Search Results

For better understanding of the combustion characteristics in a direct injection dimethyl ether (DME) engine, the chemiluminescences of a burner flame and in-cylinder flame were analyzed using the spectroscopic method. The emission intensities of chemiluminescences were measured by a photomultiplier after passing through a monochrome-spectrometer. For the burner flame, line spectra were found nearby the wave length of 310 nm, 430 nm and 515 nm, arising from OH, CH and C2 radicals, respectively. For the in-cylinder flame, a strong continuous spectrum was found from 340 nm wave length to 550 nm. Line spectra were also detected nearby 310 nm, 395 nm and 430 nm, arising from OH, HCHO, and C2 radicals, respectively, partially overlapping with the continuous spectrum. Of these line spectra, 310 nm of OH radical did not overlapped with the continuous spectrum.

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.

To better understand the combustion characteristics of DME, emission intensities of DME combustion radicals from a pre-mixed burner flame were measured by a spectroscope and photomultiplier, Results were compared to other fuels, such as methane and butane. Large peaks in the band spectra from pre-mixed and diffusion DME flames were found near 310 nm, 430 nm, and 515 nm, arising from OH, CH and C2, respectively. The DME emission intensities decreased with increasing the equivalence ratio in this study. Notably, the relative decrease in the C2 band spectra peak was greater than that of the OH band. Comparing the pre-mixed DME and butane flames, the butane band spectra peaks were similar in shape, but much stronger than those for DME. However, it was remarkable that CH and C2 band spectra peaks decreased only slightly with increase in equivalence ratio compared to the DME case.