Dynamic Parameters of Gaseous Detonations
01 Jan 1984-Annual Review of Fluid Mechanics (Annual Reviews 4139 El Camino Way, P.O. Box 10139, Palo Alto, CA 94303-0139, USA)-Vol. 16, Iss: 1, pp 311-336
TL;DR: In this paper, the authors considered homogeneous gaseous fuel-air detonations and showed that the propagation of the combustion wave is governed by the molecular diffusion of heat and mass from the reaction zone to the unburned mixture, and that the very strong exponential temperature dependence of chemical reaction rates makes possible the rapid combustion in the detonation mode.
Abstract: In addition to gases, flammable liquids and solids in the form of fine droplets and dust particles also form explosive mixtures with air. An explosive mixture can, in general, support two modes of combustion. The slow laminar deflagration mode is at one extreme; here the flame propagates at typical velocities of the order 1 m s -1 relative to the unburned gases and there is negligible overpressure development when the explosion is unconfined. At the other extreme is the detonation mode, in which the detonation wave propagates at about 2000 m s -1 accompanied by an overpressure rise of about 20 bars across the wave. The propagation of laminar defiagrations is governed by the molecular diffusion of heat and mass from the reaction zone to the unburned mixture. The propagation of detonations depends on the adiabatic shock compression of the unburned mixtures to elevated temperatures to bring about autoignition. The very strong exponential temperature dependence of chemical reaction rates in general makes possible the rapid combustion in the detonation mode. Two phase liquid droplets or dust-air mixtures are similar, but they require more physical processes (e.g. droplet break-up, phase change, mixing, etc.) prior to combustion. Thus, characteristic time or length scales associated with the combustion front are usually much larger than those of homogeneous gaseous fuel-air mixtures. The essential mechanisms of propagation of the combustion waves, however, are similar. In between the two extremes of laminar detlagration and detonation, there is an almost continuous spectrum of burning rates where turbulence plays the dominant role in the combustion process. Due to space limitations, only homogeneous gaseous fuel-air detonations are considered in this article.
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TL;DR: In this article, the state of knowledge on flame acceleration and deflagration-to-detonation transition (DDT) in smooth ducts and ducts equipped with turbulence-producing obstacles is reviewed.
613 citations
TL;DR: There is a renewed interest lately on intermittent or pulsed detonations engines as mentioned in this paper, which are an extremely efficient means of combusting a fuel-oxidizer mixture and releasing its chemical energy content.
Abstract: Introduction I Nprinciple,detonationsare an extremelyef cientmeans of combustinga fuel-oxidizermixture and releasing its chemical energy content. During the past 60 years or so, there have been numerous researcheffortsat harnessingthepotentialof detonationsfor propulsion applications.1 There is a renewed interest lately on intermittent or pulsed detonations engines. Eidelman et al. and Eidelman and Grossmann3 have reviewed some of the initial research as well as work done in the late 1980s on pulse detonation engines (PDEs). The basic theory, design concepts, and the work in the early 1990s related to pulse detonationengines have been discussedby Bussing and Pappas.4 The focus of a more recent review5 is on performance estimates fromvarious experimental, theoreticaland computational studies. More recently, work related to nozzles for PDEs has been discussed. Other reviews7i9 discussing the objectives and accomplishments of various programs are also available.The objective of this paper is to update the previousreviews, focusingon themore recent developmentsin the researchon PDEs. The review is restricted toworkopenlyavailablein the literaturebut includesongoingefforts around the world. Currently, there are several programs sponsored by Of ce of Naval Research (ONR), U.S. Air Force, NASA, Defense Advanced Research Projects Agency, and other agencies in the United States as well as several parallel efforts in Belarus, Canada, France, Japan, Russia, Sweden, and other countries.The results from some of these programs are just beginning to be published.A summary of recent progress and the various organizationsand people involved in PDE research in Japan has been presented.9 Reports of the basic PDE research sponsoredby ONR are available in the proceedingsof a recurringannualmeeting(forexample, seeRef. 10).Recentwork conducted outside the United States has been reported at international meetings on detonations such as those held in Seattle11 (for more information, see http://www.engr.washington.edu/epp/icders/) and Moscow.12 Although an attempt is made to cover a broad range of the reported research, the shear volume of papers presented with PDEs in the title make it impractical to be exhaustive. Rather than providing a chronologicalreport, an attempt is made here to discuss the recent progress in terms of broad topic areas. The key issues that need to be resolved have been addressed in a number of papers (e.g., Refs. 13 and 14). The speci c order in which to discuss the various topics was determined by considering the schematic of an idealized, laboratory pulse detonation engine shown in Fig. 1. This idealizedengine is representativeof the device
443 citations
TL;DR: In this article, a brief introduction to gas explosion safety is given, based on current knowledge of the subject and on experience in applying this knowledge to practical problems in the industry, including cloud formation, gas explosions, blast waves and structural response.
