Dynamics and structure of dusty reacting flows: Inert particles in strained, laminar, premixed flames

A detailed numerical study was conducted on the dynamics and thermal respon se of inert, spherical particles in strained, laminar. premised hydrogen/ai r flames. The modeling included the solution of the steady conservation equ ations for both the gas and particle phases along and around the stagnation streamline of an opposed-jet configuration, and the use of detailed descri ptions of chemical kinetics and molecular transport. For the gas phase, the equations of mass, momentum, energy, and species are considered, while for the particle phase, the model is based on conservation equations of the pa rticle momentum balance in the axial and radial direction, the particle num ber density, and the particle thermal energy equation. The particle momentu m equation includes the forces as induced by drag, thermophoresis, and grav ity. The particle thermal energy equation includes the convective/conductiv e heat exchange between the two phases, as well as radiation emission and a bsorption by the particle. A one-point continuation method is also included in the code that allows for the description of turning points, typical of ignition and extinction behavior. as expected, results showed that the part icle velocity can be substantially different than the gas phase velocity, e specially in the presence of large temperature gradients and large strain r ates. Large particles were also found to cross the gas stagnation plane, st agnate, and eventually reverse as a result of the opposing gas phase veloci ty. It was also shown that the particle number density varies substantially throughout the flowfield, as a result of the straining of the flow and the thermal expansion. Finally, for increased values of the particle number de nsity, substantial flame cooling to extinction states and modification of t he gas phase fluid mechanics were observed. As also expected, the effect of gravity was shown to be important for low convective velocities and heavy particles. Under such conditions, simulations indicate that the magnitude a nd direction of the gravitational force can substantially affect the profil es of the particle velocity, number density, mass flux and temperature. (C) 1999 by The Combustion Institute.