Download or read book Effect of Flow Distortion on Fuel Mixing and Combustion in an Upstream fueled Cavity Flameholder for a Supersonic Combustor written by Steven J. Etheridge and published by . This book was released on 2012 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: Typical studies of scramjet combustion employ as uniform a flowpath as possible. These studies are important to isolate the effects of a given combustor configuration. However, such studies tend to ignore the effects of a shock train created by the vehicle installation and that this shock train changes over the flight envelope. Consequently, the performance of a given configuration is measured without considering the considerable effects of this shock train or how it changes with different flight conditions. This thesis includes experimental and computational studies of the effects of an incident shockwave on the flowfield, fuel distribution and combustion within a cavity flameholder with upstream fuel injection. The effect of the shockwave location (on the upstream fuel jet or over the cavity) and shock angle are controlled by adjusting a shock generator mounted in the tunnel test section. The effect of fuel injection momentum ratio is also examined. Shadowgraphy is used to characterize the flowfield while planar laser induced fluorescence of the NO and OH molecules are used to measure the fuel mixing and combustion, respectively. These experimental data are compared with CFD solutions of the Reynolds Averaged Navier-Stokes equations provided in previous CFD work. The effect of the shock on the cavity shear layer is found to control the fuel distribution within the cavity. The shock on jet impingement forces the shear layer deep within the cavity and results in higher concentrations near the cavity centerline, but low mixing uniformity. The shock on cavity case causes the shear layer to separate upstream of the cavity, mixing uniformity is enhanced by the increased breakup of the fuel plume. Combustion is stronger and more uniform in the shock on cavity case, while it is limited to the edges of the cavity with shock impingement on the jet. The greater mixing afforded in the shock on cavity case reduces the fuel concentration near the centerline and permits stronger burning in the center of the cavity. Small changes in the fuel injection momentum ratio (doubling) do not strongly affect the pattern of fuel distribution in any case. Combustion in the shock on cavity case is reduced by increasing fuel injection momentum because the fuel concentration at the centerline is too high. Small increases in the shock angle did not strongly affect the results.

Download or read book Airbreathing Hypersonic Propulsion written by Claudio Bruno and published by Springer Nature. This book was released on 2023-11-27 with total page 314 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book details science of hypersonics especially focusing on propulsion aspects such as supersonic combustion ramjets and their applications, and also includes lift and drag in hypersonic flight and their mathematical and physical explanation. It provides charts and data from hypersonic testing and measurements from actual vehicles and engines built in the past. Criteria to dimension hypersonic powered and unpowered vehicles (gliders) based on fundamental fluid dynamics and backed by flight testing; criteria to preliminary sizing vehicles and preliminary dimensioning of supersonic combustors are introduced. The book will serve better theoretical understanding of drag, lift and how to apply them to the design of hypersonic vehicles, as well as data to size vehicles and supersonic combustion ramjet (SCRJ) systems. This book will be a useful reference for researchers and designers in hypersonic vehicles but also second or third-year graduate students.

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 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 Pylon Effects on a Scramjet Cavity Flameholder Flowfield written by Andrew B. Freeborn and published by . This book was released on 2008 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fundamental Investigations of an Integrated Fuel Injector Flameholder Concept for Supersonic Combustion written by and published by . This book was released on 1998 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes the results of a recent series of experiments designed to examine the fundamental behavior of several cavity-based flameholder candidates in a non-reacting supersonic flow. Seven geometries were tested in conjunction with a new facility nozzle. Results indicate that the cavity aft ramp plays a strong role in determining the character of the shear layer which spans the length of the cavity. For rectangular cavities, a compression wave forms as the flow separates from the upstream corner of the cavity. Thus, the pressure on the upstream face increases above the freestream value. In these cases, the recompression which occurs at the aft wall is very sharp with strong pressure gradients at the axial location corresponding to the aft wall. These cases are also visibly unsteady. Reductions in the ramp angle yield more stable, two-dimensional flowfields. However, the character of the separation wave changes gradually from compressive to expansive as the ramp angle is reduced. As such, the shear layer tends to dip into the cavity and the recompression occurs more gradually as the shear layer reattaches to the aft wall. Changes in cavity offset ratio result in more dramatic changes in the cavity flowfield. The separation wave becomes strongly expansive leading to severe shear layer intrusion into the cavity. Aft wall changes do not strongly impact the character of the shear layer, although stability is enhanced and recompression is more gradual for shallower ramp angles.

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 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 Characterization of Upstream Mixing Cavities and a Downstream Combustion Cavity in a Supersonic Flow written by Adam Quick and published by . This book was released on 2005 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Performance Measurements of Direct Air Injection in a Cavity based Flameholder for a Supersonic Combustor written by Scott G. Edens and published by . This book was released on 2005 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fuel Distribution about a Cavity Flameholder in Supersonic Flow written by K.-Y. Hsu and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Swirler mounted Mixing Venturi on Emissions of Flame tube Combustor Using Jet A Fuel written by David B. Ercegovic and published by . This book was released on 1979 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effects of Fuel Injection on Mixing and Upstream Interactions in Supersonic Flow written by Qiuya Tu and published by . This book was released on 2013 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: Simulation for shock wave/ boundary-layer interaction was conducted in Fluent for case of M=1.9 at 60% blockage by using k- RNG model with two different near wall treatments. In both cases, the shock ran out of isolator before the computation converged, this is different from experimental results. Proper actual wall friction force may have a very important effect on the computation, which needs to be evaluated.

