Deflagration-detonation Transition Research Articles

The Contribution of A. K. Oppenheim to Explaining the Nature of the Initiation of Gaseous Detonation in Tubes

Abstract This paper analyzes A.K. Oppenheim’s original works on the transition of deflagration to detonation and reviews them from the perspective of new numerical and experimental results recently obtained on such phenomena. Particular attention is focused on processes happening in the boundary layer of the tube walls ahead of the accelerating flame. The results of the theoretical analyses of temperature variations inside developing boundary layer are presented and compared to the temperature variation in a free stream away from the boundary layer. Analyses of temperature increase in such layers clearly indicate that the self-ignition of the mixture happens in the boundary layer ahead of the propagating flame front. New experimental results obtained recently by a research group from the A. V. Luikov Heat and Mass Transfer Institute in Minsk, Belarus, combined with previously conducted theoretical analyses and numerical simulations, show clearly and unambiguously that the origin of the “explosion in the explosion”, postulated by A. K. Oppenheim in 1966, is always responsible for the Deflagration-Detonation Transition (DDT) in gases and is located in the boundary layer ahead of the accelerating flame front.

Delayed Detonation Thermonuclear Supernovae with an Extended Dark Matter Component

Abstract We present spherically symmetric simulations of the thermonuclear explosion of a white dwarf admixed with an extended component of fermionic dark matter, using the deflagration model with the deflagration–detonation transition. In all the dark matter admixed models we have considered, the dark matter is left behind after the explosion as a compact dark star. The presence of dark matter lengthens the deflagration phase to produce a similar amount of iron-group elements and more thermoneutrinos. Dark matter admixed models also give dimmer but slowly declining light curves, consistent with some observed peculiar supernovae. Our results suggest a formation path for dark compact objects that mimic sub-solar-mass black holes as dark gravitational sources.

New Type Ia Supernova Yields and the Manganese and Nickel Problems in the Milky Way and Dwarf Spheroidal Galaxies

Abstract In our quest to identify the progenitors of Type Ia supernovae (SNe Ia), we first update the nucleosynthesis yields for both near-Chandrasekhar- (Ch) and sub-Ch-mass white dwarfs (WDs) for a wide range of metallicities with our 2D hydrodynamical code and the latest nuclear reaction rates. We then include the yields in our galactic chemical evolution code to predict the evolution of elemental abundances in the solar neighborhood and dwarf spheroidal (dSph) galaxies Fornax, Sculptor, Sextans, and Carina. In the observations of the solar neighborhood stars, Mn shows an opposite trend to α elements, showing an increase toward higher metallicities, which is very well reproduced by the deflagration–detonation transition of Ch-mass WDs but never by double detonations of sub-Ch-mass WDs alone. The problem of Ch-mass SNe Ia was the Ni overproduction at high metallicities. However, we found that Ni yields of Ch-mass SNe Ia are much lower with the solar-scaled initial composition than in previous works, which keeps the predicted Ni abundance within the observational scatter. From the evolutionary trends of elemental abundances in the solar neighborhood, we conclude that the contribution of sub-Ch-mass SNe Ia to chemical enrichment is up to 25%. In dSph galaxies, however, larger enrichment from sub-Ch-mass SNe Ia than in the solar neighborhood may be required, which causes a decrease in [(Mg, Cr, Mn, Ni)/Fe] at lower metallicities. The observed high [Mn/Fe] ratios in Sculptor and Carina may also require additional enrichment from pure deflagrations, possibly as SNe Iax. Future observations of dSph stars will provide more stringent constraints on the progenitor systems and explosion mechanism of SNe Ia.

