Autoignition and Stabilization of Diesel-Propane Lifted Flames Issuing into a Hot Vitiated Co-flow

Turbulent lifted flames of diesel-propane blend fuels issuing into a vitiated co-flow are recorded with a high-speed camera. The spray characteristics, flame structures, ignition delays, and lift-off heights of jet flames of diesel-propane blend fuels are analyzed in this research. As an additive to diesel fuel, propane has little influence on the autoignition process of diesel from the perspective of chemical kinetics but it improves the atomization, evaporation, and turbulence of the fuel spray. The addition of propane is beneficial for studying the interaction of the chemical kinetics and fluid dynamics in turbulent lifted flames. The experimental results show that the propane fraction has different influences on the ignition delay in two temperature ranges. The ignition delay increases with the increase of the fraction of propane when the co-flow temperature is lower than 1080 K and decreases when the co-flow temperature is higher than 1117 K. Thus, a related mechanism controlling the ignition delay of the blends is proposed by combining the physical preparation process and chemical preparation process. A zero-dimensional model based on chemical kinetics supports this conclusion. For flame stabilization, a higher fraction of propane results in a higher lift-off height in the temperature range of 1043-1098 K, a lower lift-off height in the temperature range of 1117-1155 K, and a higher lift-off height in the temperature range of 1175-1194 K. A mechanism for stabilizing lifted flames from liquid blend fuels is proposed from the perspective of autoignition and turbulence.