Sensitivity analysis of modeling parameters to soot and PAHs prediction in ethylene inverse diffusion flame

The soot formation model based on inverse ethylene diffusion flames was performed to study the sensitivity of the soot formation process to the prediction results. The effects of efficiency parameters such as soot inception, surface growth and coagulation on the simulation results were studied by using the adjustable efficiency model. In addition, the reversible soot model and conjugate heat transfer (CHT) model were also introduced to explore their advantages. Results indicated that, among adjustable efficiency parameters, the nucleation efficiency had the greatest influence on the predicted soot and PAHs distributions, while the H-abstraction-C2H2-addition (HACA) process and PAH adsorption surface growth efficiencies impacted little. The adjustable efficiency parameters had a significant effect on the concentration of soot gaseous precursors and soot particles, but their effects on temperature, gas phase molecules, and intermediate species were not obvious. When the nucleation efficiency increased from 2×10−6 to 1×10−4, the predicted value of the integrated soot was increased by nearly 50%, and the maximum primary particle number density and the number of aggregates were increased by an order of magnitude. The maximum concentration of BAPYR was doubled. However, the peak temperature along the axial direction increased by only 3.5 K. Using the reversible soot model, the approximation results of the adjustable efficiency parameters could be modified, which showed the feasibility of the model. The use of the CHT model promoted pyrolysis of the fuel below the outlet of the fuel tube, with high-temperature zones, soot zones, and PAHs zones moving towards higher flame heights. Besides, when using the reversible model and the CHT model, the maximum soot volume fraction decreased by 39% compared with the basic efficiency parameters, while the concentration of BAPYR increased by 162%, and the concentrations of gas phase species were decreased.