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 Habstraction-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.

Comparative Study on Soot Reduction, Soot Nanostructure and Oxidation Reactivity of n-heptane/DMC and Isooctane/DMC Inverse Diffusion Flames

Dimethyl carbonate(DMC)is an environmentally oxygenated compound which can be used efficiently for soot reduction.This paper compared the soot reduction,soot nanostructure and oxidation reactivity from inverse diffusion flames(IDFs)of the hydrocarbon fuels,namely n-heptane and isooctane doped with DMC.Effects of DMC additions on soot reduction were discussed.DMC addition is more effective for the soot reduction of n-heptane/DMC IDF than isooctane/DMC IDF.The morphology and nanostructures of soot particles were investigated by Transmission Electron Microscopy(TEM)and High Resolution TEM(HRTEM),and the soot graphitization and oxidation reactivity were analyzed by X-ray Diflfraction(XRD)and Thermogravimetric Analyzer(TGA),respectively.The results of HRTEM images showed that many larger aggregates were observed for the structures of soot particles from IDFs with DMC additions.The soot particles exhibited more liquid-like material,more amorphous,higher disorganized layers,and less graphitic than that of IDFs without DMC additions.With increasing of DMC blending rate,soot particles changed younger to have shorter fringe length,higher tortuosity,and greater fringe separation.Based on the XRD and TGA results,the degree of the soot graphitization level decreased;the soot mass lost significantly faster,and the soot become more reactive.

Decomposition of Toluene as a Biomass Tar through Partial Combustion

One way for reducing tar is oxidative and thermal cracking by partial combustion of the biomass producer gas in the gas reformer. Cracking and polymerization of the tar occur simultaneously at the proximity of inverse diffusion flame. Experimental study has been performed to clarify the effect of hydrogen concentration on soot formation and the growth of polycyclic aromatic hydrocarbons. In the present study, hydrogen concentration is controlled by the small amount of hydrogen addition to the oxidizer. The main results are as follows. Soot formation is suppressed by the small amount of hydrogen addition. The suppression of soot formation is caused by higher concentration of hydrogen. Carbon yield increases by hydrogen addition since carbon content in the undetectable components by the integrated gas chromatograph decreases. In addition, the increase in carbon yield is caused mainly by the increase in carbon monoxide stemmed from reforming of high-boiling components.