Ethylene augmentation of JP-8+100 in a supersonic combustor

Bateup, Mark Lee (2012). Ethylene augmentation of JP-8+100 in a supersonic combustor PhD Thesis, School of Mechanical and Mining Engineering, The University of Queensland.

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Author Bateup, Mark Lee
Thesis Title Ethylene augmentation of JP-8+100 in a supersonic combustor
Formatted title
Ethylene Augmentation of JP-8+100 in a Supersonic Combustor
School, Centre or Institute School of Mechanical and Mining Engineering
Institution The University of Queensland
Publication date 2012
Thesis type PhD Thesis
Supervisor Allan Paull
David Mee
Total pages 237
Total colour pages 43
Total black and white pages 194
Language eng
Subjects 090107 Hypersonic Propulsion and Hypersonic Aerodynamics
Formatted abstract
    The choice of fuel used in a scramjet combustor has a direct influence on the length of the combustor. The length depends upon the time required for the fuel to mix, react and complete the combustion reaction. The viscous drag within the combustor and the area subjected to combustion heat loads, also scale with length. Therefore, assessing the necessary combustor length for a particular fuel choice is a key step in scramjet combustor design. Furthermore, any means of reducing the length offers a valuable corresponding reduction of drag force and heat loads on the vehicle.

    This thesis reports an investigation to quantify the effect that short-chain hydrocarbons have on the ignition of long-chain hydrocarbons in a scramjet combustor. The fuel, JP-8+100, is tested in a representative scramjet duct in the T4 Stalker Tube at the University of Queensland. This study investigates the effectiveness of reducing the ignition length of JP-8+100 by augmenting it with ethylene. Ethylene was used as it has an order of magnitude shorter ignition delay than does JP-8+100 under comparable conditions. Ethylene is also one of the principal constituents of pyrolytic reactions during fuel decomposition. The direct addition of ethylene to JP-8+100 provides a first order approximation to the more complex reactions that occur in endothermic fuel reformation.

    In order to manage the long ignition delay times of liquid JP-8+100 in the impulsive test facility, a new fuelling technique was developed and implemented. The approach was to design a fuel supply system capable of taking both liquid and gaseous hydrocarbon fuels and heating them until they became vaporised. An experimental investigation was then carried out in which the pre-vaporised fuel was injected through a central strut into a constant area rectangular duct. The injection took place parallel to the main flow stream. The experiments were of the semi-direct-connect type, where the incoming test gas was compressed by a pair of wedges inclined to the flow to deliver the desired conditions at the combustor inlet.

    Experimental data are presented for the ignition lengths of JP-8+100 in a supersonic flow stream at Mach 2.7 and compared with data from blends of JP-8+100 with 0.01 to 0.86 mole fraction of ethylene. Combustion was observed by measuring the axial pressure distribution in the combustor. Ignition was observed when the coefficient of pressure rose above the baseline fuel-off and suppressed combustion cases. The temperature of the inlet air was varied from 1100 K to 1600 K to examine the effect on the ignition length at a pressure of 1 atm for equivalence ratios 0.1 < Φ < 2.

    Ignition correlations for hydrogen and short-chain hydrocarbon fuels have been previously verified as applicable in a scramjet combustor in impulse facilities, but this is not available for long-chain hydrocarbon fuels. The data from the JP-8+100 experiments provide this verification. Comparisons are made with data from reflected shock tube facilities to show that the experimental results measured within the scramjet combustor are consistent with ignition delay correlations generated under stationary homogeneous pre-mixed conditions.

    The addition of ethylene to the JP-8+100 is shown to have no measurable effect on shortening the ignition length across a wide range of mole fractions. The concept of ethylene augmentation does not appear to work. The JP-8+100 dominates the ignition pathway and there is no reduction in ignition length. The results suggest that the presence of parent hydrocarbons in the fuel mixture have a dominant effect on the ignition chemistry. A similar result is reported in the literature where the addition of hydrogen to a jet-fuel surrogate, in amounts representative of those formed during endothermic fuel decomposition, had a limited effect on reducing ignition delay times. Together, these results imply that the proposed benefits from endothermic fuels may be limited to the heat-sink capacity of the fuel alone, as there is no measurable benefit in reduced ignition delay times when there is un-reformed fuel present and suggests that the ignition delay is not driven by the component with the shortest ignition delay time.
Keyword Scramjet
Supersonic combustion
Ethylene augmentation
Air breathing propulsion

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Created: Wed, 07 Aug 2013, 00:30:22 EST by Mark Bateup on behalf of Scholarly Communication and Digitisation Service