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1
Debnath, Pinku, e Krishna Murari Pandey. "Computational Study of Deflagration to Detonation Transition in Pulse Detonation Engine Using Shchelkin Spiral". Applied Mechanics and Materials 772 (luglio 2015): 136–40. http://dx.doi.org/10.4028/www.scientific.net/amm.772.136.
Testo completoAbstract (sommario):
Detonation combustion wave is much more energetic combustion process in pulse detonation engine combustion system. Numerous experimental, theoretical and numerical analyses have been studied in pulse detonation engine to implement in practical propulsion system. In this present computational study the simulation was carried out for deflagration flame acceleration and deflagration to detonation transition of hydrogen air combustible mixture inside the detonation tube with and without Shchelkin spiral. A three dimensional computational analysis has been done by finite volume discretization method using ANSYS Fluent 14 CFD commercial software. The LES turbulence model with second order upwind discretization scheme was adopted with standard boundary conditions for unsteady combustion wave simulations. From the computational study it was found that intensity of detonation wave velocity and dynamic pressure is higher near to the boundary of Shchelkin spiral in detonation tube. The contour plots comparisons clearly show that deflagration flame accelerates in detonation tube as present of Shchelkin spiral. The contour plots also suggest that deflagration flame velocity and pressure are less in without Shchelkin spiral in detonation tube. The accelerating detonation waves are approximately near about Chapment-Jouguet values in detonation tube with Shchelkin spiral.
2
Ma, Hu, Zhenjuan Xia, Wei Gao, Changfei Zhuo e Dong Wang. "Numerical simulation of the deflagration-to-detonation transition of iso-octane vapor in an obstacle-filled tube". International Journal of Spray and Combustion Dynamics 10, n. 3 (13 febbraio 2018): 244–59. http://dx.doi.org/10.1177/1756827718758047.
Testo completoAbstract (sommario):
Flame acceleration and deflagration-to-detonation transition of an iso-octane vapor–air mixture in an obstacle-filled detonation tube were simulated by solving Navier–Stokes equations with a single-step reaction mechanism. A variable specific heat ratio was used in these simulations. Detonation cell size was successfully simulated for the iso-octane vapor–air mixture. Two methods for initiating detonation waves were revealed in a detonation tube with obstacles. Pressure and flame parameters, such as the temporal variation of total energy release rate, flame front location, propagation velocity of the flame front, and flame front area, were investigated during the flame acceleration and deflagration-to-detonation transition process. According to the variation of these parameters, flame acceleration and deflagration-to-detonation transition processes could be divided into four stages, i.e. the early stage of flame acceleration, the middle stage of flame acceleration, the end stage of flame acceleration, and the detonation transition stage. The effects of activation energy and pre-exponential factor on deflagration-to-detonation transition processes were examined. The results indicate that the pre-exponential factor and activation energy influence the flame parameters, but not the development law of flame acceleration or deflagration-to-detonation transition processes. For lower reactants activity, detonation wave is easy to fail in couple while bypassing obstacles in the obstacle-filled detonation tube, which causes a large fluctuation in flame propagation velocity and total energy release rate. The length of detonation tube filled by obstacles should not be more than deflagration-to-detonation transition distance. These investigations are conducive to understanding the flame acceleration and deflagration-to-detonation transition and developing detonation combustion chamber of pulse detonation engine.
3
Davis, Scott, Derek Engel, Kees van Wingerden e Erik Merilo. "Can gases behave like explosives: Large-scale deflagration to detonation testing". Journal of Fire Sciences 35, n. 5 (settembre 2017): 434–54. http://dx.doi.org/10.1177/0734904117715648.
Testo completoAbstract (sommario):
A large vapor cloud explosion followed by a fire is one of the most dangerous and high consequence events that can occur at petrochemical facilities. However, one of the most devastating explosions is when a deflagration transitions to a detonation, which can travel at speeds greater than 1800 m/s and pressures greater than 18 barg. This phenomenon is called a deflagration-to-detonation transition, whereby the deflagration (flame front) continues to accelerate due to confinement or flow-induced turbulence (e.g. obstacles) and ultimately transitions at flame speeds greater than the speed of sound to a detonation. Unlike a deflagration that requires the presence of confinement or obstacles to generate high flame speeds and associated elevated overpressures, a detonation is a self-sustaining phenomenon having the shock front coupled to the combustion. Once established, the resulting detonation will continue to propagate through the vapor cloud at speeds (1800 m/s) that are of similar order as high explosives (7000–8000 m/s). While there are differences between high explosives and vapor cloud explosions (e.g. high explosives can have pressures well in excess of 100 bar), vapor cloud explosions that transition to detonations can cause significant damage due to the extremely high pressures not typically associated with gas phase explosions (>18 barg), high energy release rate per unit mass, and higher impulses due to large cloud sizes. While the likelihood of deflagration-to-detonation transitions is lower than deflagrations, they have been identified in some of the most recent large-scale explosion incidents. The consequences of deflagration-to-detonation transitions can be orders of magnitude larger than deflagrations. This article will present the results of large-scale testing conducted in a newly developed test rig of 1500 m3 gross volume involving stoichiometric, lean, and rich mixtures of propane and methane.
4
Qiu, Hua, Zheng Su e Cha Xiong. "Experimental investigation on multi-cycle two-phase spiral pulse detonation tube of two configurations". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, n. 11 (4 dicembre 2018): 4166–75. http://dx.doi.org/10.1177/0954410018817455.
Testo completoAbstract (sommario):
The spiral tube structure is an effective method to shorten the axial length of the pulse detonation chamber. In this article, spiral pulsed detonation tube with two kinds of spiral configuration was experimentally investigated. Liquid gasoline and air were used as fuel and oxidant, respectively, and equivalence ratios were controlled to about 1.0. Based on the transient pressure along the tube, the propagation characteristics of the pressure waves in the multi-cycle spiral pulsed detonation tubes, such as pressure peaks, wave velocities and propagation process, were analyzed. Results showed that propagation of double compression waves was the common feature during the process of deflagration to detonation transition in the presented spiral tubes, and the onset of detonation was initiated by a local explosion in the second compression wave. The deflagration to detonation transition characteristics with detonation initiation and combustion characteristics without initiation in the spiral sections were both related to the dimensionless distance. Propagation characteristics of the pressure waves were influenced by the use of different spiral configuration. And some interesting phenomena were also found.
5
Smirnov, Nickolay, e Valeriy Nikitin. "Three-dimensional simulation of combustion, detonation and deflagration to detonation transition processes". MATEC Web of Conferences 209 (2018): 00003. http://dx.doi.org/10.1051/matecconf/201820900003.
Testo completoAbstract (sommario):
The paper presents results of numerical and experimental investigation of mixture ignition and detonation onset in shock wave reflected from inside a wedge. Contrary to existing opinion of shock wave focusing being the mechanism for detonation onset in reflection from a wedge or cone, it was demonstrated that along with the main scenario there exists a transient one, under which focusing causes ignition and successive flame acceleration bringing to detonation onset far behind the reflected shock wave. Several different flow scenarios manifest in reflection of shock waves all being dependent on incident shock wave intensity: reflecting of shock wave with lagging behind combustion zone, formation of detonation wave in reflection and focusing, and intermediate transient regimes. Comparison of numerical and experimental results made it possible to validate the developed 3-D transient mathematical model of chemically reacting gas mixture flows incorporating hydrogen – air mixtures.
6
Adoghe, Joseph, Weiming Liu, Jonathan Francis e Akinola Adeniyi. "Investigation into mechanisms of deflagration-to-detonation using Direct Numerical Simulations". E3S Web of Conferences 128 (2019): 03002. http://dx.doi.org/10.1051/e3sconf/201912803002.
Testo completoAbstract (sommario):
Detonation, a combustion phenomenon is a supersonic combustion wave which plays critical role in the theory and application of combustion. This work presents numerical investigation into indirect initiation of detonation using direct numerical simulations (DNS). The Adaptive Mesh Refinement in object–oriented C++ (AMROC) tool for parallel computations is applied in DNS. The combustion reactions take place in a shock tube and an enclosure with a tube respectively and are controlled by detailed chemical kinetics. The database produced by DNS accurately simulates the process of transition of deflagration to detonation (DDT), and investigates the influence of overpressure and kinetics on flame propagations during combustion processes. The numerical simulations showed the influence of pressure and kinetics to the transition of slow and fast flames and DDT during flame propagations. When the reaction rate is fast, DDT is achieved, but when slow, DDT will not occur and therefore, there will be no detonation and consequently no strong explosion. Exploring the influence of free radical H on flame propagation showed that the concentration of the reacting species decreased with flame speed increase for each propagation. Hence, the heat generated was very fast with a greater chance of DDT beingtriggered because flame speed increased.
