Asymptotics of Higher Order Ospt-Functions for Overpartitions

In this paper we obtain asymptotic formulas for positive crank and rank moments for overpartitions. Moreover, we show that crank and rank moments are asymptotically equal while the difference is asymptotically positive. This indicates that there exist analogous higher ospt-functions for overpartitions, which we define.     

Flame stabilization in high pressure LOx/GH2 and GCH4 combustion

Planar laser induced fluorescence (PLIF) of OH is used to examine flame stabilization in high pressure cryogenic flames formed by injecting a central jet of low speed liquid oxygen surrounded by a high speed gaseous stream of hydrogen or methane. In the LO_x/GH₂ experiments injection conditions are transcritical as the chamber pressure is above critical but the temperature is below critical . In the LO_x/GCH₄ experiments the chamber pressure and LO_x injection temperature are below critical , . Hydrogen or methane are injected at room temperature LIF images delineate the flame edge in the injector nearfield. The two flames are stabilized in the vicinity of the liquid oxygen injector lip but the anchor point is found to lie closer to the lip in the LO_x/GH₂ case and its displacement from shot to shot is of a smaller amplitude than that corresponding to the LO_x/GCH₄ flame. Interpretation of these data is based on a previous analysis which indicates that stabilization is essentially controlled by a dimensionless group formed by comparing the lip thickness to the flame edge thickness Ψ = h_s/δ_f. It is found that Ψ slightly exceeds unity in the LO_x/GH₂ case essentially fulfilling the stability condition while Ψ < 1 in the LO_x/GCH₄ case. In this last situation the flame is thicker than the characteristic thickness h_s and it is therefore sensitive to the high speed methane stream. Anchoring is imperfect and the flame edge moves with the turbulent eddies shed from the lip. Global stabilization is achieved dynamically but the reactive layer is not well established and the large amplitude motion of the edge is a symptom of a possible lift-off. Theoretical estimates indicate that LO_x/GCH₄ flame stabilization requires a thicker lip size than the LO_x/GH₂ propellant couple.     

PIV/PLIF investigation of two-phase vortex–flame interactions: effects of vortex size and strength

The evolution of flame surface area and rate of CH layer extinction are measured during the interaction of a two-phase counterflow diffusion flame with fuel-side vortices of varying size and strength. Planar laser-induced fluorescence (PLIF) of CH is used to mark the flame front and particle-image velocimetry (PIV) is used to measure the strain rate field at various phases of the interaction process. Vortices of similar initial circulation but differing in size showed widely disparate peak strain rates and CH decay rates because of varying levels of flame-induced vortex dissipation. Vortex size is also found to have a significant effect on flame surface area evolution during and after extinction, with the presence of droplets playing a significant role in the latter. Implications of these results for the fundamental understanding of vortex–flame interactions are discussed.     

Experimental and numerical determination of heat release in counterflow premixed laminar flames

This paper presents an experimental and numerical study of heat release in atmospheric laminar counterflow premixed flames. The measurements are based on simultaneous planar laser-induced fluorescence (PLIF) of OH and HCHO. These measurements are compared to numerical results obtained using detailed chemistry and multicomponent transport properties. A low Mach number formulation along the stagnation streamline is employed to describe the reactive flow. The conservation equations are completed with CHEMKIN and EGLIB packages. They are solved using finite differences, Newton iterations, and an adaptive gridding technique. The comparison is done along the burner axis for both, maximum heat release location and heat release profile width. It is shown that the product of OH and HCHO concentrations yields a result closely related to the heat release. These comparisons lead to the conclusion that the experimental method used seems to be a good tool for the determination of heat release in flames.     

Enthalpies and temperatures of transformation for plutonium using a differential scanning calorimeter

The enthalpies and temperatures of transformation of high purity plutonium were measured using a differential scanning calorimeter. The results of our study are presented and compared to values obtained by previous methods.Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore Laboratory under contract No. W-7405-Eng-48.