Air Filter │Engine Air Filter

Air filter or Engine intake air filter is less known among the student & engineers or even technicians. But it is an important component for the design engineer because the burning of fuel inside a cylinder during the combustion process needs an ample amount of Air. Not only air but a clean air free from dust, abrasive particles.

What does an Air filter do in Car-Bike?

Air Filter removes dust, abrasive particles that might enter into the engine cylinder through an inlet. This prevents the engine from getting damage and maintains an ample amount of air required by the engine.

Why Air Filter is Important in Car?

Suppose you are driving a Bike or Car without an air filter installed an inlet line. A car or bike without an air filter loses its performance and efficiency. What will happen next, small particles of dust start entering into cylinder and engine start filling with this particle. And damage the engine, it is inexpensive to replace Air filter instead of an expensive engine.

How does Air filter work?

Air filter made of cellulose, pleated paper, foam, or even steel wired depending upon requirements. These structures have very small pores (in microns) Air needs to pass through these pores before entering into the manifold. If the size of dust particles larger then these pores it does not get through and trapped inside it.

Air Filter and Fibers

Mechanism of Air Filtration 

There are different types of filtration mechanisms but for Air filtration most applicable is ''Interception''. In which dust particle is allowed to pass over filter fibers then get attached to it, finally, they trapped inside the filter.
Other Filtration Mechanism with pictorial representation
Here dust particle (in red) inside air (blue line) get attached and trapped inside filter fibers (Green) as they try to pass over.

(a) Diffusion  (b) Interception (c) Inertial (d) Sieving Air filtration Process

Air Filtration Mechanism 

What are the common shape and sizes of Air filters?

Three shapes are very common to see 

  1. Square Panel Box type: Automobile with Fuel Injection technology is fitted with this type of Air filter assembly in which Air filter cartage fitted inside a square box. Placed in plastic or metal box connected to throttle body allows air to pass over it.
  2. Cylindrical: a vehicle with a carburetor or throttle body injection uses a cylindrical air filter of size 100mm to 400mm.
  3. Conical: Heavy-duty diesel truck generally uses this shape air filter, its opening is large compared to its closing. 

Air Filter Material or Media

This depends upon different parameters like

  1. Filtration capacity (CFM Cubic Foot/Minute )
  2. Operational condition (kPa, ℃)
  3. Shape-size (Square, Cylindrical, Conical)
  4. Durability and Cost factor (Time period, application )

Type of Material Used for Making Air filter

  1. Pleated Paper (Engine Air filters)
  2. Cotton fibers (Aftermarket or High-performance Cars)
  3. Foam or Polyurethane (Modified Car-Bikes)
  4. Stainless Steel Wire Mesh (Harsh surrounding conditions)
  5. NanoParticle 

Generally, Car & Bike has equipped with a pleated paper filter and Oil bath foam filter.
Pleated paper filter made fiber which is a high efficiency, easy to service, and low cost. And the most common thing is you can find this in your Bike and Car.

Why does Air Filter have Oil on it?

Oil Wetted or sump type polyurethane air filter most commonly found in Off-road Car, Bike, Trucks where the chance of having large size dust, abrasive particle in the air compared to normal conditions.
Oil wetted foam filter mostly used by after-market replaceable Car, Trucks. 
These air filters can offer minimum air restriction with high dirt capacity with a self-cleaning property which makes it most suitable in an off-road rally race.

The filter is also available with Vibration, Flame, Chemical resistance.

What is the different size of the Air filter?

Air filter categorized based on what size of particle allows to pass through them without getting trapped.
  • Coarse Air filter removes particle size of 5µm
  • Fine Air filter restrict particle size up to 1µm
  • Ultra-Low Particulate Air filter restrict particle up to 0.3µm
  • High-Efficiency Particle Air filter restrict particle 0.1µm

How does often change Air Filter?

Most of the time people are confused that what is a suitable time to change the vehicle air filter?

There few points on which Air filter replacement depends.

  1. How much Km or Miles cover by vehicle (10000km or 6213mile)
  2. Surrounding driving conditions (Dusty, off-road)
  3. Time Period 

The air filter is inexpensive components so if you go for service after four or five months, I would recommend getting air filter replaced. This will not only increase performance also prevent engine damage. 
Note:- Follow your Car or Bike manuals for the best advice 

What are the symptoms of Bad Air Filter?

Air is a mixture of different gas (Oxygen), but what we are looking for here is the Oxygen contains. Oxygen is important for the burning of fuel inside the engine cylinder, more air means more oxygen molecules available for combustion to occur. But Air needs to be clean, free from dust particles, for that need efficient and reliable air filter. If Air filter not working properly you might found the following symptoms in your Car or Bike.

  • Poor Acceleration
  • Misfiring 
  • Difficult to maintain Idle condition
  • Low performance 
  • Low efficiency 

Why would an Engine Air Filter collapse or damage?

Yes, you would hear or seen Engine filter choked with dust particle but less heard of the collapsed filter. Because engine air filter are design to operate more than two or three from its normal limit.
There is some heavy-duty diesel engine that was found with a collapse Air filter.
Collapse to air filter means permanent deformation of cartridge for airflow recovered. This will happen only if the pressure drop reaches the maximum limit or design limit of the air filter.

A further reason for filter damaged 

  • Water Entered inside Filter Assembly 
  • Improper Installation of Filter
  • Quality Concern

Why would you service or clean the Air Filter?

Most of Car comes with front-engine,by opening the bonnet and lifting the cover you can easily locate Air filter, you need to follow the engine air intake path away from the engine.
Using a specified solvent, vacuum cleaner, you can easily clean the filter and remove the dust.

Timely servicing will result in maximum engine protection against dust particles and maintain an undisturbed flow of air to the engine.

Proper servicing can save you time and money by improving filter life and performance. And servicing is not expensive so it can be done on a monthly basis under OEMs guidelines.

Not servicing from a long period than soon after the maximum restriction is reached causing a high level of pressure drop across the filter, which could result in permanent damage to the air filter.

How to prevent Air Filter from getting damage or collapsed?

The most efficient and effective way to monitor Air filter conditions is to install restriction measuring devices. This could be mount on the intake duct, air cleaner outlet tube. Based on restriction reading changing filters can minimize maintenance costs drastically.

What could be minimum and Maximum price of Air Filter?

It depends upon the type, size, quality of Air filter. It is easily available at any Car- Bike service center or even online.
For Cars, price start from 300-2000/unit or $5-$30.

For Bikes, price start from 150-800/unit or $3-$10

Air Filtration Measurement: Filtration measured in Cubic Foot per minute(CFM), means how much air coming and filtered at the same time?

 CFM= [(Length x Width x Height ) x (Air Change/Hour)]/60

''Some Specified Terms''

Rated Air Flow It is the maximum airflow required by the engine and set by OEMs.

Flow Requirements:  It depends upon the type of engine if it has turbocharged (TC) or Naturally aspirated (NA) and engine horsepower.

Duct Capacity : The amount of contamination that will be collected on the filter before a specified restricted level reach.


Keep checking your vehicle or engine air filter timely, before it cause permanent damage. It is very easy to spot bad air filter just by physically checking it or realizing by vehicle performance, efficiency.  The air filter is an inexpensive part and easy to replace. There are lots of filter manufacturers available in the market but you need to choose wisely or follow the guide of vehicle manufacturers. Air filter directly affects vehicle performance, efficiency, and prevents engine form any potential damage. 

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