Author: Jarrett E. Lowe
Publisher:
ISBN:
Category : Cross-flow (Aerodynamics)
Languages : en
Pages : 250
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Book Description
The goal of this study is to establish the dominant flow structure required to effectively accelerate the turbulent deflagration flame front to detonation velocity in the shortest possible distance while using a single Jet in Cross Flow (JICF). Jets in crossflow, depending on orientation and momentum ratio, can induce two types of flow structures that propagate downstream; vortex filaments and turbulent eddies. Vortex flow structures are coherent rotating columns that can persist for a considerable distance before diffusing. Turbulent eddies are characterized as random fluctuations in flow velocity or small pockets of rotation. The test rig used for this study consists of a valveless pulse detonation combustor operating at near-ambient conditions supplying air at a rate of (0.05-0.1)kg/s and equivalence ratios of 1.0 to 1.3 using Ethylene fuel. Experimental studies comprised of four phases of testing : full obstacle configurations, single orifice, fluidic jet, and hybrid. Overall, the initial fluidic tests reveal the primary effect is an increase in peak pressure (13%-120%) and a decrease in the ion detonation time by up to 19% favoring upward facing jets while velocity displayed no discernable change from the baseline. A study was also conducted with physical transition geometry comparing both valve and valveless configurations. Findings indicate frequent obstacles leading the DDT section both improves flame acceleration and mitigate the backflow due to a porous thrust surface with insufficient supply pressures and furthermore verifies excessive obstacles are detrimental towards later flame acceleration and transition to detonation.
Author: Darren Dale Radford
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Author: Jiun-Ming Li
Publisher: Springer
ISBN: 3319689061
Category : Technology & Engineering
Languages : en
Pages : 246
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Book Description
This book focuses on the latest developments in detonation engines for aerospace propulsion, with a focus on the rotating detonation engine (RDE). State-of-the-art research contributions are collected from international leading researchers devoted to the pursuit of controllable detonations for practical detonation propulsion. A system-level design of novel detonation engines, performance analysis, and advanced experimental and numerical methods are covered. In addition, the world’s first successful sled demonstration of a rocket rotating detonation engine system and innovations in the development of a kilohertz pulse detonation engine (PDE) system are reported. Readers will obtain, in a straightforward manner, an understanding of the RDE & PDE design, operation and testing approaches, and further specific integration schemes for diverse applications such as rockets for space propulsion and turbojet/ramjet engines for air-breathing propulsion. Detonation Control for Propulsion: Pulse Detonation and Rotating Detonation Engines provides, with its comprehensive coverage from fundamental detonation science to practical research engineering techniques, a wealth of information for scientists in the field of combustion and propulsion. The volume can also serve as a reference text for faculty and graduate students and interested in shock waves, combustion and propulsion.
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: R. J. Litchford
Publisher:
ISBN:
Category : Detonation waves
Languages : en
Pages : 52
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 39
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Book Description
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.
Author: David L. Forster
Publisher:
ISBN: 9781423555230
Category :
Languages : en
Pages : 73
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Book Description
An evaluation of five liquid-fueled pulse detonation engine combustor geometries and flow field conditions was performed over a wide range of equivalence ratios. Particle sizing and spray characterization of commercially available atomizers was conducted to determine the optimum conditions that produced acceptable mass flow and particle size distribution for use in the combustor. The chosen atomizer was installed in the combustor geometries and then analyzed over a range of combustor conditions to measure deflagration to detonation transition (DDT) distances and detonation wave velocities for each condition. Testing was conducted for ambient (100-110 deg F) and higher wall temperatures (>300 deg F) at an operating frequency of 5Hz. It was found that the shortest DDT for JP10 and O2 was achieved using a stepped front-end insert under hot conditions and with a loaded equivalence ratio greater than .75, but less than 1.15.
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: 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: Nicole Gagnon
Publisher:
ISBN:
Category : Detonation waves
Languages : en
Pages : 148
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Book Description
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.
