Large Eddy Simulation of Spray Auto-ignition Under EGR Conditions

The paper describes the results of a computational study of the auto-ignition of a fuel spray under Exhaust Gas Recirculation (EGR) conditions, a technique used to reduce the production of NOx. Large Eddy Simulation (LES) is performed, and the stochastic field method is used for the solution of the joint sub-grid probability density function (pdf) of the chemical species and energy. The fuel spray is n-heptane, a diesel surrogate and its chemical kinetics are described by a reduced mechanism involving 22 species and 18 reaction steps. The method is applied to a constant volume combustion vessel able to reproduce EGR conditions by the ignition of a hot gas mixture previously introduced into the chamber. Once the prescribed conditions are reached the fuel is then injected. Different EGR conditions in terms of temperature and initial ambient chemical composition are simulated. The results are in good overall agreement with measurements both regarding the ignition delay times and the lift-off heights.