Characterization of a Spark Ignition System for Flameholding Cavities

The significant volume constraints placed on the design of airframe-integrated scramjet engines calls for fuels with high volumetric energy densities. Therefore, low-order hydrocarbons, such as ethylene and methane are candidates for use in engines such as the Mach 8 Rectangular-to-Elliptical Shape Transition (REST) engine, a flowpath which has been extensively tested for hydrogen. Cavity flameholders are being investigated as a means of ensuring the robust combustion of these fuels. A modular cavity has been designed for a Mach 8 REST engine model suitable for shock tunnel testing. The depth, L/D ratio, and aft wall angle of the cavity flameholder have been determined using previous experimental studies, coupled with axisymmetric simulations. The L/D ratio and aft wall angle have been chosen to minimise stagnation pressure losses and promote a stable flowfield for flameholding. Unsteady axisymmetric simulations reveal that for all cavity depths investigated, the recirculating cavity flow is established within a small fraction of the test time available in the University of Queensland's T4 Hypersonic Shock Tunnel. The flow temperatures and pressures achieved within the simulated cavities are used in conjunction with correlations for cavity depth and fuel ignition delay time to estimate the cavity depths required to auto-ignite low-order hydrocarbon fuels. Consideration is also given to the level of disturbance to the flow through the core of the combustor caused by cavities of various depths. The initial cavity dimensions selected to be experimentally tested are L/D ratio, depth and aft wall angle of 4.0, 4.4 mm, and 22.5 • , respectively. Analysis indicates conditions in this cavity should cause the autoignition of ethylene. An external ignition source, using conventional spark plugs, will be installed in the cavity to promote ignition of the low-order hydrocarbon fuels, should autoignition not occur. Nomenclature[C x H y ] Concentration of fuel, mol/cc [O 2 ] Concentration of oxidiser, mol/cc φ Fuel equivalence ratio τ ign Ignition delay time, s τ r Required residence of cavity, s A Empirically determined constant for ignition delay time a, b Power dependencies of ignition delay time for oxidiser and fuel concentrations D Depth of cavity, m E Global activation energy, kcal/mol

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“…26 The design of the cavity in the model engine is modular so that various dimensions may be tested.…”

Section: Iiia Cavity Design Methodologymentioning

confidence: 99%

Experimental Design of a Cavity Flameholder in a Mach 8 Shape-Transitioning Scramjet

Denman

Brieschenk

Veeraragavan

et al. 2014

19th AIAA International Space Planes and Hypersonic Systems and Technologies Conference

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“…Field-effect transistors (FET) have been widely used in microelectronic devices, from the basis for modern digital integrated circuits [1] to combustion engine ignition coils [2]. Different implementations of FETs have been developed.…”

Section: Introductionmentioning

confidence: 99%

Wire-Based Core Field Effect Transistor (CoreFET)

Chen¹,

Qiao²,

Milo³

et al. 2019

NanoWorld J

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We report a novel proof-of-concept FET design (CoreFET) based on a thin wire, which can be fabricated without any micromanufacturing processes. Zinc oxide (ZnO) and Poly(3-hexylthiophene) (P3HT) were used to develop thin film CoreFETs, with the central core of a wire acting as a gate terminal. The design may be used for multiple electronic and optoelectronic devices, and the unique wire shape renders it favorable for specific applications, such as chemical and biological sensing.

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“…Therefore, the ignition in the spray combustion of a liquid fuel can be divided into three different ignition states: droplet ignition, droplet group ignition, and spray ignition [2]. Because of the complexity and importance of spray ignition of a liquid fuel, numerous studies have been conducted over the years, and the key factors that affect the ignition performance and improved ignition measures have been determined [3][4][5][6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Effect of Airflow Temperature on the Formation of Initial Flame Kernel and the Propagation Characteristics of Flame

Chen

et al. 2018

International Journal of Aerospace Engineering

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Using liquid RP-3 aviation kerosene as the fuel to study, the effect of airflow temperature on the formation of initial flame kernel during the ignition of spray combustion and on the propagation characteristics of flame was investigated. Combining high-speed camera and dynamic temperature acquisitions at the outlet of combustor, the internal triggering mode was used under a constant fuel flow rate and airflow velocity. This combined system simultaneously recorded the formation of initial flame kernel, flame propagation, and outlet temperature variation of combustor under different airflow temperatures. MATLAB software was used to obtain the reaction zones at different moments and to analyze the effects of airflow temperature on morphological characteristics such as flame area, perimeter-to-area ratio, maximum length-to-height ratio, equivalent mean length-to-height ratio, mass center, and centroid. According to the growth rate in flame area, the ignition process can be divided into three stages: formation of flame kernel, rapid development of flame, and stable development of flame. Airflow temperature not only affects the formation time of flame kernel but also affects the growth rate of flame area. During the development of flame, the movements of mass center and centroid are irregular, and their positions do not coincide with each other. However, the overall moving trends are consistent. With the increase of the airflow temperature, the position, where the flame kernel is gradually formed, moves closer to the center of the end face of spark plug. The force of airflow on flame is the main factor that increases the flame area and heat-release rate. Therefore, the folds around the flame edge mainly result from the stretching under the action of airflow. With the increase in airflow temperature, the heat release of the initial flame kernel increases, and the ratio of perimeter to area as a characterization parameter increases by 8%, 86%, and 33%, respectively. In addition, the maximum outlet temperature rise increased by about 53%, 73.5%, and 0.65%, respectively. Meanwhile, the maximum rate of temperature rise increased by about 42.8%, 57%, and 5.1%, respectively.

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Characterization of a Spark Ignition System for Flameholding Cavities

Cited by 3 publications

References 21 publications

Experimental Design of a Cavity Flameholder in a Mach 8 Shape-Transitioning Scramjet

Experimental Design of a Cavity Flameholder in a Mach 8 Shape-Transitioning Scramjet

Wire-Based Core Field Effect Transistor (CoreFET)

Effect of Airflow Temperature on the Formation of Initial Flame Kernel and the Propagation Characteristics of Flame

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