Lubricant ash particles in diesel engine exhaust. Literature review and modelling study

Abstract

Reducing particulate emissions from diesel engines has been a concern in recent decades. The increasing use of diesel particulate filters (DPFs) has highlighted the importance of predicting ash emissions from lubricant, since ash accumulates in DPFs. Ash accumulation will increase the pressure drop across the filter, and thereby also the fuel consumption, eventually necessitating filter cleaning or replacement. This paper examines the ash transfer rate, calculated as accumulated ash divided by calculated ash consumption (oil consumption times oil ash content). Three times 500 hours of ash accumulation testing was performed on a Scania heavy-duty diesel engine; in addition, the relevant literature was reviewed. The main results of the study are: (a) the main contributor to ash particulate emissions is lubricant ash; (b) the oil ash transfer rate was found to be oil specific; testing indicated transfer rates of 38–59 per cent; (c) the slight increase in ash transfer rate when reducing the engine load indicated that the load might be dependent on the oil ash transfer rate, although the effect was clearly lower than that of the changing oil.