Spectroscopic Investigation of the Combustion Process in DME Compression Ignition Engine

For better understanding of the in-cylinder combustion characteristics of DME, combustion radicals of a direct injection DME-Fueled compression ignition engine were observed using a spectroscopic method. In this initial report, the emission intensity of OH, CH, CHO, C₂ and NO radicals was measured using a photomultiplier. These radicals could be measured with wavelength resolution (half-width) as about 3.3 nm. OH and CHO radicals appeared first, and then CH radical emission was detected. After that, the combustion radicals were observed using a high-speed image intensified video camera with band-pass filter. All of radicals were able to observe as images with half-width as 6 or about 10 nm. Rich DME leaked from nozzle was burning at the end of combustion. Therefore, the second light emission of C₂ radical after the main combustion was observed. The light of OH emitted all over the DME spray at the combustion started, then the dim light expanded in combustion chamber, so that CH radical emitted at the spray tip. After that the light intensity around the combustion chamber wall became strong with advancing the combustion. The light of NO radical emitted at around the tip of spray, which area seems to be stoichiometric combustion area.