A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds or ozone. Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines.
Some buildings, as well as aircraft and other man-made environments (e.g., satellites and space shuttles) use foam, pleated paper, or spun fiberglass filter elements. Another method, air ionizer, use fibers or elements with a static electric charge, which attract dust particles. The air intakes of internal combustion engines and compressors tend to use either paper, foam, or cotton filters. Oil bath filters have fallen out of favor. The technology of air intake filters of gas turbines has improved significantly in recent years, due to improvements in the aerodynamics and fluid-dynamics of the air-compressor part of the Gas Turbines.
The objective of air filters is the capture of solid particles such as mineral dust, soot and organic debris suspended in sucked in the engine. Thanks to advances in the design of filters and filter materials used in the current produced by the air filters achieve effective filtering contaminants at 99.9% for particles as small as several microns. Taking into account the fact that internal combustion engines consume in the combustion process a huge amount of air (an average of approx. 10m3 of air per 1 liter of fuel), the filters at such a high efficiency filter should nevertheless be characterized by a low flow resistance, and high absorption capacity with respect to contamination. Thanks to these qualities, you can extend the intervals between filter replacements.