Analysis Of DME Spray Characteristics By DPIV Measurement And Numerical Calculation

Dimethyl Ether (DME) is very prospective to use on conventional diesel and homogeneous charge compression ignition (HCCI) engines as an efficient and clean alternative fuels. The characteristics of fuel spray are important to understand fundamental mechanism and influence parameters of the DME combustion process in these kinds of engines. In this study, the mixing characteristics and mechanism of the DME fuel spray and the influence factors are investigated by experimental and numerical studies.Based on the National Basic Research Program of China (973 program) and the research work undertaken, this paper presents an study on the macroscopic and microscopic characteristics of DME spray which helps to improve the design, development and application of DME engines.First of all, the research status of the mechanism, testing methods and numerical simulation of fuel sprays are introduced and reviewed. The Digital Particle Image Velocimetry (DPIV) technique is determined for the testing of DME spray.The principle and configurations of DPIV are illustrated, and a high-pressure constant volume bomb with an optical access base on DPIV for the measurement of DME spray has been built. The scheme of this experiment is designed and some problems which need to be pay more attention to are pointed out. Then, through the analysis of DPIV experiments the detail spray structures and surface wave of DME are visualized. The qualitative analyses of concentration distributions have been made, and the factors which influence the macro-characteristic of DME spray are ascertained. The experimental results also reveal the mechanism, the development process and spray characteristics of flash boiling phenomenon.In this study, the DME spray characteristics are also investigated by numerical calculation. The mathematic models of each phase and sub-process have been built, the spray atomization and mixing mechanisms are clarified combined with the initial and boundary conditions obtained from the experiments through numerical simulations and discussions of DME and diesel spray development. Finally, the microscopic informations of velocity vector and vorticity are presented and the factors which influence the velocity characteristic of DME spray are ascertained. Good agreement exists between the DME spray and turbulent free jet in the dimensionless profile for analogue distribution of velocity. A new dimensionless profile of velocity has been developed for DME fuel spray.