ID 212

Characteristics and Dynamic Behaviour of Fuel Film Formed by Single Droplet Impingement

Di Xiao
Institute of Automotive Engineering, School of Mechanical Engineering, Shanghai Jiao Tong University, National Engineering Laboratory for Automotive Electronic Control Technology, Shanghai, China
China

Hujie Pan
Institute of Automotive Engineering, School of Mechanical Engineering, Shanghai Jiao Tong University, National Engineering Laboratory for Automotive Electronic Control Technology, Shanghai, China
China

Min Xu
Institute of Automotive Engineering, School of Mechanical Engineering, Shanghai Jiao Tong University, National Engineering Laboratory for Automotive Electronic Control Technology, Shanghai, China
China

Xuesong Li
Institute of Automotive Engineering, School of Mechanical Engineering, Shanghai Jiao Tong University, National Engineering Laboratory for Automotive Electronic Control Technology, Shanghai, China
China

David L. S. Hung
University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai, China
China

Xue Dong
Institute of Automotive Engineering, School of Mechanical Engineering, Shanghai Jiao Tong University, National Engineering Laboratory for Automotive Electronic Control Technology, Shanghai, China
China

Abstract:

Fuel adhered on IC-engine piston via spray impingement degrades the evaporation and mixture for-mation processes especially under cold-start cylinder temperatures. However, the fuel film caused by spray impingement at cold-start temperatures has not been accurately simulated nor well understood, de-spite of its significance in engine performance at cold start conditions in the near-polar regions. This pa-per presents an experimental study of the dynamic behavior of single droplet impingement, rebounding and film spreading on a cold surface. A stainless syringe needle was applied to generate a single droplet to impinge onto a dry sapphire plate. The temperature for both the impinging plate and the droplet was achieved by a thermostatic bath. High-speed laser-induced fluorescence (LIF) technique was employed to measure the spatial distribution and temporal development of the thickness of droplet film deposited on the plate. The LIF signal was converted to film thickness following a calibration procedure where LIF sig-nals from a series of known-thickness film were captured. Besides, the evolution of droplet morphology during the impinging process was captured by high-speed backlit imaging. From side view analysis, the droplet size and impinging velocity were measured. It was found that film formed with larger We number had a thinner rim, higher spreading velocity and maximum radius. Moreover, the difference of thickness distribution under different We number is quite obvious, and larger We number contributes to a larger proportion of mass reduction of the film.