Prediction of Non-premixed Combustion and Soot Formation using an Interactive Flamelet Approach

n this work, a multiple Representative Interactive Flamelet (RIF) approach for Diesel engine Compu- tational Fluid Dynamic (CFD) combustion modelling is presented. The CFD solver is responsible for the calcula- tion of the flow field, spray formation, turbulence and additional transport equations and provides boundary con- ditions to the flamelet model for one or more ‘representative’ flamelets. The interactive flamelet software package, in turn, solves the non-stationary laminar flamelet equations for chemical species, soot moments and enthalpy under the assumption of unity for the Lewis number. Thus, prediction of processes such as low tem- perature auto-ignition, high temperature energy release and emissions formation are calculated by means of a de- tailed chemical mechanism for a wide range of air/fuel (A/F) ratios and mixing scales. In this work, a detailed kinetic mechanism for n-heptane based on 209 species and 2115 reactions covering the kinetics for low/high temperature oxidation and emission formation has been applied. However, the current implementation allows also user-defined types of pure fuels and fuel blends as well as oxidiser being defined as a mixture of air and products. Moreover, in order to take into account the influence of flamelet-flamelet interactions in case of multi- ple injections, a simplified flamelet interaction model was implemented and applied to a double injection test- case. Soot modelling is approached by using the method of moments to mathematically describe the particle size distribution function (PSDF). The approach has been validated against Diesel engine experiments with single and multiple injection strategies. The numerical results show a good correlation to standard Diesel engine meas- urements as to time resolved experimental soot maps obtained through a 3D-2Color Method. Application of the multiple RIF model provides an improved prediction of pollutants and allows new insight into the soot formation process