Study of the low-temperature reactivity of large n-alkanes through cool diffusion flame extinction

Large n-alkanes are notable components of many common transportation fuels and possess rich low-temperature reactivity. However, few studies have been performed in which the n-alkane low-temperature chemistry is coupled with transport and heat release. This study addresses this through the measurement of the extinction limits of cool diffusion flames in a counterflow burner. A clear trend is observed in that the heavier n-alkanes produce stronger cool flames, which differs from the insensitivity of n-alkane hot flames to fuel size. Furthermore, there is little agreement between different chemical kinetic models in terms of their predicted cool flame extinction limits. Reduced models in particular struggle to describe cool flame behavior accurately due to the substantial number of reactions involving large molecules that contribute to the cool flame heat release. The results of this study show that well-defined measurements of cool flames can serve as valuable validation targets in the future development of low-temperature chemical kinetic models.