Download or read book Deflagration to Detonation Transition Initiation in Pulsed Detonation Engines written by and published by . This book was released on 2004 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report results from a contract tasking Imperial College Consultants Limited (ICON) as follows: It is here proposed to build upon the experience gained and extend ongoing work in two directions. The first is related to the sensitivity of the initial explosion phase to the state of the mixture resulting from injection of the relevant mixture. The second aspect of the proposed work features computations of two-dimensional unsteady flows with comprehensive chemistry and a transported PDF approach closed at the joint scalar level. The contractor proposes the evaluation of a computational approach in the context of the computation of time-dependent compressible flows in two spatial dimensions. Such computations constitute an essential step in the direction of establishing an ability to model Deflagration to Detonation Transition (DDT) in the context of POEs and are exceptionally resource intensive. Although a limited study is here proposed to be accomplished (due to funds limitations). it is expected that significant information will be gained.

Download or read book A Study of Deflagration to Detonation Transition in a Pulsed Detonation Engine written by David Michael Chapin and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A Pulse Detonation Engine (PDE) is a propulsion device that takes advantage of the pressure rise inherent to the efficient burning of fuel-air mixtures via detonations. Detonation initiation is a critical process that occurs in the cycle of a PDE. A practical method of detonation initiation is Deflagration-to-Detonation Transition (DDT), which describes the transition of a subsonic deflagration, created using low initiation energies, to a supersonic detonation. This thesis presents the effects of obstacle spacing, blockage ratio, DDT section length, and airflow on DDT behavior in hydrogen-air and ethylene-air mixtures for a repeating PDE. These experiments were performed on a 2 diameter, 40 long, continuous-flow PDE located at the General Electric Global Research Center in Niskayuna, New York. A fundamental study of experiments performed on a modular orifice plate DDT geometry revealed that all three factors tested (obstacle blockage ratio, length of DDT section, and spacing between obstacles) have a statistically significant effect on flame acceleration. All of the interactions between the factors, except for the interaction of the blockage ratio with the spacing between obstacles, were also significant. To better capture the non-linearity of the DDT process, further studies were performed using a clear detonation chamber and a high-speed digital camera to track the flame chemiluminescence as it progressed through the PDE. Results show that the presence of excess obstacles, past what is minimally required to transition the flame to detonation, hinders the length and time to transition to detonation. Other key findings show that increasing the mass flow-rate of air through the PDE significantly reduces the run-up time of DDT, while having minimal effect on run-up distance. These experimental results provided validation runs for computational studies. In some cases as little as 20% difference was seen. The minimum DDT length for 0.15 lb/s hydrogen-air studies was 8 L/D from the spark location, while for ethylene it was 16 L/D. It was also observed that increasing the airflow rate through the tube from 0.1 to 0.3 lbs/sec decreased the time required for DDT by 26%, from 3.9 ms to 2.9 ms.

Download or read book Direct Initiation Through Detonation Branching in a Pulsed Detonation Engine written by Alexander R. Hausman and published by . This book was released on 2008 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Development of a Gas Fed Pulse Detonation Research Engine written by R. J. Litchford and published by . This book was released on 2001 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Detonation Initiation Studies and Performance Results for Pulsed Detonation Engine Applications written by and published by . This book was released on 2001 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: An in-house computational and experimental program to investigate and develop an air breathing pulse detonation engine (PDE) that uses a practical fuel (kerosene based, fleet-wide use, JP type) is currently underway at the Combustion Sciences Branch of the Turbine Engine Division of the Air Force Research Laboratory (AFRL/PRTS). PDE's have the potential of high thrust, low weight, low cost, high scalability, and wide operating range, but several technological hurdles must be overcome before a practical engine can be designed. This research effort involves investigating such critical issues as: detonation initiation and propagation; valving, timing and control; instrumentation and diagnostics; purging, heat transfer, and repetition rate; noise and multi-tube effects; detonation and deflagration to detonation transition modeling; and performance prediction and analysis. An innovative, four-detonation-tube engine design is currently in test and evaluation. Preliminary data are obtained with premixed hydrogen/air as the fuel/oxidizer to demonstrate proof of concept and verify models. Techniques for initiating detonations in hydrogen/air mixtures are developed without the use of oxygen enriched air. An overview of the AFRL/PRTS PDE development research program and hydrogen/air results are presented.

