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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.

Computational analysis on the mechanism and control method for DME fueled HCCI type combustion was carried out on the basis of the chemical kinetics. The calculation results were verified experimentally using a single cylinder test engine. Analysis of the results showed that DME oxidation is governed by production/consumption behavior of OH, because DME oxidation is initiated by dehydrogenation with OH radicals. It was also shown that the overall oxidation reaction could be controlled by adding substances which react competitively with OH in the dehydrogenation reactions of DME. Of the substances we tested, formaldehyde was most effective. It was confirmed by engine testing that by adding a small amount of formaldehyde to the DME/air mixture, the heat evolved in the low temperature reactions was reduced and the reaction appearance timing was retarded.

Dimethyl Ether (DME) is a promising new alternative fuel for compression ignition DI engines. However, some problems arise from the poor lubricity of DME. Breakdown of the film bearing between needle and sleeve of the injector can lead to mechanical wear and leakage, a problem that is not mitigated easily. For example, the application of returning the leakage to fuel tank could raise a back pressure on the injection needle. This pressure can affect injection rate and consequently engine performance. In this study, fuels based on various DME to gas oil (diesel fuel) ratios were investigated, in part. Physical and chemical properties of DME and gas oil are shown to lead to mutual solubility at any ratio. Blended fuels have a higher lubricity compared with pure’ DME and a better injection spray compared with pure gas oil.

In this study, advantages of GTL fueled DI diesel engine were observed, then, some cautionary areas, notably the aptitude for sealing materials, were investigated. Some advantages of using GTL as a diesel engine fuel include reduction of soot emission levels, power output and fuel consumption with GTL to conventional diesel fuel operation is equivalent, super-low sulfur content of GTL and its liquid state at normal temperature and pressure. However, there are some problems with putting GTL fuel on the market, such as lubricity, aptitude for sealing materials, high cetane index and high pour point. It is necessary to use additives to improve GTL's lubricity, and selecting the most appropriate type of lubricity improver is also important. The influence of GTL on the swelling properties of standard rubber materials seem basically the same, but it is necessary to notice on used rubbers.

In this study, compression ratio for controlling ignition and combustion for HCCI engine is proposed. Compression ratio can be changed higher for leaner mixture or lower for richer mixture to prevent misfire and rapid combustion respectively. In order to increase the power rate of the HCCI engine to a practical use level, supercharge can be combined with various compression ratio. To ascertain the efficacy on ignition and combustion, a series of bench tests and combustion simulations with constant pressure were conducted. The testing result shows that compression ratio is very useful for HCCI control: the engine can run over a wider load range of equivalent ratio without misfire or rapid combustion, and the power rate is comparable to a DI (Direct Injection) engine when a supercharger is installed.

Homogeneous charge compression ignition (HCCI) combustion of methane was performed using dimethyl ether (DME) as an ignition improver. The ignition mechanisms of the methane/DME/air HCCI process were investigated on the basis of the chemical kinetics. The engine test was also conducted to verify the calculation results, and to determine the operation range. Analysis of the results showed that DME was an excellent ignition improver for methane, having two functions of temperature rise and OH radical supply. It was also shown that the operation range was extended to an overall equivalence ratio of 0.54 without knocking, by controlling DME quantity.

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.