According to the principle of filtration, air filters can be divided into filter type, centrifugal type, oil bath type and composite type. Commonly used air filters in engines mainly include inertial oil bath air filters, paper dry air filters, and polyurethane filter air filters. The inertial oil-bath air filter has passed through three stages of inertial filtration, oil-bath filtration, and filter filtration. The latter two air filters are mainly filtered by filter elements. The inertial oil-bath air filter has the advantages of low air intake resistance, adaptability to dusty and sandy working environment, and long service life. It was previously used in various types of cars and tractor engines. However, this kind of air filter has low filtration efficiency, heavy weight, high cost, and inconvenient maintenance, and has been gradually eliminated in automobile engines. The filter element of the paper dry air filter is made of resin-treated microporous filter paper. The filter paper is porous, loose, and folded. It has certain mechanical strength and water resistance. It has high filtration efficiency, simple structure, light weight and cost. It has the advantages of low cost and convenient maintenance. It is the most widely used air filter for automobiles. Polyurethane filter element The filter element of the air filter is made of soft, porous, and sponge-like polyurethane with strong adsorption capacity. This air filter has the advantages of a paper dry air filter, but its mechanical strength is low. It is widely used. The disadvantages of the latter two air filters are their short service life and unreliable operation under harsh environmental conditions.
