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. The after-treatment system typically includes DOC, DPF and SCR to reduce the engine out hydrocarbon, particulates & NOx respectively. For a durable functioning of the after-treatment system, cleaning of these components at regular intervals is required. One such method is to burn the diesel fuel inside DOC, to clean the DPF and SCR, a process called regeneration. Regeneration involves using extra diesel fuel injected into the exhaust stream, which gets oxidized in the DOC thereby regenerating the DPF or SCR. Present technology uses the existing injectors in the diesel engine for regeneration which is cost effective and simpler compared to the external hydrocarbon dosing system. In-cylinder hydrocarbon dosing is associated with the risk of fuel getting mixed with engine oil. This happens because the regeneration fuel is injected in the exhaust stroke where the diesel spray has a high chance of wetting the cylinder walls and getting scrapped to the oil sump. The diluted oil increases the risk of early wear and impacts the durability of the engine. This paper emphasizes on optimizing fuel in oil dilution due to regeneration, without compromising on regeneration temperatures. Using six sigma tools, the various factors impacting FIO is studied through experimental method in an engine dynamo-meter test cell. Study also considers impact of regeneration frequency and application level impact on oil drain interval. The study concludes with an optimal solution for FIO for the hardware under consideration and develops a model and method to predict FIO due to regeneration. Further based on the results, a prediction on ODI is done based on some empirical calculations for different on-highway commercial vehicle applications.