抄録
Combustion of diesel dual fuel (DDF) was investigated using a rapid compression/expansion machine (RCEM). Ignition and spreading of burnt gas region were visualized by a high-speed color digital camera. According to the visualized images, auto-ignition occurs in the pilot-spray with a part of natural gas mixture, then the burnt gas, which is observed as a bright white region, spreads out. In the latter period of the combustion, a dark region, which corresponds to a hydrocarbon emission, still remains between the sprays. For a case of early injection, the burnt gas quickly moves out from a piston bowl to a squish area, so that the natural gas mixture in the center of the bowl does not burn completely. For a case of two-stage injection, injected fuel of the first part diffuses into the natural gas mixture and the combustion.
