Engine is the most important assembly of the vehicle, it provides power for the vehicle, the performance of the engine directly affects the performance of the vehicle. The role of the intake system is to provide the engine with clean, dry air at the right temperature with low flow resistance to ensure that the engine can play a good performance. The air filter is a key component of the intake system, so the air filter should reduce the dust concentration to an acceptable level, remove large particles, reduce engine noise, reduce airflow obstruction as much as possible, and meet the requirements of the engine.
A well-matched air filter can extend engine life, improve engine performance and reduce engine wear. Engines with a good filtration system last longer and burn better. In addition, energy consumption and exhaust emissions are reduced.

1. Air filter classification
In general, there are two types of air filters, namely wet air filters (oil bath type) and dry air filters (paper air filters). Oil bath air filters can be divided into light load type and medium load type, and dry air filters are classified into light load type, medium load type, heavy load type, overweight load type and long life overweight load type.

2. Working principle of air filter
The filtration principle of the oil bath air filter: filter the incoming air through a continuous oil bath process. It is generally built one to two wire wound into the filter element, and placed under an oil pool, the air sucked into the filter is straight down to the oil pool, after hitting the oil, the direction of the air flow completely changed, the opposite direction travel. During this sudden change in flow direction, most of the impurities in the intake air are carried to the oil pool by inertia, and are adhered to and precipitated to the bottom of the oil pool. As air strikes the oil tank, oil droplets appear in the air inside the filter, and the remaining ash particles are collected into these oil droplets. The oil droplets then adhere to the gap in the wire, while clean air flows out through the top of the filter, and the separated oil droplets return to the oil pool.
The filtration principle of dry air filter: The use of a dense screen composed of filter medium fibers to screen dust particles in the air, and of course, there are filtration methods such as choke flow, collision, Brown motion, etc., to filter dust. It can be assembled with a safety filter element and various forms of optional coarse filters to achieve a higher ash content and extend the maintenance cycle of the air filter.

3. Selection of air filter
The principle of air filter selection is to meet the engine performance is given full play, the intake resistance is small, the filtration efficiency is high, usually to consider the influence of three indicators: rated air flow, intake resistance and filtration efficiency, so that the air filter is optimized.
The performance and quality of the air filter will directly affect the main performance and service life of the engine. Therefore, whether from the design, manufacturing or use, maintenance, should pay more attention to air filters.