Exhaust Gas Recirculating Systems in Diesel Engines
In recent years, engine manufacturers have been required to reduce the levels of nitrogen oxide (NOx) in diesel engine exhaust gases to meet current emission regulations. This has been achieved by changes in engine design that include retarding the timing, raising the piston rings, selective catalytic reduction and the use of exhaust gas recirculating (EGR).
New engine designs use EGR to control NOx emissions by recirculating exhaust gases back into the combustion chamber to be burned a second time. The amount of exhaust gas introduced into the combustion chamber displaces oxygen, creating cooler combustion. In doing this, many of the exhaust contaminants end up in the engine lubricating oil.
Diesel engine oils working in the EGR environment are now exposed to corrosive and acidic gases, particle build up and a higher level of contamination in general. These will accelerate oil degradation, with an increase in soot contamination becoming a major issue limiting the service life of the oil.