Modeling subgrid combustion processes in simulations of thermonuclear supernovae

Supernovae of type Ia are thought to arise from the thermonuclear incineration of a carbon-oxygen white dwarf stellar remnant. However, the detailed explosion scenario and stellar evolutionary origin scenario – or scenarios – which lead to observed supernovae are still quite uncertain. One of the principal tests of proposed scenarios is comparison with the explosion products inferred, for example, from the spectrum of the supernovae. Making this comparison requires computation of the combustion dynamics and products through simulation of proposed scenarios. Here we discuss two specific proposed explosion scenarios, the deflagration-detonation transition and the helium shell double detonation, With these two examples in mind, we proceed to discuss challenges to computational modeling of the combustion taking place in these explosions. Both subsonically and supersonically propagating reaction fronts are discussed, called deflagrations and detonations respectively. Several major stages of the combustion occur on length and time scales that are many orders of magnitude smaller than those accessible in simulations of the explosion. Models which attempt to capture this sub-grid behavior and the verification of those models is briefly discussed.

Multistage auto-ignition of undiluted methane/air mixtures under engine-relevant condition

Gas-phase auto-ignition delay times (IDTs) of methane/“air” (21% O2/79% Ar) mixtures were measured behind reflected shock waves, using a kinetic shock tube. Experiments were performed at fixed pressure of 1.8 MPa and equivalence ratios of 0.5 and 1.0, over the temperature range of 800–1000 K. Overall, the effect of equivalence ratio on IDT is negligible at entire temperatures measured in this study. The difference from traditional ignition regime at high temperatures, the undiluted methane/air mixtures present a four-stage ignition process at lower temperatures, namely deflagration delay, deflagration, deflagration-detonation transition, and detonation. Four popular kinetic mechanisms, UBC Mech 2.1, GRI Mech 3.0, Aramco Mech 2.0, and USC Mech 2.0, were used to simulate the new measurements. Only UBC Mech 2.1 showed satisfactory predictions in the reactivity of the undiluted methane mixtures; it was, thus, adopted to perform sensitivity analysis for identifying dominant reactions in the ignition process. The difference in channels contributing ȮH radicals causes a reduced global activation energy with decreasing temperatures.Keywords: Methane; multistage ignition; shock tube; sensitivity analysis

A TRACER METHOD FOR COMPUTING TYPE IA SUPERNOVA YIELDS: BURNING MODEL CALIBRATION, RECONSTRUCTION OF THICKENED FLAMES, AND VERIFICATION FOR PLANAR DETONATIONS

ABSTRACT We refine our previously introduced parameterized model for explosive carbon–oxygen fusion during thermonuclear Type Ia supernovae (SNe Ia) by adding corrections to post-processing of recorded Lagrangian fluid-element histories to obtain more accurate isotopic yields. Deflagration and detonation products are verified for propagation in a medium of uniform density. A new method is introduced for reconstructing the temperature–density history within the artificially thick model deflagration front. We obtain better than 5% consistency between the electron capture computed by the burning model and yields from post-processing. For detonations, we compare to a benchmark calculation of the structure of driven steady-state planar detonations performed with a large nuclear reaction network and error-controlled integration. We verify that, for steady-state planar detonations down to a density of 5 × 106 g cm−3, our post-processing matches the major abundances in the benchmark solution typically to better than 10% for times greater than 0.01 s after the passage of the shock front. As a test case to demonstrate the method, presented here with post-processing for the first time, we perform a two-dimensional simulation of a SN Ia in the scenario of a Chandrasekhar-mass deflagration–detonation transition (DDT). We find that reconstruction of deflagration tracks leads to slightly more complete silicon burning than without reconstruction. The resulting abundance structure of the ejecta is consistent with inferences from spectroscopic studies of observed SNe Ia. We confirm the absence of a central region of stable Fe-group material for the multi-dimensional DDT scenario. Detailed isotopic yields are tabulated and change only modestly when using deflagration reconstruction.

