There are the following types of car air filters:
1. ** Classification according to the principle of filtration **
- ** Inertial air filter ** : The use of air flow in the sharp turn or direction of the inertial force, so that the dust particles from the air separation and settlement. Its advantages are simple structure, low cost, convenient maintenance; The disadvantage is that the filtration efficiency is relatively low, the filtration effect of fine particles is not good, often used in the case of low filtration requirements, such as some construction machinery vehicles.
- ** Filter type air filter ** : through the filter element to block and filter impurities in the air. Common paper dry air filter and polyurethane filter air filter and so on. The filter element of paper dry air filter is made of microporous filter paper treated by resin, which has the advantages of high filtration efficiency, simple structure, light weight, low cost and convenient maintenance. It is the most widely used automobile air filter. The filter element of the air filter is made of soft, porous, spongy-like polyurethane, with strong adsorption capacity, but low mechanical strength, and is widely used in car engines [^1^].
- ** Compound air filter ** : combined with the advantages of inertial and filter, the inertial force is used to initially filter out the dust of large particles, and then fine filter through the filter element, so as to improve the filtration efficiency and effect.
- ** Oil bath air filter ** : also known as oil bath filter, mainly composed of central tube and oil pool. Its working principle is that after the air enters the filter, it drops along the center tube at a high speed and heads toward the oil pool oil surface. The direction of movement suddenly changes to upward, resulting in rotational movement. At this time, a large part of the dust is stuck in the oil because of inertia, and cannot move backward with the air to complete the air filtration [^5^].
2. ** Classification by structural form **
- ** Dry air filter ** : the filter element is in a dry state and does not need to add substances such as lubricating oil. For example, the paper dry air filter belongs to the dry filter, which has the advantages of high filtration efficiency, light weight and low cost, but the working reliability is relatively poor in harsh environments [^1^].
- ** Wet air filter ** : The filter element needs to be kept wet. Oil is usually used to improve the filtration effect and prevent the filter element from clogging, such as oil bath air filter. This kind of filter has a good filtration effect and can adapt to the dusty and sandy working environment, but there are shortcomings such as large intake resistance, high cost, and inconvenient maintenance [^1^][^3^][^5^].
To sum up, there are various types of automobile air filters, and different types of air filters have their own advantages and disadvantages. It is necessary to choose reasonably according to specific needs and the use environment.