Strong Deflagrations Research Articles

Effects of aluminum powder additives on deflagration and detonation performance of JP-10/DEE mixed fuel under weak and strong ignition conditions

As a high-density hydrocarbon fuel with good comprehensive properties, JP-10 is widely used in scramjets and detonation engines. Previous work has improved the ignition susceptibility and reduced incomplete combustion product concentration of JP-10 liquid fuel by blending diethyl ether (DEE). However, the density and bulk calorific value of hydrocarbons do not increase indefinitely with the increase of the ring structure, and the low temperature properties of the fuel gradually deteriorate with the increase of density. Therefore, adding metal dust with higher combustion calorific value to improve the energy density of mixed fuel is a new solution. In the present work, the deflagration and detonation properties of multiphase mixed fuels obtained by adding three aluminum powders with different morphologies and particle sizes (flake aluminum powder, small spherical aluminum powder, large spherical aluminum powder) to the JP-10/DEE mixed fuel were investigated. Under weak ignition conditions, the addition of aluminum powder increases the average burning rate of the multiphase mixed fuel and flame intensity significantly. The increase rate of the flame intensity when spherical powders are added is lower than that of the flake aluminum powder. The addition of aluminum powder is conducive to the early acceleration of deflagration, and the flame intensity reaches a high level earlier. Although the aluminum powder increases the energy of the reaction system, it also aggravates the incomplete combustion of JP-10/DEE in the oxygen-depleted state, and generates a large amount of soot. Under the strong ignition conditions, the DDT process of JP-10/DEE/aluminum powder can be divided into four stages: the slow propagation stage, shock wave formation stage as a result of compression wave superposition, coupling evolution stage of shock wave and flame front, and the detonation stage, respectively corresponding to four different pressure wave pattern. The strong ignition method greatly accelerates the evaporation of JP-10/DEE and the melting of the aluminum core in the initial stage, so that the multiphase mixture quickly changes from a slow propagation mode to a strong deflagration mode.

Baryogenesis and gravity waves from a UV-completed electroweak phase transition

We study gravity wave production and baryogenesis at the electroweak phase transition, in a real singlet scalar extension of the Standard Model, including vector-like top partners to generate the CP violation needed for electroweak baryogenesis (EWBG). The singlet makes the phase transition strongly first-order through its coupling to the Higgs boson, and it spontaneously breaks CP invariance through a dimension-5 contribution to the top quark mass term, generated by integrating out the heavy top quark partners. We improve on previous studies by incorporating updated transport equations, compatible with large bubble wall velocities. The wall speed and thickness are computed directly from the microphysical parameters rather than treating them as free parameters, allowing for a first-principles computation of the baryon asymmetry. The size of the CP-violating dimension-5 operator needed for EWBG is constrained by collider, electroweak precision, and renormalization group running constraints. We identify regions of parameter space that can produce the observed baryon asymmetry or observable gravitational (GW) wave signals. Contrary to standard lore, we find that for strong deflagrations, the efficiencies of large baryon asymmetry production and strong GW signals can be positively correlated. However we find the overall likelihood of observably large GW signals to be smaller than estimated in previous studies. In particular, only detonation-type transitions are predicted to produce observably large gravitational waves.

Ignition behavior and the onset of quasi-detonation in methane-oxygen using different end wall reflectors

The shock wave focusing technique is beneficial to the development of detonation-based engines, which can shorten the long run-up distance that is usually required for a detonation, reducing the weight of the detonation engine. In this work, we performed experiments using different end wall reflectors to facilitate the formation and intensity of the combustion wave in a stoichiometric methane-oxygen mixture diluted by argon. By changing shock wave intensity, the effects of the incident shock Mach number (Ma) on the ignition delay times in two reflectors are systematically investigated. The experimental results show that the conical reflector creates an abrupt pressure rise in the apex, resulting in a 64.5% rise in the acceleration of the reflected shock velocity compared with the planar reflector. The introduction of a conical reflector significantly shortens the ignition delay time by an order of magnitude and facilitates the amalgamation of the leading reflected shock wave and the subsequent combustion wave. The experimental results also illustrate that conical reflectors promote the formation of the second ignition. However, only a weak deflagration wave is formed in a planar reflector, and a strong deflagration wave and quasi-detonation wave are observed by using a conical reflector. Our observation sheds light on the mechanism of ignition modes induced by the shape of reflectors.