Download or read book Flame Characteristics and Fuel Entrainment Inside a Cavity Flame Holder in a Scramjet Combustor Postprint written by and published by . This book was released on 2007 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame structures and operating limits of an ethylene-fueled recessed cavity flameholder were investigated both experimentally and numerically, using a newly developed AFRL research scram jet flowpath at Wright-Patterson Air Force Base. Flush-wall low-angled injectors were used as main fuel injectors. The recessed cavity features an array of fueling ports on the aft ramp for direct cavity fueling. The cavity operating conditions include 1) direct cavity fueling, 2) direct cavity fueling with back pressurization, and 3) fueling from main injectors with and without direct cavity fueling. With direct cavity fueling, significant variation in the shape and spatial distribution of the cavity flame was observed at various fuel flow rates with and without back pressurization. It was found that both lean ignition and blowout limits increase with the characteristic air flow rate. The lean blowout limit is decreased toward a lower value as the shock train is pushed toward upstream. With fueling from main injectors, the flame is mainly distributed within the body wall comers for the present flowpath.

Download or read book Effects of Combustion Induced Vortex Breakdown on Flashback Limits of Syngas Fueled Gas Turbine Combustors written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbine combustors of advanced power systems have goals to achieve very low pollutants emissions, fuel variability, and fuel flexibility. Future generation gas turbine combustors should tolerate fuel compositions ranging from natural gas to a broad range of syngas without sacrificing operational advantages and low emission characteristics. Additionally, current designs of advanced turbine combustors use various degrees of swirl and lean premixing for stabilizing flames and controlling high temperature NOx formation zones. However, issues of fuel variability and NOx control through premixing also bring a number of concerns, especially combustor flashback and flame blowout. Flashback is a combustion condition at which the flame propagates upstream against the gas stream into the burner tube. Flashback is a critical issue for premixed combustor designs, because it not only causes serious hardware damages but also increases pollutant emissions. In swirl stabilized lean premixed turbine combustors onset of flashback may occur due to (i) boundary layer flame propagation (critical velocity gradient), (ii) turbulent flame propagation in core flow, (iii) combustion instabilities, and (iv) upstream flame propagation induced by combustion induced vortex breakdown (CIVB). Flashback due to first two foregoing mechanisms is a topic of classical interest and has been studied extensively. Generally, analytical theories and experimental determinations of laminar and turbulent burning velocities model these mechanisms with sufficient precision for design usages. However, the swirling flow complicates the flashback processes in premixed combustions and the first two mechanisms inadequately describe the flashback propensity of most practical combustor designs. The presence of hydrogen in syngas significantly increases the potential for flashback. Due to high laminar burning velocity and low lean flammability limit, hydrogen tends to shift the combustor operating conditions towards flashback regime. Even a small amount of hydrogen in a fuel blend triggers the onset of flashback by altering the kinetics and thermophysical characteristics of the mixture. Additionally, the presence of hydrogen in the fuel mixture modifies the response of the flame to the global effects of stretch and preferential diffusion. Despite its immense importance in fuel flexible combustor design, little is known about the magnitude of fuel effects on CIVB induced flashback mechanism. Hence, this project investigates the effects of syngas compositions on flashback resulting from combustion induced vortex breakdown. The project uses controlled experiments and parametric modeling to understand the velocity field and flame interaction leading to CIVB driven flashback.

Download or read book Supersonic Combustion Experiments with a Cavity Based Fuel Injector Postprint written by and published by . This book was released on 2001 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent results from combustion experiments in a direct-connect supersonic combustor are presented. Successful ignition and sustained combustion of gaseous ethylene have been achieved using an injector/flameholder concept with low-angle, flush-wall fuel injection upstream of a wall cavity. Two interchangeable facility nozzles (Mach 1.8 and 2.2) were used to obtain combustor inlet flow properties that simulate flight conditions between Mach 4 and 6 at a dynamic pressure of 47.9 kPa. Mainstream combustion was achieved at equivalence ratios between 0.25 and 0.75 using only a spark plug and no other external ignition aids. Delta-force levels between 667 and 1779 N were measured, with corresponding combustor pressure ratios between 3.1 and 4.0. Video records of the flame zone show an intensely active combustion zone with rapid flame spreading. One-dimensional performance analysis of the test data indicates a combustion efficiency around 80% with an average combustor skin friction coefficient of 0.0028.

Download or read book Scramjet Propulsion written by E. T. Curran and published by AIAA. This book was released on 2001 with total page 1354 pages. Available in PDF, EPUB and Kindle. Book excerpt: