Power Generation and Alternative Energy Branch

Flame control, particularly at very lean conditions, is a critical requirement for external combustion power sources such as thermoelectric and thermophotovoltaic generators. The availability of in-situ produced hydrogen from JP-8 fuel reforming presents a potential supply of hydrogen on the battlefield without adding a second fuel to the logistics system. Dual firing of hydrogen with light hydrocarbons has been investigated to reduce the lean flammability limit, allowing improved flame control and reduced emissions. This research investigates the use of small amounts of hydrogen co-fired with jet fuel for improved energy efficiency, operational flexibility and environmental protection. Simulations were conducted using a computational fluid dynamics model of a 6 kW (thermal), swirling flow combustor. The simulations use hydrogen and a single hydrocarbon surrogate for JP-8 with a 4 step reaction mechanism. Follow up simulations examined the effect of using reformed fuel containing hydrogen, carbon monoxide and other gases dual-fired with JP-8. Varying levels of reformate and air were examined. The results show that at lean conditions, the dual firing of hydrogen or reformate with JP-8 provides improved fuel conversion, demonstrating better flame stability and providing higher fuel burning efficiency. Dual firing with hydrogen provides little benefit to JP-8 combustion under stoichiometric or fuel rich conditions because they are limited by mixing rather than chemical kinetics. These results indicate that dual firing of hydrogen with JP-8 is a promising method for improving lean flame stability and control. This has the potential to enable small scale power applications with specific temperature requirements such as thermoelectric and thermophotovoltaic generators.