Impinged Diesel Spray Evaluation for Indirect Air-Fuel Mixing Processes and its Comparison with Non-Vaporing Impinging Spray Under Diesel Engine Conditions 2019-01-0267
Under low-temperature combustion for the high fuel efficiency and low emissions achievement, the fuel impingement often occurs in direct injection diesel engines especially when a short distance is between the injector and piston head/cylinder wall. The impingement plays an important role in the mixing-controlled combustion mode because it affects the air-fuel mixing rate through the disrupted event by the impingement. However, the air entrainment during the combustion is hard to be directly evaluated. In this study, the local boundary curvatures of non-reacting fuel spray expansion and flame propagation upon impingement are quantified as an indicator of the level of air entrainment. The experiments were performed in a constant volume combustion chamber with the ambient density of 22.8 kg/m3. Diesel was injected into the chamber at an injection pressure of 150 MPa. Under the non-reacting case, the chamber was filled with nitrogen at the ambient temperature of 423 K. The ambient temperature was varied with 800 K, 900 K and 1000 K for reacting case to study the effect of ambient temperature on the air-fuel mixing process. The liquid spray expansion and flame propagation on the impinging plate were captured by a high-speed camera from bottom view by using Mie scattering and natural luminosity, respectively. An in-house MATLAB code has been used to post-process the high-speed images. The local curvatures were correlated with the local zones of soot generation to explore the relationship between the air entrainment and soot generation. In addition, to quantify the heat loss on the cold surface by the flame impingement, local temporal heat flux and accumulated heat transfer at three locations were obtained.
Zhihao Zhao, Xiucheng Zhu, Jeffrey Naber, Seong-Young Lee