Fuel Composition and Performance Analysis of Endothermically Heated Fuels for Pulse Detonation Engines

Waste heat from a pulse detonation engine (PDE) was extracted via concentric, counter flow heat exchangers to produce supercritical pyrolytic conditions for JP-7 and JP-8 fuels. A sampling system and method was utilized to collect samples of reacted fuel to be extracted during steady state operation. Samples were collected over a range of heat exchanger exit temperatures from 820 K (1016° F) to 940 K (1232 degrees F) and for two sets of heat exchangers, one set coated with zeolite catalyst and one set left uncoated. Variation in fuel mass flow rate required the calculation of heat addition as an alternate to heat exchanger exit temperature as the independent variable when comparing fuel decomposition and engine performance. Offline chemical analysis of liquid and vapor portions of each sample indicated fuel decomposition via pyrolytic pathways. The analyses showed the formation of hydrogen, unsaturated hydrocarbons (aromatics and alkenes), and smaller alkanes in both fuels. The high thermal stability and low aromatic content of neat JP-7 resulted in the formation of more gaseous products and fewer poly-aromatic compounds than was produced by JP-8. The additional concentrations of lighter hydrocarbons reduced the ignition times by an average of 15.6%, and the reduced poly-aromatic concentrations decreased the bulk carbon deposits formed during pyrolysis by 92.5% on average