A Flamelet Model for Premixed Turbulent Combustion in SI-Engines

A Flamelet formulation for premixed turbulent combustion has been developed based on a scalar field equation. Local effects like flame stretch and flame front curvature were introduced into the equation. Direct numerical simulations of a flame propagating in a turbulent flow field revealed characteristic flame structures as they are experimentally observed. The calculated turbulent flame speed is in good agreement with correlations of experimental data.

Experimental verification of the model has been carried out by Laser tomographic experiments in a VW transparent engine. Flame front structures were visualized resolving the highest possible length scale range. The spectral properties of the flame structures were investigated and compared with the model predictions. A good agreement was found between the characteristic power spectrum of the spatial flame front fluctuations and the scalar fluctuations in the model. The probability density distribution of the local flame front curvature and the spatial flame front fluctuations were measured and fitted by the model distributions. The comparisons between measurement and model prediction were used to determine characteristic length scales of the interaction between flame propagation and turbulent flow field. The characteristic length scale of the reaction zone of the flame could be determined from a laminar flamelet library. These quantitative results for the characteristic length scales can be used as input parameters for simulations with the model. In order to investigate the turbulent flow field, the turbulence intensity could be determined by LDV measurements.