Cavity Ignition and Flameholding of High Speed Fuel-air Flows by a Repetitively Pulsed Nanosecond Discharge PDF Download
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Author: Ashim Dutta Publisher: ISBN: Category : Languages : en Pages : 183
Book Description
Kinetic modeling is used to study the mechanism of low-temperature nanosecond pulse plasma assisted ignition. The reduced kinetic mechanism of plasma assisted ignition of hydrogen has been identified and compared with the full mechanism in a wide range of temperatures and pressures, showing good agreement. Kinetic modeling calculations performed to study the effect of non-thermal radical generation in nanosecond pulse discharge plasma on oxidation/ignition of hydrogen-air mixtures demonstrated that removal of plasma chemical radical generation processes inhibits low-temperature exothermic chemical reactions, thus blocking ignition. It is also observed that presence of radicals produced by the plasma accelerates ignition process significantly and reduces ignition temperature. Finally, the kinetic model has been used to interpret the results of flameholding experiments in premixed ethylene-air and hydrogen-air flows.
Author: Ashim Dutta Publisher: ISBN: Category : Languages : en Pages : 183
Book Description
Kinetic modeling is used to study the mechanism of low-temperature nanosecond pulse plasma assisted ignition. The reduced kinetic mechanism of plasma assisted ignition of hydrogen has been identified and compared with the full mechanism in a wide range of temperatures and pressures, showing good agreement. Kinetic modeling calculations performed to study the effect of non-thermal radical generation in nanosecond pulse discharge plasma on oxidation/ignition of hydrogen-air mixtures demonstrated that removal of plasma chemical radical generation processes inhibits low-temperature exothermic chemical reactions, thus blocking ignition. It is also observed that presence of radicals produced by the plasma accelerates ignition process significantly and reduces ignition temperature. Finally, the kinetic model has been used to interpret the results of flameholding experiments in premixed ethylene-air and hydrogen-air flows.
Author: Ian Dunn Publisher: ISBN: Category : Languages : en Pages : 23
Book Description
The enhanced growth of ignition kernels through modulation of nanosecond pulsed high-frequency discharges is investigated quantitatively in a reactive flow. High-frequency discharge and new notions of rotational temperature coupling per subsequent pulse (
Author: Publisher: ISBN: Category : Languages : en Pages : 14
Book Description
The effect of direct fuel and air injection was experimentally studied in a cavity-based flameholder in a supersonic flow. Cavity- based fuel injection and flameholding offer an obstruction-free flow path in hydrocarbon-fueled supersonic combustion ramjet (scram jet) engines. Additionally, this study included characterization of the operational limits (i.e., sustained combustion limits) over a variety of fuel and air flow rates. The cavity rearward ramp includes 10 spanwise injection ports at each of 3 axial stations configured to inject air, fuel, and air, respectively. Planar laser-induced fluorescence (PLIF) techniques were utilized to collect planar distributions of the OH radical at various axial locations within the cavity under different flow conditions. A high-speed emissions camera was used to evaluate the combustion across the cavity. Direct injection of both fuel and air provided additional capability to tune the cavity such that a more stable decentralized flame results. The addition of air injection provided the most improvement over the baseline case (fuel only) near the upstream portion of the cavity close to the cavity step.
Author: Srivatsava Venkataranga Puranam Publisher: ISBN: 9781124149783 Category : Languages : en Pages : 176
Book Description
Thermodynamic analyses of gas turbine engine cycles have shown that adding energy in the turbine stage improves performance for both aero and stationary gas turbine systems. A curving and contracting test section with a cavity for flame holding was designed to mimic a turbine stator passage. A cavity was used for flame holding because it provided a low speed zone for mixing the fuel and air and allowed for the injection of liquid fuel into the test section. Combustion with a deep cavity (length/depth = 1) showed that for fixed fuel flow rates, as the air flow rate is increased, the combustion goes through three regimes. For very low flow rates, the combustion was confined to the shear layer and for high air flow rates, combustion was distributed through out the cavity and the shear layer and for intermediate flow rates, combustion was intermittent. A simple predictive model showed that the ratio of cavity velocity and the main flow velocity scaled as the square root of Reynolds number based on the momentum thickness. This result was corroborated by experiments. Combustion in a shallow cavity (length/depth = 2) showed that the interaction between the main low and cavity was enhanced compared to deep cavities. This enhancement was seen as a increases in the shear layer spreading rate and the fluctuation of the shear layer and as an improvement in the temperature pattern factor at the exit compared to deep cavities. Configuration changes such as injection location and direction, and cavity location had very little effect on the combustion inside the cavity. Liquid fuel combustion was qualitatively similar to the gaseous fuel case. This suggested that the controlling factor in both cases was the mixing of the fuel and air. A simple time-scale analysis which compared the mixing in the cavity and the mixing in the shear layer showed that the ratio of these time scales varies significantly for the three regimes. A novel image processing technique based on the scale invariant features in images was used to determine velocities in reacting flows where flow seeding was not possible.
