Download or read book Effects of Corona Spark and Surface Discharges on Ignition Delay and Deflagration to Detonation Times in Pulsed Detonation Engines Postprint written by and published by . This book was released on 2006 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of the research described herein is to compare the ignition delays in an experimental pulsed detonation engine produced by thermal and non-thermal ignitions. The commercial thermal ignition has a pulse duration of about 1 microsec, whereas the non-thermal ignitions have pulse durations of 100 nanosec. Ignition delay is an important factor, along with fill and purge times, that limit the maximum repetition rate and thrust of pulsed detonation engines. For stoichiometric fuel-air mixtures with aviation gasoline at 1 atmosphere and 360 - 480 K, an ignition delay of 6 millisec was observed with a non-thermal ignition, whereas the ignition delay was 11 millisec with an aftermarket automotive ignition. By replacing the resistive cable and resistor of the aftermarket ignition with a non-resistive cable and surface discharge igniter, its ignition delay was reduced to 7 millisec, which is comparable to that produced by the non-thermal ignitions.
Download or read book Influence of Ignition Energy Ignition Location and Stoichiometry on the Deflagration to Detonation Distance in A Pulse Detonation Engine written by John P. Robinson and published by . This book was released on 2000-06 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: The feasibility of utilizing detonations for air-breathing propulsion is the subject of a significant research effort headed by the Office of Naval Research. Pulse Detonation Engines (PDE) have a theoretically greater efficiency than current combustion cycles. However, pulse detonation technology must mature beginning with research in the fundamental process of developing a detonation wave. This thesis explores various ignition conditions which minimize the deflagration-to- detonation transition distance (Xddt) of a single detonation wave in a gaseous mixture.
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 Relation Between Spark ignition Engine Knock Detonation Waves and Autoignition as Shown by High speed Photography written by Cearcy D. Miller and published by . This book was released on 1946 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: A critical review of literature bearing on the autoignition and detonation-wave theories of spark-ignition engine knock and on the nature of gas vibrations associated with combustion and knock results in the conclusion that neither the autoignition theory nor the detonation-wave theory is an adequate explanation of spark-ignition engine knock. A knock theory is proposed, combining the autoignition and detonation-wave theories, introducing the idea that the detonation wave develops in autoignited or afterburning gases, and ascribing comparatively low-pitched heavy knocks to autoignition but high-pitched pinging knocks to detonation waves with the possibility of combinations of the two types of knock.
Download or read book Detonation Branching in a PDE with Liquid Hydrocarbon Fuel written by Kristin L. Panzenhagen and published by . This book was released on 2004-03-01 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: A pulse detonation engine (PDE) capitalizes on the large mass flux and pressure rise associated with detonations to create thrust, which is proportional to PDE cycle frequency. This research showed that using a branched detonation as an ignition source, as opposed to standard spark ignition, deposits more energy into the thrust tube head. The increase in energy decreases ignition delay and detonation to deflagration transition (DDT) time. This allows a theoretical 85% cycle frequency increase that is accompanied by an 85% increase in thrust. The increase in energy also reduces the need for a DDT enhancement device, thereby increasing thrust as much as 30%. While detonation branching has been accomplished using gaseous hydrogen, this was the first instance of detonation branching using liquid hydrocarbon fuel.
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.
Download or read book The Effect of Axial Spacing of Constant and Variable Blockages on the Deflagration to detonation Transition in a Pulse Detonation Engine written by Nicole Gagnon and published by . This book was released on 2016 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: An investigation was conducted into the effects of obstacle spacing on the deflagration-to-detonation transition section length in a pulse detonation engine. Testing was conducted with one hundred and ninety-five different obstacle, and spacing configurations. The configurations included constant, as well as variable spacing between obstacles. The goal of this investigation was to correlate the spacing between obstacles and the blockage ratio of the obstacles with the detonation success and the shortening of the DDT section. The ten cases that achieved the highest percentage of detonations were investigated further to determine the distance needed for the deflagration-to-detonation transition. A 33% blockage ratio was the most successful to induce turbulence and not quench the detonation wave. With these conditions, DDT was achievable with 100% success in a section whose length was 31 times the inner diameter of the DDT section. Detonation was unachievable in 82 times the inner diameter in a "smooth" tube. This is a greater than 63% decrease in detonation transition length. This decrease in length will further facilitate the integration of pulse detonation engines into gas turbine engines.
