1. The concept of suitable air filter filtration efficiency
At present, the filtration efficiency of air filter filters in various countries is the percentage of the amount of dust filtered by the air filter per unit time and the amount of dust that enters the air filter with air. This traditional concept is to use gravimetric methods to measure filtration efficiency. In essence, the size and amount of particles entering the engine directly affects the life of the engine. Small particles of dust entering the engine will not cause engine damage, and only when the dust particles reach a certain size will the engine be damaged. Therefore, it is necessary to change the original concept of filtration efficiency and cite a new concept that is suitable for filtration efficiency. The so-called suitable filtration efficiency is the minimum filtration efficiency to ensure reliable operation of the engine. Suitable filtration efficiency is the ratio of the size and number of dust particles filtered by the air filter to the size and number of dust particles entering the air filter with air.
Suitable filtration efficiency aligns the filtration capacity of the air filter with the degree of protection of the engine. The air filter can specifically control the large dust particles that affect the service life of the engine, and the small dust particles are not filtered. In this way, it is advantageous to reduce the air intake resistance of the air filter, reduce the volume, and reduce the cost.
2. Engine requirements for air filter filters
In order to fully exploit the potential of the engine, engine manufacturers have put forward many requirements for air filters, including intake resistance, filtration efficiency, service life, maintenance, size, weight and cost.
An air filter, regardless of application, is inevitably a series of compromises and concessions, but the core is filtration efficiency. Engine manufacturers often place too high demands on air filters, which are difficult for filter manufacturers to achieve. According to the concept of suitable filtration efficiency, it is now the industry's top priority to determine the appropriate engine efficiency requirements for air filters (http://), ie how much dust particles and quantities can provide reliable engine reliability. protection.
3. Internal combustion engine wear and particles
The wear of internal combustion engines is a very complicated problem. The air intake system, the lubrication system and the fuel system of the internal combustion engine are respectively equipped with an air cleaner, an oil filter and a fuel filter. The various dust particles and combustion products that are not filtered by the air filter mainly cause wear on the gas ring and the upper part of the cylinder. The metal chips that are not filtered by the oil filter, the dust particles in the large amount of air entering through the crankcase vents, and the debris entering the oil pan from the combustion chamber are mainly responsible for the wear of the oil ring and the lower part of the cylinder.
A great deal of scientific research has been done on the wear and tear of internal combustion engines.
3.1 Russia
Studies in the Russian and former Soviet military and industrial sectors have shown that the size of dust particles has a major impact on engine cylinder wear. When the size of the dust particles increases from 3 to 5 μm to 15 to 30 μm, the wear of the piston ring increases by 1 to 3 times; when the size of the dust particles exceeds 40 μm, the wear of the piston ring decreases instead, which is mainly determined by the gap between the piston ring and the cylinder. If the size is too large and the gap cannot be entered, it will not be worn.
According to the quartz powder specified in the former Soviet Union national standard гOCT8002 "Test Method for Internal Combustion Engine Air Filters", the particles were grouped to study the wear relationship between the cylinder and the piston ring of the internal combustion engine. The dust particles are divided into six groups: 0 to 4 μm, 4 to 7 μm, 7 to 10 μm, 10 to 20 μm, 20 to 40 μm, and 40 to 63 μm. The engine is subjected to wear test, and the test conditions of each test are the same, and the engine operating conditions are fixed. . The test results are shown in Figure 1.
Figure 1 Radial wear rate of engine cylinder liner caused by different sizes of quartz particles
1-0 to 4 μm, 2-4 to 7 μm, 3 to 7 to 10 μm, 4 to 10 to 20 μm, 5 to 20 to 40 μm, 6 to 40 to 63 μm
In Fig. 1, the wear rate φ is the wear value of the cylinder divided by the amount of dust added to the cylinder.
It can be seen from Fig. 1 that the cylinder wear of curves 1 and 2 is small because the particle size below 7 μm is small; the cylinder wear of curve 6 is the smallest because the particles exceeding 40 μm do not enter between the cylinder and the piston ring. . The dust particles of curves 3, 4, and 5 have a size of 7 to 40 μm, which is the most serious for cylinder wear.
Russia collected dust from road dust and coaching fields in major countries of the world, and analyzed the composition and particle distribution of dust. The particle distribution of road dust is more than 60% of particles with 10~40μm, which has the greatest impact on cylinder wear.
3.2 Japan
Japan has conducted extensive research and testing on engine wear. The relationship between the dust particle size and the wear of the piston ring cylinder is shown in Figure 2. The effect of dust particle size on wear.
Figure 2 Effect of dust particle size on wear
As can be seen from Fig. 2, dust particles of about 20 μm have the greatest wear on the internal combustion engine, and they believe that dust particles of 10 to 45 μm should be controlled to enter the internal combustion engine.
4. Gas turbine
4.1 Impact of dust on gas turbines
Unlike a piston ring engine, a gas turbine is a blade machine that causes erosion and wear of the gas turbine's compressor blades, pulleys, and the like. Gas turbines are characterized by high speed and high intake speed. Dust can block air passages, reduce heat transfer efficiency, cause power loss, overheating or loss of balance, and damage the engine.
Tests in the United States have shown that dust does not impact at 1 to 2 μm, which can cause deposition. 5 to 7 μm will cause corrosion and cause damage to the compressor. Dust particles larger than 10 μm cause impact on the surface of the compressor blade, and the damage of the 20 μm dust particles to the compressor is the most serious.
4.2 Requirements for the filtration accuracy of air filters
4.2.1 Requirements for filtration accuracy of gas turbine pulse automatic cleaning air filtration in a French company
Table 1: The accuracy of filtration precision for gas turbine pulse cleaning air cleaning in a French company
Particle size, μm
1
2
3
4
5
Filtration accuracy,%
99.62
99.85
99.995
100
100
Filtration efficiency is required: ACF 99.9%, ACC 99.99%.
From the above data, the requirements are quite demanding and the air filter is difficult to meet.
4.2.2 Gas Turbine Pulse Automatic Cleaning Air Filter Filtration Requirements for a Company in the United States
Table 2 Requirements for gas turbine pulse automatic cleaning air filtration in a US company
Particle size, μm
1
5
10
Filtration accuracy,%
95.5
97
99.9
5. Summary
According to the new concept of suitable filtration efficiency, that is, the minimum filtration efficiency that provides reliable protection for the engine, the air filter should filter out dust particles that cause damage to the engine. The key now is to determine how much filtration accuracy a particular air filter needs. It is generally believed that air filters should filter out dust particles above 6 μm without causing wear and damage to the engine. Because an air filter can only meet the needs of a certain engine, this requires the engine manufacturer and the filter manufacturer to work together. The engine manufacturer designs dust-resistant materials to reduce wear and select a suitable air inlet. Position to minimize dust entering the engine.
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