ON MEASURING THE METALLICITY OF A TYPE IA SUPERNOVA’S PROGENITOR

ABSTRACT In Type Ia Supernovae (SNe Ia) the relative abundances of chemical elements are affected by the neutron excess in the composition of the progenitor white dwarf. Since these products leave signatures in the spectra near maximum light, spectral features may be used to constrain the composition of the progenitor. We calculate the nucleosynthetic yields for three SN Ia simulations, assuming single degenerate, Chandrasekhar-mass progenitors, for a wide range of progenitor metallicities, and calculate synthetic light curves and spectra to explore correlations between progenitor metallicity and the strength of spectral features. We use two two-dimensional simulations of the deflagration–detonation–transition scenario with different 56Ni yields and the W7 simulation to control for differences between explosion models and total yields. While the overall yields of intermediate-mass elements (16 < A 40) differ between the three cases, trends in the yields are similar. With increasing metallicity, 28Si yields remain nearly constant, 40Ca yields decline, and Ti and 54Fe yields increase. In the synthetic spectra, we identify two features at 30 days post-explosion that appear to deepen with progenitor metallicity: a Ti feature around 4200 Å and an Fe feature around 5200 Å. In all three simulations, their pseudo equivalent widths show a systematic trend with progenitor metallicity. This suggests that these two features may allow for differentiation among progenitor metallicities of observed SNe Ia and potentially help to reduce the intrinsic Hubble scatter.

One-dimensional numerical study on pressure wave–flame interaction and flame acceleration under engine-relevant conditions

Knock is considered as a major challenge when increasing thermal efficiency of internal combustion engine. In this study, two possible causes of engine knock: flame acceleration and auto-ignition, are studied using one-dimensional simulation under engine-relevant conditions. Chemical source term is modeled using Arrhenius expression with detailed chemical mechanism of hydrogen oxidation. Interaction between pressure wave and flame during propagation of flame front is investigated. It is observed that propagation and reflection of pressure wave in cylinder might trigger Deflagration–Detonation Transition (DDT), which leads to extremely high pressure oscillation. Pressure wave initialized by auto-ignition flame is also a reason leading to detonation by enhancing main flame front. Chemical kinetics study is also carried out to analyze chemical process during auto-ignition. Pressure wave is considered to play an important role in the initiation of direct detonation due to accumulation of intermediate radicals under higher pressure. Ignition delays under varying conditions are calculated according to the effects of pressure wave induction. As a result, gradient of ignition delays is observed, which might be a possible cause of detonation initialization.

Analysis on hydrogen risk mitigation in severe accidents for Pressurized Heavy Water Reactor

Hydrogen source term and hydrogen mitigation under severe accidents is evaluated for most nuclear power plants (NPPs) after Fukushima Daiichi accident. Two units of Pressurized Heavy Water Reactor (PHWR) are under operating in China, and hydrogen risk control should be evaluated in detail for the existing design. The distinguish feature of PHWR, compared with PWR, is the horizontal reactor core surrounded by moderator in calandria vessel (CV), which may influence the hydrogen source term. Based on integral system analysis code of PHWR, the plant model including primary heat transfer system (PHTS), calandria, end shield system, reactor cavity and containment has been developed. Two severe accident sequences have been selected to study hydrogen generation characteristic and the effectiveness of hydrogen mitigation with igniters. The one is Station Blackout (SBO) which represents high-pressure core melt accident, and the other is Large Break Loss of Coolant Accident (LLOCA) at reactor outlet header (ROH) which represents low-pressure core melt accident. Results show that under severe accident sequences, core oxidation of zirconium–steam reaction will produce hydrogen with deterioration of core cooling and the water in CV and reactor cavity can inhibits hydrogen generation for a relatively long time. However, as the water dries out, creep failure happens on CV. As a result, molten core falls into cavity and molten core concrete interaction (MCCI) occurs, releasing a large mass of hydrogen. When hydrogen igniters fail, volume fraction of hydrogen in the containment is more than 15% while equivalent amount of hydrogen generate from a 100% fuel clad-coolant reaction. As a result, hydrogen risk lies in the deflagration–detonation transition area. When igniters start at the beginning of large hydrogen generation, hydrogen mixtures ignite at low concentration in the compartments and the combustion mode locates at the edge of flammable area. However, the power supply to igniters should be ensured.