Experimental investigation on helium distribution and stratification in unventilated vertical cylindrical enclosure – Effect of jet release rates and total release volume

Hydrogen leakages into enclosed spaces may occur in hydrogen storage and usage facilities and in nuclear power plants (NPP) following a severe accident. In the absence of either mitigation or combustion processes, hydrogen leaked into the enclosed space may accumulate and form large cloud of explosive mixture with air. This, when gets ignited, can lead to a strong deflagration or even detonation and cause huge threat to both life and property. In NPP, such events can cause over-pressurization of the containment, causing problems in the structural integrity of the containment and consequently result in the leakage of radioactivity into the environment. The present study reports the experimental investigation of the phenomenology of hydrogen distribution inside a cylindrical test enclosure (AIHMS). Different hydrogen leak scenarios are experimentally simulated using helium gas, which is its inert surrogate. The effect of helium release velocities on mixing and distribution of helium within the enclosure, for different quantities of helium released has been experimentally investigated. The experimental studies are conducted in a test enclosure having a volume of around 2 cubic-meters, specifically designed for the purpose and the results have been presented systematically.

10907 内部混合型回転デトネーションエンジンの成立条件に関する研究

In this study, operating conditions of a rotating detonation engine with internal mixing has been studied. Hydrogen and oxygen are supplied separately from gas storage tanks and mixed in an annular combustion chamber. The mixture is initiated by a spark discharge placed at the chamber wall surface. As a result, a strong deflagration after ignition is initially generated in the combustion chamber. The experimental results show that the following stages are involved to achieve stable propagation of the rotating detonation : i) a deflagration wave moves to the downstream, ii) a DDT process occurs in the downstream, iii) a detonation wave propagates in the upstream direction, iv) a rotating detonation is stabilized in the combustion chamber.

Improved far-field blast predictions from fast deflagrations, DDTs and detonations of vapour clouds using FLACS CFD

The CFD tool FLACS was developed from 1982 with a primary goal to predict gas explosion loads inside oil platform modules. The prediction of far-field blast loads was of secondary importance as any scenario creating a substantial far-field blast would already have collapsed the module where it originated. For the same reason the potential for a deflagration-to-detonation-transition (DDT) was not initially of interest. Over the past decade use of FLACS has been more widespread, and the tool is now frequently used to predict explosions on onshore facilities and FPSOs/FLNGs, where far-field blast loads and evaluation of DDT potential may be of significant interest. Previous work by Hansen et al. (2010) has highlighted a weakness in FLACS when predicting the far-field blast from strong gas explosions and, when using FLACS according to guidelines, far-field blast pressures will often be significantly underpredicted. For scenarios involving DDT this effect will be particularly strong. The current study will present a way to obtain more accurate far-field blast predictions by modified parameter settings in FLACS for strong deflagrations. Using modified settings, it is also possible, with good precision, to predict flame speeds, pressures and far-field blast from DDT-scenarios and directly initiated gas detonations, physics which are beyond the accepted capabilities of FLACS. Selected full-scale experiments from the DNV GL test site at Spadeadam will be used to compare with the simulations. Convincing evidence for DDT in large scale natural gas experiments (91% methane) was found in simulations of one of these tests.

Combustion of a neutron star into a strange quark star: The neutrino signal

There are strong indications that the process of conversion of a neutron star into a strange quark star proceeds as a strong deflagration implying that in a few milliseconds almost the whole star is converted. Starting from the three-dimensional hydrodynamic simulations of the combustion process which provide the temperature profiles inside the newly born strange star, we calculate for the first time the neutrino signal that is to be expected if such a conversion process takes place. The neutrino emission is characterized by a luminosity and a duration that is typical for the signal expected from protoneutron stars and represents therefore a powerful source of neutrinos which could be possibly directly detected in case of events occurring close to our Galaxy. We discuss moreover possible connections between the birth of strange stars and explosive phenomena such as supernovae and gamma-ray bursts.

