Diesel engine is not easy to start, or the speed is not easy to increase after starting.
2 . Cause Analysis
The force generated by the combustion of fuel in the cylinder of the engine for fuel expansion work, in addition to overcoming the frictional resistance of various parts of the engine and driving the auxiliary devices (such as pumps, injection pumps, fans, air compressors , generators, oil pumps, etc.), finally passed The flywheel outputs power externally. If the heat generated in the cylinder of the engine is small or the thermal efficiency is not high, the frictional resistance is too large, or the power consumption of the auxiliary devices is increased, the engine output power will be reduced, and the engine will appear weak. The reasons for the above phenomena are:
(l) Effect of fuel supply system failure
1 Insufficient oil supply
 The fuel system should be able to spray good atomized fuel into the cylinder in a timely and appropriate manner. If the fuel system fails, the amount of oil in the spray cylinder is small, the heat generated by the combustion is reduced, and when the heat is reduced to the extent that the engine load cannot be satisfied, the engine is weak.
2 Spray quality is too bad
When the engine is working, the injector spray quality is poor, so that the surface area of ​​the fuel injected into the cylinder is small, and the oxygen binding rate is reduced. Even if a lot of oil is sprayed into the cylinder, the atomization quality is poor, and the oxygenation reaction is less. The heat is also less.
3 Influence of Fuel Injection Advance Angle
The amount of fuel in the spray cylinder should be suitable. If the pressure increase rate of fuel during the fast season is increased, it can easily cause the engine to work rough. Crude labor will consume part of the power, which means that the thermal efficiency is not high, and the effective power of the external output will be reduced. When the injection advance angle is too small, most of the combustion process moves to the expansion work process, so that the pressure increase rate decreases, the maximum pressure decreases, the exhaust gas temperature increases, the heat loss of the cooling water increases, and the thermal efficiency drops significantly.
4 Influence of the amount of aeration
The fuel can be burned in the cylinder, mainly because the carbon atoms in the diesel react with the oxygen atoms (generate carbon dioxide) and release the heat. If the air filter is blocked, the cross section of the air circulation is reduced (with turbocharger) When the turbocharger of the engine is degraded, the intake air amount is reduced, or the influence of the valve train mechanism causes the engine to inflate. As a result, the carbon atoms in the fuel cannot fully react with the oxygen atoms, so the heat released is reduced and the engine is weak.
5 Poor sealing of working media
If the cylinder gasket is damaged, the valve is not closed tightly, and the clearance between the piston and the cylinder wall is too large, leakage may occur and the compression may be poor, resulting in poor combustion of the fuel in the cylinder and inability of the engine .
6 Influence of Ambient Temperature
When the ambient temperature is too high, it often causes the engine to overheat. In the dual role of high ambient temperature and engine overheating, the air expands, thereby affecting the engine 's aeration, so that the engine power down. When the ambient temperature is too low, it will cause the fuel to evaporate badly in the cylinder, resulting in incomplete combustion, that is, the heat generated by the working medium in the cylinder is reduced.
(2) Influence of engine resistance
If the engine is over-tightened and the oil is too thick, it will cause excessive engine resistance. In addition to the power generated by the engine itself to overcome the frictional resistance of the outer and the auxiliary device, the effective power output is reduced, i.e., the engine weakness.
 3, diagnosis and elimination
Diagnosis is based on the analysis of the causes and symptoms.
(1) If the engine starts with low exhaust and is not easy to start, the reason is that the fuel system is not sufficiently supplied with oil. The faults described in the fuel system should be diagnosed and eliminated.
(2) If the engine starts smoothly, but the exhaust pipe is black smoke, and the engine speed is not easy to increase, the main reason is that the air into the cylinder is too small, you should check the air filter part of the air intake (with turbine The supercharger's engine must also inspect the supercharger and remove it.
(3) If the engine is overheated, most of it is caused by too late fuel injection time. It is the cause of engine power failure and should be adjusted. The adjustment method can be seen in the narrative part where the engine cannot start.
(4) If blue and white smoke is emitted from the exhaust pipe of the engine , it indicates that the engine power is due to cylinder blow-by and should be handled.
(5) Check for leaks
Move the engine flywheel so that the piston of the cylinder under inspection is compressed to the top dead center, remove the fuel injector, hang the low gear and pull the hand brake , then use the hose to fill the combustion chamber with compressed air from the nozzle hole. One person listened to the sound of air leakage at the inlet or exhaust port, oil filling port, cylinder pad or radiator water inlet. If a gas leak is heard somewhere, the cylinder is badly sealed. For example, a sound of air leakage can be heard at the exhaust pipe or intake pipe, indicating that the air is not closed tightly, or a sound of air leakage is heard at the water inlet of the radiator, indicating that the cylinder pad is damaged. After identification, it should be excluded.
(6) Check engine resistance
Using a crowbar to shake the engine flywheel, if the feel is more arduous than that of other diesel engines of the same type, it means that the resistance of the diesel engine is excessive. If the diesel engine has just been repaired, it is mostly due to over-tightening and it should be worn or re-assembled.
(7) Check the valve timing
 If all of the above checks are normal, then the reason for the inability of the diesel engine may be in the valve timing. Then check the valve clearance of the valve train and the angle of the crankshaft when the intake and exhaust valves are opened or closed. Then check with the coordination chart. Find out.
Gas phase inspection method: valve clearance adjustment should meet the technical document value. Open the engine flywheel housing observation window cover, and rotation of the flywheel with a crowbar pry the first cylinder piston compression top dead center, to make a fertilizer dial 3 and pointer, and the dial is fixed to the pulley, fixed on the front cover pointer Above, point the pointer to “J†on the dial. Remove the valve chamber cover, place the dial gauge and frame on the cylinder head and start to rotate the flywheel. Turn the push rod of the air distribution mechanism by hand. When the push rod does not move, it means that the valve will open. At this moment, when the hands touch the stem and the valve so that the rocker arm (push rod end) against the surface conditioning zero, then continuing rotation of the crankshaft, when the dial gauge pointer and return to zero,; pointer value on the disc, i.e. the valve opening angle Then turn the push rod by hand, from the moment of rotation to the circle of rotation, the valve is closed. At this time, the indicator on the dial is the valve closing angle.
From valve opening to closing, the angle that the crankshaft rotates is the valve open angle. The valve timing specified in the technical document of FIG test results compared with the unit, if large tolerance, tolerance should further identify the reasons, such as severe wear of the transmission gear, the correctness of the installation position of the transmission gear, the cam shaft and keyway And whether the key is damaged or not, whether the wear of the cam working surface is equal, and it should be excluded after being ascertained.
The general diesel engine can only check the first cylinder, and the phase of the other cylinders is ensured by the camshaft.
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