| Being high cetane number and combustion with soot-free emission, Dimethyl ether (DME)is considered an ideal alternative fuel for diesel engines. However, the problems of serious wear abrasion and leakage to the sealing couplings of fuel injection system caused by DME low viscosity become a major obstacle to DME's application in vehicles. From fuel supply and fuel injection, an innovative solution of a new type of electronic control common-rail injection system suitable for DME injection was put forward in this paper. Because of effective avoidance to the above two difficulties, the program could solve the problems completely.The DME injector design ideas based on the collision principle was proposed: in the free lift , the armature stored the electromagnetic energy and transformed into kinetic energy, and when the collision between the armature and needle occurred, the needle could open quickly and reliably because of electro-magnetic force and impact force acting on it. By simulation and prototype experiment, the new type injector working principle was confirmed. Studies have shown that: the new type common-rail electric control injector has the characteristics of no internal couplings, no spill port, driven by 24V directly and flexible pre-injection. Further research shows that the injector exists the best free lift, and the overlong free lift causes the needle's opening response lag and too short free lift results in difficulty to the needle opening.The fuel supplying idea with converting the machine oil pressure to the DME pressure by pressure converter was proposed. Two kinds of pressure converters with a plunger and diaphragm accumulators were developed, successfully solved the problem of DME pressurization and skirted round the wear abrasion and leakage problem to the plunger of DME pump.Addressing the DME physical properties and the characteristics of DME injection system, the DME fuel injection law test system was developed. By experiments of fuel injection law under condition of different parameters, the results of simulation model were verified,and proved that the system simulation model has the better credibility. The practical opening response time of the injector is 0.38ms, the corresponding closing response time is 0.68ms under the condition of PWM-driven, and the injection system can achieve pre-injection with 0.4ms dwell. Reasonable matching of free and effective lift and optimization of pipeline parameters can improve the characteristics of fuel injection..According to the DME properties and new type injection system, the simulation model of DME combustion process in a diesel engine was established, the effects of critical parameters on the combustion process and the engine performance were predicted and the theory guidance for the later engine bench experiments were prepared. The results show that: under the condition of meeting economy and power performance, 25MPa injection pressure can achieve better NO emission and lower ratio of pressure rise. With reasonable fuel amount of pre-injection and main injection advance angle, NO emissions and combustion noise can be reduced effectively and the trade-off curves of pre-injection is better than the single injection in NO-indicated efficiency and ratio of pressure rise-indicated efficiency.The above work built a stable base of theory and technology for DME common-rail technology practical application...
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