7
Cojocea, Andrei Vlad, Ionuț Porumbel, Mihnea Gall e Tudor Cuciuc. "Experimental Investigations on the Impact of Hydrogen Injection Apertures in Pulsed Detonation Combustor". Energies 17, n. 19 (1 ottobre 2024): 4918. http://dx.doi.org/10.3390/en17194918.
Testo completoAbstract (sommario):
Combustion through detonation marks an important leap in efficiency over standard deflagration methods. This research introduces a Pulsed Detonation Combustor (PDC) model that uses Hydrogen as fuel and Oxygen as an oxidizer, specifically targeting carbon-free combustion efforts. The PDC aerodynamic features boost operating cycle frequency and facilitate Deflagration-to-Detonation Transition (DDT) within distances less than 200 mm by means of Hartmann–Sprenger resonators and cross-flow fuel/oxidizer injection. The achievement of quality mixing in a short-time filling process represents not only higher cycle operation but also enhanced performances. The scope of this paper is to assess the impact of different fuel injectors with different opening areas on the performances of the PDC. This assessment, expressed as a function of the Equivalence Ratio (ER), is conducted using two primary methods. Instantaneous static pressures are recorded and processed to extract the maximum and average cycle pressure and characterize the pressure augmentation. Thrust measurements obtained using a load cell are averaged over the detonation cycle to calculate the time-averaged thrust. The specific impulse is subsequently determined based on these thrust measurements and the corresponding mass flow data.
8
Huang, Xiaolong, Ning Li e Yang Kang. "Research on Optical Diagnostic Method of PDE Working Status Based on Visible and Near-Infrared Radiation Characteristics". Energies 14, n. 18 (10 settembre 2021): 5703. http://dx.doi.org/10.3390/en14185703.
Testo completoAbstract (sommario):
Fill fraction not only has a profound impact on the process of deflagration to detonation in pulsed detonation engine, but also affects the propulsion performance in both flight and ground tests. In this paper, a novel optical diagnostic method based on detonation exhaust radiation in visible and near-infrared region within 300–2600 nm is developed to determine the current working state in the gas–liquid two-phase pulsed detonation cycle. The results show that the radiation characteristic in each stage of detonation cycle is unique and can be a good indicator to infer the fill fraction. This is verified experimentally by comparison with the laser absorption spectroscopy method, which utilizes a DFB laser driven by ramp injection current to scan H2O transition of 1391.67 nm at a frequency of 20 kHz. Due to concentrated radiation intensity, time duration reaching accumulated radiant energy ratio of 50% in detonation status would be smaller than 1.2 ms, and detonation status would be easily distinguished from deflagration with this critical condition. In addition, the variation of important intermediates OH, CH, and C2 radicals during detonation combustion are obtained according to the analysis of detonation spectrum, which can also be proposed as a helpful optical diagnostics method for the combustion condition based on C radical concentration. The study demonstrates the feasibility of optical diagnostics based on radiation in visible and near-infrared regions, which could provide an alternative means to diagnose and improve pulsed detonation engine performance.
9
Frolov, Sergey M., Igor O. Shamshin, Viktor S. Aksenov, Vladislav S. Ivanov e Pavel A. Vlasov. "Ion Sensors for Pulsed and Continuous Detonation Combustors". Chemosensors 11, n. 1 (1 gennaio 2023): 33. http://dx.doi.org/10.3390/chemosensors11010033.
Testo completoAbstract (sommario):
Presented in the article are the design and operation principles of ion sensors intended for detecting the propagating reaction fronts, the deflagration/detonation mode, apparent subsonic/supersonic propagation velocity of the reaction front, and duration of heat release by measuring the ion current in the reactive medium. The electrical circuits for ion sensors without and with intermediate amplifiers, with short response time and high sensitivity, as well as with the very wide dynamic range of operation in the reactive media with highly variable temperature and pressure, are provided and discussed. The main advantages of ion sensors are their very short response time of about 1 ms, versatility of design, and capability of detecting and monitoring reaction fronts of different intensities directly in combustion chambers. Several examples of ion sensor applications in sensing deflagration-to-detonation transition in pulsed detonation engines and developed detonations in rotating detonation engines operating on different fuel–air and fuel–oxygen mixtures are presented and discussed.
10
Brailovsky, I., L. Kagan e G. Sivashinsky. "Combustion waves in hydraulically resisted systems". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, n. 1960 (13 febbraio 2012): 625–46. http://dx.doi.org/10.1098/rsta.2011.0341.
Testo completoAbstract (sommario):
The effects of hydraulic resistance on the burning of confined/obstacle-laden gaseous and gas-permeable solid explosives are discussed on the basis of recent research. Hydraulic resistance is found to induce a new powerful mechanism for the reaction spread (diffusion of pressure) allowing for both fast subsonic as well as supersonic propagation. Hydraulic resistance appears to be of relevance also for the multiplicity of detonation regimes as well as for the transitions from slow conductive to fast convective, choked or detonative burning. A quasi-one-dimensional Fanno-type model for premixed gas combustion in an obstructed channel open at the ignition end is discussed. It is shown that, similar to the closed-end case studied earlier, the hydraulic resistance causes a gradual precompression and preheating of the unburned gas adjacent to the advancing deflagration, which leads (after an extended induction period) to a localized autoignition that triggers an abrupt transition from deflagrative to detonative combustion. In line with the experimental observations, the ignition at the open end greatly encumbers the transition (compared with the closed-end case), and the deflagration practically does not accelerate up to the very transition point. Shchelkin's effect, that ignition at a small distance from the closed end of a tube facilitates the transition, is described.
11
Vasyliv, S. S., N. S. Pryadko e S. G. Bondarenko. "Combustion and detonation of paste fuel of rocket engine". Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu, n. 5 (30 ottobre 2023): 72–76. http://dx.doi.org/10.33271/nvngu/2023-5/072.
Testo completoAbstract (sommario):
Purpose. Confirmation of the possibility of using a paste fuel based on ammonium perchlorate in a rocket engine and identifying the characteristics of its combustion. Methodology. Previous experimental studies on the burning of paste fuel in a constant pressure bomb determined the burning rate at different pressures. The stability of deflagration combustion without transition to the detonation mode was confirmed. An explosion occurred during the fire test of the engine model on paste-like fuel. The analysis of the causes of the explosion made it possible to put forward a hypothesis about the enrichment of the paste fuel with ammonium perchlorate, which created the prerequisites for its detonation. The conducted additional experiments showed a change in the combustion mode when enriching paste fuel with ammonium perchlorate. Findings. Theoretical and experimental studies have shown the possibility of obtaining detonation fuel based on the enrichment of paste fuel with ammonium perchlorate. It has been proven that, under certain production conditions, paste fuels can detonate, which opens up a new way of using such fuels for rocket engines. The conditions for the transition of the burning mode of pasty fuel from deflagration to detonation combustion are determined. The speed of the engine element during the explosion was evaluated and it was shown that during explosive combustion due to the large area and, accordingly, the mass flow, it is not possible to obtain a pressure value that could ensure the movement parameters registered in this engine design. Originality. Another criterion is established of engine operability when designing an engine on paste fuel. The effect of enrichment of pasty fuel with ammonium perchlorate during its flow through the supply system at the time of start-up was revealed. Practical value. The given information makes it possible to improve the design of the engine on paste fuel and to modernize the stand for its tests.
12
Bai, Qiaodong, Jiaxiang Han, Shijian Zhang e Chunsheng Weng. "Experimental study on the auto-initiation of rotating detonation with high-temperature hydrogen-rich gas". Physics of Fluids 35, n. 4 (aprile 2023): 045121. http://dx.doi.org/10.1063/5.0144322.
