Kinetic analysis of coupled effects of CO2 and H2 additions on laminar lean premixed dimethyl ether flames is performed at atmospheric pressure. The coupled effects of H2/CO2 additions on major species, intermediate stable species and radicals are discussed and analyzed in detail. The dilution, thermal and chemical effects of H2 and CO2 are separated and identified. The results show that H2 addition can slightly mitigate the CO2 chemical effects on decreasing the temperatures, H radical concentration, acetylene mole fraction and formaldehyde concentration. After CO2 is added, the H2 chemical effects on increasing the temperatures are enhanced. DME oxidation is promoted by the H2 chemical effects, which is further strengthened by the CO2 addition. Moreover, CO2 addition can reduce the H2 chemical effects on increasing the H radical mole fraction, but strengthen the H2 chemical effects on increasing the production of HO2 and C2H2. CH2O formation can be promoted by the H2 chemical effects, which is enhanced by the CO2 addition. In actually, the H2/CO2 coupled chemical effects almost have no obvious influence on the temperatures and HO2 mole fraction. DME consumption is delayed by the H2/CO2 coupled chemical effects. Furthermore, the H2/CO2 coupled chemical effects can decrease the H radical mole fraction, CH4 concentration, C2H2 mole fraction, CH2O concentration and CH3CHO mole fraction, but increase the CO concentration.

•TiO2 catalyzed K-based sorbent is developed.•The CO2 desorption performances under different atmospheres are investigated.•The catalytic mechanism of TiO2 in K-based sorbent is calculated with DFT method.•The kinetic of the catalyzed K-based sorbent is analyzed.The high energy required for CO2 desorption process is one of the significant problems that inhibit the development of using potassium-based sorbent for CO2 capture. Proper catalysis should be studied to enhance the desorption kinetics and TiO2 is supposed as the promising catalyst but the catalytic mechanism is not clear. This paper was designed to simulate the catalytic performance of TiO2 with density functional theory (DFT) method and investigate the CO2 desorption performances of KHCO3/TiO2/Al2O3 sorbent. Results showed that, the existent catalyst TiO2 in the sorbent can adsorb the regeneration product (H2O and CO2), which can break the equilibrium of KHCO3 decomposition reaction and lead the equilibrium to move to the right side. Also, the unstable intermediary TiO(OH)+ and OH−, which formed by the adsorption of H2O on the catalyst TiO2 surface, can accelerate the consumption of HCO3−. Therefore, the existence of TiO2 changed the KHCO3 decomposition reaction pathway thus enhanced CO2 desorption reaction kinetics and reduced the activation energy. The absorption energy and reaction barrier of H2O adsorbed on anatase-TiO2 (101) surface is much lower than that of CO2, which means H2O is easy to be captured on catalyst TiO2 surface. So, the promising catalyst should perform great H2O adsorption performance. Also, compared with CO2 atmosphere, moisture is thought to be the promising desorption atmosphere in the desired temperature. In addition, some of the calculated results were confirmed with thermos-gravimetric analyzer (TGA) tests.Download full-size image

•The particles from butanol-doped IDF are highly heterogeneous in nanostructure.•The samples from butanol-doped NDF show a typical core-shell nanostructure.•For IDF, the reactivity ranks as n-butanol > iso-butanol > sec-butanol > tert-butanol.•For NDF, the reactivity ranks as sec-butanol > tert-butanol > n-butanol > iso-butanol.•A high correlation is found between soot nanostructure and reactivity.This paper explored the effects of butanol isomers, n-butanol, iso-butanol, sec-butanol, and tert-butanol, as fuel-side additives on soot nanostructure and reactivity in ethylene inverse diffusion flames (IDF) and normal diffusion flames (NDF). The variations of structures and oxidation rates among the soot samples derived from ten different flames were studied and compared using high resolution transmission electron spectroscopy (HRTEM), Raman spectroscopy, thermogravimetric analyzer (TGA), surface area and porosimetry analyzer, and elemental analyzer. Results demonstrated that soot from IDF with the additions of butanol isomers had irregular shapes with film-like materials and highly heterogeneous nanostructures, which showed both amorphous carbon and fullerenic lamellae. The shells presented more prevalently in tert-butanol-doped IDF soot, which had the longest fringe length and smallest fringe tortuosity. Whereas in the NDF as butanol isomers were individually added, the soot samples were aggregated by several tens or hundreds nearly rounded particles. All the NDF soot exhibited a typical core-shell structure with extended and planar lamellae. Soot from sec-butanol added NDF presented the lowest degree of graphitization with the shortest fringe length and largest fringe tortuosity. The TGA results revealed that the oxidation rates of the IDF soot particles were much higher than that of the NDF soot. Moreover, when butanol isomers were individually added in IDF, soot produced with n-butanol (1.34E-03 s−1) showed the highest reactivity with the least degree of crystallization in structure, followed by iso-butanol (1.31E-03 s−1), sec-butanol (1.29E-03 s−1) and tert-butanol (1.14E-03 s−1) in the sequence of reactivity. However, the oxidation rates of the soot samples generated from butanol isomers-doped NDF were in the order of sec-butanol (4.26E-04 s−1), tert-butanol (3.70E-04 s−1), n-butanol (3.52E-04 s−1) and iso-butanol (3.23E-04 s−1) from the highest to lowest. The results confirmed a relationship on structure-property between soot nanostructure and reactivity.Download high-res image (56KB)Download full-size image

