Truck users often complain about the deflagration and lack of power of LNG engine, which is not a single situation. Serious pollution, blockage and excessive carbon deposition will lead to deflagration, and too large ignition advance angle of engine will also lead to deflagration. Too high mixing temperature entering cylinder or too long storage time of LNG in storage tank will also lead to deflagration. Xiaobian today sorted out the cause analysis of deflagration of LNG engine, as follows:
1. The quality of LNG fuel used is poor or the anti explosion performance is reduced; 2. The ignition timing is inaccurate and the ignition advance angle is too large; 3. The mixture is too rich, exceeding 5% of the set concentration; 4. The turbocharging is abnormal, which can not limit the intake pressurization, resulting in over pressurization; 5. The intake intercooler is seriously polluted and the intake temperature is too high; 6. Improper selection of lubricating oil quality and use of engine oil with too high ash content lead to excessive carbon deposition in the cylinder and relatively increased compression ratio.
In the gas supply system, the temperature of gasified natural gas shall not be too high, and the temperature of natural gas passing through the gas buffer tank and heat exchanger shall be controlled. Too high temperature will lead to engine detonation. The actual storage time of LNG fuel in the storage tank is too long after new vehicle transportation, handover and inspection. When the tank absorbs external heat and increases the internal pressure by more than 1.6Mpa, the safety valve will automatically discharge the overpressured natural gas and accelerate the evaporation of natural gas in the tank. Due to the evaporation of methane with good explosion resistance, the methane content in liquid LNG gradually decreases, which directly affects the explosion resistance of the engine, and is easy to knock the LNG engine, which can cause engine damage in serious cases.
Generally, the part where detonation occurs is in the combustion chamber, which is easy to cause melting damage on the upper part of the cylinder, but it will not cause the whole cylinder block to break. From the perspective of overall crushing, improper cylinder liner material and quenching heat treatment are also directly related to cylinder block crushing.
There were similar knocking and blowby sounds in several truck engines. After increasing the throttle, the engine trembled and the power decreased, and even stalled and black smoke was emitted from the exhaust pipe. After analysis, it may be the engine cylinder pulling phenomenon. After disassembly, it is confirmed that there are vertical grooves and galling scratches with different depths on the longitudinal cylinder wall. This is because when the sliding contact area between the piston or piston ring and the cylinder wall is too small, high temperature will be generated by friction, metal melting will occur between the piston or piston ring and the cylinder wall, and the hardened material will pull the cylinder wall out of the groove mark after cooling, that is, cylinder pulling.
Broken heart, the news of reducing the toll of LNG vehicles in Shanxi is untrue