Detonation Initiation Research Articles

Numerical study on the deflagration to detonation transition promoted by transverse jet

To reveal the mechanism of deflagration to detonation transition promoted by transverse jet, the flame acceleration and detonation initiation process of H2/Air under transverse jet was numerically investigated. According to the flame propagation characteristics and the main factors that promote flame acceleration in different periods, the process of deflagration to detonation transition was divided into four stages: initial flame development stage, turbulence-flame interaction stage, shock-flame interaction stage, detonation initiation stage. The flame acceleration process of each stage was analyzed in detail. The results indicated that the curling and stretching effect of the transverse jet and vortexes on the flame can effectively increase the flame velocity. The flame would constantly produce compression waves during acceleration. The transverse wave formed by the superposition of the compression waves would be reflected multiple times between the walls and act on the flame front, which is critical for flame acceleration. In addition, the positive feedback between the leading shock wave and the flame was also important for the continuous increase of flame velocity.

Shock Initiation and Propagation of Detonation in ANFO

The ammonium nitrate (AN) and fuel oil (FO) mixture known as ANFO is a typical representative of non-ideal explosives. In contrast to ideal explosives, the detonation behavior of ANFO exhibits a strong dependence on charge diameter, existence, and properties of confinement, with a large failure diameter and long distance required to establish steady-state detonation. In this study shock initiation and propagation of detonation in ANFO were studied experimentally by determining the detonation velocity at different distances from the initiation point, as well as by numerical modeling using AUTODYN hydrodynamics code and a Wood–Kirkwood detonation model incorporated into EXPLO5 thermochemical code. The run-to-steady-state detonation velocity distance was determined as a function of charge diameter, booster charge mass, and confinement. It was demonstrated that a Lee–Tarver ignition and growth reactive flow model with properly calibrated rate constants was capable of correctly ascertaining experimentally observed shock initiation behavior and propagation of detonation in ANFO, as well as the effects of charge diameter, booster mass, and confinement.

Numerical simulation on the shock wave focusing detonation process in the semicircle reflector

Shock wave focusing is considered a new type of initiation method that does not require external ignition devices. For this method, understanding the shock wave/flame interaction accurately is one of the critical issues for revealing the ignition and triggering mechanisms during shock wave focusing processes. In this study, numerical simulations were carried out to investigate the detailed flow field evolution of the focusing process with kerosene as fuel. Two detonation initiation modes were found during the shock wave focusing processes, which were the direct initiation mode and the reflected shock wave collision initiation mode, respectively. At the detonation wave propagation stage, the primary detonation wave decouples and fails to propagate out of the cavity. The multiple initiation phenomenon occurs in the cavity, and it dominated detonation waves to propagate outside of the cavity to accomplish one thermal cycle. There is no positive correlation between jet temperature and detonation wave propagation velocity. When the jet temperature is low, the detonation wave velocity dominated by the multiple initiation mode is the fastest. The analysis of the shock wave focusing process under different jet velocities showed that when the jet velocity was lower than 2 Ma, the decoupling of the primary detonation wave failed to induce multiple detonation waves. Driven by the vortex in the semicircular cavity, the flame is almost stationary, which means the failure of the detonation wave propagation process.

Experimental and numerical study of flame acceleration and DDT in a channel with continuous obstacles

Flame acceleration and deflagration-to-detonation transition (DDT) in obstructed channels is an important subject of research for propulsion and explosion safety. Experiment and numerical simulation of DDT in a stoichiometric hydrogen–oxygen mixture in a channel equipped with continuous triangular obstacles were conducted in this work. In the experiment, high-speed schlieren photography was used to record the evolution of reaction front and strong pressure waves. A pressure transducer was used to record the pressure build-up. In the numerical simulation, a high-order numerical method was used to solve the fully compressible reactive Navier–Stokes equations coupled with a calibrated chemical-diffusive model. The calculations are in good agreement with experimental observations. The result shows that the triangular obstacles can significantly promote flame acceleration and provide conditions for the occurrence of DDT. In the early stages of flame acceleration, the main cause for flame roll-up and distortion is the effect of vortices generated in the gaps between neighbouring triangular obstacles. The scales and velocities of vortices are determined by the positive feedback process between combustion-generated flow and flame propagation. The continuous triangular obstacles create an intricate flow field and increase the complexity of shock reflections. This complicated flow leads to local detonation initiation through different mechanisms, i.e. flame-flame collisions and flame-shock interactions. Successive local detonation ignitions and failures are produced in the obstacle gaps due to the continuous layout of the triangular obstacles. It was found that successive local detonation ignitions are critical for the eventual success of DDT formation because the shock waves generated by them continually strengthen the leading shock. The detonation failure or survival due to diffraction depends on the height of the narrow space (h*) between the bulk flame and obstacle vertex, and can be quantitatively characterised by the ratio of the space height to detonation cell size (), h*/.