Download or read book Detonation Initiation of Hydrocarbon Air Mixtures in a Pulsed Detonation Engine written by and published by . This book was released on 2005 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: Detonation initiation of hydrocarbon-air mixtures is critical to the development of the pulsed detonation engine (PDE). Conventionally, oxygen enrichment (such as a predetonator) or explosives are utilized to initiate detonations in hydrocarbon/air mixtures. While often effective, such approaches have performance and infrastructure issues associated with carrying and utilizing the reactive components. An alternative approach is to accelerate conventional deflagration-to-detonation speeds via deflagration-to-detonation transition (DDT). Analysis of hydrocarbon-air detonability indicates that mixing and stoichiometry are crucial to successful DDT. A conventional Schelkin-type spiral is used to obtain DDT in hydrocarbon-air mixtures with no excess oxidizer. The spiral is observed to increase deflagrative flame speeds (through increased turbulence and flame mixing) and produce 'hot-spots' that are thought to be compression-wave reflections. These hot spots result in micro-explosions that, in turn, then give rise to DDT. Time-of-flight analysis of high-frequency pressure-transducer traces indicate that the wavespeeds typically accelerate to over-driven detonation during DDT before stabilizing at Chapman-Jouget levels as the combustion front propagates down the detonation tube. Results obtained for a variety of fuels indicate that DDT of hydrocarbon-air mixtures is possible in a PDE.

Download or read book Detonation Initiation and Evolution in Spray Fueled Pulsed Detonation Rocket Engines written by and published by . This book was released on 2007 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: Successful pulsed detonation engine operation requires robust, reliable, repetitive detonation initiation and evolution, up to 100 times per second. Spark-initiated combustion of fuel-oxidizer mixtures appears to be the operational technology. Our research program was designed to model the transient events following time-resolved deposition of thermal energy into a finite volume of reactive mixture. Computational solutions of the reactive Euler equations are used to predict the time history of deflagration to detonation transitions (DDT's). Solutions describe the temporal variation of the spatial distributions of temperature, pressure and fuel concentration. The presence of shocks, localized reactive hot spots and high speed reaction zones are noted. Solution dependence on the location of the initial power deposition, the amount of power deposition and the activation energy on a one step reaction is investigated. In all cases the DDT process is facilitated by the spontaneous appearance of localized high pressure and temperature ":reaction centers" that are the subsequent sources of acoustic compression waves.

Download or read book High Speed Deflagration and Detonation Fundamentals and Control International Colloquium on Control and Detonation Processes Held in Moscow Russia on July 4 7 2000 written by and published by . This book was released on 2001 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: Twenty two papers on fundamentals of high-speed deflagrations and detonations written by international experts are assembled in this volume. The papers have been presented at the International Colloquium on Control of Detonation Processes held in Moscow, Russia on July 4-7, 2000. Various aspects of deflagration to detonation transition as well as direct detonation initiation in gaseous and heterogeneous media are discussed with the emphasis on control of the predetonation distance and parameters of transient high-speed combustion regimes. Applications of various explosion control techniques to pulsed detonation engines (PDE) are described.

Download or read book Belle Meader Collection written by and published by . This book was released on 1860 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Deflagration to Detonation Transition Processes in Pulsed Detonation Engines written by and published by . This book was released on 2002 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of the work performed in the current contract is to assess the accuracy of potential modelling techniques applied to the formation of Deflagration to Detonation (DDT) kernels in mixtures of hydrocarbons with air. The application area is of direct relevance to the transition to detonation in pulsed detonation engines featuring premixed gases. The latter technology is currently pursued at Wright Laboratories and the current evaluation is directly linked to this technology. Key aspects covered include guidance on suitable theoretical development directions and a preliminary investigation of optimal conditions for transition to detonation. The work is technically demanding and features several aspects that has not previously been accomplished. The main conclusions of the study are perhaps surprisingly positive. The work does show, for the first time, that the application of higher moment closures to model the initial onset of DDT is technically possible. Furthermore, the work illustrates that two physical limits on the chemical source term closure does in most cases bracket the experimental data. It is also shown that the transported PDF approach can be successfully applied to the modelling of premixed turbulent flames with scalar spaces of sufficient size to model auto-ignition type phenomena. It is also evident from the current work that the modelling of explosion kernels in pre-existing turbulence fields is very sensitive to both the details of the injection process and to the chemical source term closure. The present work does lay the foundations and also indicates the directions for further studies.

