Thermal Efficiency of DME Fuelled Diesel Engine

DME is known for its high cetane number and high oxygen contents. Higher cetane number is more favourable in the application of diesel engine, since the fuel will be auto-ignited, while higher oxygen contents is favourable in the low oxygen condition, which introduced by the usage of EGR system. EGR is currently one of the viable ways available to reduce emissions, particularly the NOx emission. However, introduction of EGR into the system has one major drawback, reduced overall engine performance, including thermal efficiency.The literature review study on this thesis compares the performance of DME fuelled diesel engine and petrol diesel fuelled diesel engine. The parameters involved in the comparison are: emissions level, which investigates emissions emitted by DME fuel, and engine performance which investigates performance characteristics such as fuel consumption and thermal efficiency.From the study it can be concluded in this thesis that, in overall, DME fuelled diesel engine performs better than petrol diesel fuelled diesel engine. From the emission study, DME fuelled diesel engine shows a reduced amount of NOx, HC, and CO2 and particularly shows no smoke or soot. However, DME fuelled diesel engine shows higher amount of CO. The higher amount of CO is the side effect of the lower combustion temperature that introduced by the usage of DME.In the study of engine performances, DME marks good combustion behaviour by showing significant increase in torque and engine power as well as thermal efficiency. During the introduction of EGR system, DME fuelled diesel engine able to maintain its performance and recorded a consistent thermal efficiency with only slight reduction during the high speed. Fuel consumption also recorded lower during low to medium speed range, but higher during the high speed range.An optimisation of engine performance, particularly the thermal efficiency comes in the optimisation of injector or nozzle opening pressure and swirl intensity, which DME requires lower pressure opening pressure, lower swirl ratio, as well as different type of nozzle.