Implementation of the Onsager Theorem to Evaluate the Speed of the Deflagration Wave

While considering the deflagration regime, the thermal theory of combustion proposes that the mechanism of heat transfer from the flame exothermic zone to the front neighborhood reactants layer dominates the flame behavior. The introduction of the Fourier law allows a closed solution of the continuity and energy conservation equations to yield the burning velocity. It is, however, clear that this classical solution does not conform to the momentum equation. In the present work, instead of introducing the Fourier law, we suggest the introduction of a simplified version of the Onsager relationship, which accounts for the entropy increase due to the heat transfer process from the front layer to its successive layer. Solving for the burning velocity yields a closed solution that also definitely conforms to the momentum equation. While it is realized that the pressure difference across the flame front in the deflagration regime is very small, we believe that violating the momentum equation is intolerable. Quite a good fitting, similarly to the classic theory predictions, has been obtained between our predictions and some experimentally observed values for the propagation flame deflagration velocity, while here, the momentum equation is strictly conserved.

Visualization and Parametric Study of Reaction Propagation in Meso-Scale Tubes

Reaction propagation of ethylene/oxygen and methane/oxygen mixtures in capillary tubes of 1 and 2 mm in diameters with initial pressure and temperature at ambient condition were experimentally visualized and analysed using high speed cinematography. Deflagrative flame was initiated in middle of the smooth tube, and the reaction fronts accelerated as they propagated towards the exits in the opposite directions. Lengths of the tubes investigated ranged from 0.4 to 1 m (one side), and deflagration-to-detonation transitions were observed for equivalence ratios between 0.5 and 3. The visible reaction front propagates at speeds approach Chapman-Jouguet speed for ethylene/oxygen mixture in the 1 mm and 2 mm tubes. An overshoot in propagation velocity was found during transition process. For leaner and richer mixtures beyond the detonation limits, steady deflagration wave propagation was observed. Reaction propagation in methane/oxygen mixture was also investigated. Several near-limit propagation modes were found.

A Determination of the Properties of the Peculiar SNIa 1991T through Models of its Early-time Spectra

A series of early-time optical spectra of the peculiar SNIa 1991T, obtained from 2 weeks before to 4 weeks after maximum, have been computed with our Monte Carlo code.The earlier spectra can be successfully modelled if 56Ni and its decay products, 56Co and 56Fe, dominate the composition of the outer part of the ejecta. This atypical distribution confirms that the explosion mechanism in SN 1991T was different from a simple deflagration wave, the model usually adopted for SNe Ia.As the photosphere moves further into the ejecta the Ni Co Fe fraction drops, while intermediate mass elements become more abundant. The spectra obtained 3–4 weeks after maximum look very much like those of the standard SN Ia 1990N. A mixed W7 composition produces good fits to these spectra, although Ca and Si are underabundant. Thus, in the inner parts of the progenitor white dwarf the explosion mechanism must have been similar to the standard deflagration model.The fits were obtained adopting a reddening E(B – V) = 0.13. A Tully-Fisher distance modulus μ = 30.65 to NGC 4527 implies that SN 1991T was about 0.5 mag brighter than SN 1990N. At comparable epochs, the photosphere of SN 1991T was thus hotter than that of SN 1990N. The high temperature, together with the anomalous composition stratification, explains the unusual aspect of the earliest spectra of SN 1991T.The model results allow us to follow the abundances as a function of mass. In particular, spectroscopic evidence is found that about 0.6M⊙ of 56Ni must have been synthesized in the outermost 1M⊙ of the exploding white dwarf. This implies that almost twice as much 56Ni was produced in SN 1991T than in normal SNe Ia, and explains the unusual brightness of this SN.