaft speed;
- engine air pressure sensor (boost sensor);
- temperature sensor of the air entering the engine;
- coolant temperature sensor;
- diesel fuel temperature sensor;
- spool position potentiometer. Based on the information from this sensor, the actual amount of injected fuel is determined.
The air entering the engine in the intake ducts is twisted in a spiral, as a result of which the combustion process in the engine cylinders improves. It also makes it easier to start a cold engine, and the engine must be preheated at air temperatures below -10°C.
Before fuel enters the high pressure fuel pump, the fuel passes through the fuel filter, which also separates water from it, which must be drained periodically.
The fuel pump is driven by the engine crankshaft through a toothed belt. The internal moving parts of the fuel pump are lubricated with diesel fuel.
Warning: Do not allow diesel fuel to come into contact with the cooling system hoses. Hoses that have been exposed to diesel fuel for a long time must be replaced.
Warning: The diesel engine fuel system is particularly sensitive to contamination, so when working on the fuel system, be as clean as possible. Before disconnecting the fuel lines, thoroughly clean them of dirt.
Warning: Do not use compressed air to clean engine-mounted fuel system components.
Warning: When checking the operation of the fuel injectors, never put your hands or any part of your body under the jet of fuel coming out of the injector. The fuel exits the nozzle at high pressure and can enter the body through the skin.
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