Evaluation of Straight and Swept Ramp Obstacles on Enhancing Deflagration-to-Detonation Transition in Pulse Detonation Engines PDF Download
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Author: Carlos A. Medina
Publisher:
ISBN:
Category : Engineering
Languages : en
Pages : 129
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Book Description
The use of detonations to achieve thrust in pulse detonation engines (PDEs) offers significant advantages in efficiency, simplicity, and versatility. An enabling mechanism for practical PDE implementation will likely utilize an efficient deflagration-to-detonation transition (DDT) process. This method simplifies detonation generation, but the required length is prohibitive in many applications and limits the frequency of repeatability. Obstacles have historically been employed to minimize the DDT distance, but often result in significant total pressure losses that degrade the delivered efficiency advantages of PDEs. This thesis explored the use of straight and swept ramp obstacles to accelerate DDT while minimizing the overall pressure losses. Computer modeling examined three-dimensional disturbances caused by such obstacles. Experimental tests measured combustion shockwave speed, flame velocity, and flame front interactions with obstacles. Evaluations were completed for several straight ramp obstacle configurations in a modeled two-dimensional flow. The placement of consecutive ramps resulted in flame acceleration accompanied by significant pressure spikes approaching 500 psi. Although detonation was not verified across the instrumented section, experimental data prove that straight ramp obstacles successfully accelerate the DDT process. Computer modeling predicts that swept ramps may be even more effective by introducing streamwise vorticity with a relatively low pressure drop.
Author: Carlos A. Medina
Publisher:
ISBN:
Category : Engineering
Languages : en
Pages : 129
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Book Description
The use of detonations to achieve thrust in pulse detonation engines (PDEs) offers significant advantages in efficiency, simplicity, and versatility. An enabling mechanism for practical PDE implementation will likely utilize an efficient deflagration-to-detonation transition (DDT) process. This method simplifies detonation generation, but the required length is prohibitive in many applications and limits the frequency of repeatability. Obstacles have historically been employed to minimize the DDT distance, but often result in significant total pressure losses that degrade the delivered efficiency advantages of PDEs. This thesis explored the use of straight and swept ramp obstacles to accelerate DDT while minimizing the overall pressure losses. Computer modeling examined three-dimensional disturbances caused by such obstacles. Experimental tests measured combustion shockwave speed, flame velocity, and flame front interactions with obstacles. Evaluations were completed for several straight ramp obstacle configurations in a modeled two-dimensional flow. The placement of consecutive ramps resulted in flame acceleration accompanied by significant pressure spikes approaching 500 psi. Although detonation was not verified across the instrumented section, experimental data prove that straight ramp obstacles successfully accelerate the DDT process. Computer modeling predicts that swept ramps may be even more effective by introducing streamwise vorticity with a relatively low pressure drop.
Author: Charles B. Myers
Publisher:
ISBN:
Category : Combustion chambers
Languages : en
Pages : 91
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Book Description
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.
Author: William T. Dvorak
Publisher:
ISBN:
Category : Astronautics
Languages : en
Pages : 79
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Book Description
Pulse Detonation technology offers the potential for substantial increases in thrust and fuel efficiency in subsonic and supersonic flight Mach ranges through the use of a detonative vs. deflagrative combustion process. One of the approaches to reliably obtain a fuel-air detonation is to accelerate a deflagration combustion wave to detonation through the use of turbulence devices, known as detonation-to-deflagration transition. Current geometries for deflagration-to-detonation transition sacrifice much of the gains through losses from high velocity flows over obstacle fields required for detonation initiation. In this study, experimental swept ramp obstacle fields were characterized in an effort to realize decreased pressure losses while still creating the gas dynamic and turbulence necessary for detonation initiation. Characterization included measurement of pressure loss across the combustor during "cold flow" operation with no ignition or fuel present, and detonability testing that employed ion probe measurement of combustion wave velocity. Minimizing pressure losses existing in current designs will result in dramatic improvement of system performance. In addition to swept ramp fields, other configurations were analyzed using computational fluid dynamics (CFD) and subjected to performance testing. Of particular interest were obstacles of similar blockage area, but without the swept sides associated with streamwise vorticity in the flow field. Testing of unswept configurations allowed insight into the mechanisms for DDT and narrowed the field of practical obstacle geometries.
Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
ISBN: 9781794371569
Category : Science
Languages : en
Pages : 34
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Book Description
A sub-model is developed to account for the drag and heat transfer enhancement resulting from deflagration-to-detonation (DDT) inducing obstacles commonly used in pulse detonation engines (PDE). The sub-model is incorporated as a source term in a time-accurate, quasi-onedimensional, CFD-based PDE simulation. The simulation and sub-model are then validated through comparison with a particular experiment in which limited DDT obstacle parameters were varied. The simulation is then used to examine the relative contributions from drag and heat transfer to the reduced thrust which is observed. It is found that heat transfer is far more significant than aerodynamic drag in this particular experiment. Paxson, Daniel E. and Schauer, Frederick and Hopper, David Glenn Research Center NASA/TM-2012-217629, AIAA Paper 2009-502, E-18219
Author: Daniel E. Paxson
Publisher: BiblioGov
ISBN: 9781289167028
Category :
Languages : en
Pages : 22
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Book Description
A sub-model is developed to account for the drag and heat transfer enhancement resulting from deflagration-to-detonation (DDT) inducing obstacles commonly used in pulse detonation engines (PDE). The sub-model is incorporated as a source term in a time-accurate, quasi-onedimensional, CFD-based PDE simulation. The simulation and sub-model are then validated through comparison with a particular experiment in which limited DDT obstacle parameters were varied. The simulation is then used to examine the relative contributions from drag and heat transfer to the reduced thrust which is observed. It is found that heat transfer is far more significant than aerodynamic drag in this particular experiment.
Author: Benjamin W. Knox
Publisher:
ISBN:
Category :
Languages : en
Pages : 101
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Book Description
The current research explored the fluidic obstacle technique and obtained relative performance estimates of this new approach for enhancement of deflagration-to-detonation transition. Optimization of conventional physical obstacles has comprised the majority of deflagration-to-detonation enhancement research but these devices ultimately degrade the performance of a pulsed detonation engine. Therefore, a new approach has been investigated that demonstrates a fluidic obstacle has the potential to maximize turbulence production and enhance the flame acceleration process, leading to successful DDT. A fluidic obstacle is also able to reduce total pressure losses, "heat soaking", and ignition times. A reduction in these variables serves to maximize available thrust. In addition, the fluidic obstacle technique is an active combustion control method capable of adapting to off-design conditions. Steady non-reacting and unsteady reacting flow have been utilized in two facilities, namely the UB Combustion Laboratory and AFRL Detonation Engine Research facility, to provide experimental measurements and observations into the feasibility of this new approach.
Author: David Michael Chapin
Publisher:
ISBN:
Category : Propulsion systems
Languages : en
Pages :
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Book Description
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.
Author: Daniel E. Paxson
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
Author: R. J. Litchford
Publisher:
ISBN:
Category : Detonation waves
Languages : en
Pages : 52
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Book Description
Author: Daniel A. Nichols
Publisher:
ISBN:
Category : Engineering
Languages : en
Pages : 69
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Book Description
Pulse detonation combustion technologies promise the potential of increased thermodynamic efficiency and performance, across a wide range of thrust and power generation applications. Thrust applications would require initial combustor pressures of about 1-4 atm while power applications would require about 4-20 atm. Most of the previous testing of Pulse Detonation Combustors (PDCs) utilized standard atmospheric pressure conditions at sea level, but at elevated temperatures of 300-500°F in the combustor. The current work was motivated by a need to experimentally evaluate the detonation initiation performance of a PDC at elevated combustor pressures. Detonability was evaluated at initial combustor pressures from 2-5 atmospheres and at equivalence ratios of about 0.9-1.1. The experimentation utilized a previously constructed and evaluated three inch diameter combustor that employed swept-ramps as the mechanism for Deflagration-to-Detonation (DDT) initiation. Ramps were removed as the pressure was increased to determine how many sets were necessary to achieve DDT. The legacy PDC was adapted with new and modified components, enabling it to operate at higher pressures and temperatures and for longer durations. It was found that for initial combustor pressures up to 5 atm at least four sets of ramps are required to achieve DDT.
