A Study of High Load Operation Limit for Premixed Compression Ignition Engine

NOχ emission was remarkably reduced by PREDIC (PREmixed lean DIesel Combustion) system in which fuel was injected at very early stage of compression stroke and the major part of the fuel is considered to be burned with self-ignition of premixed charge around TDC. However PREDIC system had some problems, a restriction of a high load operation was one of these problems. In order to investigate the combustion characteristics of PREDIC at the richer operation limit, a test engine was operated with gaseous fuel-air mixture where less heterogenoeus mixture can be formed than that of conventional diesel engines. A steep pressure rise or the abrupt increase in NOχ emission determined the richer operation limit. This was at 2 to 2.4 of excess air ratio. Supercharging operation enabled the high load operation more than 2.4 of excess air ratio.