Spray Targeting to Minimize Soot and CO Formation in Premixed Charge Compression Ignition (PCCI) Combustion with a HSDI Diesel Engine 2006-01-0918

The effect of spray targeting on exhaust emissions, especially soot and carbon monoxide (CO) formation, were investigated in a single-cylinder, high-speed, direct-injection (HSDI) diesel engine. The spray targeting was examined by sweeping the start-of-injection (SOI) timing with several nozzles which had different spray angles ranging from 50° to 154°. The tests were organized to monitor the emissions in Premixed Charge Compression Ignition (PCCI) combustion by introducing high levels of EGR (55%) with a relatively low compression ratio (16.0) and an open-crater type piston bowl.

The study showed that there were optimum targeting spots on the piston bowl with respect to soot and CO formation, while nitric oxide (NOx) formation was not affected by the targeting. The soot and CO production were minimized when the spray was targeted at the edge of the piston bowl near the squish zone, regardless of the spray angle. Targeting this spot is believed to enhance the pre-ignition mixing of air and the spray effectively with the help of the squish flow. The results from the narrow angle nozzles (50° and 85°) indicated that soot could be optimized when the spray was targeted at the bottom of the piston bowl which provided the longest spray travel distance. However, CO emission increased but was significantly reduced when the spray was targeted at the inner surface of the bowl with a corresponding increase in soot emission. In the standard diesel combustion regime, the soot and CO increased as SOI was retarded, and the minimum soot was achieved with SOI of about -20 degree ATDC. This SOI timing provides a rough boundary between conventional diesel and PCCI combustion as seen from the heat release rate data.