Flowfield modelling of soot formation at elevated pressure

A simplified two-equation model of soot formation is described which extends the laminar flamelet approach to combustion chemistry modelling and thereby admits application to turbulent non-premixed flames. The critical roles for mixture fraction and temperature are identified and extensive property maps have been generated experimentally in a laminar ethylene-air diffusion flame for purposes of model development and validation. Detailed measurements of mixture fraction by microprobe sampling and mass spectrometric analysis, temperature by fine wire thermocouple and soot volume fraction by laser extinction are reported. The problems of probe measurements in sooting regimes are briefly reviewed and a strategy based on transient thermocouple measurements, compensated for the effects of thermal inertia, is advocated. Measurements are reported up to pressures of 3 bar and compared with detailed model predictions. A model for soot formation, incorporating in an approximate manner the effects of nucleation, surface growth and agglomeration on particle number density and soot volume fraction, has been adapted to two-dimensional flame flow-field prediction. Encouraging agreement is achieved between the extensive data set and numerical simulation at atmospheric and elevated pressure.