The J-58 was the bi-modal engine under development in the ANP program. The SNAP reactors operate at the auto-ignition temperature of the JP-7 fuel of the Blackbird.
Autoignition of Aviation Fuels: Experimental and Modeling Study P. Gokulakrishnan1, G. Gaines 2, M. S. Klassen 3 and R. J. Roby 4Combustion Science & Engineering, Inc., 8940 Old Annapolis Road, Suite L, Columbia, MD 21045. Atmospheric pressure flow reactor experiments were performed to measure the ignition delay times of JP7, JP8, and S8 fuels between 900 K [1160F] and 1200 K [1700F]. The equivalence ratio of fuel/air mixtures was varied between 0.5 and 1.5. Based on the ignition delay time measurements, the overall activation energies for JP7, JP8, and S8 were determined to be 33, 38, and 49 kcal/mole, respectively. A detailed kinetics model was employed to predict the ignition delay times at these experimental conditions using a surrogate kinetics model consisting of n-decane (n-C10H22), n-propylcyclohexane (C9H18), n-propylbenzene (C9H12), and decene (C10H20) to represent paraffins, naphthenes, aromatics and olefins, respectively. The model predictions are in good agreement with the experimental data. The kinetics model was also able to predict the negative temperature coefficient (NTC) behavior of the jet fuels. The ignition delay time measurements of JP7 were also modeled using a cracked-JP7 surrogate fuel mixture that consisted of CH4, C2H6, C2H4, C3H8, and C3H6. I. Introduction crenamjets that fly between Mach 5 and 15 present great engineering challenges, since flights with hypersonic gines have to successfully operate in different flight regimes1. Currently, hydrogen-fueled propulsion is preferred for hypersonic air-breathing engines with flight Mach numbers of 10 or greater, because of the rapid burning and high mass-specific energy content of hydrogen2. However, lower energy content per unit volume of hydrogen increases the space needed to carry the fuel on-board, and in turn increases the weight of scramjet engine. As a result, liquid hydrocarbon fuels have become viable alternatives to hydrogen at Mach numbers below 10, because of their greater fuel densities and endothermic cooling properties3. In hypersonic engines, endothermic fuels act as a heat sink by cracking into smaller hydrocarbons. However, hydrocarbon fuels pose an inherent difficulty for flame holding under high speed supersonic flows due to their longer ignition delay times and shorter stability windows for blow-off relative to hydrogen. In addition, changes in the chemical composition of fuel, which occur during endothermic cooling via thermal-catalytic reforming4, will have an impact on fuel injection, fuel/air mixing, and flame-stability. Therefore, chemical kinetics models become useful tools for combustion predictions when experimental measurements are not feasible. Thus, the validation of the kinetics models against target experimental data is of paramount importance to obtain reliable model predictions for a given application. Ethylene has been a widely studied hydrocarbon fuel, both experimentally and numerically, for supersonic combustion applications5–8. Ethylene is the most reactive hydrocarbon among the species formed via thermal and/or catalytic cracking of liquid jet fuels during active cooling of the hypersonic engines9 and may be an important component for ignition or extinction events.
Holloway's Commentary
The JP7 fuel for the Blackbird was developed to autoignite in the afterburner of the nuclear engine allowing it to escape into LEO?
The JP7 fuel for the Blackbird was developed to autoignite in the afterburner of the nuclear engine allowing it to escape into LEO?
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