Download or read book Cavity Ignition and Flameholding of High Speed Fuel air Flows by a Repetitively Pulsed Nanosecond Discharge written by Ashim Dutta and published by . This book was released on 2011 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Fuel Air Injection Effects on Combustion in Cavity Based Flameholders in a Supersonic Flow Postprint written by and published by . This book was released on 2005 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Flame Kernel Ignition and Evolution Induced by Modulated Nanosecond pulsed High frequency Discharge written by Ian Dunn and published by . This book was released on 2020 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 (

Download or read book Fuel air Injection Effects on Combustion in Cavity based Flameholders in a Supersonic Flow written by William H. Allen (Jr.) and published by . This book was released on 2005 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Combustion in Cavities and Accelerating Flows written by Srivatsava Venkataranga Puranam and published by . This book was released on 2010 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Experiments on Electrically Controlled Flameholding on a Plane Wall in Supersonic Airflow POSTPRINT written by and published by . This book was released on 2010 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Combustion in High Speed Flows written by John Buckmaster and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 639 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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).

Download or read book Ignition and Flame Stabilization in High Speed Flows written by and published by . This book was released on 1997 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book On Recessed Cavity Flame holders in Supersonic Cross flows written by Ghislain Jean Retaureau and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book High Gravity g Combustion written by and published by . This book was released on 2006 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Experimental Study of Cavity strut Combustion in Supersonic Flow postprint written by K.-Y. Hsü and published by . This book was released on 2007 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation of cavity-based flameholders with strut injectors in a supersonic flow is reported. In this ongoing research program, emphases are placed on understanding cavity-based flameholders and providing alternative methods for improving overall combustor performance in scramjet engines. Three different struts with fuel injectors are mounted near the cavity leading edge to study flame propagation and ignition of fuel in the core flow region. OH-PLIF (planar laser induced fluorescence) is used to identify the flame zone around the cavity and strut-wake regions over a range of conditions. Shadowgraphy is used to capture the flow features around the strut and cavity. In-stream probing is conducted to characterize the flow features associated with the different strut configurations. Stagnationtemperature profiles are obtained for all struts operating over the same conditions in the combusting-flow study. Two cavity fueling schemes are used to compare flameholder performance. Direct cavity air injection is found to improve combustion significantly. For each strut, upstream and downstream fueling schemes are compared over a range of conditions.--P. i.

Download or read book Spark Ignition of Flowing Gases written by Clyde C. Swett and published by . This book was released on 1954 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advanced ignition for automotive engines written by Daniel Ivan Pineda and published by . This book was released on 2005 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spark plugs have been igniting combustible mixtures like those found in automotive engines for over a century, and the principles of the associated ignition techniques using thermal plasma (inductive or capacitive sparks) have remained relatively unchanged during that time. However, internal combustion engines are increasingly operating with boosted intake pressures (i.e. turbo- or super-charged) in order to maintain power output while simultaneously reducing engine size and weight, and they are also operating with increased recirculated exhaust gas dilution to reduce the production of harmful nitrogen oxides. This “downsizing” to increase fuel economy compounded with diluting to decrease emissions leads to challenges in both obtaining traditional ignition and promoting sufficiently fast combustion under this operating paradigm. In conjunction with appropriate electrode design, transient non-thermal plasma can exploit certain non-equilibrium chemistry and physics to bypass these challenges and ultimately promote more reliable ignition and faster combustion. Applied and fundamental experimental investigations of two different advanced ignition techniques are presented: 1) corona discharges igniting gasoline/air/exhaust mixtures in a boosted direct- injection single cylinder research engine and 2) repetitively pulsed nanosecond discharges igniting methane/air mixtures in a constant volume chamber. The engine experimental results show significant decreases in fuel consumption and nitrogen oxide emissions under boosted operation, and both experiments demonstrate more robust ignition and faster flame development. The constant volume chamber results in particular raise important questions about the relative contributions of chemistry and transport to the experimentally observed combustion enhancement. These results highlight the critical importance of electrode design in advanced ignition techniques—the shape and position of electrodes greatly influences the hydrodynamics of developing flame kernels into fuel-air charges. While this work demonstrates that non-thermal plasma ignition is a promising solution to both increase fuel economy and decrease emissions of future automotive engines, much work remains to be done to understand the beneficial coupling between the detailed non-thermal plasma chemistry and the hydrodynamics associated with these real ignition devices.

