Typical failure (machine failure case) example 1 On July 21, 1998, a DF4B locomotive hauled train 2203. During the journey, the locomotive crew suddenly heard a “click” in the power room, and at the same time, the diesel engine speed dropped from about 950r/min to 600r/min. about. After the flight attendant returned the handle, the inspection found that a large amount of engine oil was sprayed from the front chimney, and the diesel engine had been automatically stopped at this time. The flight attendant requested rescue (when the flight attendant was patrolling on the way, he found redness in the exhaust manifold). After inspection, it was found that the front turbocharger had serious fuel injection marks and the author’s introduction: Chen Yuenian, graduated from Southwest Jiaotong University in 1985, majoring in diesel locomotives, and is now engaged in teaching and lecturer.
The rotor is stuck. The turbocharger was disassembled and inspected. One turbine blade was broken (there was an old crack at the break), three were broken, and the radial bearing at the turbine end was broken. Analysis believes that the redness of the exhaust manifold indicates that the temperature of the exhaust gas is too high, and the broken blade itself has defects, so it is broken. One piece of the turbine blade was broken and three pieces were broken, resulting in the destruction of the dynamic balance of the rotor group, which caused the radial bearing to break due to the impact load. At the same time, the radial bearing fracture has two consequences: one is that the rotor is stuck; the other is that a large amount of oil is sprayed from the bearing fracture, causing the oil pressure to drop, the stop oil pressure relay will act, and the diesel engine will automatically stop.
Case 2 On October 31, 1999, a DF4B locomotive hauled the Y204 train. During operation, the diesel engine speed suddenly dropped from about 920r/min to about 650r/min. The flight attendant set the main handle to the “up” position, but the diesel engine speed did not rise accordingly; after the flight attendant returned the handle, the main handle was set to the “up” position again. When the rotation speed is about 750r/min, it will no longer rise, and a lot of black smoke will be emitted from the chimney. After the flight attendant returned the handle, the gauges were normal, the parts were normal, and the fuel system was also normal. The flight attendant set the main handle to the “up” position again, and the phenomenon was the same as before.
After inspection, it was confirmed that the turbocharger rotor was stuck. The supercharger was disassembled and inspected, and it was found that its bearing was lack of oil and burned, and the shaft had been hung. After further inspection, it was found that a piece of iron was blocked at the outlet of the turbocharger oil inlet pipe. The oil inlet pipe was dissected and it was found that the inner wall was peeled off. The peeling produced a piece of iron that was blocked in the oil inlet pipe, causing the turbocharger bearing to run out of oil. The shaft is burned and the rotor is stuck.
General failure surge mechanism The essence of surge is gas vibration. Simply put, when the air intake of the compressor is greater than the air output, part of the air at the compressor inlet cannot be pressed in, and gathers between the compressor blades, causing a vortex and causing surge. Surge causes the turbocharger rotor shaft to produce high-frequency axial vibration, and the working state of the diesel engine tends to be unstable, and the life of the turbocharger and the diesel engine is seriously affected.
The cause is the bad factor of the supercharging system. The air filter is too dirty, the cooling capacity of the intercooler is reduced due to some reason, etc., so that the air volume in the cylinder cannot meet the needs of combustion, causing the exhaust temperature to rise, prompting the turbocharger rotor speed to rise, and the compressor suction volume Increase, and this increased part of the air is difficult to all enter the cylinder, resulting in surge.
The supercharger nozzle ring has carbon deposits or the cross-sectional area is too small, the rotor is stuck, etc. The former makes the exhaust gas flow through the nozzle ring to increase the flow rate, the turbine speed increases, and the compressor suction volume increases, so that the “excess” part of the air is blocked at the compressor inlet and causes surge. The latter first reduces the intake of the compressor, which causes the combustion in the cylinder to deteriorate, and the exhaust temperature rises, which in turn increases the speed of the turbocharger rotor and the intake of the compressor. Surge occurs.
In addition, the surge margin of the supercharger is generally required to be above 12%, such as the minimum surge margin when the 45GP802-1A supercharger works with a 16V240ZJB diesel engine (when the diesel engine speed is around 900r/min, according to the traction characteristics When the power value is working, the surge margin of the supercharger is the smallest) it is difficult to reach this value. Therefore, when the 16V240ZJB diesel engine works at 900r/min, the turbocharger is more prone to surge.
The bad factor of diesel engine. The main reasons are that the valve cannot be opened or closed tightly, the quality of fuel atomization is poor, the diesel engine is overloaded or the load fluctuates greatly, and the diesel engine suddenly unloads due to the function of the protective device. When the intake valve cannot be opened or the opening is very small, the cylinder cannot be filled with fresh air or the amount of charge is small, making the turbocharger “excessive”. Because the valve opens early and closes later, the exhaust gas from the exhaust manifold will flow backwards into the cylinder, causing deterioration of combustion in the cylinder, thereby increasing the temperature of the exhaust gas.
As for poor valve closing, poor fuel atomization quality, diesel engine overload and other factors, combustion will deteriorate and exhaust temperature will rise. When the power of the diesel engine fluctuates downward, especially when the load is suddenly unloaded, the amount of air required in the cylinder also drops sharply. During this process, the speed of the supercharger rotor cannot drop rapidly, so that the supercharger’s air supply is “excessive” and surging occurs.
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