Testo completoAbstract (sommario):
An experimental study on the auto-initiation process of rotating detonation waves (RDWs) was conducted with high-temperature hydrogen-rich gas as the fuel and air as the oxidant. Spontaneous combustion of high-temperature hydrogen-rich gas and air occurred after they were injected into a rotating detonation chamber (RDC), which resulted in hot spots in the RDC and induced the formation of a rotating deflagration flame. Then, an RDW formed through the deflagration-to-detonation transition process in the RDC. The auto-initiation process of high-temperature hydrogen-rich gas and the formation mechanism of RDWs were studied in detail through experiments. The influences of the equivalence ratio on the RDW propagation characteristics of high-temperature hydrogen-rich gas were analyzed. The results showed that with the increase in the equivalence ratio from 0.61 to 1.93, five RDW propagation modes appeared in the RDC: Failure, two counter rotating detonation wave (TCRDW), Mixed, intermittent single rotating demodulation wave, and single rotating detonation wave (SRDW) modes. The Mixed mode was the transition mode from the TCRDW mode to the SRDW mode. The highest RDW velocity was 1485.9 m/s when the equivalence ratio was 1.32, in which the propagation mode was the stable SRDW mode.
13
Shamsadin Saeid, Mohammad Hosein, e Maryam Ghodrat. "Numerical Simulation of the Influence of Hydrogen Concentration on Detonation Diffraction Mechanism". Energies 15, n. 22 (20 novembre 2022): 8726. http://dx.doi.org/10.3390/en15228726.
Testo completoAbstract (sommario):
In this study, the impact of hydrogen concentration on deflagration to detonation transition (DDT) and detonation diffraction mechanisms was investigated. The combustion chamber was an ENACCEF facility, with nine obstacles at a blockage ratio of 0.63 and three mixtures with hydrogen concentrations of 13%, 20%, and 30%. Detonation diffraction mechanisms were numerically investigated by a density-based solver of OpenFOAM CFD toolbox named ddtFoam. In this simulation, for the low Mach numbers, the pddtFoam solver was applied, and for high speeds, the pddtFoam solver switched to the ddtFoam solver to simulate flame propagation without resolving all microscopic details in the flow in the CFD grid, and to provide a basis for simulating flame acceleration (FA) and the onset of detonation in large three-dimensional geometries. The results showed that, for the lean H2–air mixture with 13% hydrogen concentration, intense interaction between propagating flame and turbulent flow led to a rapid transition from slow to fast deflagration. However, the onset of detonation did not occur inside the tube. For the H2–air mixture with 20% hydrogen concentration, the detonation initiation appeared in the acceleration tube. It was also found that following the diffraction of detonation, the collision of transverse waves with the wall of the tube and the reflection of transverse waves were the most essential and effective parameters in the re-initiation of the detonation. For the H2–air mixture with 30% hydrogen concentration, the detonation initiation occurred while passing through the obstacles. Subsequently, at detonation diffraction, the direct initiation mechanism was observed.
14
Debnath, Pinku, e K. M. Pandey. "Computational fluid dynamics simulation of detonation wave propagation in modified pulse detonation combustor". E3S Web of Conferences 430 (2023): 01243. http://dx.doi.org/10.1051/e3sconf/202343001243.
Testo completoAbstract (sommario):
In this paper effect of Schelkin spiral material on thermal load and detonation combustion wave propagation in pulse detonation combustor has been simulated. As detonation combustion is supersonic combustion process and energy release rate is very high. In this regards present researches are focusing on flame acceleration process to reduce the DDT run up length. Hence the Schelkin spiral is inserted in detonation tube, which creates a bluff body and enhanced the turbulence of flame propagation. During simulation three turbulence models are used to carry out the reliable and repeatable detonation wave in pulse detonation combustor near thin boundary layer of helical shape Shchelkin spiral. The computational fluid dynamics (CFD) simulation has been performed using Ansys fluent platform. The Large Eddy Simulation (LES), detached eddy simulation with realizable k-ε turbulence model and detached eddy simulation with SST k-ω turbulence model are used for reacting flow simulation. From this simulation the LES turbulence model shows better turbulence initiation of detonation wave with velocity magnitude of 3040 m/s in detonation tube compared to other two turbulence models. This velocity is higher than C-J velocity of 1800 m/s. Further computational result shows that deflagration to detonation transition take place at several waves traveling region, in presence of Shchelkin spiral in detonation tube.
15
Prokopenko, V. M., e V. V. Azatyan. "Chain-Thermal Explosions and the Transition from Deflagration Combustion to Detonation". Russian Journal of Physical Chemistry A 92, n. 1 (gennaio 2018): 42–46. http://dx.doi.org/10.1134/s0036024418010193.
Testo completo
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Chen, Shaozhong, Jiequan Li e Tong Zhang. "Transition from a Deflagration to a Detonation in Gas Dynamic Combustion". Chinese Annals of Mathematics 24, n. 04 (ottobre 2003): 423–32. http://dx.doi.org/10.1142/s0252959903000426.
Testo completo
17
Oran, Elaine S., e Vadim N. Gamezo. "Origins of the deflagration-to-detonation transition in gas-phase combustion". Combustion and Flame 148, n. 1-2 (gennaio 2007): 4–47. http://dx.doi.org/10.1016/j.combustflame.2006.07.010.
Testo completo
18
Krivosheyev, P. N., A. O. Novitski e O. G. Penyazkov. "Evolution of the Reaction Front Shape and Structure on Flame Acceleration and Deflagration-to-Detonation Transition". Russian Journal of Physical Chemistry B 16, n. 4 (agosto 2022): 661–69. http://dx.doi.org/10.1134/s1990793122040248.
Testo completoAbstract (sommario):
Abstract Flame acceleration (FA) and the deflagration-to-detonation transition (DDT) are among the most interesting and exciting phenomena in the field of combustion and explosion of gases. From both practical and theoretical points of view, it is important to understand the basic laws governing these phenomena as well as the physical and/or chemical mechanisms and features of the process. High-speed flame-front photography during the deflagration of a premixed gas mixture in a long smooth tube with transparent walls was performed. A stoichiometric mixture of acetylene with oxygen diluted with argon by 25% is used. The experiments are carried out in a transparent cylindrical tube with an inner diameter of 60 mm and a length of 6 meters. The evolution of the structure and shape of the flame front from the moment of initiation of deflagration by a weak ignition source to the formation of a detonation wave is determined. Four characteristic phases of the propagation process are distinguished: at the first stage, the flame accelerates, then slows down, followed by flame propagation at an almost constant speed, and finally repeated acceleration, during which detonation is formed. It is shown how the dynamics of the process changes with a change in the initial pressure of the mixture. The most interesting and poorly studied stage of the DDT, the stage of intensive reacceleration, during which the flame abruptly changes shape, is described in detail.
19
Смирнов, Н. Н., В. В. Тюренкова, Л. И. Стамов e Дж. Хадем. "Simulation of Polydisperse Gas-Droplet Mixture Flows with Chemical Transformations". Успехи кибернетики / Russian Journal of Cybernetics, n. 2 (30 giugno 2021): 29–41. http://dx.doi.org/10.51790/2712-9942-2021-2-2-3.
Testo completoAbstract (sommario):
В статье представлен обзор результатов теоретических, численных и экспериментальных исследований процессов горения и инициирования детонации в гетерогенных полидисперсных смесях. Обсуждаются проблемы распыления, испарения и горения капель топлива, а также неравновесные эффекты при распылении капель и фазовых переходах. Влияние неоднородности размеров капель и неоднородности пространственного распределения на воспламенение смеси и ускорение пламени было исследовано для сильного и мягкого инициирования детонации: ударной волной и искровым зажиганием с последующим переходом от дефлаграции к детонации (ДДТ). Изучены особенности впрыска и зажигания струи в реакционной камере. The paper presents the results of theoretical, numerical and experimental investigations of combustion and detonation initiation in heterogeneous polydispersed mixtures. The problems of fuel droplets atomization, evaporation and combustion, and the nonequilibrium effects in droplets atomization and phase transitions are discussed. The effects of droplets size nonuniformity and spatial distribution nonuniformity on mixture ignition and flame acceleration were investigated for strong and mild initiation of detonation: by a shock wave and spark ignition followed by deflagration to detonation transition (DDT). The features of jet injection and ignition in a reaction chamber are studied.