Deflagration-to-Detonation Transition in a Semi-Confined Slit Combustor Filled with Nitrogen Diluted Ethylene-Oxygen Mixture

The conditions for the mild initiation of the detonation of homogeneous stoichiometric ethylene-oxygen mixtures diluted with nitrogen up to ~40%vol. in a planar semi-confined slit-type combustor with a slit 5.0 ± 0.4 mm wide, simulating the annular combustor of a Rotating Detonation Engine (RDE), are determined experimentally using self-luminous high-speed video recording and pressure measurements. To ensure the mild detonation initiation, the fuel mixture in the RDE combustor must be ignited upon reaching a certain limiting (minimal) fill with the mixture and the arising flame must be transformed to a detonation via deflagration-to-detonation transition (DDT). Thus, for mild detonation initiation in a C2H4 + 3O2 mixture filling the slit, the height of the mixture layer must exceed the slit width by approximately 10 times (~50 mm), and for the C2H4 + 3(O2 + 2/5 N2) mixture, by approximately 60 times. The limiting height of the mixture layer required for DDT exhibits a sharp increase at a nitrogen-to-oxygen mole ratio above 0.25. Compared to the height of the detonation waves continuously rotating in the RDE combustor in the steady-state operation mode, for a mild start of the RDE, the fill of the combustor with the explosive mixture to a height of at least four times more is required.

Effect of fluidic obstacles on flame acceleration and DDT process in a hydrogen-air mixture

Using solid obstacles to accelerate the deflagration to detonation transition (DDT) process induces additional thrust loss, and fluidic obstacles can alleviate this problem to a certain extent. A detailed simulation is conducted to investigate the effects of multiple groups of fluidic obstacles on the flame acceleration and DDT process under different initial velocities and gas types. The results show that, initially, the propagation of reflected shock wave formed by jet impingement is opposite to the flame acceleration direction, thus increasing the initial jet velocity will hinder the flame acceleration. Later, the vortex structure and enhanced turbulence can promote flame acceleration. As the flame accelerates, the virtual blockage ratio of the fluidic obstacles decreases, and increasing initial jet velocity or using reactive jet gases both affect the virtual blockage ratio. Further, increasing initial jet velocity or using reactive jet gases can shorten the detonation initiation time and distance. Compared with solid obstacles, it is concluded that fluidic obstacles can achieve faster detonation initiation with a smaller blockage ratio. Overall, the detonation phenomena in this study are all triggered by hot spots formed by the interaction between reflected waves and distorted flame, but the formation of reflected waves varies.

Influence of longitudinal obstacle spacing on the deflagration-to-detonation transition through a bank of obstacles in a hydrogen-air mixture

Flame acceleration and deflagration-to-detonation transition (DDT) in a channel containing an array of staggered cylindrical obstacles and a stoichiometric hydrogen-air mixture were studied by solving the fully-compressible reactive Navier-Stokes equations using a high-order numerical algorithm and adaptive mesh refinement. Four different longitudinal spacings (ls) of the neighboring obstacle rows (i.e., ls = 15.28, 19.1, 25.4, and 38.2 mm, corresponding to 1.2, 1.5, 2 and 3 times of obstacle diameter, respectively) were used to examine the effect of obstacle spacing on flame acceleration and DDT. The results show that the main mechanisms of flame acceleration and transition to detonation in all the cases studied are consistent. While the flame acceleration is caused by the growth of flame surface area in the initial stage, it is governed by shock-flame interactions in the later stage when shock waves are generated. The focusing of strong shocks at flame front is responsible for the initiation of detonation. It was found that the flame propagation speed and the DDT run-up distance and time are highly dependent on ls. Specifically, the flame acceleration declines as ls increases, since a larger ls leads to less disturbance of flow by obstacles per unit channel length. For detonation initiation, both the run-up distance and time increase with the increase of ls. It is interesting to note that the DDT distance and time increase significantly as ls increases from 19.1 mm to 25.4 mm. This is related to the slowdown of the increase rate of energy release over a period before DDT occurs under large ls condition, because every time the flame passes over an obstacle row the shock-flame interaction is delayed and numerous isolated pockets of unburned gas material are formed.

