The air filter is designed to protect the engine from direct contamination by external pollutants. An engine’s air intake is between 200 and 500 m3 of air per hour, depending on its cubic capacity. The absorbed air is full of impurities depending on climate, ground surface, level of atmospheric pollution etc… In addition there is dust which, if mixed into the engine oil, eventually becomes an abrasive paste, lethal to the engine.
What does it do?
The engine air filter could be compared to the automobile’s lungs. It is designed to eliminate the dust contained in the ambient air taken in by the engine. Simplistically an internal combustion engine functions by drawing in air to be mixed with fuel in the right proportions and at the right instant this mixture is ignited providing the power to drive the engine, vehicle or equipment attached. The air is drawn in from the atmosphere that contains abrasive dirt and sooty exhaust particles. If not filtered these particles will cause rapid wear on internal engine components and ultimately considerably shorten engine life. It takes a very small amount of road dust to ruin an engine, only a cupful, approx. 220 grams would do the job. As a rough measure, for every gallon of fuel burned in the combustion process 10 to 12,000 liters of air are consumed. This gives an idea of the magnitude of the job to be done by the air filter or air cleaner as it is sometimes called.
Although the principal reason for the air filter is to reduce intake of harmful and contaminant (abrasive dust, airborne exhaust soot, etc.) it often has other roles. In nearly all cases a properly designed air filter housing not only carries the filtration cartridge but by careful design of the intake system can reduce intake noise, which is considerable. Air filter housings also play a large part in reducing water ingress, which can cause considerable engine damage, by allowing the designer to place the air intake at the most advantageous position.
In heavy duty commercial vehicles in particular air filter housings are designed to cause precipitation of excess water prior to the air stream arriving at the filtering element.
Another role of the air filter is to provide a carrier for air intake temperature control sensors and diverted valves, particularly important in controlling emissions as well as assisting in optimizing combustion efficiency. As part of the air intake system on a car, for example, the air filter and in particular the intake tube can often be tuned to minimize power loss. If the air filter is dirty, three things can happen, all of them bad: reduced engine power (a key to peak engine performance is the flow of clean air to the ignition point), decreased throttle response and increased engine wear.