Download or read book Characterization of Transient Plasma Ignition Flame Kernel Growth for Varying Inlet Conditions written by and published by . This book was released on 2009 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pulse detonation engines (PDEs) have the potential to significantly improve the efficiency of a variety of internal combustion engine designs. This efficiency improvement hinges on the ability of the engine to detonate fuel/air mixture through deflagration-to-detonation transitions at 60 to 100 times a second. A major breakthrough in reducing the cycle time of a pulse detonation device is through the use of a Transient Plasma Ignition (TPI) system vice the normal Capacitive Discharge Ignition (CDI) system. The TPI system deposits an equivalent amount of energy as the CDI system but in a fraction of the time and over a larger combustor volume. The TPI also creates high quantities of OH due to the high density of energetic electrons produced by the TPI event. The combination of decreased energy deposition time, larger ignition volume, and a high density of free radicals reduces the flame kernel growth time, which in turn creates a choked flame condition more rapidly. This thesis characterized the flame kernel growth following a transient plasma ignition event for various combustor inlet configurations so as to better understand the flame patterns within the combustion chamber. High-speed images of the combustor were taken from a side profile and end view to observe the flame growth. Time from ignition event until initial flame kernel observation and from ignition event until fully developed flame were gathered from the images and plotted to find the most favorable inlet condition.

Download or read book Fuel Spray Ignition by Hot Surfaces and Aircraft Fire Stabilization written by J. G. Skifstad and published by . This book was released on 1986 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: In Task 1 an experimental study of the ignition of Jet-A fuel sprays by an isothermal hot surface was conducted in a vertical axisymmetric duct. In addition to measurements of the wall temperature necessary for ignition, local measurements of velocity, turbulence intensity, fuel concentration, and the fraction of fuel vaporized were measured in the boundary layer at surface temperatures just below that required for ignition. In Task 2 two combustion tunnel facilities were used to investigate the stabilization of aircraft fires. Results showed that the shape of a bluff-body flameholder affects its stability characteristics through its influence on the size and shape of the wake region. Another significant finding was that the flameholding properties of the single-vortex flow pattern are markedly superior to those of the double-vortex pattern. In Task 3 experimental studies were conducted on: (1) Entrainment of an external flow into a cavity, with a small opening or vent in a side wall, when there is a small flow through the cavity; and (2) Fluid dynamics and ignition and flame stability characteristics of a jet of gaseous fuel through a protrusion of different shapes and heights in the wall of a cavity with a small flow of air through the cavity.

Download or read book Knocking Combustion Observed in a Spark ignition Engine with Simultaneous Direct and Schilieren High speed Motion Pictures and Pressure Recorders written by Benjamin Pinkel and published by . This book was released on 1947 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mean Pressure Gradient Effects on Flame flow Dynamics in a Cavity Combustor written by David Michael Smerina and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pressure gradient confinement effects are experimentally investigated within a cavity combustor to analyze the flame interactions of premixed, cavity stabilized, flames in a high-speed combustor. Pressure gradient confinement effects are generated in a dual mode ramjet-scramjet (DMSR) by varying the wall geometry to form converging, diverging, and nominal configurations. The velocity field and flame position are captured temporally using simultaneous high-speed particle image velocimetry (PIV) and CH chemiluminescence. The evolution of the flow field and flame structure are analyzed, and the high temporal resolution of these measurements allows for the characterization of turbulence-flame interactions. Consideration of the combustion mode and inlet conditions, such as the inflow velocity and turbulence, are vital in studying flame-vortex interaction dynamics and its effect on the flame stabilization process and is essential in ensuring efficient, complete combustion. The results from the experiment will provide a greater understanding of how flame-vorticity interactions and pressure gradient confinement effects play a key role in the flame-stabilization and combustion process.