Control of Diesel Engine Exhaust Gas Recirculation System Deposits with Fuel Additives

Exhaust Gas Recirculation (EGR) is employed in diesel engines to reduce engine-out NOx emissions. Despite the concerted design efforts of manufacturers, high-pressure Exhaust Gas Recirculation (HP-EGR) systems can be susceptible to fouling as the particulate matter, hydrocarbons and other entrained species deposit from the exhaust gas flow as it cools on its passage through the EGR system. Such deposits can lead to a number of problems including deterioration of emissions, fuel efficiency, performance and drivability, as well as breakdowns. The development of an engine test method to enable the study of the impact of fuel on deposits in the HP-EGR system was reported in 2020. In the test, a 4-cylinder light-duty diesel engine of 1.6L displacement runs at conditions conducive to EGR deposit formation over 24 hours and the impact of fuels on deposit formation is determined through weighing of the EGR system components before and after the test. This paper describes the application of the test method to screening fuel additives to determine their potential to reduce EGR deposits relative to unadditivated diesel conforming to EN590 and containing 7% volume of Fatty Acid Methyl Ester (FAME). A range of chemistry classifications were trialed pursuant to different potential modes of action on reducing deposit formation. Additive chemistries imparting clearly measurable deposit reduction benefits were identified. The effective additives were found to reduce the engine-out emissions which are the pre-cursors of EGR deposits and in turn reduce the deposits themselves. Work is ongoing on fuel additive technology optimisation to maximise potential benefits in diesel engines with HP-EGR systems.