We all know that diesel engines require efficient mixing of air and diesel to achieve power. If the inhaled air contains dust and impurities, it will directly affect the combustion efficiency of the engine, and even exacerbate the wear of components, leading to the phenomenon of engine "cylinder pulling". So there has been an air filter. Today, I will introduce the structure of the air filter to you and give you a hint for future drivers when choosing an air filter.
Air filters are generally installed in front of the engine intake pipe, and truck air filters are divided into dry and wet types based on the operating environment.
A dry air filter is a filter element (such as a paper filter element) that separates impurities from the air. The filtering material is filter paper or non-woven fabric. The end cover of the filter element is made of metal or polyurethane, and the outer shell material is metal or plastic. At the rated air volume flow rate, the original filtration efficiency of the filter element should not be less than 99.5%. Due to the harsh working environment of heavy-duty vehicles, their air filters must be multi-stage.
The first stage is a swirling pre filter (such as blade rings, swirling tubes, etc.) used to filter out coarse particle impurities, with a filtration efficiency of over 80%. The second stage of fine filtration is a microporous paper filter element (commonly referred to as the main filter element), with a filtration efficiency of over 99.5%. After the main filter element, there is also a safety filter element, which is used to prevent dust from entering the engine when installing and replacing the main filter element, or when the main filter element is accidentally damaged. The materials used for safety cores are mostly non-woven fabrics, and some also use filter paper.
Wet air filters also include two types: oil immersed and oil bath. The oil immersed type is a filter element that has been immersed in oil to separate impurities from the air. The filter element material includes metal wire fabric and foam material.
The oil bath type is to introduce the inhaled dust containing air into the oil pool to remove most of the dust, and then further filter it when the air with oil mist flows upwards through a metal wire wound filter element. The oil droplets and trapped dust return to the oil pool together.
The filtration efficiency of paper filter cartridges is over 99.5%, while the filtration efficiency of oil bath filters is 95-96% under normal conditions.
When the engine is running, the intake air is intermittent, causing air vibration inside the air filter housing. If the air pressure fluctuates too much, it can sometimes affect the engine's intake air. In addition, this will also increase the intake noise. In order to suppress intake noise, the volume of the air filter housing can be increased, and some even have partitions arranged in it to reduce resonance.