No matter how good the quality of a diesel engine is in terms of design, manufacturing and assembly processes, after a certain working time, its parts will inevitably have a kind of normal wear, or various failures will occur due to improper use and maintenance. Decreased engine power, uneven speed, increased fuel consumption, exhaust (black, blue, white) smoke, difficulty in starting, and abnormal noises. If the engine has a fault, it must be checked and eliminated in time. If we do not pay attention to observing and judging the various faults that occur during the operation of the diesel engine in our daily life, and do not take necessary technical measures in time, we may cause serious mechanical accidents due to small losses, and even make the diesel engine unrepairable. and use. Therefore, we must clarify the fault phenomenon in a timely and accurate manner, and provide sufficient objective materials and basis for analyzing the cause and troubleshooting. Correctly judging the fault phenomenon is the key to successfully troubleshooting the diesel engine.
We often hear such words: yellow and thin people are sick, the sky is cloudy and it will rain, and the auspicious snow heralds a good year. Sallow complexion is a sign of illness, cloudy sky is a sign of rain, auspicious snow is a symbol of good harvest. Diesel engine failure is no exception, and there are symptoms, which is what we usually call failure phenomena.
Fault phenomenon is the performance of certain fault causes under certain working conditions. When a diesel engine breaks down, it often shows one or several unique failure phenomena. Different working conditions, the fault phenomenon will be different. These fault phenomena are generally audible, olfactory, visible, palpable or measurable. It can be summed up in the following points.
- Abnormal functions such as the generator set is not easy to start, does not carry the load (that is, decelerates or stops after adding the load), the speed and frequency are abnormal, the fuel or engine oil consumption is too large, the voltage fluctuates up and down or the voltage disappears, and the generator set vibrates violently wait.
- Abnormal sound such as abnormal knocking sound, blasting sound, whistle sound, exhaust sound, periodic friction sound, pin sound, valve foot sound, gear sound, and unstable speed (cruising car) sound, etc.
- Abnormal Temperature The normal operating temperature of diesel generators is around 85°C. Abnormal temperature mainly refers to excessively high engine oil temperature, excessively high cooling water temperature, overheated bearings, and excessively large temperature differences among exhaust manifolds.
- Abnormal appearance mainly refers to abnormal smoke exhaust (white smoke, blue smoke, black smoke), “three leaks” (oil leak, water leak, air leak) and electric leakage (flickering sparks), etc.
- Abnormal smell such as odor, burnt smell, exhaust gas with diesel or incomplete combustion of oil, etc. The above are several abnormal phenomena that are common in diesel generator failures. They are often related to each other. Sometimes one failure may cause several failure phenomena, and it is also possible that one failure phenomenon is caused by several failures at the same time. Therefore, if the situation permits, various means should be used to clarify the fault phenomenon from all aspects as much as possible, so as to judge the cause of the fault in a timely and accurate manner.
Principles and methods of analyzing and judging faults
In order to quickly and accurately eliminate engine faults, do not disassemble the engine before the cause of the fault is clarified. The general principles for analyzing and judging engine failures are: combining the structure and connecting the principle; clarifying the phenomenon and connecting it with reality.
Disassembly should be minimized when analyzing failures. Blind disassembly, or easy disassembly due to confusion and luck, will not only prolong the time of troubleshooting and delay use, but may also cause undue damage or cause new failures. Disassembly should only be used as a last resort after careful analysis.
Generally, after the possible causes of the failure are preliminarily clarified through comprehensive inspection and careful analysis, start from the main aspects of the cause of the failure and gradually narrow down the scope (or location) of the failure in order to quickly and accurately eliminate the failure. Therefore, this step is the key to the whole process of troubleshooting. In the long-term practice, the majority of users and maintenance personnel have accumulated and created many effective, simple and practical methods for judging and troubleshooting. Some main methods are introduced below.
- Isolation method In the process of failure analysis, it is often necessary to stop or isolate the work of a certain part or system intermittently, so as to observe the change of the failure phenomenon, or make the failure phenomenon more obvious, so as to judge the faulty part or machine. When analyzing diesel engine faults, the commonly used cylinder stop method is a kind of isolation method, that is, to stop the oil supply to a certain cylinder of the multi-cylinder engine in order to check the cylinder, or to distinguish the fault according to the change of the fault phenomenon. Local or universal. For example, it is found that the exhaust is intermittently smoking, and the fault phenomenon disappears after stopping the work of a certain cylinder, which indicates that the fault is located in this cylinder, and further analysis should be done to find the cause of the fault in this cylinder; If there is no obvious change in the phenomenon, it indicates that the failure is not a failure of individual cylinders, and the cause that affects the work of each cylinder should be found. When analyzing electrical equipment faults, sometimes the isolation method can also be used to temporarily isolate a certain part from the circuit to determine the fault location.
- Comparison method When analyzing failures, if there is any doubt about a certain part, the comparison method can be used to replace the part with a spare part or exchange it with the same part. According to the change of the fault phenomenon, it is judged whether the component is faulty, or the location of the fault is determined.
- The verification method uses tentative disassembly and adjustment measures to observe the change of the fault phenomenon for some faulty parts or parts of the diesel engine, so as to verify whether the conclusion of the fault analysis is in line with the reality, or as a compensation due to lack of experience, it is impossible to determine the fault location. frequently used method. When abnormal phenomena caused by several different reasons appear at the same time, or the cause of the failure is related to improper adjustment, it is often difficult to distinguish the cause of the failure. In this case, using the verification method can also receive better results. For example, if you suspect that the cylinder liner is severely worn, which is caused by poor compression of a certain cylinder, you can pour a little oil (about 4-5g) into the cylinder. If the compression force increases, the suspicion is true. Another example is black smoke from a diesel engine, and it is suspected that the fuel supply is too large, and the fuel supply can also be tentatively reduced to verify whether the suspicion is true. When adopting tentative measures, the principle of “less dismantling” should be followed, and random disassembly of the assembly should be avoided. Whether it is a tentative disassembly or adjustment, it should be carried out only when it is sure to return to the normal state and it is confirmed that there will be no adverse consequences. In addition, several tentative disassembly and adjustment of several parts or the same part should be avoided at the same time, so as to prevent mutual influence and cause illusion.
- Variable speed method If the diesel generator is faulty, the fault phenomenon may change at the moment of increasing or reducing the speed of the diesel generator. When we observe the fault phenomenon, we should choose the appropriate speed to make the fault phenomenon more prominent. Generally speaking, low-speed operation is often used, because the diesel generator speed is low, and the fault phenomenon lasts for a long time, which is easy to observe. For example, the valve mechanism of diesel generators causes “da da da” knocking sound due to excessive valve clearance, which can be quickly eliminated by using this method.
When analyzing and judging the faults of each system and part of the diesel engine, many specific methods can also be adopted according to their respective characteristics. For example, when looking for faults in the oil circuit of the diesel fuel supply system or the circuit of electrical equipment, it can be checked segment by segment so as to isolate the fault in the smallest possible range. During the inspection, the parts and corresponding parts that are most prone to failure should be checked first, and then other parts (parts) should be checked.
After the fault location is determined, it should be completely eliminated correctly and meticulously according to the specific situation of the fault. After the fault is eliminated, a test machine should be carried out to check the working conditions of the diesel engine to determine whether the fault has been completely eliminated.