RANKINE-HUGONIOT RELATIONS IN RELATIVISTIC COMBUSTION WAVES

As a foundational element describing relativistic reacting waves of relevance to astrophysical phenomena, the Rankine-Hugoniot relations classifying the various propagation modes of detonation and deflagration are analyzed in the relativistic regime, with the results properly degenerating to the non-relativistic and highlyrelativistic limits. The existence of negative-pressure downstream flows is noted for relativistic shocks, which could be of interest in the understanding of the nature of dark energy. Entropy analysis for relativistic shock waves are also performed for relativistic fluids with different equations of state (EoS), denoting the existence of rarefaction shocks in fluids with adiabatic index \Gamma < 1 in their EoS. The analysis further shows that weak detonations and strong deflagrations, which are rare phenomena in terrestrial environments, are expected to exist more commonly in astrophysical systems because of the various endothermic reactions present therein. Additional topics of relevance to astrophysical phenomena are also discussed.

Deflagration to detonation transitions and strong deflagrations in alkane and alkene air mixtures

Deflagration to detonation transitions and strong deflagrations for a large range of stoichiometric alkane (CH 4, C 2H 6, C 3H 8, C 4H 10) and air mixtures and alkene (C 2H 4, C 3H 6, C 4H 8) and air mixtures have been studied systematically by varying surface roughness via the introduction of Shchelkin spirals. The use of such spirals, rather than repeated obstacles such as orifice plates, is preferred, as improved acceleration and higher flame speeds are obtained due to reduced momentum losses. The results obtained indicate that deflagration to detonation transitions (DDT) and quasi-detonations can be obtained for all fuels tested. Using short obstacles it is demonstrated that quasi-stable strong deflagrations of considerable duration, supported only by a smooth-walled tube, can easily be established and typically serve as a basis for further acceleration and transition to detonation. The effects of different obstacle exit velocities on the duration of the strong deflagration phase and on DDT parameters have been investigated. By further increasing the obstacle length, DDT via quasi-detonations has been investigated and it is demonstrated that the relative detonability of the fuels under strongly turbulent conditions differs systematically from that obtained in smooth tube experiments.

Deflagration to detonation transition in mixtures of alkane LNG/LPG constituents with [formula omitted

Deflagration to detonation transitions (DDT) of methane, methane ethane , ethane, propane, and butane in mixtures with increasing dilution of nitrogen have been studied in a smooth 2″ id detonation tube with a length/diameter ratio of 220. The results obtained demonstrate the presence of two regimes of DDT depending on the reactivity of the mixture. The first regime displays rapid acceleration to a stable detonation, while the second regime contains a quasistable, strong deflagration of rapidly increasing duration with decreasing mixture reactivity. It is established that the order of DDT under the conditions employed follows the order of autoignition temperatures for the fuels considered. The conditional use of transition parameters for estimates of relative detonabilities based on a qualitative similarity between induction times and times to transition is demonstrated to hold only for the first transition regime.

Limit Behavior and the Existence of Combustion Shock Layers

This paper contains a comprehensive study of the global and limit behavior of integral curves in the three‐dimensional phase space for the system of nonlinear ordinary differential equations governing the structure of combustion shock layers. A significant general result is a list of admissible routes for the integral curves representing the four combustion types. Perhaps most noteworthy is a theorem on the nonexistence of strong deflagrations. A special aspect of the study points to the significance of the stoichiometric parameters for a reaction, and the need to distinguish between first‐order and higher‐order reactions. The detailed information contained in this paper concerning the various possible modes of combustion for the different reactions should have potential application in the search for efficient energy conversion by combustion processes.

Ionization front in interstellar gas: The structure of ionization fronts

A complete analysis of the structures of all types of ionization front is given, together with computed examples. It is shown that the solutions given by Goldsworthy for the propagation of ionization fronts, considered as discontinuities, can be made unique, and the unique solutions are given for the case of cylindrical symmetry. Ionization fronts of all types are shown to be possible, depending on the density of the ionized gas and the spectral type of the radiation. In particular strong D -type and weak R -type ionization fronts (corresponding to strong deflagrations and weak detonations, respectively, in combustion theory) prove to be of importance. The existence of these discontinuities conflicts with the Chapman-Jouguet hypothesis and the reasons for this behaviour are examined in detail. It is concluded that the most important condition for waves of this type to occur is that strong cooling effects should be present, which allow the stagnation enthalpy of the flow to have a maximum before decreasing to an equilibrium value at the rear of the wave. It is suggested that this may be of significance in the theory of other gas-dynamic discontinuities, and in determining the validity of the Chapman—Jouguet hypothesis in general.