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Starikovskiy, Andrey, Nickolay Aleksandrov e Aleksandr Rakitin. "Plasma-assisted ignition and deflagration-to-detonation transition". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, n. 1960 (13 febbraio 2012): 740–73. http://dx.doi.org/10.1098/rsta.2011.0344.
Testo completoAbstract (sommario):
Non-equilibrium plasma demonstrates great potential to control ultra-lean, ultra-fast, low-temperature flames and to become an extremely promising technology for a wide range of applications, including aviation gas turbine engines, piston engines, RAMjets, SCRAMjets and detonation initiation for pulsed detonation engines. The analysis of discharge processes shows that the discharge energy can be deposited into the desired internal degrees of freedom of molecules when varying the reduced electric field, E / n , at which the discharge is maintained. The amount of deposited energy is controlled by other discharge and gas parameters, including electric pulse duration, discharge current, gas number density, gas temperature, etc. As a rule, the dominant mechanism of the effect of non-equilibrium plasma on ignition and combustion is associated with the generation of active particles in the discharge plasma. For plasma-assisted ignition and combustion in mixtures containing air, the most promising active species are O atoms and, to a smaller extent, some other neutral atoms and radicals. These active particles are efficiently produced in high-voltage, nanosecond, pulse discharges owing to electron-impact dissociation of molecules and electron-impact excitation of N 2 electronic states, followed by collisional quenching of these states to dissociate the molecules. Mechanisms of deflagration-to-detonation transition (DDT) initiation by non-equilibrium plasma were analysed. For longitudinal discharges with a high power density in a plasma channel, two fast DDT mechanisms have been observed. When initiated by a spark or a transient discharge, the mixture ignited simultaneously over the volume of the discharge channel, producing a shock wave with a Mach number greater than 2 and a flame. A gradient mechanism of DDT similar to that proposed by Zeldovich has been observed experimentally under streamer initiation.
21
Bolodyan, I. A., L. P. Vogman, V. P. Nekrasov e A. V. Mordvinova. "Experimental Research of the Combustion of Spherical Hydrogen-Air Mixtures in an Open Space under the Influence of Slowing and Accelerating Factors". Occupational Safety in Industry, n. 1 (gennaio 2022): 33–38. http://dx.doi.org/10.24000/0409-2961-2022-1-33-38.
Testo completoAbstract (sommario):
It is shown that the experimental studies of flame propagation speed, the maximum pressure of the explosion of hydrogen-air mixtures were carried out in free space under the influence of slowing down and accelerating factors, such as power and type of ignition source, the effect of flame acceleration in the pipe, the effect of obstacles on the flame propagation path, the volume and composition of the combustible mixture when the content of the oxidizing agent or phlegmatizer changes in it. The dependence was established allowing to estimate the volume of a hydrogen-air mixture, during the combustion of which one can expect the burning speed that is close to the speed of sound in the initial mixture, and at which the transition of deflagration combustion to detonation is possible. When phlegmatizing hydrogen-air and oxygen-hydrogen mixtures with inert gases, such as nitrogen for example, the effect of reducing the burning speed and explosion pressure is achieved. The processes and conditions for the transition of deflagration combustion to detonation of free volumes of hydrogen-air mixtures and mixtures enriched and depleted of oxygen, depending on the power of the ignition source, volume, composition of the mixture and its turbulence, were studied. It is noted that as the content of the inert gas in the mixture increases, these indicators decrease, and the profile of the pressure wave changes qualitatively. Turbulization of hydrogen-air and hydrogen-oxygen mixtures with dilution using nitrogen to certain limits by turbulators leads to an increase in the values of the apparent burning speed and the maximum speed of explosion burning, up to the transition to detonation. Irrigation of combustible mixtures with atomized water leads to the same effect.
22
HORVATH, J. E. "PROPAGATING COMBUSTION MODES OF THE NEUTRON-TO-STRANGE-MATTER CONVERSION: THE ROLE OF INSTABILITIES". International Journal of Modern Physics D 19, n. 05 (maggio 2010): 523–38. http://dx.doi.org/10.1142/s0218271810016531.
Testo completoAbstract (sommario):
We discuss the propagation of the hypothetical "combustion" n → SQM in a dense stellar environment. We address the instabilities affecting the flame and a present new results of application to the turbulent regime. The acceleration of the flame, the possible transition to the distributed regime and a further deflagration-to-detonation mechanism are addressed. As a general result, we conclude that the burning happens in (at least) either the turbulent Rayleigh–Taylor or the distributed regime, but not in the laminar regime. In both cases the velocity of the conversion of the star is several orders of magnitude larger than u lam , making the latter irrelevant in practice for this problem. A transition to a detonation is by no means excluded; actually, it seems to be favored by the physical setting, but a definitive answer would need a full numerical simulation.
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DOGRA, Bharat Ankur, Mehakveer SINGH, Tejinder Kumar JINDAL e Subhash CHANDER. "Technological advancements in Pulse Detonation Engine Technology in the recent past: A Characterized Report". INCAS BULLETIN 11, n. 4 (8 dicembre 2019): 81–92. http://dx.doi.org/10.13111/2066-8201.2019.11.4.8.
Testo completoAbstract (sommario):
Pulse Detonation Engine (PDE), is an emerging and promising propulsive technology all over the world in the past few decades. A pulse detonation engine (PDE) is a type of propulsion system that uses detonation waves to combust the fuel and oxidizer mixture. Theoretically, a PDE can be operate from subsonic to hypersonic flight speeds. Pulsed detonation engines offer many advantages over conventional air-breathing engines and are regarded as potential replacements for air-breathing and rocket propulsion systems, for platforms ranging from subsonic unmanned vehicles, long-range transportation, high-speed vehicles, space launchers to space vehicles. This article highlights the operating cycle of PDE, starting with the fuel-oxidizer mixture, combustion and Deflagration to detonation transition (DDT) followed by purging. PDE combustion process, a unique process, leads to consistent and repeatable detonation waves. This pulsed detonation combustion process causes rapid burning of the fuel-oxidizer mixture, which cannot be seen in any other combustion process as it is a thousand times faster than any other mode of combustion. PDE not only holds the capability of running effectively up to Mach 5 but it also changes the technicalities in space propulsion. The present paper is the extension of the previous study which is also a well characterized status report of PDE in different areas. The present study deals with the categorization of the design approach, computations & simulations, flow visualization, DDT & Thrust enhancement, PDRE’s, experimental detonation engines with some of the experience and research undertaken in Punjab Engineering College under the complete supervision and guidance of Prof. Tejinder Kumar Jindal followed by applications of PDE technology.
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Funk, David J., W. Dale Breshears, Gary W. Laabs e Blaine W. Asay. "Laser Diode Reflectometry and Infrared Emission Measurements of Permeating Gases at High Driving Pressures and Temperatures". Applied Spectroscopy 50, n. 2 (febbraio 1996): 257–62. http://dx.doi.org/10.1366/0003702963906555.
Testo completoAbstract (sommario):
We report the use of infrared diode lasers in a diffuse reflection geometry for detection of the cyclotetramethylentetranitramine (HMX) combustion product CO permeating through a silicon carbide bed. We find that infrared emission and transient absorption are coincident with these pressure waves and demonstrate the feasibility of these diagnostics for detecting molecular species in hostile environments. We conclude from the experimental evidence that macroscopic convective heating may play a limited role in the deflagration-to-detonation transition (DDT) of porous explosives.
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Frolov, S. M., V. S. Aksenov, K. A. Avdeev, A. A. Borisov, V. S. Ivanov, A. S. Koval’, S. N. Medvedev, V. A. Smetanyuk, F. S. Frolov e I. O. Shamshin. "Cyclic deflagration-to-detonation transition in the flow-type combustion chamber of a pulse-detonation burner". Russian Journal of Physical Chemistry B 7, n. 2 (marzo 2013): 137–41. http://dx.doi.org/10.1134/s1990793113020024.
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Ornano, Francesco, James Braun, Bayindir Huseyin Saracoglu e Guillermo Paniagua. "Multi-stage nozzle-shape optimization for pulsed hydrogen–air detonation combustor". Advances in Mechanical Engineering 9, n. 2 (febbraio 2017): 168781401769095. http://dx.doi.org/10.1177/1687814017690955.