Download or read book Initiation Mechanisms of Low loss Swept ramp Obstacles for Deflagration to Detonation Transition in Pulse Detonation Combustors written by Charles B. Myers and published by . This book was released on 2009 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to enhance the performance of pulse detonation combustors (PDCs), an efficient deflagration-to-detonation transition (DDT) process is critical to maintain the thermodynamic benefits of detonation-based combustion systems and enable their use as future propulsion or power generation systems. The DDT process results in the generation of detonation and can occur independently, but the required length is excessive in many applications and also limits the frequency of repeatability. Historically, obstacles have been used to reduce the required distance for DDT, but often result in a significant total pressure loss that lessens the delivered efficiency advantages of PDCs. This thesis evaluated various swept-ramp obstacle configurations to accelerate DDT in a single event PDC. Computer simulations were used to investigate the three-dimensional disturbances caused by various swept-ramp configurations. Experimental tests were conducted using various configurations that measured combustion shockwave speed and flame front interactions with the swept-ramp obstacles. Detonation was verified across the instrumented section through high-frequency pressure transducers, and experimental data proved that swept-ramp obstacles successfully accelerate the DDT process with minimal pressure losses.

Download or read book Investigation of Sustained Detonation Devices written by Robert B. Driscoll and published by . This book was released on 2016 with total page 241 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study is conducted on a Pulse Detonation Engine-Crossover System to investigate the feasibility of repeated, shock-initiated combustion and characterize the initiation performance. A PDE-crossover system can decrease deflagration-to-detonation transition length while employing a single spark source to initiate a multi-PDE system. Visualization of a transferred shock wave propagating through a clear channel reveals a complex shock train behind the leading shock. Shock wave Mach number and decay rate remains constant for varying crossover tube geometries and operational frequencies. A temperature gradient forms within the crossover tube due to forward flow of high temperature ionized gas into the crossover tube from the driver PDE and backward flow of ionized gas into the crossover tube from the driven PDE, which can cause intermittent auto-ignition of the driver PDE. Initiation performance in the driven PDE is strongly dependent on initial driven PDE skin temperature in the shock wave reflection region. An array of detonation tubes connected with crossover tubes is developed using optimized parameters and successful operation utilizing shock-initiated combustion through shock wave reflection is achieved and sustained. Finally, an air-breathing, PDE-Crossover System is developed to characterize the feasibility of shock-initiated combustion within an air-breathing pulse detonation engine. The initiation effectiveness of shock-initiated combustion is compared to spark discharge and detonation injection through a pre-detonator. In all cases, shock-initiated combustion produces improved initiation performance over spark discharge and comparable detonation transition run-up lengths relative to pre-detonator initiation. A computational study characterizes the mixing processes and injection flow field within a rotating detonation engine. Injection parameters including reactant flow rate, reactant injection area, placement of the fuel injection, and fuel injection distribution are varied to assess the impact on mixing. Decreasing reactant injection areas improves fuel penetration into the cross-flowing air stream, enhances turbulent diffusion of the fuel within the annulus, and increases local equivalence ratio and fluid mixedness. Staggering fuel injection holes produces a decrease in mixing when compared to collinear fuel injection. Finally, emulating nozzle integration by increasing annulus back-pressure increases local equivalence ratio in the injection region due to increased convection residence time.

