Performance of synthetic jet fuels in a meso-scale heat recirculating combustor

The performance of two synthetic aviation fuels was evaluated in a meso-scale heat recirculating combustor and the respective results compared with the combustion characteristics of a conventional petroleum-based jet fuel. One of the alternative jet fuels was synthesized via a Fischer–Tropsch (F–T fuel) process, while the other was produced from tallow (bio-jet fuel). The petroleum-based fuel used in this study was JP-8. The combustion and extinction behavior of the above fuels and their mixtures (50% synthetic fuel and 50% JP-8 by volume in JP-8) in the meso-scale combustor using oxygen under fuel-rich and fuel-lean non-premixed combustion conditions was examined. The synthetic fuels exhibited stable combustion over a range of equivalence ratios at each fuel flow rate; however, stable combustion was not achieved for JP-8 under any of the examined conditions. The mixtures also exhibited somewhat unstable combustion phenomena as those seen with JP-8, but dampened enough such that mostly stable combustion could occur. Fuel characterization analysis was performed for each fuel, and their respective thermal performances evaluated. Both the F–T and bio-jet fuels reached a maximum thermal efficiency of about 95% near their respective rich extinction limits. The mixtures exhibited somewhat poor thermal performances, with a maximum thermal efficiency of about 75%. The results reveal that composition of the fuel plays a prominent role in the flame stability and thermal performance in meso-scale combustors, as more complex species (such as aromatics, found in JP-8) have a slower reaction rate than simple species. The short residence time available in the combustion zone of the micro-combustion chamber does not allow to fully combust the complex fuel species, resulting in flame instability and formation of soot.