According to the filtration principle, air filters can be divided into filter type, centrifugal type, oil bath type and compound type. The air filters commonly used in engines mainly include inertial oil bath air filters, paper dry air filters, and polyurethane filter element air filters. The inertial oil bath air filter has undergone three-stage filtration: inertial filtration, oil bath filtration, and filter filtration. The latter two types of air filters are mainly filtered through the filter element. Inertia oil bath air filter has the advantages of small air intake resistance, can adapt to dusty and sandy working environment, and has long service life.