Testo completoAbstract (sommario):
Thermal engines based on pressure gain combustion offer new opportunities to generate thrust with enhanced efficiency and relatively simple machinery. The sudden expansion of detonation products from a single-opening tube yields thrust, although this is suboptimal. In this article, we present the complete design optimization strategy for nozzles exposed to detonation pulses, combining unsteady Reynolds-averaged Navier–Stokes solvers with the accurate modeling of the combustion process. The parameterized shape of the nozzle is optimized using a differential evolution algorithm to maximize the force at the nozzle exhaust. The design of experiments begins with a first optimization considering steady-flow conditions, subsequently followed by a refined optimization for transient supersonic flow pulse. Finally, the optimized nozzle performance is assessed in three dimensions with unsteady Reynolds-averaged Navier–Stokes capturing the deflagration-to-detonation transition of a stoichiometric, premixed hydrogen–air mixture. The optimized nozzle can deliver 80% more thrust than a standard detonation tube and about 2% more than the optimized results assuming steady-flow operation. This study proposes a new multi-fidelity approach to optimize the design of nozzles exposed to transient operation, instead of the traditional methods proposed for steady-flow operation.
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Starikovskii, A. Yu, N. B. Anikin, I. N. Kosarev, E. I. Mintoussov, S. M. Starikovskaia e V. P. Zhukov. "Plasma-assisted combustion". Pure and Applied Chemistry 78, n. 6 (1 gennaio 2006): 1265–98. http://dx.doi.org/10.1351/pac200678061265.
Testo completoAbstract (sommario):
This paper presents an overview of experimental and numerical investigations of the nonequilibrium cold plasma generated under high overvoltage and further usage of this plasma for plasma-assisted combustion.Here, two different types of the discharge are considered: a streamer under high pressure and the so-called fast ionization wave (FIW) at low pressure.The comprehensive experimental investigation of the processes of alkane slow oxidation in mixtures with oxygen and air under nanosecond uniform discharge has been performed. The kinetics of alkane oxidation has been measured from methane to decane in stoichiometric and lean mixtures with oxygen and air at room temperature under the action of high-voltage nanosecond uniform discharge.The efficiency of nanosecond discharges as active particles generator for plasma-assisted combustion and ignition has been investigated. The study of nanosecond barrier discharge influence on a flame propagation and flame blow-off velocity has been carried out. With energy input negligible in comparison with the burner's chemical power, a double flame blow-off velocity increase has been obtained. A signicant shift of the ignition delay time in comparison with the autoignition has been registered for all mixtures.Detonation initiating by high-voltage gas discharge has been demonstrated. The energy deposition in the discharge ranged from 70 mJ to 12 J. The ignition delay time, the velocity of the flame front propagation, and the electrical characteristics of the discharge have been measured during the experiments. Under the conditions of the experiment, three modes of the flame front propagation have been observed, i.e., deflagration, transient detonation, and Chapman-Jouguet detonation. The efficiency of the pulsed nanosecond discharge to deflagration-to-detonation transition (DDT) control has been shown to be very high.
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Tripathi, Saurabh, Krishna Murari Pandey e Pitambar Randive. "Computational Study on Effect of Obstacles in Pulse Detonation Engine". International Journal of Engineering & Technology 7, n. 4.5 (22 settembre 2018): 113. http://dx.doi.org/10.14419/ijet.v7i4.5.20025.
Testo completoAbstract (sommario):
Deflagration to Detonation transition is an important factor in the operation of pulse detonation engine which is basically working on the constant volume cycle. Insertion of obstacles decreases the DDT length. Hydrogen and the oxygen-enriched air was used as fuel and oxidizer respectively. The Purge gas is not required used. K-ԑ turbulence model is being used for the simulation and for combustion species transport model is being used. Effect of blockage ratio and obstacle spacing is also discussed. A blockage ratio of 0.5 is considered for the Shchelkin spiral. Temperature profile, flame propagation velocity and average peak pressure variation are discussed. Two-dimensional geometry and Shchelkin shape of obstacles are being considered. The comparison is done between straight tube and tube with obstacles. Numerical simulation is done and the results are being compared with those obtained through experimental investigation.
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Kiverin, A. D., A. V. Semikolenov e Yakovenko. "Non-stationary combustion regimes inside closed volumes, deflagration-to-detonation transition and dynamic loads". Vestnik Ob"edinennogo instituta vysokikh temperatur 1, n. 1 (2018): 82–87. http://dx.doi.org/10.33849/2018118.
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SUN, MEINA. "ENTROPY SOLUTIONS OF A CHAPMAN–JOUGUET COMBUSTION MODEL". Mathematical Models and Methods in Applied Sciences 22, n. 09 (31 luglio 2012): 1250018. http://dx.doi.org/10.1142/s0218202512500182.
Testo completoAbstract (sommario):
We consider the Riemann problem for a Chapman–Jouguet combustion model which comes from Majda's model with a modified, bump-type ignition function proposed in [G. Lyng and K. Zumbrun, Arch. Rational Mech. Anal. 173 (2004) 213–277; Physica D 194 (2004) 1–29]. The unique Riemann solutions are obtained constructively under the pointwise and global entropy conditions. Furthermore, we prove rigorously that these solutions are the limits of the Riemann solutions for the corresponding self-similar Zeldovich–von Neumann–Döring model as the reaction rate goes to infinity. Finally we analyze the ignition problem for this Chapman–Jouguet combustion model, and the solutions show that the unburnt state is stable (respectively unstable) when the binding energy is small (respectively large), which is the desired property for a combustion model. We can also observe the phenomenon of the transition from a weak deflagration to a strong detonation which cannot occur for the Chapman–Jouguet combustion model corresponding to Majda's model with a step-type ignition function.
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Wheeler, J. Craig. "Astrophysical explosions: from solar flares to cosmic gamma-ray bursts". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, n. 1960 (13 febbraio 2012): 774–99. http://dx.doi.org/10.1098/rsta.2011.0351.
Testo completoAbstract (sommario):
Astrophysical explosions result from the release of magnetic, gravitational or thermonuclear energy on dynamical time scales, typically the sound-crossing time for the system. These explosions include solar and stellar flares, eruptive phenomena in accretion discs, thermonuclear combustion on the surfaces of white dwarfs and neutron stars, violent magnetic reconnection in neutron stars, thermonuclear and gravitational collapse supernovae and cosmic gamma-ray bursts, each representing a different type and amount of energy release. This paper summarizes the properties of these explosions and describes new research on thermonuclear explosions and explosions in extended circumstellar media. Parallels are drawn between studies of terrestrial and astrophysical explosions, especially the physics of the transition from deflagration-to-detonation.
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Goldin, Andrei Yu, Shamil M. Magomedov, Luiz M. Faria e Aslan R. Kasimov. "Study of a qualitative model for combustion waves: Flames, detonations, and deflagration-to-detonation transition". Computers & Fluids 273 (aprile 2024): 106213. http://dx.doi.org/10.1016/j.compfluid.2024.106213.
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Volkov, Victor E. "Mathematical and information models of decision support systems for explosion protection". Applied Aspects of Information Technology 5, n. 3 (25 ottobre 2022): 179–95. http://dx.doi.org/10.15276/aait.05.2022.12.
Testo completoAbstract (sommario):
This paper is dedicated to the issue of mathematical and information modeling of the combustion-to-explosion transition that makes it possible to create an adequate mathematical and information support for decision support systems (DSS) for automatedcontrol of explosive objects.A simple mathematical model for the transition of combustion to explosion is constructed. This model is based on solving mathematical problems of the hydrodynamic stability of flames and detonation waves. These problems are reduced to solving eigenvalue problems for linearized differential equations of gas dynamics. Mathematical model is universal enough. It provides opportunities for making simple analytical estimates for the explosive induction distance and the time of the shock wave formation. The possibilities of the transition of slow combustion to both a deflagration explosion and a detonation wave are considered. Theoretical estimates of the explosive induction distance and the time of the combustion-to-explosion transition are obtained. These estimates are expressed by algebraic a formula, the use of which save computer resources and does not require significant computer time. The application of fuzzy logic makes it possible to use the proposed mathematical model of the combustion-to-explosion transition for real potentially explosive objects in industry and transport.Mathematical models of potentially explosive objects are based on combination of the fuzzy logic and classical mathematical methods. These models give possibilities for creating corresponding information models. Thus mathematical and information support of DSS for automated control systems of explosive objects is developed. The main advantage of these DSS is that it makes it possible for decision makers to do without experts. In particular, developed mathematical and information models create the base forsoftware of DSS for explosion safety of grain elevators. Appropriate software is developed and some calculations are performed. These calculations are useful not only from the point of view of testing the proposed method of mathematical modeling of a grain elevator as a potentially explosive object or testing the software itself, but also from the point of view of the grain elevator designing.
