Effects of n-alkane chain length on cool diffusion flames

Large n-alkanes are an important component of many common transportation fuels and possess rich low-temperature reactivity. However, relatively few studies have been performed in which the n-alkane low-temperature chemistry is coupled with both transport and chemical heat release. To address this issue, this investigation examines the effect of n-alkane chain length on the cool flame extinction limits in a counter flow burner system. The cool flames are studied both with and without continuous ozone addition. It observed that, unlike their hot flame counterparts, the extinction limits of n-alkane cool flames are quite sensitive to the size of the fuel molecules and their low-temperature reactivity. The experimental results are compared to both detailed and reduced chemical kinetic models. An over prediction of the cool flame extinction strain rate is consistently observed. It is seen that the complexity of the cool flame heat release makes it particularly difficult for reduced chemical kinetic models to capture the cool flame behavior. The results of this study show that the measurement of cool flames can serve as a useful contribution to fuel screening and a valuable validation target in the future development of low-temperature n-alkane chemical kinetic models.