Introduction
Internal combustion engines in cars most commonly use a four-stroke cycles, such as intake, compression, combustion and exhaust. In these processes, air intake is an essential. However, if any foreign matter enters into the engine, it may be a cause of problem.
So, it is necessary that clean air must be supplied inside the engine through the filter. In case of a passenger car, if one opens the car hood, there is a round or rectangular shape of plastic box in which air filter is placed. In truck or big vehicle, size of air filter is so big that it is commonly installed outside the vehicle.

Air filter is also called the air cleaner and it must be replaced when it becomes contaminated. Unless it is being replaced properly, it may result in a cause of high fuel consumption and slow down of speed.

Due to the reason, the more frequent change of air filter will be the better maintenance of a car. For saving the cost of replacement, it may be reused after eliminating particulate matter.

Type
- First air filter was made by using paper, attached on the steel board, to filter

  out dust particles regardless of passenger car or truck. However, it is the

  current trend that passenger cars use either

- Used a paper on which soft and lightweight foam of Urethane has been applied.

  (European style)

- Used either paper or felt(composed of high grade of fibrous material) through
  the plastic injection process. Aside from theory, each car manufacturers have their

  own types and materials they prefer to use. In case of Toyota, they prefer to use

  felt material for passenger car and the Nissan prefer to use paper, respectively.

  Also it is the current trend that big vehicles use felt material and small cars use

  paper. (Japanese style)

- The utility of filter media in USA is likely to vary between paper and felt material

  depending on the man in charge of developing the filter.