Here is a little something from the American Separations and Filtrations Society :
How Does Air Filter Performance Affect Engine Life?
Engine wear is very complex and depends on; 1)Type of contaminants; 2) Shape of contaminants; 3) Contaminant size; 4) Contaminant concentrations ; 5) Driving conditions; 6)Engine load conditions and 7) Air filter performance. Engines have to be protected from abrasive contaminants ingested into the combustion chamber.
Wear Process
A new engine generally goes through normal wear during the break in period. Abnormal wear (abrasive wear) is associated with contaminant levels found inside the engine. Majority of the engine failures are directly related to abnormal wear. Efficient combustion and well filtered air are essential to protect engines from wear and also extend oil drain intervals [2]. Two key filtration systems for engine protection are the engine intake and the lube oil systems. There is a certain synergy between the design of oil filters and engine air filters. What penetrates through the engine air filter system also affects the lube oil filter system. A well designed engine air induction filtration system will; a) Remove and reduce abrasive contaminants; b)Reduce and control the ingested dust concentration levels within acceptable limits; c) Control and remove contaminant sizes most harmful to the engine; d)Reduce overall engine wear; e) Reduce oil contamination; f) Reduce blow-by conditions; g) Control emissions; h) Increase engine life and durability; i) Increase lube oil service interval; j) Reduce overheating of the engine; k)Smooth engine performance
Fodor [4, 5] in his study found that about 80% of all engine failures were attributed to engine wear. It is absolutely necessary to have improved filtration for air and oil filters to reduce engine wear [4]. Both, contaminant concentrations and sizes ingested by the engine are important to reduce wear and improve engine durability and life. It has been demonstrated that by using high efficiency air and oil filters, engine wear can be significantly reduced [6]. Studies have shown that engine life is a function of induction air cleanliness [7] and that cleanliness of an engine is a pre-requisite for problem free operation [7].
Wear Causing Contaminants
Airborne dust contaminants and Dirt are very abrasive in nature and the most common cause of high metal wear in engines [1, 9, 12, 13, 14 and 15]. Even small amounts of airborne contaminants can significantly increase the wear on piston rings and cylinder walls. Dirt ingested by the engine eventually ends up in the oil as silica. A study recommends maximum amount of silica or dirt in the oil should be less than 5ppm for 4 cylinder engines and less than 10ppm for 6 cylinder engines, when the engine is operated for 50hrs or 2500 miles [1]. Laboratory studies have shown that engine wear is produced by particles in the size range of 1 - 40 µm. Studies also indicate that the most harmful particle size is in the range of 1 - 20 µm [9, 10, 11, 12]. Studies have also shown that particles smaller than 1µm do not cause any significant wear, but their presence weakens the oil film [5]. Studies have shown that measuring various oil film thicknesses may indicate the different sizes of contaminants that may cause excessive wear.
Typical oil film thickness and clearances found in engines are listed in table 1. Investigations have also shown that during the power stroke or high load conditions the piston ring - cylinder wall gap could be reduced to almost zero [13,14]. This tells us that it is important and necessary to control or remove abrasive particles down to very fine sizes.
Piston skirt - cylinder wall /liner
~ 25 µm - 100 µm
oil film thickness between piston ring - cylinder wall
< 1µm - 15 µm
piston - pin bosses
~ 8 µm - 15 µm
other bearing film thickness
~ 2 µm - 22 µm
Engine air cleaners are typically designed for normal to typical driving conditions. In a dusty environment such filters may not adequately protect the engine. This causes excessive wear and irreversible damage to the engine. Fodor [4] indicated that the air cleanliness ingested by the engine should be < 0.01mg/m3 to reduce engine wear. Figure 1 shows the effect of engine air filter life (loading) on filter efficiency and engine wear. Data was collected for heavy-duty air cleaners. It is important to note that the filter efficiency increases with loading (life) and hence the wear rate also reduces.
