Research Of DME Fuel Supply System In Diesel Engine

Developing reproducible, alternative and environmentally friendly fuels has become one of the most important tasks for human beings in the 21st century. Dimethyl ether (DME) is a potential ultra-clean diesel alternative fuel that-could be synthesized from a variety of feedstock, which can support the use of alternative energy resources. DME has been considered as a compound fuel by many countries for future use.DME has high cetane value, great vaporization heat, good quality atomization, and zero C-C keys in the molecular structure. All these characteristics decide that DME is the best alternative fuel of diesel oil. However, DME is of low viscidity, low liquid state density, small elasticity module, and high saturation vapor pressure. Those disadvantages put forward a new challenge towards the supply system of traditional diesel engines, and affect the process of development to some extent.On the basis of wide knowledge of theoretical and applied research on new clean alternative fuel DME at home and abroad, in view of methodology of designing the supply system of diesel engines, this paper tries to give an improvement to the fuel supply system of multi-cylinder engines, so that it can provide diesel engines with DME fuel continually and reliably. DME is gaseous under the condition of standard atmosphere and temperature, which requires the oil supply system of diesel engines and the vessel storing up DME maintain seal with enough pressure. In order to make sure the equal sum of power can be produced when applying DME to an engine, the main components of the system need to be improved, including the plunger matching part in the oil spraying pump, the delivery valve matching part, and the nozzle matching part. The new fuel supply system can meet the power performance and emission regulation of diesel engine 490. With the simulation software AMEsim, an fuel injection system model of DME engines has been built, which includes a piston pump model, a delivery valve model and a fuel injector model. Parameters are set with Diesel 490 as a target model, and the situation of diesel and DME used by new fuel injection system is simulated in a computer. Key design parameters of fuel injection system are adjusted combined with the physical and chemical properties of DME. Making use of the batch disposal function of AMEsim, working characteristics study is also made towards the fuel injection system by using the simulation model of DME. Simulation calculation mainly concerns several influential parameters, such as the unlocking pressure, the hole diameter, the engine speed, the cam-line and so on.The simulation calculation results shows that, the unlocking pressure has less effect on the highest injection pressure, but greater impact on continued angle of fuel injection, the needle open crank angle displacement and the second jet. Injection hole diameter affects the fuel injection rate, continued angle of fuel injection and fuel injection volume; cam speed has a greater impact on the fuel supply volume, fuel supply rate, needle valve lift and so on; cam-line largely decides the fuel advanced angle, fuel supply laws and fuel supply volume. Combined with practical tests, diesel engines with DME need to use nitrogen to keep pressure in the fuel tank. Fuel injection system needs to increase the plunger diameter, strengthen the tightness of pipelines, and add appropriate lubricants in the DME. Better effect can be achieved when it is used in large diesel engines. The conclusions above will provide some directional guidance for further research on DME engine.