Comprehensive kinetic study on ammonia/ethylene counter-flow diffusion flames:influences of diluents

This study aimed to investigate the effects of ammonia addition on ethylene counter-flow diffusion flames with different diluents on the fuel or oxidizer side,using kinetic analyses.A special emphasis was put on assessing the coupled chemical effects of NH_(3) and CO_(2) on C2H4 combustion chemistry.The chemical effects could be evaluated by comparing fictitious inert NH_(3) or CO_(2) with normal active NH_(3) or CO_(2).The results revealed that the addition of NH_(3) decreased the mole fractions and production rates of key soot precursors,such as acetylene,propynyl,and benzene.When CO_(2) was used as the dilution gas,the coupled chemical effects of NH_(3) and CO_(2) were affected by the chemical effects of CO_(2) to varying degrees.With the oxidizer-side CO_(2) addition,the coupled chemical effects of NH_(3) and CO_(2) reduced the mole fractions of H,O,OH radicals,acetylene,propynyl,and benzene,while the effects differed from the fuel-side CO_(2) addition.The coupled chemical effects of NH_(3) and CO_(2) also promoted the formation of aldehyde contaminants,such as acetaldehyde,to some extent,particularly with CO_(2) addition on the oxidizer side.

Soot reduction by addition of dimethyl carbonate in normal and inverse ethylene diffusion flames:Nanostructural evidence

Oxygenated fuel represents an attractive alternative as an additive for reducing soot emissions.Dimethyl carbonate（DMC） is an oxygenated compound which is a good option to reduce soot,but the detailed characteristics of soot produced from combustion of hydrocarbon fuels blended with DMC are still lacking. The present research studied the nanostructure and reactivity of soot particles in ethylene/DMC normal and inverse diffusion flames. High resolution transmission electron microscopy（HRTEM）, X-ray diffraction（XRD）, and thermogravimetric analysis（TGA）were used to analyze the nanostructure and reactivity of soot. It was found that DMC addition was effective in decreasing the average weights of soot formed in flames. The results of HRTEM images showed that soot particles obtained with DMC addition showed liquid-like material and tight bonding, and exhibited more highly disorganized layers, which give it higher reactivity than soot obtained without DMC addition. Furthermore, HRTEM was used to analyze soot fringe characteristics consisting of fringe tortuosity, fringe length, and fringe separation. XRD was used to crosscheck the results for fringe separation, and was consistent with HRTEM results. In addition, the mass loss curve of TGA experiments showed that DMC addition could enhance the reactivity of soot particles.

Nanostructure and reactivity of soot from biofuel 2,5-dimethylfuran pyrolysis with CO_(2) additions

This paper investigated the nanostructure and oxidation reactivity of soot generated from biofuel 2,5-dimethylfuran pyrolysis with different CO_(2) additions and different temperatures in a quartz tube flow reactor.The morphology and nanostructure of soot samples were characterized by a low and a high resolution transmission electron spectroscopy(TEM and HRTEM)and an X-ray diffraction(XRD).The oxidation reactivity of these samples was explored by a thermogravimetric analyzer(TGA).Different soot samples were collected in the tail of the tube.With the increase of temperature,the soot showed a smaller mean particle diameter,a longer fringe length,and a lower fringe tortuosity,as well as a higher degree of graphization.However,the variation of soot nanostructures resulting from different CO_(2) additions was not linear.Compared with 0%,50%,and 100%CO_(2) additions at one fixed temperature,the soot collected from the 10%CO_(2) addition has the highest degree of graphization and crystallization.At three temperatures of 1173 K,1223 K,and 1273 K,the mean values of fringe length distribution displayed a ranking of 10%CO_(2)>100%CO_(2)>50%CO_(2) while the mean particle diameters showed the same order.Furthermore,the oxidation reactivity of different soot samples decreased in the ranking of 50%CO_(2) addition>100%CO_(2) addition>10%CO_(2) addition,which was equal to the ranking of mean values of fringe tortuosity distribution.The result further confirmed the close relationship between soot nanostructure and oxidation reactivity.