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Kiverin, A. D., A. E. Smygalina e I. S. Yakovenko. "The Classification of the Scenarios of Fast Combustion Wave Development and Deflagration-to-Detonation Transition in Channels". Russian Journal of Physical Chemistry B 14, n. 4 (luglio 2020): 607–13. http://dx.doi.org/10.1134/s1990793120040168.
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Zhou, Fei, Ning Liu e Xiangyan Zhang. "Numerical study of hydrogen–oxygen flame acceleration and deflagration to detonation transition in combustion light gas gun". International Journal of Hydrogen Energy 43, n. 10 (marzo 2018): 5405–14. http://dx.doi.org/10.1016/j.ijhydene.2017.11.134.
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Krishnamoorthy, Gautham, e Lucky Mulenga. "Impact of Radiative Losses on Flame Acceleration and Deflagration to Detonation Transition of Lean Hydrogen-Air Mixtures in a Macro-Channel with Obstacles". Fluids 3, n. 4 (8 dicembre 2018): 104. http://dx.doi.org/10.3390/fluids3040104.
Testo completoAbstract (sommario):
While there has been some recognition regarding the impact of thermal boundary conditions (adiabatic versus isothermal) on premixed flame propagation mechanisms in micro-channels (hydraulic diameters <10 mm), their impact in macro-channels has often been overlooked due to small surface-area-to-volume ratios of the propagating combustion wave. Further, the impact of radiative losses has also been neglected due to its anticipated insignificance based on scaling analysis and the high computational cost associated with resolving it’s spatial, temporal, directional, and wavelength dependencies. However, when channel conditions promote flame acceleration and deflagration-to-detonation transitions (DDT), large pressures are encountered in the vicinity of the combustion wave, thereby increasing the magnitude of radiative losses which in turn can impact the strength and velocity of the combustion wave. This is demonstrated for the first time through simulations of lean (equivalence ratio: 0.5) hydrogen-air mixtures in a macro-channel (hydraulic diameter: 174 mm) with obstacles (Blockage ratio: 0.51). By employing Planck mean absorption coefficients in conjunction with the P-1 radiation model, radiative losses are shown to affect the run-up distances to DDT in a long channel (length: 11.878 m). As anticipated, the differences in run-up distances resulting from radiative losses only increased with system pressure.
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Frolov, Sergey M., Igor O. Shamshin, Maxim V. Kazachenko, Viktor S. Aksenov, Igor V. Bilera, Vladislav S. Ivanov e Valerii I. Zvegintsev. "Polyethylene Pyrolysis Products: Their Detonability in Air and Applicability to Solid-Fuel Detonation Ramjets". Energies 14, n. 4 (4 febbraio 2021): 820. http://dx.doi.org/10.3390/en14040820.
Testo completoAbstract (sommario):
The detonability of polyethylene pyrolysis products (pyrogas) in mixtures with air is determined for the first time in a standard pulsed detonation tube based on the measured values of deflagration-to-detonation transition run-up time. The pyrogas is continuously produced in a gas generator at decomposition temperatures ranging from 650 to 850 °C. Chromatographic analysis shows that at a high decomposition temperature (850 °C) pyrogas consists mainly of hydrogen, methane, ethylene, and ethane, and has a molecular mass of about 10 g/mol, whereas at a low decomposition temperature (650 °C), it mainly consists of ethylene, ethane, methane, hydrogen, propane, and higher hydrocarbons, and has a molecular mass of 24–27 g/mol. In a pulsed detonation mode, the air mixtures of pyrogas with the fuel-to-air equivalence ratio ranging from 0.6 to 1.6 at normal pressure are shown to exhibit the detonability close to that of the homogeneous air mixtures of ethylene and propylene. On the one hand, this indicates a high explosion hazard of pyrogas, which can be formed, e.g., in industrial and household fires. On the other hand, pyrogas can be considered as a promising fuel for advanced propulsion powerplants utilizing the thermodynamic Zel’dovich cycle with detonative combustion, e.g., solid-fuel detonation ramjets. In view of it, the novel conceptual design of the dual-duct detonation ramjet demonstrator intended for operation on pyrogas at the cruising flight speed of Mach 2 at sea level has been developed. The ramjet demonstrator has been manufactured and preliminarily tested in a pulsed wind tunnel at Mach 1.5 and 2 conditions. In the test fires, a short-term onset of continuous detonation of ethylene was registered at both Mach numbers.
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Zhang, Jiaqing, Xianli Zhu, Yi Guo, Yue Teng, Min Liu, Quan Li, Qiao Wang e Changjian Wang. "Numerical Study of Homogenous/Inhomogeneous Hydrogen–Air Explosion in a Long Closed Channel". Fire 7, n. 11 (18 novembre 2024): 418. http://dx.doi.org/10.3390/fire7110418.
Testo completoAbstract (sommario):
Hydrogen is regarded as a promising energy source for the future due to its clean combustion products, remarkable efficiency and renewability. However, its characteristics of low-ignition energy, a wide flammable range from 4% to 75%, and a rapid flame speed may bring significant explosion risks. Typically, accidental release of hydrogen into confined enclosures can result in a flammable hydrogen–air mixture with concentration gradients, possibly leading to flame acceleration (FA) and deflagration-to-detonation transition (DDT). The current study focused on the evolutions of the FA and DDT of homogenous/inhomogeneous hydrogen–air mixtures, based on the open-source computational fluid dynamics (CFD) platform OpenFOAM and the modified Weller et al.’s combustion model, taking into account the Darrieus–Landau (DL) and Rayleigh–Taylor (RT) instabilities, the turbulence and the non-unity Lewis number. Numerical simulations were carried out for both homogeneous and inhomogeneous mixtures in an enclosed channel 5.4 m in length and 0.06 m in height. The predictions demonstrate good quantitative agreement with the experimental measurements in flame-tip position, speed and pressure profiles by Boeck et al. The characteristics of flame structure, wave evolution and vortex were also discussed.
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Yakush, Sergey, Oleg Semenov e Maxim Alexeev. "Premixed Propane–Air Flame Propagation in a Narrow Channel with Obstacles". Energies 16, n. 3 (3 febbraio 2023): 1516. http://dx.doi.org/10.3390/en16031516.
Testo completoAbstract (sommario):
Flame interaction with obstacles can affect significantly its behavior due to flame front wrinkling, changes in the flame front surface area, and momentum and heat losses. Experimental and theoretical studies in this area are primarily connected with flame acceleration and deflagration to detonation transition. This work is devoted to studying laminar flames propagating in narrow gaps between closely spaced parallel plates (Hele–Shaw cell) in the presence of internal obstacles separating the rectangular channel in two parts (closed and open to the atmosphere) connected by a small hole. The focus of the research is on the penetration of flames through the hole to the adjacent channel part. Experiments are performed for fuel-rich propane–air mixtures; combustion is initiated by spark ignition near the far end of the closed volume. Additionally, numerical simulations are carried out to demonstrate the details of flame behavior prior to and after penetration into the adjacent space. The results obtained may be applicable to various microcombustors; they are also relevant to fire and explosion safety where flame propagation through leakages may promote fast fire spread.
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Михальченко, Елена Викторовна, Валерий Федорович Никитин, Любен Иванович Стамов e Юрий Григорьевич Филиппов. "Modelling of a rotating detonation engine combustion chamber". Вычислительные технологии, n. 1(26) (2 aprile 2021): 33–49. http://dx.doi.org/10.25743/ict.2021.26.1.003.
