Chemiluminescence Analysis from In-Cylinder Combustion of a DME-Fueled DI Diesel Engine

To date, the DME combustion mechanism has been investigated by in-cylinder gas sampling, numerical calculations and observation of combustion radicals. It has been possible to quantify the emission intensities of in-cylinder combustion using a monochromator, and to observe the emitting species as images by using band-pass filters. However, the complete band images were not observed since the broadband (thermal) intensity may be stronger than band spectra intensities. Emission intensities of DME combustion radicals from a pre-mixed burner flame have been measured using a spectroscope and photomultiplier. Results were compared to other fuels, such as n-butane and methane, then, in this study, to better understand the combustion characteristics of DME, emission intensities near CH bands of an actual DI diesel engine fueled with DME were measured, and band spectra emitted from the engine were defined. Near TDC, emission intensities did not vary with wavelength. This baseline intensity seems to be continuous spectrum emission. Two emission intensity peaks were observed; one near 427 nm and the other at 431.4 nm, and these were apparently DME combustion emission lines. The intensity of the 427 nm line increases from the early to middle stage of diffusion combustion, compared to the continuous spectrum. As combustion advances, the light intensity strengthens around the combustion chamber walls. That is, active heat release occurs near the chamber walls.