Small‐Scale Characterization of Shock Sensitivity for Non‐Ideal Explosives Based on Imaging of Detonation Failure Behavior

AbstractThe plethora of potential homemade explosive (HME) formulations combined with the fact they often exhibit large critical diameters make them expensive to characterize with traditional large‐scale tests. A relatively new method for small‐scale characterization was investigated using non‐ideal explosive charges consisting of ammonium nitrate (AN) and various fuels. Here, we extend this method using an optical characterization technique that utilizes the decay rate of the reaction wave velocity in failing detonations of sub‐critical diameter charges as a metric for the shock sensitivity of an explosive. The conditions required for successful detonation initiation and failure have long been used to investigate shock sensitivity (critical diameter, gap tests, run‐to‐detonation experiments); however, the failure regime still remains largely unexplored. The utility of this small‐scale characterization technique lies in its ability to determine the relative shock sensitivity of explosive with minimal material and experiments while simultaneously providing transient velocity data for potential use in modeling efforts. In this work, high speed imaging was used and analyzed to determine rates of reaction wave velocity decay in the AN‐fuel samples. Among the fuels tested with AN were diesel (ANFO), nitromethane (ANNM), and aluminum (AN−Al). It was found that nitromethane was the most effective at sensitizing the AN of the systems considered. In both ANNM and AN−Al, maximum shock sensitivity (here measured as the minimum reactive wave velocity decay rate) occurred at fuel percentages below stoichiometric mixtures. This was interpreted to be due to the competing effects of stoichiometry and hot spot criticality. Sensitivity results were compared to run‐to‐failure (RTF) distances and published critical diameter trends which showed good correlation.

Numerical investigation of the effect of reactive gas jets on the flame acceleration and DDT process

Jet obstacles can quickly induce the deflagration to detonation transition (DDT) process and reduce the thrust loss of an engine. However, there are few studies on the use of combustible premixed gases as the reactive jet obstacle. Based on the OpenFOAM platform, a detailed numerical investigation of the flame acceleration and DDT process is carried out with different initial jet velocities and the number of jet obstacles. The results show that, although the stronger flame generated by the reactive jet obstacles will reduce the virtual blockage ratio to a greater extent, the turbulence and combustion heat release effect generated by them still significantly promote the flame acceleration. In terms of flame acceleration, initially, increasing the initial jet velocity has no obvious effect on the flame acceleration. Later, turbulence and combustion heat release begin to dominate the flame acceleration and significantly promote the flame acceleration. Since the jets in this study adopt the same combustible premixed gases, increasing the number of reactive jet obstacles downstream does not improve the upstream flame acceleration. In DDT, increasing the initial velocity of the reactive jet can improve the detonation initiation, but the effect of the obstacle number on DDT is greatly affected by the initial jet velocity. Specifically, at a low initial jet velocity, more jet obstacles can significantly promote the detonation initiation, while at a high initial jet velocity, the enhanced turbulence caused by the jet is the dominant factor for the flame acceleration. Therefore, compared with the number of jet obstacles, the detonation initiation process of the premixed gases is more sensitive to the change in the initial jet velocity.

Effects of staggered opposed hot jets on the initiation and propagation of gaseous detonation in a supersonic combustible inflow

In this paper, the detonation initiation mechanism of a supersonic combustible mixture triggered by a staggered opposing combined hot jets was performed. Two-dimensional reactive Navier–Stokes equations with a one-step Arrhenius chemistry model were solved using a structured adaptive mesh refinement framework. The results show that a high temperature and pressure region triggers a rapid detonation initiation after the jet-induced bow shock focusing. Further analysis showed that there is a large baroclinic torque behind the local detonation wave induced by the staggered hot jet, which leads to a large Richtmyer–Meshkov instability at the end of the unburned jet, and the generated periodic shedding vortex structure thereby enhances the diffusion effect in the unburned region. However, the released heat cannot support the propagation of the detonation wave. In addition, different jet intensity distribution schemes and jet spacing will change the ignition point position. It is worth noting that the distance of detonation initiation can be significantly shortened by reducing the front jet intensity while maintaining the total jet energy. Increasing the jet spacing will significantly slow down the detonation initiation process.

