Effect of Injection Pressure and Split Injection on Exhaust Odor and Engine Noise in DI Diesel Engines

This study investigated the effects of injection pressure and split injection on exhaust odor and engine noise in DI diesel engines. At idle, an injection pressure of 60 to 80 MPa resulted in the minimum exhaust odor with the least aldehyde and minimum THC formation. This is because of decreases in fuel adhering to the combustion chamber walls due to the shortest ignition delay and improved mixture formation 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 higher injection pressure of 60 to 80 MPa is favorable for emission reductions, but there are increases in engine noise and engine instability at idle. To reduce engine noise, further experiments with split injection were attempted.

Three kinds of splitting are used in this study: pre-pilot, 50-50 split and post-pilot at different injection pressures, timings and intervals. The exhaust odor and THC are higher at 50-50 split injection than at the no-split (single injection) injection, but engine noise is much improved. The effects on emissions at different pilot injections are as follows. Pre or post-pilot injection has a little lower odor and lower aldehyde production. In the post-pilot injection the aldehyde concentration is at a minimum. This is due to the shorter ignition delay present in pre or post-pilot injection as compared to no-pilot injection. The post-pilot injection showed a significant noise reduction also. Therefore, the high pressure fuel injection that improves the exhaust odor of DI diesel engines is more effective with proper split injection strategy for simultaneous odor and noise reduction.