Mixing-related low frequency oscillation of combustion in an ethylene-fueled supersonic combustor

The present work investigated combustion instabilities inside an ethylene-fueled scramjet combustor mounted on a Mach 2.1 direct-connect test facility with an inflow stagnation temperature of 846K. Effects of fueling schemes on the combustion stability characteristics were examined. The experimental results suggest that the oscillation modes correlate with mixing status closely. For the cases with a quasi-steady thermal throat or stable shock trains, flame fluctuation exists in a mode of thermo-acoustic type oscillation with a broad frequency range. For the cases with a transient thermal throat, if a fuel/air premixed region from the injection to the cavity flameholder exists, the cavity pilot flame could reignite the fuel/air mixture and undergo a process similar to deflagration–detonation transition (DDT). This process couples with the flame quenching upstream of the injection location, and a DDT-type low frequency oscillation can be formed.

Investigation on the Criterion of Deflagration Detonation Transition for Methane-Oxygen Mixture

In this paper, a study on the combustible methane-oxygen mixture was conducted, using the linear stability theory to analyze the deflagration mechanism of methane. The criterion of deflagration detonation transition was proposed. The criterion can be used as a theoretical support for the prevention and control of methane explosion.

EVALUATING SYSTEMATIC DEPENDENCIES OF TYPE Ia SUPERNOVAE: THE INFLUENCE OF PROGENITOR22Ne CONTENT ON DYNAMICS

We present a theoretical framework for formal study of systematic effects in Supernovae Type Ia (SN Ia) that utilizes 2-d simulations to implement a form of the deflagration-detonation transition (DDT) explosion scenario. The framework is developed from a randomized initial condition that leads to a sample of simulated SN Ia whose Ni56 masses have a similar average and range to those observed, and have many other modestly realistic features such as the velocity extent of intermediate mass elements. The intended purpose is to enable statistically well-defined studies of both physical and theoretical parameters of the SN Ia explosion simulation. We present here a thorough description of the outcome of the SN Ia explosions produced by our current simulations. A first application of this framework is utilized to study the dependence of the SN Ia on the Ne22 content, which is known to be directly influenced by the progenitor stellar population's metallicity. Our study is very specifically tailored to measure how the Ne22 content influences the competition between the rise of plumes of burned material and the expansion of the star before these plumes reach DDT conditions. This competition controls the amount of material in nuclear statistical equilibrium (NSE) and therefore Ni56 produced by setting the density at which nucleosynthesis takes place during the detonation phase of the explosion. Although the outcome following from any particular ignition condition can change dramatically with Ne22 content, with a sample of 20 ignition conditions we find that the systematic change in the expansion of the star prior to detonation is not large enough to compete with the dependence on initial neutron excess discussed by Timmes, Brown & Truran (2003). (Abridged)

Beyond the Bubble Catastrophe of Type Ia Supernovae: Pulsating Reverse Detonation Models

We describe a mechanism by which a failed deflagration of a Chandrasekhar-mass carbon-oxygen white dwarf can turn into a successful thermonuclear supernova explosion, without invoking an ad hoc high-density deflagration-detonation transition. Following a pulsating phase, an accretion shock develops above a core of 1 M_sun composed of carbon and oxygen, inducing a converging detonation. A three-dimensional simulation of the explosion produced a kinetic energy of 1.05E51 ergs and 0.70 M_sun of 56Ni, ejecting scarcely 0.01 M_sun of C-O moving at low velocities. The mechanism works under quite general conditions and is flexible enough to account for the diversity of normal Type Ia supernovae. In given conditions the detonation might not occur, which would reflect in peculiar signatures in the gamma and UV-wavelengths

Nucleosynthesis as a result of multiple delayed detonations in type Ia supernovae

The explosion of a white dwarf of mass 1.36 M ⊙ has been simulated in three dimensions with the aid of a SPH code. The explosion follows the delayed detonation paradigm. In this case the deflagration-detonation transition is induced by the large corrugation of the flame front resulting from Rayleigh-Taylor instability and turbulence. The nucleosynthetic yields have been calculated, showing that some neutronized isotopes such as 54 Fe or 58 Ni are not overproduced with respect to the solar system ratios. The distribution of intermediate-mass elements is also compatible with the spectra of normal SNIa. The exception is, however, the abundance of carbon and oxygen, which are overproduced.

