Hydrocarbons and Particulate Matter in EGR Cooler Deposits: Effects of Gas Flow Rate, Coolant Temperature, and Oxidation Catalyst

Compact heat exchangers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases, resulting in decreased NO_x emissions. These exhaust gas recirculation (EGR) coolers experience fouling through deposition of particulate matter (PM) and hydrocarbons (HCs) that reduces the effectiveness of the cooler. Surrogate tubes have been used to investigate the impacts of gas flow rate and coolant temperature on the deposition of PM and HCs. The results indicate that mass deposition is lowest at high flow rates and high coolant temperatures. An oxidation catalyst was investigated and proved to effectively reduce deposition of HCs, but did not reduce overall mass deposition to near-zero levels. Speciation of the deposit HCs showed that a range of HCs from C₁₅ - C₂₅ were deposited and retained in the surrogate tubes. Analysis of the deposit mass of eicosane (C₂₀) showed that the deposition of HCs is very sensitive to the coolant temperature in the range investigated. The results suggest that use of an oxidation catalyst and/or reduction of the amount of high-boiling point HC species in the fuel may be pathways toward reduced EGR cooler fouling.