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 The Significance of the Time Concept in Engine Detonation written by W. A. Leary and published by . This book was released on 1942 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental method has been developed by means of which the variables affecting the time element in the detonation process in a spark-ignition engine can be controlled and approximately measured. In the investigation of the time element it was found that higher maximum permissible pressures can be used if the rate of compression of the end gas is increased. In order to draw fundamental conclusions, experimental data of engine detonation should be accomplished by the pressure-temperature-time history of the unburned charge. A discussion on the precision of various methods of determining the pressure and temperature of the unburned charge is included. Certain aspects of ignition delay and the mechanism of normal and detonating combustion are considered on the basis of chain-reaction theory.
Download or read book Influence of Spark Energy Spark Number and Flow Velocity on Detonation Initiation in a Hydrocarbon fueled PDE written by Ilissa Brooke Schild and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Pulsed Detonation Engines (PDEs) have the potential to revolutionize fight by better utilizing the chemical energy content of reactive fuel/air mixtures over conventional combustion processes. Combustion by a super-sonic detonation wave results in a significant increase in pressure in addition to an increase in temperature. In order to harness this pressure increase and achieve a high power density, it is desirable to operate PDEs at high frequency. The process of detonation initiation impacts operating frequency by dictating the length of the chamber and contributing to the overall cycle time. Therefore a key challenge in the development of a practical PDEs is the requirement to rapidly initiate a detonation in hydrocarbon-air mixtures. This thesis evaluates the influence of spark energy and airflow velocity on this challenging initiation process. The influence of spark energy, number of sparks and airflow velocity on Deflagration-to-Detonation Transition (DDT) was studied during cyclic operation of a small-scale PDE at the General Electric Global Research Center. Experiments were conducted in a 50 mm square transitioning to cylindrical channel PDE with optical access operating with stoichiometric ethylene-air mixture. Total spark energy was varied from 250 mJ to 4 J and was distributed between one and four spark plugs located in the same axial location. Initial flame acceleration was imaged using high-speed shadowgraph and was characterized by the time to reach 20 cm from the spark plug. Measurements of detonation wave velocity and emergence time, the time it takes the detonation wave to exit the tube, was measured using dynamic pressure transducers and ionization probes. It was found that the flame front spread was faster at higher spark energies and with more spark locations. Initial flame acceleration was 16% faster for the 4-spark, 4 J case when compared to the baseline 1-spark, 1 J case. When looking at the effect of airflow on the influence of spark energy, it was found that airflow had a larger effect on emergence time at high energies, versus energies less than 1 J. Finally, for a selected case of 0.25 J spark energy and 4 sparks, the velocity of the fuel-air mixture during fill was found to have a varying influence on detonation initiation and emergence time.
Download or read book Deflagration to detonation Control by Non equilibrium Gas Discharges and Its Applications for Pulsed Detonation Engine written by A. Yu Starikovskii 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 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 On Determnation of Ignition Delay Times for the Modeling of DDT written by Agnieszka Jach (energetyka) and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Dotyczy: szczegółowy mechanizm reakcji chemicznych, przejście z deflagracji do detonacji, głebokie uczenie maszynowe, czas opóźnienia samozapłonu, walidacja, detailed reaction mechanism, deflagration to detonation transition, deep learning, ignition time, validation.
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 Tableaux modernes figuration et abstraction sculptures peintres contemporains paysagistes written by and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Liquid Hydrocarbon Detonation Branching in a Pulse Detonation Engine written by and published by . This book was released on 2004 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pulse detonation engines operate on a fill-detonate-exhaust cycle with thrust directly proportional to the cycle frequency. That is, a decrease in cycle time results in increased thrust. This paper shows that the detonate portion of the cycle can he shortened by using a branched detonation as the ignition source as opposed to a spark plug type of ignition. The combustion energy from a branched detonation allows ignition and deflagration-to-detonation transition to occur more quickly, shortening overall cycle time. Further, while detonation branching has been previously accomplished using gaseous hydrogen fuel, this paper reports the first application of detonation branching using liquid hydrocarbon fuel. For this application, a pressurized heating system was designed to vaporize the fuel and mix it with an airstream to stoichiometric conditions.
Download or read book Investigation of Pulse Detonation Engines written by Christopher Tate and published by . This book was released on 2015 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Detonation and constant volume combustion is well known to be thermodynamically more efficient than the typically utilized constant pressure. There have been numerous approaches of achieving detonation through deflagration-to-detonation transition most of which use evenly spaced obstacles with a specified constant blockage ratio to generate turbulence and pressure fluctuations. There have been few efforts to study effects of varying blockage ratio as a function of axial distance. This research analyzes the effect of variable blockage ratio on deflagration-to-detonation transition in ethylene-air mixtures. The experiments show that with certain blockage ratio functions detonation is more repeatable and produces a smaller variation in both peak pressure and wave velocity representative of consistently stable detonations.
