The air filter is an important component in the intake system of a car engine. 

The following is a detailed introduction:

Function

• Protect the engine: filter out dust, sand and other impurities in the air to prevent them from entering the engine cylinder, 

reduce the wear of parts such as pistons, cylinders, valves, avoid serious faults such as "cylinder pulling" and "cylinder explosion", 

and extend the service life of the engine.

• Ensure combustion efficiency: provide clean air for the engine, so that the fuel and air are fully and evenly mixed, ensure normal 

combustion of the engine, improve fuel economy, and reduce exhaust emissions.

• Stabilize engine performance: ensure that the amount of air entering the engine is stable, so that the engine's intake system 

maintains normal pressure and flow, which helps to stabilize the engine's power output and improve its performance.

Classification

• According to the filtering principle: it can be divided into inertial type, filter type, oil bath type and composite type. The inertial type 

uses the inertial effect of the airflow to separate large particles of impurities under the action of centrifugal force or inertial force; the 

filtration type allows air to pass through filter paper, non-woven fabrics and other filter materials to intercept impurities on the surface 

of the filter material; the oil bath type allows air to pass through the oil pool first, allowing dust and other impurities to be adsorbed by the oil, 

and then further filtered through the filter element.

• According to the material of the filter element: there are microporous filter paper filter elements, non-woven filter elements, fiber filter elements, 

polyurethane filter elements, composite filter materials, etc. Microporous filter paper filter elements have high filtration efficiency, simple structure, 

and wide application; non-woven filter elements can adjust the thickness according to needs, but the aperture design is more difficult; fiber filter 

elements have high filtration efficiency, slow resistance growth, and strong ash storage capacity; polyurethane filter elements have strong adsorption 

capacity, but low mechanical strength.

• According to dry and wet types: mainly divided into dry and wet types. The filter element of the dry air filter is mostly made of filter 

paper or non-woven fabric. It has the advantages of high filtration efficiency, light weight, low cost, and easy maintenance. It is the most 

commonly used type in cars at present. The filter element of the wet air filter is usually made of sponge-like polyurethane and other materials. 

It needs to be immersed in oil. It has the characteristics of small intake resistance, adaptability to dusty environment, and long service life. 

However, the filtration efficiency is relatively low and the maintenance is more complicated.

Structure

It is mainly composed of intake duct, filter cover, filter housing and filter element. The intake duct is responsible for guiding the air into the filter; 

the filter cover and housing provide protection and support for the filter element; the filter element is the core filtering component and undertakes 

the main task of gas filtration.

Working principle

• Dry inertial air filter: Using the suction force generated by the cylinder intake, the external air enters the filter at high speed under the 

action of pressure difference, and the larger dust is thrown into the dust cup to complete the initial filtration.

• Wet inertial air filter: After the air enters, it falls along the center tube at high speed to the oil level of the oil pool, and the change in the direction 

of movement causes rotation. The larger dust is stuck in the oil due to inertia, and air filtration is achieved.

• Dry filter air filter: When the air passes through the paper filter element, the dust is separated by the filter element or adheres to the filter element, 

thereby being purified.

• Wet filter air filter: After the gas is filtered through the oil bath, it passes through the metal filter soaked in the engine oil. The fine dust particles 

are blocked and fall with the oil, further improving the filtering effect.

Maintenance

Generally, the replacement cycle of the car air filter is 10,000 to 15,000 kilometers, but if the car is often driven in a heavily polluted area, 

it is recommended to replace it in advance 5,000 to 10,000 kilometers. In case of mild pollution, the dry filter element can be blown clean from 

the inside to the outside with compressed air, or the end face of the filter element can be tapped to shake off the dust; if the wet filter element 

is contaminated, it can be cleaned with cleaning oil, and it needs to be replaced if it is severely contaminated.