Prediction of soot for pressurized turbulent kerosene-air diffusion flames using method of moments

Abstract

A comprehensive CFD model is developed to predict soot for a turbulent kerosene-air diffusion flame. The method of moments (MOM) soot model has better prediction capability with meaningful soot behavioral predictions than semi-empirical models. The coupled model is primarily validated with experimental measurements from the literature in the form of major species concentration, flame temperature, and soot volume fraction. A surrogate mix comprising 80% n-decane and 20% toluene on a liquid volume basis constitutes kerosene fuel. The 20% aromatic content is able to reproduce the sooting behavior with considerable accuracy. The model can replicate CO, CO2, CH4, C2H2, C2H4, and C6H6 concentrations, flame temperature, soot volume fraction, and soot aggregation parameters for a laminar JetA-1 flame at atmospheric pressure. The reproduction of flame temperature and major species concentrations for a laminar kerosene flame validates the applicability of the gas-phase kinetic mechanism and PAH formation pathway for the reacting flow system. The model also performs appreciably for measurements of a turbulent kerosene flame at higher operating pressures up to 6.44 bar. The peak soot volume fraction matches significantly well with the measurements for all the flames. The predicted peak soot volume fractions are 8.8, 27.3, 68, and 82 ppm compared to measured values of 9.3, 28.3, 63, and 67 ppm at pressures 1, 2.7, 4.81, and 6.44 bar, respectively. However, the location of the peak soot has a slight discrepancy at low pressures till 2.7 bar, showing the predicted peak earlier compared to a later appearance in the measurements. The simulated peak flame temperatures are 1377, 1393, 1412, and 1477 K as operating pressure increases from 1 to 2.7, 4.81, and 6.44 bar. The thermal absorbance from soot and species radiation plays a vital role in predicting the flame temperature. Soot radiation reduces flame temperature by ~ 500 K compared to gaseous radiation (CO2, H2O, CO, CH4, etc.), reducing approximately 100 K. The predictive soot number density, mean diameter, surface area, primary particle count in soot aggregates, and primary particle diameter carry a substantial dependency on the operating pressure.