The control of injection quantity is divided into open-loop control Du and closed-loop control.

The open-loop control is to store the best fuel supply parameters of various engine operating conditions determined by the experiment into the computer in advance to form the so-called control map. When the engine is running, the computer judges the operating condition of the engine according to the input signals of each sensor in the system, calculates the optimal fuel supply quantity, and controls the injection time of the electromagnetic injector through the power amplifier, so as to accurately control the air-fuel ratio of the mixture and optimize the operation of the engine.
Closed loop control means that oxygen sensor is installed in the exhaust pipe. According to the change of oxygen content in the exhaust, the air-fuel ratio of combustible mixture entering the cylinder is measured and compared with the set value continuously. According to the comparison results, the fuel injection quantity is corrected, and finally the air-fuel ratio is kept near the set value.
Plunger coupling, Bai delivery valve coupling and injection Du needle valve coupling are the three precision coupling parts of diesel engine fuel system.

1. Plunger and plunger sleeve

The plunger coupling part is a pressure oil component which produces high pressure oil. The main damage of plunger coupling parts is wear, and the wear parts are mainly concentrated on the local working surface, that is, the corresponding parts of plunger head and plunger sleeve oil inlet hole, chute stop supply edge and oil return hole edge.

2. Oil outlet valve coupling parts: oil outlet valve, oil outlet valve seat

The wear parts of the outlet valve are mainly in the pressure reducing ring belt and sealing cone surface. When the pressure reducing ring belt is worn, the unloading capacity of the oil delivery valve is reduced, and the residual pressure of the high-pressure oil pipe is increased when the injection is finished, so that the injection time is advanced, the fuel cut-off is not simple, and even causes the drop of oil or secondary injection after injection, the injection duration angle is increased, and the circulating oil supply quantity is increased.

3. Injector needle valve matching parts: needle valve, needle valve body

Among the three precision coupling parts of diesel engine fuel system, the working reliability and average service life of injector needle valve coupling are the worst. The damage of the fuel injector after being used for a long time includes: the spring of the injector becomes soft; the relative moving parts are worn too much, especially the sealing between the needle valve and the needle valve body is not tight; the injection hole is blocked or reduced by carbon deposition; and the needle valve is stuck.