Practical testing technology of the hottest engine

Practical detection technology of engine

practical detection technology of engine is a technology that qualitatively and quantitatively analyzes the technical status and hidden trouble of engine according to the comparison and change trend of some indicators of engine under normal and abnormal conditions, so as to provide scientific basis for fault diagnosis and decision-making. This technology can be used to determine the timing and means of engine repair, so as to achieve the most economical use cost in its life cycle

with the development of science and technology, modern diesel engines have adopted more electronic control technology, information sensing technology, automatic fault monitoring technology and automatic working condition selection technology

however, at present, the backward means of analyzing the technical status, fault judgment and maintenance methods of the engine, which were used decades ago, are still used. At least, the maintenance opportunity is delayed, and at worst, malignant damage occurs

in order to meet the needs of modern diesel engine use and maintenance, it is necessary to strengthen the monitoring of fault incubation period based on detection and diagnosis technology, and realize targeted maintenance under condition monitoring

I. application status of engine detection and diagnosis technology

1 There is a lack of communication between the development of detection and diagnosis technology and users

since the 1980s, China has continuously researched and developed engine detection and diagnosis technology, but due to the lack of inheritance of craftsmanship, the lack of participation of users and maintenance personnel, and the lack of understanding of the real application of the engine, the detection and diagnosis technology is disconnected from the actual application. Therefore, some seemingly advanced testing equipment and instruments are difficult to find users for the time being because they cannot directly determine the nature and location of the fault and evaluate the technical status of the engine, which is still a big gap from the requirements of simple application, strong pertinence and good repeatability

2. There are some problems in the application of engine detection and diagnosis technology

some units blindly purchase detection equipment and instruments, even for the sake of coveting the world, decorating the facade, and meeting the acceptance of the superior, when they are still preoccupied with the specific problems to be solved, and lack in-depth understanding and analysis of the use and performance needs of detection and diagnosis equipment, as well as the technical level of use and maintenance personnel, As a result, a large number of testing equipment and instruments are idle. This fully reflects the wrong understanding and practice of some enterprise leaders on this issue

3. Lack of promotion and communication on the application of detection and diagnosis technology

for decades, the promotion and application of detection and diagnosis technology has been uneven among enterprises, some started early, and some are still in the exploration stage. If the industry can often organize some experience exchange activities, or carry out some academic activities and on-site observation of detection and diagnosis technology, it will increase the promotion and application of this technology, and also promote the research and development of detection equipment and instruments

II. Common practical engine detection and diagnosis methods

1 Diagnosis of abnormal sound of moving parts

all moving parts of the engine are installed on one body, and the abnormal sound caused by the vibration of each moving part interferes with each other, affecting the diagnosis of abnormal sound of local components. At present, the effective method is to measure and analyze it by using the vibration frequency adjustable I stethoscope

2. Detection of deterioration trend of engine performance indicators with the continuous wear and tear of the engine, its performance indicators continue to deteriorate. Before it reaches the level of shutdown and repair, some performance indicators of the engine should be regularly detected, and early predictive maintenance and repair should be decided according to the change trend of the indicators

at present, there are several mature performance index test methods:

(1) no-load dynamometer

generally, the domestic no-load acceleration dynamometer is used to accelerate the engine from medium and low speed (generally at 1000 R/min) to the rated speed, and the measured power value is not less than 80% of the rated power as the use standard

(2) measurement of speed

use the measured values of maximum idle speed, speed at rated power and speed at maximum torque to compare LB with its corresponding calibration value, and take not less than 90% of the calibration value as the use standard

the evaluation method of economic performance is that when the measured value of fuel and lubricating oil consumption does not exceed 10% of the specified value of the manufacturer, it can still be used

(3) detection and analysis of wear degree of engine running parts

at present, the more mature method is ferrography analysis, which observes the changes in the number, size, morphology, concentration and color of metal particles in lubricating oil through ferrography, so as to determine their wear parts, properties and degrees. It provides an effective basis for engine wear analysis

in addition to the above commonly used detection methods, there are many mature single test technologies. For example, the testing of engine sealing, cylinder pressure and its balance, crankcase blowby, exhaust emissions, and fuel supply system and starting system are simple and effective means

