Effects of High Pressure Injection and Oxidation Catalyst on Exhaust Odor in DI Diesel Engines

This study investigated the effect of high pressure injection and an oxidation catalyst on the exhaust odor of DI diesel engines. At idling an injection pressure of 60∼80 MPa resulted in the minimum exhaust odor, with the least aldehyde and minimum total hydrocarbon (THC). This is because of decreases in fuel adhering to the combustion chamber walls due to the shortest ignition delay at this pressure range. However, above 60 MPa there is no further shortening of the ignition delay and overleaning of the local mixture dominates at injection pressures above 100 MPa, where the exhaust odor increases again. The odor reduction at the optimum injection pressure and injection timing is not significant, and further experiments with an oxidation catalyst were performed.

The oxidation catalyst was found less effective to reduce exhaust odor at long idling where the maximum catalyst temperature is only about 120°C. However a preconditioned catalyst reduces aldehydes, THC, and exhaust odor significantly just after starting due to good adsorption. The exhaust temperature at standard idling is low, and the activity of the catalyst was investigated after a hot exhaust condition. Above catalyst temperatures of 200°C, there were remarkable reductions in THC and aldehydes and there was almost no exhaust odor. Below 200°C the aldehydes in the exhaust increase sharply and objectionable exhaust odor appears.