Author: John Buckmaster Publisher: Springer Science & Business Media ISBN: 9401110506 Category : Technology & Engineering Languages : en Pages : 639
Book Description
This volume contains the proceedings of the Workshop on Com bustion, sponsored by the Institute for Computer Applications in Science and Engineering (ICASE) and the NASA Langley Research Center (LaRC). It was held on October 12-14, 1992, and was the sec ond workshop in the series on the subject. The first was held in 1989, and its proceedings were published by Springer-Verlag under the title "Major Research Topics in Combustion," edited by M. Y. Hussaini, A. Kumar, and R. G. Voigt. The focus of the second workshop was directed towards the development, analysis, and application of basic models in high speed propulsion of particular interest to NASA. The exploration of a dual approach combining asymptotic and numerical methods for the analysis of the models was particularly encouraged. The objectives of this workshop were i) the genesis of models that would capture or reflect the basic pllysical phenomena in SCRAMJETs and/or oblique detonation-wave engines (ODWE), and ii) the stimulation of a greater interaction between NASA exper imental research community and the academic community. The lead paper by D. Bushnell on the status and issues of high speed propulsion relevant to both the SCRAMJET and the ODWE parallels his keynote address which set the stage of the workshop. Following the lead paper were five technical sessions with titles and chairs: Experiments (C. Rogers), Reacting Free Shear Layers (C. E. Grosch), Detonations (A. K. Kapila), Ignition and Struc ture (J. Buckmaster), and Unsteady Behaviour ('1'. L. Jackson).
Author: Publisher: ISBN: Category : Languages : en Pages : 46
Book Description
Reduced mechanisms for ignition of hydrogen by heated air were deduced for the high-temperature/low-pressure and the low-temperature/high-pressure regimes. The reduced mechanisms were subsequently applied to the physical situations of the supersonic mixing layer and the counterflow through numerical simulation and activation energy asymptotics. Various ignition criteria were derived, and the issues of thermal versus radical induced ignition, external versus internal heating in inducing ignition, and quasi-steady versus transient ignition, were explored.
Author: Ghislain Jean Retaureau Publisher: ISBN: Category : Combustion Languages : en Pages :
Book Description
Flame-holding in a recessed cavity is investigated experimentally in a Mach 2.5 preheated cross-flow for both stable and unstable combustion, with a relatively low preheating. Self-sustained combustion is investigated for stagnation pressures and temperatures reaching 1.4 MPa and 750 K. In particular, cavity blowout is characterized with respect to cavity aspect ratio (L/D =2.84 - 3.84), injection strategy (floor - ramp), aft ramp angle (90 deg - 22.5 deg) and multi-fuel mixture (CH4-H2 or CH4-C2H4 blends). The results show that small hydrogen addition to methane leads to significant increase in flame stability, whereas ethylene addition has a more gradual effect. Since the multi-fuels used here are composed of a slow and a fast chemistry fuel, the resulting blowout region has a slow (methane dominant) and a fast (hydrogen or ethylene dominant) branch. Regardless of the fuel composition, the pressure at blowout is close to the non-reacting pressure imposed by the cross-flow, suggesting that combustion becomes potentially unsustainable in the cavity at the sub-atmospheric pressures encountered in these supersonic studies. The effect of preheating is also investigated and results show that the stability domain broadens with increasing stagnation temperature. However, smaller cavities appear less sensitive to the cross-flow preheating, and stable combustion is achieved over a smaller range of fuel flow rate, which may be the result of limited residence and mixing time. The blowout data point obtained at lower fuel flow rate fairly matches the empirical model developed by Rasmussen et al. for floor injection phi = 0.0028 Da^-.8, where phi is the equivalence ratio and Da the Damkohler number. An alternate model is proposed here that takes into account the ignition to scale the blowout data. Since the mass of air entrained into the cavity cannot be accurately estimated and the cavity temperature is only approximated from the wall temperature, the proposed scaling has some uncertainty. Nevertheless the new phi-Da scaling is shown to preserve the subtleties of the blowout trends as seen in the current experimental data.
Author: Publisher: ISBN: Category : Languages : en Pages : 25
Book Description
Ultra-short combustors to minimize residence time, with special flame-holding mechanisms to cope with increased through-velocities are likely in the future. The Ultra-Compact Combustor (UCC), a novel design based on trapped-vortex combustor (TVC) work that uses high swirl in a circumferential cavity to enhance reaction rates via high cavity g-loading on the order of 3000 g's. Increase in reaction rates translates to a reduced combustor volume. Three combustor geometric features were varied during experiments (1) high-g cavity flame-holding method, (2) high-g cavity to main airflow transport method, and (3) fuel injection method. Results have shown promise for advanced engine applications. Lean blowout fuel-air ratio limits at 25-50% the value of current systems were demonstrated. Combustion efficiency was measured over a wide range of UCC operating conditions. This data begins to build the design space required for future engine designs that may use these novel, compact, high-g combustion systems.
Author: Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
We describe experiments on gaseous fuel ignition and flameholding controlled by an electrical discharge in high speed airflow. The geometrical configuration does not include any mechanical or physical flameholder. The fuel is nonpremixed and injected directly into the air crossflow from the combustor bottom wall. A multi-electrode, nonuniform transversal electrical discharge is excited, also on the bottom wall, between flush-mounted electrodes. The initial gas temperature is lower than the value for autoignition of hydrogen and ethylene. Results are presented for a wide range of fuel mass flow rate and discharge power deposited into the flow. This coupling between the discharge and the flow presents a new type of flameholder over a plane wall for a high-speed combustor.
Author: Ashim Dutta
Author: Ashim Dutta
Author: Ian Dunn
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Author: William H. Allen (Jr.)
Author: Srivatsava Venkataranga Puranam
Author: John Buckmaster
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Author: Ghislain Jean Retaureau
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