Flame Studies of Conventional and Alternative Jet Fuels

Laminar flame speeds and extinction limits of premixed and nonpremixed flames of conventional jet fuels, such as jet propellant 7 and jet propellant 8, and alternative jet fuels, such as synthetic and bioderived, were determined in the counterflow configuration at atmospheric pressure and elevated unburned reactant temperature. The results were compared against those of flames of n-decane and n-dodecane, both being candidate components of jet fuel surrogates. Results indicate that jet propellant 8/air and jet propellant 7/air flames exhibit lower propagation speeds and resistance to extinction compared with flames of alternative fuels. The reduced reactivities of jet propellant 8/air and jet propellant 7/air flames are caused by the alkylcycloparaffins and alkylbenzenes that are present in notable quantities in conventional jet fuels. The combustion characteristics of bioderived jet fuels were found to be indistinguishable from those produced synthetically via the Fischer-Tropsch process. The phenomena of flame propagation and extinction were modeled using n-decane and n-dodecane flames, for which kinetic models are available and for which the molecular weight is representative of that of practical jet fuels. Sensitivity analysis was performed, and results revealed that, compared with flame propagation, flame extinction is, in general, more sensitive to kinetics and diffusion, especially under nonpremixed conditions.