Laminar Flame Speeds, Flammability Limits, and Flame/Reaction Zone Thicknesses for a Surrogate Kerosene Fuel at Engine Operating Conditions

Abstract

Values of laminar flame speed, flame thickness, and reaction zone thickness have been computed for premixed flames of a surrogate kerosene fuel using a detailed chemical kinetics mechanism and associated thermochemistry and transport properties from the literature. Computations were performed at stoichiometric conditions throughout a range of rig and engine operating conditions. In addition, for selected points, computations were performed over the equivalence ratio range of 0.5 to 2.2. Radiation losses were not treated. Literature data on flammability limits were collected for a variety of fuels and used to develop a correlation that was extrapolated to engine conditions. The results for both the lean and rich limits are in reasonable agreement with the computed flame speeds, extrapolated to zero flame speed. From these computed data sets and the flammability limits, correlations were developed for flame speeds, flame (thermal zone) thicknesses, and reaction zone thicknesses as a function of temperature (400-1000K), pressure (1-35 atmospheres), and equivalence ratio (lean to rich limits). Reaction zone thicknesses are found to be about 50% of the thermal zone thickness, significantly larger than those reported in an earlier study. This relatively large reaction zone thickness suggests that the threshold Karlovitz number for flame extinction is closer to 4 rather than 100 as inferred from the earlier estimate of the relative reaction zone thickness. The lower value is consistent with experimental determinations of flame quenching.