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Xin, Yuxuan

Publications and source records attributed to Xin, Yuxuan.

3 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

In situ X-ray Scattering and Dynamical Modeling of Pd Catalyst Nanoparticles Formed in Flames

It has previously been demonstrated that organopalladium precursors can break down under combustion conditions, forming nanoparticles that catalyze ignition. Here, we use in situ small-angle X-ray scattering (SAXS) to probe the formation and growth of palladium nanoparticles in an ethylene fl ame doped with 28 ppm (mol) of Pd(acetate) 2 . The particles appear to nucleate in the fl ame front and are observed by SAXS to grow in size and mass in the high-temperature region of the fl ame ( ~ 2200 K) with median diameters that evolve from 1.5 to 3.0 nm. Transmission electron microscopy of particles collected on a grid located outside the fl ame shows that the particles are metallic palladium with sizes comparable to those determined by SAXS. Molecular dynamics simulation of particles of selected sizes indicates that at the fl ame temperature the particles are molten and the average mass density of the particle material is notably smaller than that of bulk, liquid Pd at the melting point. Both experimental and computational results point to homogeneous nucleation and particle - particle coalescence as mechanisms for particle formation and growth. Aerosol dynamics simulation reproduces the time evolution of the particle size distribution and suggests that a substantial fraction of the particles must be electrically charged during their growth process.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A reduced multicomponent diffusion model

Here, the diffusion models for multicomponent mixtures are investigated in planar premixed flames, counterflow diffusion flames, and ignition of droplet flames. Discernable discrepancies were observed in the simulated flames with the mixture-averaged and multicomponent diffusion models, respectively, while the computational cost of the multicomponent model is significantly higher than that of the mixture-averaged model. A systematic strategy is proposed to reduce the cost of the multicomponent diffusion model by accurately accounting for the species whose diffusivity is important to the global responses of the combustion systems, and approximating those of less importance. The important species in the reduced model are identified with sensitivity analysis, and are found to be typically among those in high concentrations with exception of a few radicals, e.g. H and OH, that are known to participate in critical reactions. The reduced model is validated in simulating the propagation of planar premixed flames, extinction of counterflow non-premixed flames and ignition of droplet flames. The reduced model was shown to feature similar accuracy to that of the multicomponent model while the computational cost was reduced by a factor of approximately 5 for an n -heptane mechanism with 88 species.

42 ENGINEERING↗