Views: 1 Author: Site Editor Publish Time: 2021-11-04 Origin: Site
The principle of operation of the power supply system of a diesel engine with a mechanically controlled injector is as follows. To a high pressure fuel pump (fuel pump) is supplied fuel from a fuel tank . The booster pump is responsible for the supply, which creates a low pressure required to pump diesel fuel through the fuel lines.
Further, the high-pressure fuel pump, in the required sequence, distributes and injects fuel under high pressure in the lines leading to the mechanical nozzle. Each injector of this type opens for the next injection of a portion of diesel fuel into the cylinders under the influence of high fuel pressure. Decreasing pressure causes the diesel fuel injector to close.
A simple mechanical injector has a body, atomizer, needle and one spring. In the device, the shut-off needle moves freely along the guide channel of the atomizer. The injector nozzle closes tightly at the moment when there is no required pressure from the high-pressure pump. At the bottom, the needle rests on a tapered nebulizer seal. The clamping of the needle is realized by means of a spring fixed from above.
The atomizer is one of the most important components among other elements in the device of the injection nozzle. Sprayers can have a different number of spray holes, differ in the way of adjusting the fuel supply.
Simple diesel engines that have a split combustion chamber often have a single orifice and needle atomizer. Diesel engines, which are based on direct fuel injection, are equipped with injectors with multiple spray holes. The number of holes in such a spray gun ranges from two to six.
The fuel supply is regulated depending on the design of the atomizer, since there are two main types of such solutions:
spray with the possibility of overlapping channels;
overlapping volume nebulizer;
In the first case, the nozzle needle shuts off the fuel supply by closing each hole. The second type of nozzle means that the needle closes a kind of chamber at the bottom of the atomizer.
The pressure of the fuel pumped by the injection pump forces the needle to rise due to the presence of a special step on the surface of such a needle. Diesel fuel enters the housing under the specified step. At the moment when the fuel pressure is stronger than the force created by the pressure spring, the needle moves up. This opens the spray channel. Diesel fuel under pressure passes through the nozzle and is sprayed in the form of a torch. This is how fuel injection is implemented.
Further, a certain amount of fuel, which is supplied by the high-pressure pump, will pass through the atomizer and enter the combustion chamber. After that, the pressure on the step of the needle begins to decrease, as a result of which the needle from the force of the spring returns to its original position and tightly closes the channel. Then the supply of diesel fuel to the sprayer is completely stopped.
The efficiency of fuel supply and subsequent combustion of fuel in the cylinders of a diesel engine can be influenced by changing various characteristics of the injector, such as the structure and number of nozzle ports, spring force, etc. One of the design solutions was the introduction of a special needle lift sensor into the nozzle device. This rise is taken into account by special electronic control units that interact with the injection pump.
Diesel injectors with two springs became another round of development. The design of these injectors is more complex, but the result is greater flexibility in the fuel delivery process. The combustion of the working mixture becomes softer, the diesel runs quieter.
A feature of the operation of these injectors is a two-stage needle lift. It turns out that the fuel pumped by the high-pressure fuel pump first exceeds the pressure force of the resistance of one spring, and then the other. In idle mode and at low engine loads, injection is carried out only through the first stage, supplying a small amount of diesel fuel to the engine. When the engine enters the load mode, the pressure of the pumped fuel injection pump increases, the fuel is supplied in two metered portions. The first injection of a small volume (1/5 of the total), and then the main injection (about 80% diesel fuel). The difference in injection pressures for opening the first and second stages is not particularly large, which ensures smooth fuel delivery.
This approach made it possible to increase the uniformity, efficiency and usefulness of the combustion of the mixture. The diesel engine began to consume less fuel, the amount of toxic impurities in the exhaust gases decreased. Diesel injectors with two springs were actively used on units with direct fuel injection until the advent of power systems called the Common Rail.
Further development of diesel ICE fuel supply systems led to the emergence of injectors in which diesel fuel is supplied to the cylinders by means of electromechanical injectors. In such injectors, the nozzle needle opens and closes access to the atomizer not under the influence of fuel pressure and counteraction to the force of the spring, but with the help of a special controlled solenoid valve. The valve is controlled by the engine ECU , without a corresponding signal from which the fuel will not enter the atomizer.
The control unit is responsible for the moment of the start of the fuel injection and the duration of the fuel supply. It turns out that the ECU doses diesel fuel for a diesel engine by supplying a certain number of pulses to the injector valve. The parameters of the pulses directly depend on the frequency with which the engine crankshaft rotates , in what mode the diesel engine is operating, what is the temperature of the internal combustion engine, etc.
In the Common Rail power system, an electromechanical injector can deliver fuel in one cycle by means of several separate impulses (injections). Fuel injection is carried out up to 7 times per cycle. The injection pressure has also increased significantly compared to previous systems.
Due to the metered high-precision supply, the gas pressure on the piston as a result of the combustion of the mixture grows smoothly, the fuel-air mixture itself is more evenly distributed over the diesel cylinders, it is better sprayed and completely burns out.
The following video clearly illustrates the principle of operation of an electromechanical injector using a gasoline engine as an example. The main difference is that the fuel pressure in the diesel injector is significantly higher.
This approach made it possible to finally shift the task of controlling the injection from injectors and high-pressure fuel pumps to the electronic unit. Electronic injection works much more accurately, diesel with similar solutions has become even more powerful, economical and environmentally friendly. The developers managed to significantly reduce vibrations and noise during the operation of the diesel unit, and to increase the total resource of the internal combustion engine.
One of the varieties of diesel power systems are designs in which there is no injection pump at all. The so-called diesel unit injectors are responsible for creating high injection pressure. The principle of operation of the system is that the low-pressure pump first supplies diesel fuel directly to the injector, which already has its own plunger pair to create a high injection pressure. The plunger pair of the injector operates from the direct action of the camshaft cams on it . This system allows to achieve the best quality of diesel fuel atomization due to its ability to create very high injection pressure.
We also recommend reading the article on how to clean your diesel particulate filter yourself . In this article, you will learn about the basic methods of cleaning the filter element both with removal and directly on the car.
The elimination of the injection pump from the fuel supply system makes it possible to make the placement of the diesel internal combustion engine under the hood more compact, to get rid of the drive of the fuel pump and power take-off for its constant rotation. It also became possible to remove solutions from the power supply system that distribute fuel from the injection pump to the cylinders. The injectors in the unit injector system have an electric valve, which allows fuel to be supplied in two pulses.
The principle is similar to that of a mechanical two-spring injector. The solution makes it possible to implement first post-injection, and only then supply the main portion of fuel to the cylinder. The pump-injectors realize the fuel supply at the most precisely specified moment of the injection start, and the diesel fuel is better dosed. A diesel engine with such a system is economical, runs smoothly and quietly, and the content of harmful substances in the exhaust gases is minimized.
The main disadvantage of the solution is that the fuel injection pressure of the pump-injector directly depends on the engine speed. The list of shortcomings also noted: the complexity of execution, high demands on engine oil, purity and quality of fuel. In the process of operation, difficulties in the process of repair and maintenance are highlighted, as well as the overall high cost in comparison with systems that are equipped with the usual high pressure fuel pump.
