Lost revenue due to equipment downtime is often a direct result of some type of contamination, whether from dirt, water, an incorrect lubricant or a combination of these. Oil analysis testing can identify these contaminants. The main purpose of lubricating oils is the reduction of friction between surfaces, prevention of wear and rust, cooling by removing the heat resulting from the contact of the surfaces and the cleaning of automotive engines as a protection from damage caused by friction and wear. The sliding contact between engine parts comprises a variety of different friction and wear mechanisms during one working cycle of the engine. Due to the variations in speed, load and counter surface effects, the lubrication conditions in an engine are strongly transient, which is reflected by variations in the friction and wear behavior. These values depend on the particular lubricant used, the surface quality and surface material. The major sources of these contaminants in lubricating oils are prior blowby, lubricant breakdown, and wear of engine parts.
Solid contaminants such as iron (Fe), copper (Cu), aluminum (Al), lead (Pb) and silicon oxide (SiO2) are a result of the wear of the engine parts as a consequence of external contaminants mixing with the lubricating oil, fuel and intake air. The damage of the parts is dependent on grain size of particles, concentrations, texture of the particles and operating pressure. The presence of solid contaminants enhances the oxidation of lubricating oils. A high-level contaminant concentration in the form of solid particles leads to high thin-film wear at the start of sliding. The reason for an engine oil change could be due to its deterioration in terms of viscosity and oxidation, as well as solid contaminants that become mixed or dissolved in the lubricating oils. The presence of contaminants in engine oil is generally undesired, as solid contaminant particles are a potentially cause of abrasive wear. Contamination of lubricating oils causes wear of piston ring, which generates more contamination. This proceeds via internal wear generating fresh wear debris leading to the opening of the dynamic sealing surfaces. Bore polishing is another undesired impact of small abrasive particles the lubricating oils, while larger particles can cause scratches in the bore. The total friction in an engine immediately after a cold-start is four to five times higher than at fully warmed-up conditions.
The source of the contamination particles may be soot from combustion, silica dust and similar minerals, and wear particles consisting of ferrous, lead, chromium, copper, aluminum, nickel alloys and tin. The diesel soot interacts with lubricating oils and ultimately leads to wear of engine parts. The harmful effect of solid particles in the lubricating oils is particularly obvious with softer parts like piston skirts, bearings, and cam-follower contacts. The major categories of solid contaminant particles in crankcase oils are carbon, or combustion particles and metallic or wear particles. The carbon contaminants particle can be determined by means of Fourier transform infrared spectroscopy (FT-IR), a method that is suitable for the determination of the presence of different organic compounds including reaction products. It is necessary for all lubricated systems that the particle size should remain well below the oil film thickness between surfaces in any lubricated mechanism, and this very well applies to engines. Engine air induction filters are designed to effectively remove airborne contaminants in order to protect the engine. The engine requires a certain level of ingested air cleanliness to reduce friction and wear to improve engine efficiency.