Abstract
Keywords: Computational Fluid Dynamics, Combustion Modeling, Preflame Autoignition, Pollutant Formation.
The paper presents a coupled Flame Tracking - Lagrangian Particle algorithm for simulating turbulent combustion, pollutant formation, and autoignition in enclosures at conditions relevant to IC engines. The Flame Tracking technique implies continuous tracing of the mean reactive surface and application of the laminar/turbulent flame velocity concepts. The Lagrangian Particle method is based on the joint velocity - scalar probability density function approach for simulating reactive mixture autoignition in the preflame zone and pollutant formation in the postflame region. The coupled algorithm is supplemented with the database of tabulated laminar flame velocities as well as reaction rates of fuel oxidation and pollutants (NO, soot, etc.) formation in the wide range of initial temperature, pressure, and equivalence ratio for several premixed hydrocarbon - air compositions. The look-up tables contain information on flammability limits to identify the conditions of flame quenching. Several 2D and 3D computational examples are presented for combustion of propane and n-heptane in enclosures with simple geometries. A possibility of low-temperature preflame autoignition in multiple hot spots has been successfully demonstrated. Space and time resolved dynamics of nitrogen oxide (both prompt and thermal) has been obtained. The coupled algorithm was compared with some conventional approaches and proved to be computationally efficient and to provide less grid dependency of the results.