Fuel entry into oil sump dilutes oil and affects its tribological properties, leading to increased engine wear and failure. Higher oil levels can also lead to uncontrolled combustion and unintended vehicle acceleration. In modern BS6 Diesel engines equipped with Diesel Particulate Filters (DPF), the late post injections are a major source of oil dilution. Other sources of fuel in oil dilution are pump failure and improper geometric sealing of moving parts. In vehicles with NOx Storage Catalyst (NSC) installed, the rich mode would also have a high share in the oil dilution. The SAE paper addresses ways to reduce fuel entry rate from post-injections without compromising the DPF performance.
The accumulated soot is regenerated at high exhaust temperature. The high exhaust temperature is achieved by introducing late post injections (PoI1) continuously throughout the regeneration duration (approximately 20 to 30 mins). These late post injections are timed closer to exhaust valve opening during the expansion stroke. Due to the engine geometry, injected quantity may reach the cylinder liner quench and Diesel may drop into the oil sump. Over the life of the vehicle, with subsequent regeneration events, the oil in the sump gets diluted with the Diesel fuel. Hence, the oil dilution must be well within acceptable limits based on the application.