Fuel-cooled thermal management, including endothermic cracking and reforming of hydrocarbon fuels, is an enabling technology for advanced aero engines and offers potential for cycle improvements and pollutant emissions control in gas turbine engine applications. The successful implementation of this technology is, however, predicated on the use of conventional multicomponent hydrocarbon fuels and an understanding of the combustion characteristics of the reformed fuel mixture. The objective of this research is to develop and demonstrate the technologies necessary for utilizing conventional multicomponent hydrocarbon fuels for fuel-cooled thermal management, including the development of the endothermic potential of JP-7 and JP-8+100, a demonstration of the combustion of supercritical/endothermic fuel mixtures, and conceptual design of a fuel-air heat exchanger. The ability to achieve high heat sinks with existing jet fuels (e.g., JP-7 and JP-8+100) was demonstrated with a bench-scale test rig operating under flow conditions and passage geometries simulative of practical heat exchangers for aircraft and missile applications. Key measurements included fuel heat sink, reaction products, and extent of conversion. Full-scale sector rig tests were conducted to characterize the combustion and emissions of supercritical jet fuel, and demonstrate the safety and operability of the fuel system, including a fuel-air heat exchanger.

A series of shock-tube experiments was conducted to measure and compare the ignition-delay times of several fuel candidates for scramjet propulsion and to evaluate the importance of fuel cracking on the autoignition of endothermic-fuel/product mixtures. Ignition delays of ethylene, heptane, and JP-10 were measured in dilute mixtures behind re ected shock waves for temperatures in the range 1100-1500 K, pressures of 3-8 atm, and equivalence ratios of 0.5-1.5. The experimental data were compared to results published for heptane and ethylene, and new ignition-delay correlations were determined from the combined data sets. The resulting expressions were also compared to prior work on methane and hydrogen. In addition, typical endothermic-fuel product mixtures (representing different degrees of cracking of the parent fuel) were simulated and their ignition-delay times measured for equivalence ratios 0.5 and 1.0. The relative ignition-delay times for the different fuels were found to be methane > JP-10 = » » heptane > reformed endothermic fuel > ethylene > hydrogen. The results support the premise that fuel cracking enhances ignition. However, autoignition of the endothermic reaction product mixture is not driven entirely by the constituent with the shortest ignition delay (i.e., ethylene or hydrogen). Furthermore, small changes in concentrations of the individual component species are not likely to make dramatic changes in the ignition-delay times of the fuel. The empirical data were compared to ignition-delay times predicted using detailed chemical kinetics models and they support the validity of published reaction mechanisms for methane and heptane. Introduction I N scramjets rapid spontaneous ignition and reaction of the fuelair mixture are required to achieve ef cient combustionin a practical length. The relatively long ignition-delay times of hydrocarbons relative to hydrogen present a key obstacle to development of storable-fueled scramjets. In addition, autoignition affects heatrelease rates, and, if too rapid, it can promote dynamic instabilities or choking.High-speed propulsion systems are being designed to utilize storable hydrocarbon fuels for cooling and endothermic decomposition of the fuel to increase the available heat sink. Implementation of endothermic reaction technology involves cracking the fuel into a mixture of small hydrocarbons and hydrogen in a heatexchanger/reactor prior to combustion. This reaction will result in the formation of some species (e.g., ethylene and hydrogen) that are more reactivethan the parenthydrocarbonand others(e.g., methane) that are less reactive. Therefore, the design and development of endothermic-fueledcombustors require knowledge of the autoignition characteristics of typical cracked product mixtures as well as the component species.Consequently, shock-tube experiments were performed to measure the ignition-delay times of several candidate scramjet fuels, namely ethylene,heptane,and JP-10, as well as model endothermicfuel/cracked product mixtures. Testing of ethylene...

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Storable hydrocarbon fuels that undergo endothermic reaction provide an attractive heat sink for future high-speed aircraft. An investigation was conducted to explore the endothermic potential of practical fuels, with inexpensive and readily available catalysts, under operating conditions simulative of high-speed flight applications. High heat sink capacities and desirable reaction products have been demonstrated for n-heptane and Norpar 12 fuels using zeolite catalysts in coated-tube reactor configurations. The effects of fuel composition and operating condition on extent of fuel conversion, product composition, and the corresponding endotherm have been examined. The results obtained in this study provide a basis for catalytic-reactor/heat-exchanger design and analysis.