Experimental study on fracture processes of granite cylinders with different decoupling conditions

Fracture processes of granite cylinders (a diameter of 240mm and a length of 300mm) subjected to blast loading were investigated using data from three-dimensional digital image correlation (DIC) method on images captured with two high-speed cameras. The five cylinders had a centric decoupled charge (PETN) of approximately 3 g or 4 g. The centric borehole with diameter 10mm or 20mm was drilled in each cylinder, and the charge diameter was around 6 mm/7 mm. Two decoupling ratios were applied, and each specimen has a decoupled charge with water or air. A partial cylindrical surface was captured by the high-speed cameras. Both the decoupling ratio and the filled-in medium influence the fracture pattern and initiation on the surface. The specimens with the air-decoupled charge produces gas ejection 440 μs-460 μs after detonation, while the specimen with the water-decoupled charge presents gas ejection at 960 μs. Displacement fields determined from the 3D DIC analysis were used to obtain strain fields on the observed surface. It is found that the initial strain on the surface was seen approximately 40 μs after the detonator initiation. The air-filled gap yields the vertical strain concentration zone in priority, while the water-filled gap produces horizontal concentration zone. The strain concentration corresponded well with the locations and direction of the developed cracks. The experimental findings of this investigation indicate that the decoupling ratio and decoupled materials have a great impact on rock fracturing.

Field Test Summary of Two Kinds of Electronic Detonator for Seismic Exploration

Electronic detonators are widely used because of their advantages in real-time supervision of the whole life cycle (Zang, 2022). Due to the high requirements of the time difference synchronization between the electronic initiation system and the seismic wave recording system, the Electronic detonator has not been widely used for Seismic exploration (Yang, 2020). This paper expounds the systematic and scientific test method from the aspects of the comprehensive performance of electronic detonators for exploration, the compatibility between the electronic detonator initiation system and the geophysical blasting machine system, the constraints of the geophysical explosion-related collaborative Danling managment cloud platform, and the quality of data collected by electronic detonator blasting in wells., and based on the analysis of the test results, the problems that need to be improved in the application of electronic detonators and detonation systems in the large-scale production of geophysical prospecting industry are put forward.

Effect of hydrogen concentration distribution on flame acceleration and deflagration-to-detonation transition in staggered obstacle-laden channel

A staggered arrangement of solid obstacles promotes flame acceleration (FA) and the deflagration-to-detonation transition (DDT) in a homogeneous concentration field. Many combustible premixed gases, however, are inhomogeneous. The present numerical study explores the effects of different hydrogen–air distributions on the FA and DDT processes in a staggered obstacle-laden channel. The results show that, in the early stage of flame evolution, the flame accelerates faster when there are no obstructions on the side of the channel with the high hydrogen concentration. Under the suction effect of the aperture formed between an obstacle and the wall, the flame experiences multiple periods of velocity augmentation during its evolution. In terms of detonation initiation, the process can be classified as either detonation induced by the interaction between the flame surface and the reflected shock wave from the wall/obstacle, or detonation induced by the collision between the leading shock wave and the reflected shock wave from the obstacle. As the detonation wave propagates, regions with a hydrogen content of less than 12.7 vol. % cause a decoupling of the detonation wave. The morphology of the detonation wave (length, angle, and height) is related to the specific distribution of the hydrogen concentration. From the overall FA and DDT processes, a more homogeneous hydrogen concentration distribution leads to faster flame state variations and a faster triggering of the detonation.

ODMR active bright sintered detonation nanodiamonds obtained without irradiation

We present the results of study the structure and composition of microcrystalline diamonds obtained by high-pressure high temperature sintering of detonation nanodiamond particles. Using optical detected magnetic resonance method, photoluminescence spectroscopy and Raman spectroscopy we found sintering of detonation nanodiamond significantly differ from initial detonation nanodiamonds and can be compared to high quality diamonds. Monocrystals of diamonds obtained by the method of oriented attachment have dimensions of up to tens of microns, possess the habitus of high-quality diamonds, and do not contain metal catalysts in the lattice structure. In those crystals, the presence of optically active nitrogen impurities in the crystal lattice is observed. In particular, there is a bright nitrogen-vacancy defects. They are characterized by optical detected magnetic resonance method, which shows that spin properties of the obtained single crystals correspond to high-quality natural diamonds and surpass synthetic diamonds obtained from graphite in the presence of metal catalysts, followed by irradiation and annealing to obtain nitrogen-vacancy defects optical defects in the diamond lattice. The presence of nitrogen-vacancy defects defects and the high-quality of the crystal structure of sintering of detonation nanodiamond allows us to consider them as potential candidates in quantum magnetometry. For this purpose, the possibility of a simple way to improve the AFM probe by fixing a microcrystalline sintering of detonation nanodiamond particle on its tip is demonstrated. Keywords: detonation nanodiamond, HPHT sintering, ODMR, single crystalline, photoluminescence, defects.

