Effect of SO sub(2) concentration in recirculated exhaust gas on wear of diesel engines (relationship between amount of SO sub(2) absorbed into oil layer and wear)

In both spark ignition engines and diesel engines, the exhaust gas recirculation (EGR) system is well known as an effective technique to reduce nitric oxide emission. However, it has not been applied practically to heavy-duty diesel engines because wear of piston rings and cylinder liner is increased by EGR. It is widely considered that sulfur oxide in exhaust gas strongly relates to the wear. This paper presents a numerical model to reveal the mechanism of wear which estimates the amount of sulfur oxide diffused into lubricating oil film. The calculated results show that the sulfur oxide concentration in the oil layer is related strongly to the EGR rate, inversely with engine speed, and decreases under light load conditions. There is a good agreement between the results and the experimental facts.