| Summary: | 碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 98 === Dimethyl-ether (DME) is a new alternative fuel for diesel engines. Engine tests are conducted on a single-cylinder DI diesel engine with modified fuel system. Compared to the original design, a 1.51 times of plunger displacement and a 1.69 times of total injection area are used in this study to investigate the engine performance and emissions characteristics for D50 and D70 blend fuels under different injection pressures and timings.
The results reveal that a higher brake torque is obtained at an adequate lower injection pressure. The full throttle brake torque and power output of blend fuel are higher than diesel fuel at low/medium engine speeds, while lower at high engine speeds. Generally, better full throttle brake torque, bsfc, bsEC, bsHC, bsNOX and smoke level are achieved under an injection pressure of 157.4bar, while lower bsCO at 137.8 bar. Both the bsfc and bsEC of blend fuels are higher than diesel fuels except the bsEC of D70 under 157.4 bar injection pressure and retarded injection timings.
The bsHC of DME/diesel blend fuels is generally higher than the level of diesel fuel. The bsCO of DME/diesel blend fuels is higher than diesel at high engine speeds but lower at low engine speeds. The bsNOX of D50 fuel under 157.4 bar injection pressure decreased substantially than diesel fuel, while the bsNOX of D70 fuel with retarded injection timings is generally lower than diesel fuel. The smoke level of DME/diesel blend fuels generally decrease from diesel level, except that when the engine is at a high speed and high load under the original setting of injection timing.
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