Study of Fuel in Oil Dilution Due to Aftertreatment Regeneration in Automotive Diesel Engine

The Bharat Stage VI emission norms in India is driving the use of more complex after treatment systems for diesel engines, to meet the stringent emission limits. The after-treatment system typically includes theSelective Catalytic Reduction (SCR) catalyst and the Diesel Oxidation Catalyst (DOC) - Diesel Particulate Filter (DPF) systems to reduce engine out emissions of Nitrogen Oxides (NOx), hydrocarbons (HC), and particulates respectively. For a durable functioning of the aftertreatment system, cleaning of these components at regular intervals is required, the process termed as ‘regeneration’. The most common industry technique for regeneration is to use the existing injectors in the engine, to dose the extra fuel which is burnt in the DOC for regeneration. This has been a cost effective and simpler technique compared to the external hydrocarbon dosing system. But the tradeoff involved with this in-cylinder dosing technique is the risk of fuel in oil (FIO). The extra fuel injected impinges the cylinder wall and eventually get mixed with engine oil thereby diluting it. The diluted oil increases the risk of early wear and impacts the durability of the engine. This paper emphasizes on parameters impacting fuel in oil dilution due to regeneration, associated tradeoffs and some system level analysis of the same. Through six sigma, the various factors impacting FIO is studiedexperimentally using a mid-range diesel engine in an engine dynamometer. Study also considers impact of regen frequency and application level impact on oil drain interval for some on-highway commercial vehicle applications. A system level approach is formulated to understand FIO which can be used in the early phase of design and calibration of aftertreatment system.