The general principle of judging failures is to combine the structure, connection principle, clarify the phenomenon, connect with reality, from simple to complex, from the outside to the inside, section by system, and check and analyze.

case study:

Case study 1: failure phenomenon, diesel engine emits black smoke

The unit raised and lowered the pipe string normally during the construction process, and the load was lighter during the process of raising and lowering the pipe string. It was discovered that the engine was originally unable to be oiled and then smoked and stopped for inspection. Theoretically speaking, black smoke is caused by too much fuel injected into the combustion chamber, and combustion is carried out under extreme oxygen deficiency, resulting in incomplete combustion to form free carbon, and black smoke will appear when exhausted with exhaust gas.

Theoretically, the possible reasons for the black smoke of the diesel engine are analyzed in detail: the fuel supply system, the valve mechanism, and the diesel engine is overloaded.

① Reasons for the fuel supply system: fuel injector failure, injector oil hole blockage, poor atomization; uneven fuel supply in each cylinder or loose gear ring of the fuel injection pump, resulting in excessive fuel supply; fuel injection advance angle is too small, Injection is too late, causing part of the fuel to burn in the exhaust pipe; the fuel quality is poor. ② Reasons for the air distribution mechanism: incorrect valve clearance, poor valve sealing, leading to air leakage and poor combustion; blockage of the intake passage or blockage of the air filter, resulting in reduced intake volume; unsmooth exhaust, causing exhaust gas from the combustion chamber to be discharged Not thorough enough. ③Excessive load of diesel engine: Step by step investigation according to the cause of the fault, first check the fuel supply system, and eliminate one by one according to his actual working conditions. Then check the various parts of the valve mechanism. During the inspection, it was found that the air filter was seriously blocked. Treatment method: After replacing the filter element, smoke exhaust is normal.

Observe the engine that has just been repaired, and the result is that it emits black smoke again after 1 hour of operation; check the filter element again and find that the filter element is blocked again; after careful inspection, it is found that the exhaust pipe and the air filter are backfired. After replacing the exhaust pipe, After observing for several hours, the exhaust gas color was normal, and the problem was solved.

Case study 2: failure phenomenon, black smoke

During the normal start and stop of the engine, the engine suddenly emits black smoke, the engine is weak, and the power is insufficient. Stop and check immediately to find the cause. First, check in sequence according to the content and sequence of the previous case; after inspection, it was found that the screws of the high-pressure oil pump connecting plate were loose. The cause of the accident: The connection plate of the high-pressure fuel pump was not inspected in time, which caused the screw of the connection plate of the high-pressure fuel pump to loosen, changed the fuel injection pump advance angle, and made the fuel injection too late, causing part of the fuel to burn in the exhaust pipe and part of the fuel to burn insufficiently. The consequence of causing the engine to emit black smoke is the lack of engine power; the treatment method should adjust the fuel supply time according to the cause of the failure.

It can be seen that the diagnosis and elimination of diesel engine faults must first have a solid theoretical foundation, master the general principles of judging faults, and analyze specific problems in combination with actual conditions.