Testo completoAbstract (sommario):
Рассмотрено трехмерное численное моделирование камеры сгорания двигателя с непрерывной детонационной волной с помощью авторского программного пакета. Программное обеспечение использует для многокомпонентного химически реактивного газа математическую модель с опциональным подключением модели турбулентности. В основе модели химической кинетики лежит механизм элементарных реакций, в зависимости от механизма меняется число реакций. В программе, в том числе, реализован авторский кинетический механизм. Рассмотрены шесть кинетических механизмов: Мааса-Варнаца-Поупа, Хонга, Вильямса, Gri-Mech 3.0, Ли-Джоу-Казакова-Драера и авторский, проведено их сравнение. Код распараллелен с помощью технологий OpenMP и MPI. В результате работы программы получена оптимальная форма камеры сгорания с самоподдерживающейся детонационной волной на смеси водорода с кислородом. Purpose. To create software for studying the features of the transition from ignition and deflagration to a detonation mode in a three-dimensional configuration, including the formation and propagation of a rotating detonation complex, which takes transient processes into account. Methodology. The software is based on a mathematical model for multi-component gas dynamics with chemical reactions and turbulent transport for diffusion, viscosity, and thermal conductivity. High-order calculation schemes are used. To solve a stiff subsystem of kinetic equations, a hybrid implicit-explicit Novikov method is used (a specific variant of a Rosenbrock method). Findings. Authors created a code which calculates physical processes within a multi-component gas dynamics paradigm. The code accounts for chemical processes and turbulence modelling. The shape of computation domain and the type of boundary conditions is user defined. These include boundary conditions at the wall, as well as inflow and outflow conditions for both subsonic, and supersonic modes. Initial conditions can be set up differently in different regions of the domain. The software consists of several modules: a mesh-building module, initial state creation, calculation of new time layers saving the intermediate and final results at control points with a possibility to resume interrupted calculations, and post-processing modules. Authors developed blocks of solutions for various elementary chemical kinetic mechanisms, one of considered mechanisms is build up by themselves, others are published previously. It was obtained that the details of the 3D transient problem solution significantly depend on the chosen mechanism. Оriginality/value. The software complex makes it possible to process numerical modelling of a detonation engine combustion chamber in a 3D configuration considering chemical reactions and turbulent transport. Different chemical kinetics mechanisms are utilizable, and thrust characteristics could be obtained.
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Li, Zhijie, Changhui Zhai, Xiaoxiao Zeng, Kui Shi, Xinbo Wu, Tianwei Ma e Yunliang Qi. "Review of Pre-Ignition Research in Methanol Engines". Energies 18, n. 1 (31 dicembre 2024): 133. https://doi.org/10.3390/en18010133.
Testo completoAbstract (sommario):
Methanol can be synthesized using green electricity and carbon dioxide, making it a green, carbon-neutral fuel with significant potential for widespread application in engines. However, due to its low ignition energy and high laminar flame speed, methanol is susceptible to hotspot-induced pre-ignition and even knocking under high-temperature, high-load engine conditions, posing challenges to engine performance and reliability. This paper systematically reviews the manifestations and mechanisms of pre-ignition and knocking in methanol engines. Pre-ignition can be sustained or sporadic. Sustained pre-ignition is caused by overheating of structural components, while sporadic pre-ignition is often linked to oil droplets entering the combustion chamber from the piston crevice. Residual exhaust gas trapped within the spark plug can also initiate pre-ignition. Knocking, characterized by pressure oscillations, arises from the auto-ignition of hotspots in the end-gas or, potentially, from deflagration-to-detonation transition, although the latter requires further experimental validation. Factors influencing pre-ignition and knocking, including engine oil, in-cylinder deposits, structural hotspots, and the reactivity of the air–fuel mixture, are also analyzed. Based on these factors, the paper concludes that the primary approach to suppressing pre-ignition and knocking in methanol engines is controlling the formation of pre-ignition sources and reducing the reactivity of the air–fuel mixture. Furthermore, it addresses existing issues and limitations in current research, such as combustion testing techniques, numerical simulation accuracy, and the mechanisms of methanol–oil interaction, and offers related recommendations.
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Ge, Haiwen, Ahmad Hadi Bakir e Peng Zhao. "Knock Mitigation and Power Enhancement of Hydrogen Spark-Ignition Engine through Ammonia Blending". Machines 11, n. 6 (16 giugno 2023): 651. http://dx.doi.org/10.3390/machines11060651.
Testo completoAbstract (sommario):
Hydrogen and ammonia are primary carbon-free fuels that have massive production potential. In regard to their flame properties, these two fuels largely represent the two extremes among all fuels. The extremely fast flame speed of hydrogen can lead to an easy deflagration-to-detonation transition and cause detonation-type engine knock that limits the global equivalence ratio, and consequently the engine power. The very low flame speed and reactivity of ammonia can lead to a low heat release rate and cause difficulty in ignition and ammonia slip. Adding ammonia into hydrogen can effectively modulate flame speed and hence the heat release rate, which in turn mitigates engine knock and retains the zero-carbon nature of the system. However, a key issue that remains unclear is the blending ratio of NH3 that provides the desired heat release rate, emission level, and engine power. In the present work, a 3D computational combustion study is conducted to search for the optimal hydrogen/ammonia mixture that is knock-free and meanwhile allows sufficient power in a typical spark-ignition engine configuration. Parametric studies with varying global equivalence ratios and hydrogen/ammonia blends are conducted. The results show that with added ammonia, engine knock can be avoided, even under stoichiometric operating conditions. Due to the increased global equivalence ratio and added ammonia, the energy content of trapped charge as well as work output per cycle is increased. About 90% of the work output of a pure gasoline engine under the same conditions can be reached by hydrogen/ammonia blends. The work shows great potential of blended fuel or hydrogen/ammonia dual fuel in high-speed SI engines.
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Chow, Wan Ki, Tsz Kit Yue, Yiu Wah Ng, Zheming Gao e Ye Gao. "Clean Hydrocarbon Refrigerant Explosion Hazards". Journal of Civil Engineering and Construction 11, n. 2 (15 maggio 2022): 104–11. http://dx.doi.org/10.32732/jcec.2022.11.2.104.
Testo completoAbstract (sommario):
Explosion hazards are fire safety concerns resulting from the development of clean hydrocarbon refrigerants (environmental friendly flammable refrigerants) to reduce the emission of substances with high global warning potential. Several clean hydrocarbon refrigerants are flammable with propane. Explosion hazards due to flammable refrigerant leakage from refrigerators put inside a small cupboard may give a concentration higher than its lowest flammability. A small amount of ignition energy can ignite the flammable gas to give combustion. Limiting the pressure development in a small cupboard will result in deflagration, and then transition to detonation. Since the compositions of many of environmental friendly flammable refrigerants are not disclosed and odourless, it is very difficult to assess their hazard upon leakage. This study reveals that the hidden hazard of environmental friendly flammable refrigerants would lead to serious consequences using earlier experimental studies on explosion. This is a big problem taking time to solve. Indoor aerodynamics would affect the mixing between leaked refrigerant with air in the room. Appropriate ventilation should be provided to avoid keeping the heavier explosive gas at lower levels. Different ventilation modes with air inlets and outlets at high and low positions should be considered. Use of environmental friendly flammable refrigerants and the ways in protecting against possible explosion hazards for refrigerators commonly put in kitchen cupboards in small rooms, inter alia, economy-class hotel rooms, small apartments, or subdivided units in densely populated cities, such as Hong Kong have to be watched. At the moment, fire safety management must be enhanced to address the problem.
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Huang, Diyun, Jiayong Wang, Minshuo Shi, Puze Yang e Binyang Wu. "Combustion Mechanism of Gasoline Detonation Tube and Coupling of Engine Turbocharging Cycle". Energies 17, n. 11 (22 maggio 2024): 2466. http://dx.doi.org/10.3390/en17112466.
Testo completoAbstract (sommario):
Traditional exhaust-gas turbocharging exhibits hysteresis under variable working conditions. To achieve rapid-intake supercharging, this study investigates the synergistic coupling process between the detonation and diesel cycles using gasoline as fuel. A numerical simulation model is constructed to analyze the detonation characteristics of a pulse-detonation combustor (PDC), followed by experimental verification. The comprehensive process of the flame’s deflagration-to-detonation transition (DDT) and the formation of the detonation wave are discussed in detail. The airflow velocity, DDT time, and peak pressure of detonation tubes with five different blockage ratios (BR) are analyzed, with the results imported into a one-dimensional GT-POWER engine model. The results indicate that the generation of detonation waves is influenced by flame and compression wave interactions. Increasing the airflow does not shorten the DDT time, whereas increasing the BR causes the DDT time to decrease and then increase. Large BRs affect the initiation speed of detonation in the tube, while small BRs impact the DDT distance and peak pressure. Upon connection to the PDC, the transient response rate of the engine is slightly improved. These results can provide useful guidance for improving the transient response characteristics of engines.
