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.

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The impact of lubrication oil on particle exhaust emissions has attracted increasing attention as emissions of fuel-derived particles have been reduced. This paper presents a model for assessing the oil-related exhaust particle emissions of heavy-duty diesel engines. The model contains four sub-models describing the hydrocarbon, ash, carbon and sulphate particles. All sub-models were developed based on the results of a literature review, complemented by controlled engine tests to fill the knowledge gaps and verify assumptions where necessary. Exhaust after-treatment devices, such as diesel particulate filters, are not included in the model at this stage; in engines equipped with such devices, the modelling results could be used to assess the input of oil-related particulate matter into the exhaust after-treatment system or serve as a basis for further development. The modelling results indicate that the contribution of oil to airborne exhaust particles is substantial under low-load and motoring conditions. Reducing oil consumption is an effective way to reduce oil-related particle emissions.

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