Application of an Optimized Mechanism of Primary Reference Fuel to Single Hole Sprays

Abstract

The present work focuses on the derivation and evaluation of a chemical kinetic mechanism of Primary Reference Fuel (PRF, binary blends of n-heptane and isooctane) with a homogeneous reactors approach starting from a detailed one. Results show that the optimized mechanism can replicate the results of the detailed one with high accuracy. The mechanism is integrated into a Computational Fluid Dynamics workflow combining a Reynolds-Averaged Navier–Stokes approach, a diffuse-interface spray and an unsteady flamelet progress variable combustion models. The workflow is validated against spray combustion measurements following the standards of the Engine Combustion Network (ECN). Test cases sweep binary blends of PRF fuels from pure n-heptane to pure iso-octane using an ECN Spray A nozzle. The model can provide accurate predictions of typical reacting spray metrics such as ignition delay and lift-off length, which have been evaluated following a reconstruction of the experimental methods of schlieren and OH* chemiluminescence. Different definitions of the previous combustion metrics have been compared. The model captures the decreasing reactivity with increasing iso-octane fraction, which results in flame stabilizing at much leaner conditions. However, deficiencies are observed for low reactivity cases, either with high PRF or low temperature cases.