Role of temperature-gradient steepness on development of hydrogen-oxygen detonation with ozone sensitization

This work carries out one-dimensional simulations on spontaneous initiation and development of detonations from hot spots with initial temperature gradients embedded with non-autoignitive H2O2 mixtures. Role of temperature-gradient steepness on the development of detonations inside and outside hot spots and the relationship of it to ozone sensitization are examined by changing gradient slope and O3 addition. It is found that steepening temperature gradient has negative effect on initiations and a critical gradient is identified for different O3 additions, below which spontaneous initiation fails. However, the sustenance of a developing detonation is not only related to the steepness, but also to the reactivity of mixtures with O3 additions. High O3 additions permit a detonation to be more likely to sustain outside hot spots; while for low O3 additions, the sustenance depends nonmonotonically on the slope, which cannot be predicted by the idealized reactive flow system with a constant specific heat ratio and the reduced reaction model. The results clarify the suggestions of He & Clavin [1] that temperature gradient may prevent sustenance of a developing detonation and the transmission of detonation to the uniform fresh mixture.

Effects of low-temperature chemistry on direct detonation initiation by a hot spot under engine conditions

This study investigates the effect of low-temperature chemistry (LTC) on the minimum runup distance, lm, of direct detonation initiation by an autoignitive hot spot under engine conditions. A newly predictive model is proposed to determine an a priorilm. The temperature and pressure increase and the radical build-up prior to the main ignition resulting from LTC are incorporated in the model that allows a better prediction of ignition modes. A series of 1D simulations are performed by varying the initial temperature, the hot spot size and its temperature difference at constant-volume and engine conditions. DME (ethanol) is used to represent a two (single) stage ignition fuel. It was found that taking the transient evolution of the mixture state as an initial condition to the ZND model results in a better representative exothermic characteristic length scale, which exhibits a strong linear correlation with lm regardless of fuel types over a wide range of conditions. The LTC oxidation is found to reduce lm by approximately a factor of two for the low-temperature cases, leading to a comparable value of lm to that of the high-temperature cases. It was also found that the ignition modes are better predicted by identifying an alternative characteristic length scale based on the variation of ignition delay time τig within its range of monotonic distribution. For a hot spot that has temperature variation spanning across the NTC regime, the runup distance was found to be shortened by approximately a factor of two, such that a longer hot-spot size is required to form detonation. In addition, a better prediction of ignition modes was achieved by defining the normalized front speed as a statistical mean for each runup-distance element than that determined at the midpoint of a hot spot.

Studies on the valveless scheme to produce high-frequency detonations with different purge methods

Producing high-frequency detonations is an important topic for pulse detonations which has received considerable attentions. The valveless scheme has been verified to be able to obtain high-frequency detonations more than 100 Hz. This work has been conducted to investigate the possibility to achieve a higher detonation frequency and clarify the limits of stable operations preliminarily for the valveless scheme with different purge methods. Oxygen, ethylene, and nitrogen or liquid water are utilized as oxidizer, fuel, and purge medium in the experiments while two injection configurations are employed. The maximum detonation frequencies of 180 Hz and 330 Hz have been achieved in stable operations for two different injection configurations when nitrogen is used as the purge gas. The ceiling frequency for stable detonations is 300 Hz if nitrogen is replaced by liquid water, which indicates that water vapor is capable to create an efficient buffer zone to ensure stable operations. The results imply that the injection configuration also has a great impact on the ceiling stable detonation frequency. Three operating modes have been observed in this study, i.e., a stable detonation mode, an unstable detonation mode, and a deflagration mode. In the unstable mode, failure of detonation initiation occurs frequently and one interesting phenomenon is that the detonation frequency is reduced by half exactly when insufficient filling happens. The supply pressure ratios of oxidizer to fuel and purge to fuel are obtained for different operating modes when the purge method is changed. Furthermore, the equivalence ratios have been also studied for different operating modes which reveals that the range will change when different purge methods and injection configurations are employed. According to the equivalence ratio and the mass flow rates, an equivalent volume fraction of oxygen is defined and its range for the stable detonation mode is clarified.