Download or read book Proceedings written by and published by . This book was released on 1989 with total page 892 pages. Available in PDF, EPUB and Kindle. Book excerpt: Papers presented in this publication cover special problems in the field of energetic materials, particularly detonation phenomena in solids and liquids. General subject areas include shock-to-detonation transition, time resolved chemistry, initiation modeling, deflagration-to-detonation transition, equation of state and equation of state and performance, composites and emulsions, and composites and emulsions/underwater explosives, reaction zone, detonation wave propagation, hot spots, detonation products, chemistry and compositions, and special initiation.

Download or read book Alternative Pulse Detonation Engine Ignition System Investigation Through Detonation Splitting written by August J. Rolling and published by . This book was released on 2002-03-01 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Pulse Detonation Engine (PDE) combusts fuel air mixtures through a form of combustion: detonation. Recent PDE research has focused on designing working subsystems. This investigation continued this trend by examining ignition system alternatives. Existing designs required spark plugs in each separate thrust tube to ignite premixed reactants. A single thrust tube could require the spark plug to fire hundreds of times per second for long durations. The goal was to minimize hardware and increase reliability by limiting the number of ignition sources. This research used a continuously propagating detonation wave as both a thrust mechanism and an ignition system and required only one initial ignition source. This investigation was a proof of concept for such an ignition system. First a systematic look at various geometric effects on detonations was made. These results were used to further examine configurations for splitting detonations, physically dividing one detonation wave into two separate detonation waves. With this knowledge a dual thrust tube system was built and tested proving that a single spark could be used to initiate detonation in separate thrust tubes. Finally, a new tripping device for better deflagration to detonation transition (DDT) was examined. Existing devices induced DDT axially. The new device attempted to reflect an incoming detonation to initiate direct DDT in a cross flow.

Download or read book Detonation Initiation in a Pulse Detonation Engine with Elevated Initial Pressures written by Andrew George Naples and published by . This book was released on 2008 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: An experimental study was done to examine the effects of elevated initial tube pressure in the PDE. Measured parameters were the ignition time, DDT run-up distance, DDT times, and C-J velocity. Mixed with air, three fuels, i.e., aviation gasoline, ethylene, and hydrogen, were tested at various initial pressures and equivalence ratios. A stock automotive ignition system was employed, along with a transient and thermal plasma ignition system, to quantify the benefits of each. Measured results show a reduction in the ignition time of roughly 50% and in the DDT distance of roughly 30%, for all three fuels at an initial tube pressure of 3 atmospheres. At roughly 2 atmospheres of initial pressure the thermal plasma ignition system showed no benefit over the stock automotive ignition system. In addition to the experimental results, a brief Chemkin analysis was done to model the stock automotive ignition system.

Download or read book Detonation Initiation in Pulse Detonation Engines written by Chiping Li and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evaluation and Selection of an Efficient Fuel Air Initiation Strategy for Pulse Detonation Engines written by and published by . This book was released on 2005 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rapid and efficient initiation of hydrocarbon/air mixtures has been identified as one of the critical and enabling technologies for Pulse Detonation Engines (PDEs). Although the NPS Rocket Propulsion Laboratory has successfully demonstrated fuel/air detonations in a valveless pulse detonation engine using ethylene, propane, and JP-10 fuels, past engine designs have relied upon a sensitive fuel/oxygen initiator unit. To realize the increased thermodynamic efficiencies of PDEs and thus compete with ramjets and other supersonic platforms, it is imperative to eliminate any need for supplementary oxygen in an air-breathing PDE design. This thesis examined ignition technologies and initiator designs which did not require auxiliary oxygen, including capacitive discharge systems and the developing technology of Transient Plasma Ignition (TPI). The current NPS pulse detonation engine architecture was modified to evaluate the various ignition strategies in a PDE operating on an ethylene/air mixture at simulated supersonic cruising conditions. Comparisons were based upon ignition success rate, ignition delay time, detonation wave speed, and Deflagration-to-Detonation (DDT) distance. Reliability and performance of the TPI system proved to be superior to conventional ignition systems. Furthermore, successful initiation of a PDE operating at a frequency of up to 40 hertz was demonstrated without the use of supplementary oxygen.