364 citations
Cites background from "Dynamic Parameters of Gaseous Deton..."
...The size of the fish shell pattern generated by the triple point (Mach stem) of the shock wave is a measure of the reactivity of the mixture representing a length scale characterising the overall chemical reaction in the wave (Lee, 1984)....
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01 Jan 2011
TL;DR: In this article, the authors highlight three areas where quantitative sensing based on laser absorption has had strong influence: chemical kinetics, propulsion, and practical energy systems, and provide an overview of the current power and future potential of these modern diagnostic tools.
Abstract: Laser diagnostic techniques play a large and growing role in combustion research and development. Here we highlight three areas where quantitative sensing based on laser absorption has had strong influence: chemical kinetics, propulsion, and practical energy systems. In the area of chemical kinetics, measurements in shock tubes of high-temperature reaction rate coefficients using species-specific laser absorption techniques have provided new and accurate answers to questions about combustion chemical processes. In the area of propulsion, wide-bandwidth measurements of flow temperatures, species concentrations, and velocity have provided engine designers with the necessary information to improve operation and performance. In the area of practical energy systems, real-time measurements of combustor operating conditions and emissions have enabled needed incremental improvements in large power plants and improved safety of operation. Yet, there is still more to be done, and opportunities for new applications will grow as laser sensors evolve. This review seeks to provide an overview of the current power and future potential of these modern diagnostic tools.
313 citations
01 Jan 2005
TL;DR: In this article, the authors assess accomplishments of theory in combustion over the past fifty years and prospects for the future and emphasize that development of theory necessarily goes hand-in-hand with specification of a model.
Abstract: In honor of the fiftieth anniversary of the Combustion Institute, we are asked to assess accomplishments of theory in combustion over the past fifty years and prospects for the future. The title of our article is chosen to emphasize that development of theory necessarily goes hand-in-hand with specification of a model. Good conceptual models underlie successful mathematical theories. Models and theories are discussed here for deflagrations, detonations, diffusion flames, ignition, propellant combustion, and turbulent combustion. In many of these areas, the genesis of mathematical theories occurred during the past fifty years, and in all of them significant advances are anticipated in the future. Increasing interaction between theory and computation will aid this progress. We hope that, although certainly not complete in topical coverage or reference citation, the presentation may suggest useful directions for future research in combustion theory.
279 citations
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302 citations
TL;DR: In this paper, the critical tube diameters dc for the successful transformation of a planar to a spherical detonation have been measured in nine gaseous fuels (CH4, C2H2, C 2H4, c2H6, C3H8, C4H10, MAPP and H2) in stoichiometric fuel-oxygen mixtures diluted with nitrogen at atmospheric initial pressure.
250 citations
TL;DR: In this article, a theoretical model including a detailed chemical kinetic reaction mechanism for hydrocarbon oxidation was used to examine detonation properties for mixtures of fuel, including methane, ethylene, acetylene, and methanol.
173 citations
01 Jan 1979
TL;DR: In this article, the critical energy for direct initiation of spherical detonation for eight gaseous fuels (C 2 H 2, C 2 H 4 O, C 2 HO 4 O, C 3 H 6, C 1 H 8, CH 4 and H 2 ) have been measured using a planar detonation from a linear tube for initiation.
Abstract: The critical energy for direct initiation of spherical detonation for eight gaseous fuels (C 2 H 2 , C 2 H 4 , C 2 H 4 O, C 3 H 6 , C 2 H 6 , C 3 H 8 , CH 4 and H 2 ) have been measured using a planar detonation from a linear tube for initiation. On the basis of the minimum value of the critical energy (corresponding to about the stoichiometric composition) a dimensionless parameter D H is defined by the ratio of the minimum energy of the fuel to that of acetylene-oxygen mixture. The magnitude of D H is then used for comparing the relative detonation sensitivity of the various fuels. Based on the values of D H for fuel-oxygen mixtures, it is found that ethylene oxide with a value of D H ⋍10 is about 10 times less sensitive than acetylene (D H =1). The olefins (i.e., ethylene and propylene) having values of D H ⋍10 2 are about 100 times less sensitive than acetylene. The alkanes (i.e., propane, ethane, etc.) have values of D H ⋍10 3 with the exception of methane which is particularly insensitive with a value of D H ⋍10 5 . Hydrogen is found to be similar to the normal alkanes with a value of D H ⋍10 3 . Fuel-air mixtures in general have values of D H about 10 6 times larger than the corresponding values for the same fuel with pure oxygen. The relative sensitivities of the various fuels remain the same for fuel-air mixtures as in the case of fuel-oxygen mixtures.
149 citations