III. actual detection and diagnosis of engine faults

1 Detect and diagnose the symptoms according to the procedure

① find out the fault phenomenon

② analyze the mechanism of the fault and list the fault causes in the form of fault tree

② formulate the detection procedure according to the failure mechanism analysis

④ analyze the test data to determine the fault location

⑤ propose a repair plan

2. Application of practical engine detection and diagnosis technology

if the engine power is insufficient, there are many influencing factors. In addition to the factors of improper adjustment, through the analysis of the fault, it is known that the main reason is the decline of sealing performance caused by wear. The detection and diagnosis procedures and methods are as follows:

(1) measure the power and formulate its minimum service limit

measure the effective power of the engine with the no-load acceleration dynamometer method. If the measured value is less than 80% of the rated power, it is considered as insufficient power, and then measure the sealing performance of the engine to find out the cause of insufficient power

the tightness of the engine is analyzed by measuring the cylinder pressure, cylinder leakage and crankcase blowby

(2) measure the cylinder pressure

the method of measurement is to remove the fuel injectors of each cylinder after the engine operates to the normal operating temperature, and use the cylinder pressure gauge to measure the pressure of each cylinder at the starting speed. After the measurement, reinstall the fuel injectors. When the measured value is 5% lower than the specified value or the pressure difference of each cylinder reaches 5% 8%, it is considered that the cylinder pressure is insufficient. Then, do the test of cylinder leakage and crankcase blowby to find out the cause of insufficient cylinder pressure. (3) Measurement of cylinder leakage

the test method is to place the inlet and exhaust valves of the tested cylinder at the top dead center of the compression stroke under the static state of the engine, inflate the cylinder continuously with a pressure of 0.8MPa, and use the cylinder leakage tester to determine whether its pressure can reach the specified value. If the pressure value is lower than 0.25MPa, it is considered that the air leakage of the cylinder exceeds the standard. At the same time, the sound of air leakage in the intake pipe or exhaust pipe and crankcase will be heard, so the air leakage position of the cylinder can be determined

(4) determination of crankcase blowby

if the measured air leakage of the cylinder exceeds the standard, the crankcase blowby test should be carried out to determine the specific parts that cause the excessive air leakage. Crankcase blowby tester can be divided into two types: pressure type small watch and even the part spring and displacement type of a product. The test conditions, methods and steps of both are the same. Place the tester at the exhaust vent of crankcase. When the engine runs to normal operating temperature and the rotating speed is 1000r/min, use pressure type or volume type tester to detect. The qualified standards of blowby are not more than 4kPa or 40L respectively. If this standard is exceeded, it can be determined that the leakage and pressure reduction are caused by the severe wear of piston rings, pistons and cylinder walls since they were first used in the metal field by the universal material testing machine; Otherwise, it is air leakage and pressure reduction caused by lax sealing of inlet and exhaust valves

after the above tests, the main cause of power reduction caused by insufficient pressure can be basically found out. If the test results meet the requirements and the power is still insufficient, the fuel supply system should be tested

(5) measurement of fuel supply advance angle and its variation at high and low speeds

the detection of fuel supply advance angle of diesel engine is carried out under the dynamic condition of the engine, and the supporting material manufacturers and downstream users jointly establish a batch of production and utilization demonstration platform. The change of fuel supply advance angle at low or high speed of the engine shall meet the following requirements: the change of fuel supply advance angle of the engine with and without fuel supply advance shall not be greater than 12 respectively. And 6. (relative to the crankshaft angle), if the limit value is exceeded, it indicates that the plunger, outlet valve or injector of the fuel high-pressure pump has been seriously worn, which will lead to combustion deterioration and power reduction

(6) ferrography analysis of engine lubricating oil

ferrography analysis technology is simple and low-cost, and the analysis time of each oil sample is not more than 20min. The wear condition of engine cylinder liner, piston ring, connecting rod bearing and main bearing can be determined by ferrography analysis

based on the results of the above detection and diagnosis and oil sample analysis, we can basically master the technical status and fault location of the engine