The filtering methods are different.

When the internal combustion engine is working, if the inhaled air contains dust and other impurities, it will increase the wear of parts and reduce the service life of the engine, so an air filter must be installed. The air filter is a device that filters and removes particulate impurities in the air. It consists of a filter element and a housing. Most of the original air filters are dry and made of paper. In order to increase the filtering area, the filter element is also processed into many wrinkles.

The ash filter is a device that is matched with the carbon canister. Its function is to block dust from the carbon canister and prevent the carbon canister from being blocked. For example, the ash filter of Citroen C4 Sega is installed at the root of the right rear wheel shock absorber and above the wheel arch, and the shape is a tapered thing. Since the early Sega had no ash filter, it was easy for the carbon canister to become clogged, severely flatten the fuel tank, and crush the fuel pump and fuel pipes.