Typical Faults (Crashing Cases) Example 1 On July 21, 1998, a DF4B locomotive towed 2203 trains, the locomotive crew suddenly heard a â€œbangâ€ in the power room, while the diesel engine speed was reduced from about 950r/min to 600r/min. about. After the flight attendant returned the handle, the inspection revealed that the front chimney had a large amount of oil that was ejected. At this time, the diesel engine was automatically shut down. The flight attendant requested rescue (when the flight attendant visited the station and found that the exhaust mains had redness). After inspection, it was found that the front turbocharger had serious injection marks and the author's profile: Chen Yuenian, graduated from Southwest Jiaotong University in 1985, majoring in diesel locomotives, is currently engaged in teaching work, lecturer.
Rotor stuck phenomenon. The turbocharger was disassembled and examined, one blade of the turbine blade was broken (an old crack was broken), three pieces were broken, and the radial bearing at the turbine end was broken. According to the analysis, the phenomenon of redness in the exhaust manifold indicates that the temperature of the exhaust gas is high, and the broken blade itself is already defective, and therefore a fracture occurs. As the turbine blade breaks one piece and breaks three pieces, the dynamic balance of the rotor group is destroyed, so that the radial bearing breaks due to the impact load. At the same time, the radial bearing breakage caused two consequences: First, the rotor stuck; Second, a large number of oil sprayed from the bearing breakage, causing the oil pressure drop, stop the oil pressure relay action, the diesel engine automatically shut down.
Case 2 On October 31, 1999, a DF4B locomotive pulled Y204 train. During operation, the diesel engine speed suddenly dropped from about 920r/min to about 650r/min, and the flight attendant put the main handle â€œupâ€ position, and the diesel engine speed did not increase accordingly; after the flight attendant returned the handle, the main handle was set â€œupâ€ position, diesel engine When the rotation speed rises to 750r/min or so, it does not rise again, and the chimney emits a lot of black smoke. After the flight attendant returned to the handle, each meter showed normal and all parts were not abnormal, checking that the fuel system was also normal. The flight attendant again set the main handle to â€œupâ€ position, as before.
Upon inspection, confirm that the turbocharger rotor is stuck. The supercharger was disassembled and checked, and it was found that the bearings were oil-losing and they had been hung. Upon further inspection, it was found that a sheet-like iron object was blocked at the outlet of the turbocharger inlet pipe, and the inlet pipe was dissected to find that the inner wall was peeled off. The peeling produced a sheet-like iron object that blocked the inlet pipe, making the turbocharger bearing lack of oil. When the shaft is worn out, the rotor is stuck.
General Fault Surge Mechanism The essence of surge is the vibration of the gas. In simple terms, when the suction volume of the compressor is greater than the outlet volume, some of the air at the inlet of the compressor will not enter and will accumulate between the compressor blades, causing vortexing and causing surge. The surge causes the supercharger rotor shaft to generate high-frequency axial vibration, and the working state of the diesel engine tends to be unstable, and the life of the supercharger and the diesel engine is seriously affected.
The cause of the supercharging system is the bad factor. The air filter is too dirty, the intercooler cooling capacity is reduced for some reason, etc., so that the amount of air in the cylinder can not meet the burning needs, resulting in an increase in the temperature of the exhaust, which will increase the speed of the supercharger rotor, and the amount of air in the compressor. Increased, but the increase in this part of the air is difficult to enter the cylinder, resulting in surge.
Supercharger nozzle ring carbon deposit or cross-sectional area is too small, the rotor stuck and so on. The former increases the flow velocity when the exhaust gas flows through the nozzle ring, the turbine rotational speed increases, and the compressor suction volume increases, so that the â€œexcessâ€ part of the air is blocked at the compressor intake and generates surge. The latter reduces the air intake of the compressor first, which causes the combustion in the cylinder to deteriorate and the temperature of the exhaust gas to rise, which in turn causes the rotor speed of the supercharger to rise, the air intake of the compressor to increase, and finally the air is â€œsurplusâ€. Surge.
In addition, it is generally required that the supercharger has a surge margin of 12% or more, such as the minimum surge margin when the 45GP802-1A supercharger and the 16V240ZJB diesel engine work together (when the diesel engine speed is about 900r/min, the traction characteristic is When the power value works, the surge margin of the supercharger is the minimum. It is more difficult to reach this value. Therefore, when the 16V240ZJB diesel engine is operated at 900r/min, the turbocharger is more prone to surge.
The bad factors of the diesel engine. There are mainly valves that cannot be opened or closed, fuel atomization quality is poor, diesel engines are overloaded or load fluctuations are large, and the diesel engine suddenly unloads due to the protection device acting. 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 aeration is small, so that the supercharger gas supply is â€œsurplusâ€. As the valve is opened early and closed, the exhaust gas of the exhaust manifold will fall back into the cylinder, causing the combustion in the cylinder to deteriorate, thereby increasing the temperature of the exhaust gas.
The factors such as lax valve closing, poor fuel atomization quality, and diesel engine overload will all worsen combustion and increase exhaust temperature. When the power of the diesel engine fluctuates downward, in particular the sudden unloading load, the amount of air required in the cylinder also drops sharply. In this process, the speed of the turbocharger rotor cannot be rapidly reduced. In this way, the supercharger gas supply is â€œsurplusâ€ and surge occurs.
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