Drop-size effects in spray detonations

Dabora, Eliahou K.; Ragland, Kenneth W.; Nicholls, James A.

doi:10.1016/s0082-0784(69)80388-7

Cited by 69 publications

(14 citation statements)

References 5 publications

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“…They outlined a "theory of discrete interactions" in which initiation of subsequent sources would be described by a nonlinear recursion relation. In spray detonations with millimeter-sized droplets of fuel, a similar propagation mechanism, i.e., blast waves generated by each individual droplet releasing its energy, merging with and reinforcing the leading shock wave, was experimentally identified by Dabora et al [8] and theoretically described Pierce & Nicholls [45]. Propagation of detonation in media with a sinusoidal variation in properties was explored computationally by Morano & Shepherd [39] in one dimension and extended to two dimensions by Li et al [35].…”

Section: Introductionmentioning

confidence: 80%

Effect of spatial discretization of energy on detonation wave propagation

Timofeev

Higgins

2017

J. Fluid Mech.

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Detonation propagation in the limit of highly spatially discretized energy sources is investigated. The model of this problem begins with a medium consisting of a calorically perfect gas with a prescribed energy release per unit mass. The energy release is collected into sheet-like sources that are now embedded in an inert gas that fills the spaces between them. The release of energy in the first sheet results in a planar blast wave that propagates to the next source, which is triggered after a prescribed delay, generating a new blast, and so forth. The resulting wave dynamics as the front passes through hundreds of such sources is computationally simulated by numerically solving the governing one-dimensional Euler equations in the lab-fixed reference frame. Two different solvers are used: one with a fixed uniform grid and the other using an unstructured, adaptively refined grid enabling the limit of highly concentrated, spatially discrete sources to be examined. The two different solvers generate consistent results, agreeing within the accuracy of the measured wave speeds. The average wave speed for each simulation is measured once the wave propagation has reached a quasi-periodic solution. The effect of source delay time, source energy density, specific heat ratio, and the spatial discreteness of the sources on the wave speed is studied. Sources fixed in the lab reference frame versus sources that convect with the flow are compared as well. The average wave speed is compared to the ideal Chapman-Jouguet (CJ) speed of the equivalent homogenized media. Velocities in excess of the CJ speed are found as the sources are made increasingly discrete, with the deviation above CJ being as great as 15%. The deviation above the CJ value increases with decreasing values of specific heat ratio γ. The total energy release, delay time, and whether the sources remain lab-fixed or are convected with the flow do not have a significant influence on the deviation of the average wave speed away from CJ. A simple, ad hoc analytic model is proposed to treat the case of zero delay time (i.e., source energy released at the shock front) that exhibits qualitative agreement with the computational solutions and may explain why the deviation from CJ increases with decreasing γ. When the sources are sufficiently spread out so as to make the energy release of the media nearly continuous, the classic CJ solution is obtained for the average wave speed. Such continuous waves can also be shown to have a time-averaged structure consistent with the classical ZND structure of a detonation. In the limit of highly discrete sources, temporal averaging of the wave structure shows that the effective sonic surface does not correspond to an equilibrium state. The average state of the flow leaving the wave in this case does eventually reach the equilibrium Hugoniot, but only after the effective sonic surface has been crossed. Thus, the super-CJ waves observed in the limit of highly discretized sources can be understood as weak detonations due to the...

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Section: Introductionmentioning

confidence: 80%

Effect of spatial discretization of energy on detonation wave propagation

Timofeev

Higgins

2017

J. Fluid Mech.

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“…Experimental studies have also reported that the detonation velocity in heterogeneous mixtures is a function of droplet size. Earlier, Dabora et al [9] revealed that the multiphase detonation velocity is in general lower than an ideal Chapman-Jouguet (CJ) velocity. The smallest droplet size studied was 290 μm in diameter and the largest observed velocity deficit was ~30-35% for 2600 μm droplets.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulations of the Effects of Droplet Size and Concentration on Vapour-Droplet JP-10/Air Detonations

Liu¹,

Zhou²

2018

Cent. Eur. J. Energ. Mater.

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Two-dimensional simulations were conducted for JP-10 mono-dispersed vapour-droplet detonation in air, based on the detonation mechanism for clouds and validation of the extending critical droplet size limits in previous tests. In the simulations, the discrete phase model combined with the droplet evaporation and droplet breakup models was used. Utilizing a wide range of mono-dispersed droplet sizes and initial droplet concentrations, all cases of JP-10 droplets with a certain amount of pre-vaporized fuel can successfully achieve the deflagration to detonation transition. Detonation velocities at the equivalent concentration with droplet diameters no larger than 50 μm are in good agreement with the theoretical detonation velocities. The effects of droplet size and initial droplet concentration on the detonation behaviour were also investigated. Detonation velocities attained with droplet diameters below 50 μm appear to decrease very slightly with droplet size, but are almost equal to the velocity in gases. When the droplet diameter is above 50 μm, there is a decrease in simulated detonation velocity compared with fine droplets, and no secondary pressure peak was observed. For fuel-rich combustion, detonation velocities decrease rapidly with an increase in initial droplet concentration, and post-wave pressure fluctuation was obviously irregular, caused by the secondary local explosion of the droplets.

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“…Studies on spray detonation presented that PDE efficiency (check again!) is highly related to the droplet size and vaporization of liquid fuel [8,9]; thus, atomization and vaporization of liquid fuel should be considered for liquidfueled PDE.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Pulse Detonation Engine with Two-Phase Inhomogeneous Mixture

Gong

2020

International Journal of Aerospace Engineering

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In order to investigate the effects of fuel distribution on the operation of two-phase pulse detonation engine (PDE), a series of cold flow and multicycle PDE experiments was carried out with 9 mixing schemes. Homogeneity degree with fuel distribution considered in terms of space and time was proposed to quantitatively evaluate the mixing of liquid fuel and air by particle image velocimetry (PIV) in cold flow experiments. Operation stability of multicycle PDE was presented by statistical analysis of peak pressure at the outlet of a detonation tube. The relationship between operation stability and homogeneity degree was quantitatively elaborated. These experimental results indicated that not only using mixing reinforcement devices (such as pore plate and reed valve) was fuel distribution improved but also the effect of inlet ways on the homogeneity degree was weakened. The homogeneity degree of fuel distribution ζ=0.72 was a critical value for stable working of multicycle PDE. When homogeneity degree was lower than 0.72, stable state was not maintained and detonation wave in some cycles was not established due to poor fuel distribution. Therefore, it is necessary to hold homogeneity degree larger than 0.72 to achieve stable operation of PDE. These results contribute to enhancing the operation stability and offering guidelines for the design of PDE’s mixing scheme.

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Drop-size effects in spray detonations

Abstract: Schlieren and direct light photographs of the phenomenon are also presented. They show a rather complicated structure of the flow field behind the front due to the interaction of the gaseous convective flow and the initially stationary drops.

Cited by 69 publications

References 5 publications

Effect of spatial discretization of energy on detonation wave propagation

Effect of spatial discretization of energy on detonation wave propagation

Numerical Simulations of the Effects of Droplet Size and Concentration on Vapour-Droplet JP-10/Air Detonations

Experimental Study on Pulse Detonation Engine with Two-Phase Inhomogeneous Mixture

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