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The paper is concerned with the identification of the key mechanisms controlling deflagration-to-detonation transition in a stellar medium. The issue of thermal runaway triggered by positive feedback between the advancing flame and the flame-driven precompression is discussed in the framework of a one-dimensional flame-folding model. The paper is an extension of the authors' previous study dealing with the non-stoichiometric fusion, f u e l → p r o d u c t s , kinetics (Phys.Rev.E, 103(2021)) over physically more relevant, f u e l + f u e l → p r o d u c t s , kinetics. Despite this change the runaway effect endures. The mean velocity ⟨ D f ⟩ of the pretransition flame does not reach the threshold of Chapman–Jouguet deflagration. [ABSTRACT FROM AUTHOR]

The paper is concerned with identification of the key mechanisms controlling deflagration-to-detonation transition in unconfined gaseous systems. The issue of thermal runaway triggered by positive feedback between the advancing flame and the flame-driven precompression wave is discussed in the context of expanding spherical flames. Depending on parameters of the system the transition may occur either within a subsonic or supersonic range of flame propagation. The paper is an extension of the previous study concerned with planar flames. [ABSTRACT FROM AUTHOR]

The paper is concerned with identification of the key mechanisms controlling deflagration-to-detonation transition in confined and unconfined gaseous systems. The issue of thermal runaway triggered by positive feedback between the advancing flame and the flame-driven precursor shock is revisited. A new mechanism for parametric transition based on the flame-speed sensitivity to pressure changes is discussed. Depending on the parameters of the system the transition may occur either within the subsonic, sonic or supersonic range of deflagrations. In the latter case the deflagration obeys the classical Chapman–Jouguet (CJ) condition. In a certain parameter range the adopted model reproduces the experimentally known situation where the transition occurs close to the sonic point. [ABSTRACT FROM AUTHOR]

The problem of flame propagation through a spatially periodic shear flow is revisited. When the flow intensity exceeds a certain critical level the corrugated flame either quenches or transitions to detonation. The quenching takes place for relatively small-scale flows where the impact of the flame stretch is strong. In large-scale flows the stretch weakens, while the impact of precompression increases, and the flame transitions to detonation, provided the flow intensity is high enough. In the parametric space a change of the dynamical picture occurs in an abrupt nearly jumpwise manner. [ABSTRACT FROM AUTHOR]

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recently become a subject of active research. In this paper, the flamelets resulting from the disintegration of the continuous front are interpreted in terms of the Zeldovich flame-balls stabilized by volumetric heat losses. A complicated free-boundary problem for 2D self-drifting near circular flamelets is reduced to a 1D model. The 1D formulation is then utilized to obtain the locus of the flamelet velocity, radius, heat losses and Lewis numbers at which the self-drifting flamelet exists. The existence and limits of self-propagating 2D flame-balls have been substantiated theoretically for the first time. They have been investigated analytically, displaying the crucial role of heat losses. The regime arises in praxis in thin enclosures such as Hele-Shaw cells. The design of flame arresters may well be influenced by these findings. [ABSTRACT FROM AUTHOR]

Within the Boussinesq approximation an elementary model for the deflagration-to-detonation transition triggered by self-acceleration of an expanding flame in a central gravitational field is formulated and explored numerically. The self-acceleration is sustained by the intrinsic Rayleigh-Taylor instability until the Deshaies-Joulin deflagrability threshold is reached, followed by an abrupt transition to detonation. Emergence of the threshold is caused by positive feedback between the accelerating flame and the flame-driven pressure shock that results in the thermal runaway when the flame speed reaches a critical level. The model offers a simple mechanism that may be responsible for the transition to detonation in thermonuclear supernovae. The present study is an extension of the preceding models dealing with constant gravitational fields. [ABSTRACT FROM AUTHOR]

This paper is concerned with the identification of the key interactions controlling the deflagration-to-detonation transition in narrow smooth-walled channels. Two agencies contributing to the transition are discussed: hydraulic resistance and flame folding. Depending on the kinetics and parameters of the system, nucleation of detonation may occur near the channel wall and/or in the channel interior. A possibly unexpected outcome of the resistance-folding interplay is the non-monotonicity of the dependence between the predetonation run up time/distance and the channel width. [ABSTRACT FROM PUBLISHER]

A weakly nonlinear model for a self-accelerating outward propagating corrugated flame is formulated and explored. The self-acceleration is sustained by the intrinsic Darrieus-Landau and Rayleigh-Taylor instabilities until the Deshaies-Joulin deflagrability threshold is reached, followed by an abrupt transition to detonation. Emergence of the threshold is caused by positive feedback between the accelerating flame and the flame-driven pressure shock that results in the thermal runaway when the flame speed reaches a critical level. The model offers a simple mechanism that may be responsible for the transition to detonation in thermonuclear supernovae. [ABSTRACT FROM AUTHOR]

Whereas deflagration-to-detonation transition in confined systems is a matter of common knowledge, feasibility of the transition in unconfined space is still a matter of controversy. With a freely expanding self-accelerating spherical flame as an example, it is shown that deflagration-to-detonation transition in unconfined gaseous systems is indeed possible provided the flame is large enough. The transition is caused by positive feedback between the accelerating flame and the flame-driven pressure buildup, which results in the thermal runaway when the flame speed reaches a critical level. [ABSTRACT FROM AUTHOR]

This study is motivated by the observation that in combustion of hydrogen–oxygen/air and ethylene–oxygen mixtures the global activation energy appears to be high at low enough temperatures and low at high enough temperatures, reflecting the complex nature of the underlying chemistry. Stability analysis of a uniformly propagating planar premixed flame controlled by a stepwise ignition-temperature kinetics (representing the activation energy temperature-dependence) is carried out. It is shown that, for all its schematic nature, the diffusive-thermal model based on the ignition-temperature kinetics reproduces quite successfully the basic features of both cellular and pulsating instabilities typical of low and high Lewis number mixtures. [ABSTRACT FROM AUTHOR]