Nucleosynthesis in Chandrasekhar Mass Models for Type Ia Supernovae and Constraints on Progenitor Systems and Burning‐Front Propagation

The major uncertainties involved in the Chandrasekhar mass models for Type Ia supernovae (SNe Ia) are related to the companion star of their accreting white dwarf progenitor (which determines the accretion rate and consequently the carbon ignition density) and the flame speed after the carbon ignition. We calculate explosive nucleosynthesis in relatively slow deflagrations with a variety of deflagration speeds and ignition densities to put new constraints on the above key quantities. The abundance of the Fe group, in particular of neutron-rich species like 48Ca,50Ti,54Cr,54,58Fe, and 58Ni, is highly sensitive to the electron captures taking place in the central layers. The yields obtained from such a slow central deflagration, and from a fast deflagration or delayed detonation in the outer layers, are combined and put to comparison with solar isotopic abundances. To avoid excessively large ratios of 54Cr/56Fe and 50Ti/56Fe, the central density of the average white dwarf progenitor at ignition should be as low as 2 ? 109 g cm-3. To avoid the overproduction of 58Ni and 54Fe, either the flame speed should not exceed a few percent of the sound speed in the central low Ye layers or the metallicity of the average progenitors has to be lower than solar. Such low central densities can be realized by a rapid accretion as fast as -->img1.gif 1 ? 10-7 M? yr-1. In order to reproduce the solar abundance of 48Ca, one also needs progenitor systems that undergo ignition at higher densities. Even the smallest laminar flame speeds after the low-density ignitions would not produce sufficient amount of this isotope. We also found that the total amount of 56Ni, the Si-Ca/Fe ratio, and the abundance of some elements like Mn and Cr (originating from incomplete Si burning), depend on the density of the deflagration-detonation transition in delayed detonations. Our nucleosynthesis results favor transition densities slightly below 2.2 ? 107 g cm-3.

On the role of turbulence in detonation induced by Mach stem reflection

A series of experiments conducted by Chan has shown that while some shock waves may not be strong enough to induce detonation when they collide with an obstacle the resulting Mach stem will induce detonation if it collides with a subsequent obstruction. A series of numerical simulations, however, failed to demonstrate the expected results if either the Euler or laminar Navier-Stokes equations are solved. On the other hand, calculations using the Favre averaged Navier-Stokes equations with a k-\(\epsilon\)-F turbulence model are able to reproduce the experimental results, indicating that turbulent effects may play an important role in the ignition process. A detailed examination of the results shows that turbulence causes the formation of activated kernels in a similar process to that observed in deflagration-detonation transition. The simulations in this paper have been undertaken using a modern high resolution hydrocode and a reduced kinetics mechanism for hydrogen combustion. The paper describes the reduced mechanism, the solution methods employed in the hydrocode and discusses the results of the simulations and their implications.

Deflagration-detonation transition in hydrogen-air-steam mixtures — Relevance of the experimental results for real accident situations

After ignition of an explodable gas—air-mixture the combustion process, which starts as a deflagration, may turn into a much more destructive detonation if sufficiently high hydrogen concentration and suitable geometry are given. Geometric conditions for a deflagration-to-detonation transition (DDT) must be appropriate for flame acceleration and for the establishment of the DDT process itself by the SWACER mechanism. The objective of the experiments, performed from 1987 until 1988 at Battelle, was to determine, in quantitative terms, the detonation sensitivity under the influence of steam and to compare the DDT-limits thus determined with detonation limits measured elsewhere by direct initiation. A total of 30 experiments were carried out under this programme. The results of the experimental series are, that the following criterion needs to be fulfilled to achieve a DDT: — DDT is possible if the smallest compartment width is larger than or equal to the detonation cell width which allows a stable detonation to propagate in a given mixture. This criterion permits to apply the detonation cell width as a correlation between mixture properties and geometric dimensions also to DDT.