Experimental Investigations on Detonation Initiation Characteristics of a Liquid-Fueled Pulse Detonation Combustor at Different Inlet Air Temperatures

The detonation initiation characteristics of a single tube liquid-fueled pulse detonation combustor (PDC) is investigated at different inlet air temperatures in this paper. The inner diameter of the PDC is 62 mm. Gasoline and air are used as fuel and oxidant, respectively. The inlet air temperature is 288–523 K and the operating frequency of the PDC is 10~30 Hz. The experimental results show that the deflagration to detonation transition (DDT) distance, detonation initiation time, DDT time and jet ignition time decrease with the increasing operating frequency at the same inlet temperature. When the inlet temperature is 288 K, the DDT distance is shortened from 860.5 mm to 787.7 mm as the operating frequency increases from 10 Hz to 30 Hz. The detonation initiation time, the jet ignition time and the DDT time are reduced from 10.01 ms, 7.66 ms and 2.35 ms to 6.55 ms, 4.99 ms and 1.56 ms, respectively. When the inlet air temperature increases, the atomization and evaporation of the gasoline is improved, which also leads to the decrease in the DDT distance, the detonation initiation time, the jet ignition time and the DDT time. For example, when the inlet air temperature increases from 288 K to 523 K at the frequency of 10 Hz, the DDT distance is shortened from 860.5 mm to 747.2 mm and the detonation initiation time, the jet ignition time and the DDT time is reduced to 5.867 ms, 2.51 ms and 1.11 ms, respectively. Additionally, the self-ignition caused by high inner wall temperature occurs when PDC is operating at high frequency under high inlet air temperature.

Initiation and propagation of one-dimensional detonations in aluminum-particle/C2H2/air system

This work carries out simulations on the initiation and propagation of aluminum (Al)-particle/C2H2/air detonations in a one-dimensional (1D) planar geometry, based on the Euler–Euler two-phase flow models and the fifth-order weighted essentially non-oscillatory scheme. The effect of Al particles on 1D detonation is studied by changing Al-particle diameter and concentration. It is found that for the two-phase detonation, the initiation is achieved by the sudden transition to a detonation and undergoes an extended overdriven stage, which is caused by the afterburning effect of Al particles in the products. During the steady propagation, the detonations with the proper Al-particle diameter manifest the double-front feature created by afterburning of Al particles in the products. For the big Al particles, the second front is formed more slowly and propagates stably. As Al particles are too big to be ignited downstream, the second front disappears. However, the smaller Al particles make a shorter distance between these two fronts. Nevertheless, as Al particles are sufficiently small, a successful initiation is prone to be more difficult because the evaporation of Al particles absorbs heat.

One-dimensional Numerical Study on Ignition of the Helium Envelope in Dynamical Accretion during the Double-degenerate Merger

In order for a double-detonation model to be viable for normal type Ia supernovae, the adverse impact of helium-burning ash on early time observables has to be avoided, which requires that the helium envelope mass should be at most 0.02 M ⊙. Most of the previous studies introduced detonation by artificial hot spots, and therefore the robustness of the spontaneous helium detonation remains uncertain. In the present work, we conduct a self-consistent hydrodynamic study on the spontaneous ignition of the helium envelope in the context of the double-degenerate channel, by applying an idealized one-dimensional model and a simplified seven-isotope reaction network. We explore a wide range of the progenitor conditions and demonstrate that the chance of direct initiation of detonation is limited. Especially, the spontaneous detonation requires the primary envelope mass of ≳0.03 M ⊙. Ignition as deflagration is instead far more likely, which is feasible for the lower envelope mass down to ∼0.01 M ⊙, which might lead to subsequent detonation once the deflagration-to-detonation transition (DDT) is realized. High-resolution multidimensional simulations are required to further investigate the DDT possibility, as well as accurately derive the threshold between the spontaneous detonation and deflagration ignition regimes. Another interesting finding is the effect of the composition: while mixing with the core material enhances detonation as previously suggested, it rather narrows the chance for deflagration due to the slower rate of the 12C(α,γ)16O reaction at the lower temperature ∼108K, with the caveat that we presently neglect the proton-catalyzed reaction sequence of 12C(p,γ)13O(α,p)16O.