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Debnath, Pinku, e Krishna Murari Pandey. "Numerical analysis on detonation wave and combustion efficiency of PDC with U-shape combustor". Journal of Thermal Science and Engineering Applications, 7 giugno 2023, 1–23. http://dx.doi.org/10.1115/1.4062702.
Testo completoAbstract (sommario):
Abstract The research work is carried out for deflagration and detonation combustion process at different equivalence ratio of hydrogen-air mixtures in pulse detonation combustor. Furthermore, the U-shape channel curvature radius and thickness effect on detonation wave propagation are also investigated. This numerical simulation has been done using SIMPLE algorithm with finite volume discretization method and laminar finite rate chemistry for volumetric reaction in Ansys Fluent platform. The numerical result shows that the U-bend radius of R=3.5 cm can enhance the faster deflagration to detonation transition. So far, the fully developed detonation wave was found near curvature area of detonation tube having width of W=8 cm. This enhanced detonation wave velocity reaches to 2775 m. s−1, which is higher than C-J detonation velocity. Furthermore, the entropy generation has been analyzed in two modes of combustion process. The entropy generation number of 0.76 and 0.7 are obtained from deflagration and detonation combustion process. However entropy production rate is less in detonation combustion process, but thermal entropy generation is more in deflagration combustion process with magnitude of 3.5 kJ/kg K for an equivalence ratio of Φ=1.5. The combustion efficiency of 78% is found in detonation combustion process, which is comparatively higher than deflagration process.
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Huang, Zhiwei, e Huangwei Zhang. "Ignition and deflagration-to-detonation transition in ethylene/air mixtures behind a reflected shock". Physics of Fluids, 18 luglio 2022. http://dx.doi.org/10.1063/5.0103013.
Testo completoAbstract (sommario):
Dynamics of ethylene autoignition and Deflagration-to-Detonation Transition (DDT) are first numerically investigated in a one-dimensional shock tube using a reduced chemistry including 10 species and 10 reactions. Different combustion modes are investigated through considering various premixed gas equivalence ratios (0.2 2.0) and incident shock wave Mach numbers (1.8 3.2). Four ignition and DDT modes are observed from the studied cases, i.e., no ignition, deflagration combustion, detonation after reflected shock and deflagration behind the incident shock. For detonation development behind the reflected shock, three autoignition hot spots are formed. The first one occurs at the wall surface after the re-compression of the reflected shock and contact surface, which further develops to a reaction shock because of "the explosion in the explosion" regime. The other two are off the wall, respectively caused by the reflected shock/ rarefaction wave interaction and reaction induction in the compressed mixture. The last hot spot develops to a reaction wave and couples with the reflected shock after a DDT process, which eventually leads to detonation combustion. For deflagration development behind the reflected shock, the wave interactions, wall surface autoignition hot spot as well as its induction of reaction shock are qualitatively similar to the mode of detonation after incident shock reflection, before the reflected shock / rarefaction wave collision point. However, only one hot spot is induced after the collision, which also develops to a reaction wave but cannot catch up with the reflected shock.
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"Thermally initiated detonation through deflagration to detonation transition". Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences 435, n. 1895 (9 dicembre 1991): 459–82. http://dx.doi.org/10.1098/rspa.1991.0156.
Testo completoAbstract (sommario):
The initiation of a planar detonation via deflagration to detonation transition is studied in a reactive mixture confined between two infinite parallel plane walls. The mixture is ignited by bulk power deposition of limited duration in a thin layer adjacent to the left-hand wall. A combustion wave starts to propagate into the reactant, supported by expansion of the burned hot gases. Compression waves generated ahead of the combustion front coalesce quickly to form a shock wave strong enough to trigger considerable chemical reaction. This newly started reaction evolves into a reaction centre in which the chemical heat release rate increases rapidly. The subsequent explosion of the reaction centre creates compression waves that steepen to form a new shock. The strengthened lead shock ignites a new strongly coupled reaction zone that supports the formation of an initially overdriven detonation. Subsequently, the wave decays to an oscillating planar detonation with mean properties of a Chapman-Jouguet wave.
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Yang, Rui, Qibin Zhang, Zaijie Feng, Yujia Yang, Minghao Zhao e Wei Fan. "Characteristics of multi-cycle two-phase pulse detonation waves traveling near the lean combustion limit". Physics of Fluids 35, n. 11 (1 novembre 2023). http://dx.doi.org/10.1063/5.0165922.
Testo completoAbstract (sommario):
The need for high combustion efficiency in two-phase pulse detonation engines necessitates the implementation of a lean combustion concept. However, there have been no research initiatives attempting to conduct two-phase pulse detonation in a lean combustion environment due to the highly sensitive nature of the deflagration-to-detonation transition toward the reactivity of the reactant composition. The present study explores methods to realize lean combustion organization in two-phase pulse detonation through the incorporation of secondary air injection. Valveless pulse detonation operation based on gasoline was carried out, while the frequency varies from 20 to 100 Hz. The initiation and propagation characteristics of the pulse detonation wave are influenced first by the equivalence ratio of the detonation initiation section and then by the equivalence ratio of the detonation propagation section. Furthermore, secondary air injection enabled a reduction in the minimum global equivalence ratio for the stable operation of multi-cycle two-phase pulse detonation waves to 0.38, while maintaining an 80% detonation rate.
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Zhao, Minghao, Hua Qiu, Yong Liang, Cha Xiong, Xinlu He e Huangwei Chen. "Numerical simulation study of hydrogen/air flame propagation and detonation characteristics in an annular cross section of gas turbine combustion chamber". Physics of Fluids 36, n. 12 (1 dicembre 2024). https://doi.org/10.1063/5.0233505.
Testo completoAbstract (sommario):
The trends and future directions of hydrogen safety research cannot be separated from the thermodynamic behavior of combustion and explosion, hydrogen spontaneous combustion, flame propagation behavior, thermodynamic mechanisms, and other related topics. In this paper, through the method of numerical simulation, considering the hydrogen flame propagation and detonation characteristics in the annular section of the combustion chamber commonly used in gas turbines, the form of detonation and detonation impact in the channel are evaluated. By discussing the deflagration to detonation transition of hydrogen/air premixed gas and premixed gas under different working conditions, it is found that the flame in the annular channel propagates close to the inner wall and forms a strong expansion and turbulence between the outer wall and the outer wall of the flame. The flame surface and the airflow shear accelerate the detonation of hydrogen. The area close to the wall on the outer side of the flame surface and the tip of the flame surface are prone to set off detonation. The high-pressure area after the detonation mainly acts on the symmetrical end face of the outer wall surface and ignition area. There is a critical working temperature to make the impact strength strongest when the detonation occurs. Reducing the equivalence ratio of the filling gas can significantly reduce the reaction speed and weaken the impact strength of the wall. When the equivalence ratio is less than a certain value, the filling gas is completely consumed in the form of deflagration.
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Sulaiman, S. Z., R. M. Kasmani, A. Mustafa e R. Mohsin. "Effect of Obstacle on Deflagration to Detonation Transition (DDT) in Closed Pipe or Channel–An Overview". Jurnal Teknologi 66, n. 1 (19 dicembre 2013). http://dx.doi.org/10.11113/jt.v66.1326.
Testo completoAbstract (sommario):
Due to complicated and rapid process, deflagration-to-detonation transition (DDT) becomes one of the major challenges in combustion theory where the exact mechanism is still poorly understood. Theoretically, the presence of obstacle may disturb flame propagation and hence make the DDT predictions more complex. Thus a comprehensive study is required to acknowledge DDT performance precisely. Lacking of information in literature causes the prediction of the transition period is still uncertain. In contrast, appropriate estimation of the DDT event is crucial for explosion safety. Thus, this present paper discusses the effect of obstacle on prediction transition deflagration to detonation event in pipeline system in order to apply an effective protection and safety systems to prevent and mitigate the gas explosion in industries. In addition the effect of bending on flame acceleration and explosion development would also be explored.