Spray-Wall Dynamics of High-Pressure Impinging Combustion 2019-01-0067
The fuel spray impingement on the piston head and/or chamber has frequently occurred in IC engines especially the small size ones with high injection pressure. The impingement plays a key role in combustion since it affects the air-fuel mixing process and leads to more emission due to deviated air-fuel ratio. In this study, the impinging combustion has been experimentally investigated to understand the mechanism and dynamics of spray-wall interaction. The experiments were performed in a constant volume combustion chamber over a wide range of ambient conditions, the ambient temperature was varied from 800 to 1000 K and ambient gas oxygen was varied from15% to 21%. Diesel was injected at the injection pressure of 150 MPa into ambient gas at a density of 22.8 kg/m3 and impinged on a surface at 523 K. The natural luminosity technique was applied in the experiment to explore the impinging combustion process using a Photron high-speed camera from two different views (bottom and side). An in-house Matlab program was used to post-process the images. The most reactive region was found based on the local luminosity intensity to define the potential soot generated region. The effect of air entrainment on the flame propagation was investigated by studying the curvature of the flame outer boundary. In addition, to quantify the heat transfer through the impinged plate more clearly, the effects of flame impingement on transient heat flux to the wall were investigated. The heat transfer from the impinged wall to flame and ambient air resulted in the relatively cool flame, leading to soot formation. Further, to better understand the impingement behavior, different governing combustion modes (premixed and diffusion) in impinging combustion were studied. After comparing the heat release rate with free spray combustion, the effect of impingement on the heat release rate was observed and a new combustion model which explains the mechanism of impinged spray combustion is defined based on the observation.
Zhihao Zhao, Xiucheng Zhu, Le Zhao, Jeffrey Naber, Seong-Young Lee
Michigan Technological University
International Powertrains, Fuels & Lubricants Meeting