Analysis of the reasons why the engine cannot start

Diesel engine starting difficulty is a common comprehensive fault on diesel engines. The cause of the fault is complex and often occurs in diesel engines that have been used for a period of time. Because after the diesel engine has been running for a period of time, due to natural wear and human factors, the technical state will deteriorate and it is easy to start difficulty. Starting difficulty means that when the diesel engine cannot be started for more than 3 consecutive times according to the starting procedure, and even when auxiliary means are taken, it is considered that the diesel engine has a starting difficulty fault.

Conditions required for the smooth start of the diesel engine

The diesel engine must meet the following 3 conditions for smooth start, and none of them can be missing.

1. The inhaled air must form a strong swirl, and the compression end temperature must be 200 to 400°C higher than the diesel auto-ignition point at the end of compression, that is, 500 to 700°C. If the cylinder or valve leaks, the pressure in the combustion chamber is insufficient, and the temperature and pressure at the end of compression do not meet the requirements, which will cause the diesel to fail to burn and explode normally, causing the diesel engine to fail to start.

2. Spray fine atomized diesel into the combustion chamber at high pressure at the right time. The fuel system has a complex structure and precise parts. Once a fault occurs in a certain part in the middle, it will cause abnormal fuel supply, which will cause the diesel engine to start difficultly or unable to start.

3. The crankshaft rotation speed must be higher than 110 r/min. If the starter of the starting device is underpowered and does not work properly, the crankshaft speed will be lower than 110 r/min, which will directly affect the normal start of the diesel engine.

Starting speed is too low

1. The air vortex is weak, the mixing of fuel and air deteriorates, the temperature in the cylinder drops, the fuel is not easy to evaporate, and the ignition conditions are not met;

2. The injection pressure is low, the injection quality deteriorates, and the injection amount is significantly reduced, which does not meet the required fuel supply at the start;

3. It makes it easy for the compressed gas to leak through the lax sealing of the cylinder, causing the compression end temperature and pressure to decrease, making it difficult to start the diesel engine. In addition, low ambient temperature and failure of the lubrication system cause poor lubrication of the matching motion pair, resulting in increased movement resistance of the crank-connecting rod mechanism, difficulty in crankshaft rotation, and difficulty in starting the diesel engine.

Reasons for Difficult Diesel Engine Starting

1. Failure of the compression system.

The main reason is that the pressure at the end of cylinder compression does not reach the specified value, and the mixture in the cylinder cannot ignite and burn normally. This is mainly due to the wear of the intake and exhaust valves, carbon deposits, incorrect adjustment of the valve clearance, etc., which causes the valve to close loosely and leak, or the wear clearance between the piston ring and the piston and the cylinder liner is too large, which makes the combustion chamber seal poorly and leak.

2. Fuel supply system failure.

It can be analyzed according to the low-pressure oil circuit and the high-pressure oil circuit. Low-pressure oil circuit failures include: insufficient oil in the tank or the tank switch is not turned on, there is air or water in the oil circuit; the vent hole of the tank cap is blocked; the oil circuit or diesel filter is blocked and does not supply oil; the filter of the oil pump is blocked; the oil pump oil valve is sticky or not sealed; the upper oil pipe in the tank is broken or loose; the oil pump connecting the oil pipe locking nut is inhaled; the oil pump is not working properly. High-pressure oil circuit failures include: excessive wear of the injection pump plunger and sleeve; loose, sticky, oil leakage or broken spring of the oil outlet valve seat; throttle lever or plunger stuck in the non-fuel supply position; carbon deposits or sintering of the injector needle valve; less fuel injection, low pressure and poor atomization; blocked spray holes; pressure regulating springs adjusted too tight or broken; high-pressure oil pipes ruptured, joints loose or air in the pipes.

3. Failures of the starting system and electrical system.

Mainly poor circuit contact, manifested as loose joints; insufficient battery power, reduced power of the starter motor; poor contact between the starter motor carbon brush and the commutator or too weak spring force of the carbon brush holder; severe wear of the starter motor carbon brush; starter motor gear cannot be embedded in the flywheel gear ring to mesh with each other.

4. Lubrication system failure.

Air in the oil circuit; oil filter blockage; oil filter blockage; low oil pressure or insufficient oil supply of the oil pump; blockage or leakage of the oil pressure pipeline and oil channel.

5. Others.

The air filter is seriously blocked, so that the cylinder cannot inhale air; the cylinder head exhaust duct or exhaust pipe is blocked, making the exhaust resistance too large; the starting hole on the vortex chamber insert is blocked.