Air Filters and Internal Combustion Engine Air Filters (2)

Pleated paper elements are pretty much the only choice for car engine air filters because they are efficient, easy to repair and cost-effective.The word "paper" is a bit misleading as filter media is very different from paper used for writing or packaging etc.There has been a belief among tuners that paper filters flow poorly and limit engine performance, fueled by aftermarket ads for non-paper alternative filters.In fact, as long as the pleated paper filter is sized for the volume of airflow encountered in a particular application, such a filter will only negligibly restrict flow until the filter becomes severely clogged with dust.Construction equipment engines also use it.The reason is that the paper is bent into a jagged shape, and the total area of the paper is large, within the range of 50 times the air outlet.

Foam  

Oil-wet polyurethane foam elements are used in some aftermarket replacement car air filters.In the past,foam was widely used in air filters on small engines for lawn mowers and other power equipment,but automotive-style paper elements have largely replaced oil-wet foam in these applications.Foam filters are still commonly used in air compressors for air tools up to 5 hp (3.7 kW).Depending on the grade and thickness of the foam used,oil-wet foam filters can offer minimal airflow restriction or very high dirt-holding capacity,the latter characteristic making foam filters a popular choice in off-road,rally and other motorsport applications where dust is encountered.Due to the way the foam filter traps dust,it is possible to trap a large amount of dust with no measurable change in airflow restriction.

Cotton

An increasing number of aftermarket automotive air filters are marketed as high performance products using oiled cotton gauze.In the past,gauze had limited use in original car air filters.However, since the introduction of the Abarth SS version, the Fiat subsidiary offers cotton yarn air filters as OE filters.

Stainless steel

Stainless steel mesh is another example of a media that allows more air to pass through. Stainless steel mesh has different meshes, providing different filtration standards. In an extremely modified engine, where there is not enough room for a conical air filter,some people will choose to install a simple stainless steel mesh over the turbo to ensure that no particles enter the engine through the turbo.

Oil bath

Oil bath air cleaners consist of a sump containing the oil sump and an insert filled with fiber, mesh,foam or other coarse filter media. The cleaner removes particles by adhering them to oil-soaked filter media rather than traditional filtration,with openings in the filter media that are much larger than the particles being filtered.When the cleaner is assembled,the media containment body of the insert is positioned a short distance above the sump surface.The edge of the insert overlaps the edge of the sump.This arrangement creates a labyrinthine path through which the air must make a series of U-turns: up through the gap between the edge of the insert and the sump, and down through the gap between the outer and inner walls of the insert into the sump , and up through the filter media in the insert body.This U-turn moves air at high velocity across the sump surface.Larger, heavier dust and dirt particles in the air are unable to turn due to inertia,so they fall into the oil and settle to the bottom of the bowl.Lighter and smaller particles adhere to the filter media in the insert,wetted by oil droplets drawn into it by normal airflow.The oil is continuously sucked onto the filter media,slowly sending most of the finer particles down, the oil drips back into the tank where the particles accumulate.Oil bath air filters were used extensively in automotive and small engine applications until paper filters became widely adopted in the industry in the early 1960's. This type of cleaner is still used on off-road equipment that encounters very high levels of dust, as oil bath air cleaners can isolate large amounts of dirt relative to their overall size without loss of filtration efficiency or airflow.However, liquid oil makes cleaning and servicing of such air filters cumbersome and inconvenient, they must be relatively large to avoid over-restriction at high airflow rates, and when used for spark ignition they tend to fail due to oil absorption Engines that increase exhaust emissions of unburned hydrocarbons.

Water bath

In the early 20th century (approximately 1900 to 1930), water bath air cleaners were used in certain applications (cars,trucks, tractors, and portable and stationary engines).They work in much the same way as oil bath air cleaners.For example, the original Fortson tractor had a water bath air cleaner.By the 1940s, oil bath designs replaced water bath designs due to better filtration.

Bulk solids handling filters

Bulk solids handling involves the transport of solids, possibly in powder form (mechanical, pneumatic).Many industries deal with bulk solids (mining,chemical industry, food industry) and for regulatory reasons or economic reasons (loss of material) the gas stream escaping from the process needs to be treated to avoid the emission of fine particles.Air filters are therefore located at many points in the process,especially at the reception of the pneumatic conveying line,where the air volume is important and so is the fine particle load.Filters can also be placed at any point of air exchange in the process to avoid contamination entering the process, this is especially true in the pharmaceutical and food industries.The physics involved in the capture of particles by the filter are mainly inertial and diffusive