A turbulent reaction rate model for premixed turbulent combustion in spark-ignition engines

A new reaction rate model has been developed and validated for premixed tur bulent combustion in spark-ignition (SI) engines. The formulation is within the context of the Bray-Moss-Libby (BML) formalism for turbulent transport in premixed flames. The laminar flamelet concept is employed to split the volumetric reaction rate into a reaction rate per unit surface area and a s urface area per unit volume. The development has involved the implementatio n of an algebraic functional dependence of the laminar burning velocity on the reaction mixture strength, temperature, and pressure [1]. Also, the fla me surface area per unit volume is modeled in a novel and physically reason able manner that avoids any explicit dependence on local turbulent length a nd time scales, by modeling the laminar flamelet wrinkling length scale as a function of laminar flame properties as well as turbulent quantities. The resulting expression for the mean turbulent reaction rate is implemented i n a computer code together with the BML second moment model for turbulent t ransport. Second-order accurate bounded spatial discretization is employed. The governing equations have been transformed into a moving coordinate sys tem to take into account the piston motion. A feasibility study is carried out on the application of the new model to computation of flame propagation in SI engines. The empirical constants of the new modification of the mode l have been tuned and evaluated by capturing experimental engine cylinder p ressure histories. A comparison between the present calculations and identi cal computations of engine cylinder pressure demonstrates the validity of a pplying the model in SI engine computations. Also, and unlike the standard Eddy Break-up (EBU) and basic flamelet models, the new model displays no te ndency to produce excessive reaction rates in the presence of solid walls. A parametric study shows the model to behave in a satisfactory manner in re sponse to changes in fuel type, equivalence ratio, ignition timing, compres sion ratio, and engine speed. (C) 2000 by The Combustion Institute.