Development of an Engine Test to Rate the EGR Deposit Formation Propensity of Fuels in Light-Duty Diesel Engines

Exhaust Gas Recirculation (EGR) is employed in diesel engines to reduce engine-out NOx. Carbon-containing deposits form in the EGR systems of modern diesel engines as the particulate matter, hydrocarbons and other entrained species deposit from the exhaust gas flow as it cools. Much work has been done by Original Equipment Manufacturers (OEMs) to reduce deposits and mitigate their effects by optimized dimensioning of EGR coolers and valves, introduction of EGR cooler bypass for use in the most sensitive cold conditions and experimenting with oxidation catalysts upstream of the EGR system. Nevertheless, deposits forming in the high-pressure Exhaust Gas Recirculation (HP-EGR) systems of modern diesel engines can sometimes lead to a number of problems including emissions and fuel consumption deterioration, poor performance and drivability, as well as breakdowns. An engine test method has been developed to enable the impact of fuel on deposits in the HP-EGR system to be studied. This paper describes the work undertaken in the test development and initial fuel effects testing to prove the discriminatory power of the method. In the test method 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. Initial tests comparing a B7 representative of European EN590 diesel fuel and a Fischer-Tropsch Gas-to-Liquid (GTL) gasoil fuel showed that 72% less deposit formed with GTL than with B7. This work provides a foundation for further study of fuel effects on EGR deposits.