In the present study, Fe nanoparticles (NPs) can ignite when exposed to a conventional camera flash. The ignition process of Fe NPs was composed of the initial ignition stage with the maximum temperature level of 2000 K and the burning stage with temperature level of 800 K. The microstructure characterization indicated Fe NPs were oxidized to Fe2O3 via the exposure-melt mechanism. It was found that more particle numbers per unit area can lead to lower minimum ignition energy which may be caused by the enhancement light energy absorption. The light energy absorbed from the flash was influenced by wavelengths but the conversion of Fe was only related to the packing mass.

Combustion characteristics of nanofluid fuels containing aluminum nanoparticles were investigated in half-opening slot tubes from the fundamental view. The effects of particle loading rates (0.25% and 2.5% by weight), type of base fuels (ethanol and butanol), and fuel flow rates (0.2, 0.6, and 1 mL/min) were studied in details. The combustion characteristics of the nanofluid fuels and pure based fuels were also examined to provide a comparison. Flame was unstable with reignition, stable state, nearly extinguishment repeatedly at low flow rate. At medium flow rate, flame height was increased and flame tended to be stable. At high flow rate, flame became unstable and was disturbed by the droplet forming and dripping significantly. Al atoms inside the oxide layer should be melted before the particles combustion, while Al oxide layer should be melted before the particles aggregates combustion. The effects of particles on the combustion characteristics, especially on the evaporation rate of base fuel, were discussed. The reasons for various combustion phenomena of nanofluid fuels were given, which can provide the useful guidance for the experimental research and practical applications of nanofluid fuels.

•The char gasification mechanism is influenced by the specific surface area of char.•The gasification mechanism is influenced by the ash of char.•The separate and common active sites assumptions of char gasification can be unified.The gasification mechanism of char in the mixture of H2O, CO2, H2 and CO is controversial for a long time, and the reasons leading to different results of validation experiments of gasification mechanism are yet not clear. In this study, the specific surface area (SSA) and ash of char are assumed to be the possible reasons leading to the controversial results. The large-SSA char, the small-SSA char, and the ash-free char were prepared for validation experiments. The gasification experiments were performed in the mixture of H2O, CO2, H2 and CO using a modified TGA system. The experimental results indicate that SSA and ash really have significant effects on char gasification mechanism. The gasification mechanism of large-SSA char is close to the separate active sites assumption, while the gasification mechanism of small-SSA char is close to the common active sites assumption. The gasification mechanism will transition from the separate active sites assumption to common active sites assumption if the ash is removed from the large-SSA char, and will become closer to the separate active sites assumption again if Na is loaded to the ash-free char. Therefore, for char gasification in the mixture of H2O, CO2, H2 and CO, the separate and common active sites assumptions are two extreme situations of the same gasification mechanism. Finally, a unified model was proposed based on this char gasification mechanism. This model is applicable to the char samples that have different specific surface areas and ash contents.

•The pyrolysis and gasification performances of waste textile under CO2 atmosphere with different catalysts were evaluated.•Effects of several parameters were investigated to evaluate the catalysts.•A Zn-Fe composite catalyst was prepared by sol gel method to contrast with single catalyst.•The corresponding kinetics was evaluated.With thermogravimetric apparatus (TGA), X-ray diffraction (XRD) and Scanning electron microscopy (SEM), the catalytic pyrolysis and gasification characteristics of waste textiles (Polyester Fiber (PF), Cotton and Woolen) using several common metallic oxide as catalysts were studied at atmospheric pressure under CO2 atmosphere, several parameters including catalysts' types, loadings and reaction temperatures were also conducted. Results showed that the pyrolysis reaction of the three textiles was best enhanced by 5 wt% ZnO while the gasification reaction was best enhanced by 5 wt% Fe2O3.·The pyrolysis and gasification processes were also quantitatively evaluated by using shrinking core model. The apparent pyrolysis activation energies for textile with 5 wt% ZnO loading were 65.1 kJ/mol, while the apparent gasification activation energies for textile char with 5 wt% Fe2O3 loading were 89.0 kJ/mol, which is significantly lower than un-catalytic textiles in our previous study. Besides, a Zn-Fe composite catalyst was prepared by sol gel method, and the catalytic effect of the composite catalyst was better than that of the single catalyst. The findings reported in the manuscript are beneficial to the development of energy utilization of waste textile under carbon dioxide atmosphere.Download high-res image (51KB)Download full-size image

•Chemical effects of H2 addition on PRF flames are isolated from other effects.•H2 chemical effects promote formations of CH2O, C2H2 and C3H3.•H2 chemical effects on H radical are larger than those on O and OH radicals.•H, O and OH radicals decrease caused by H2 dilution and thermal effects.•The presence of iso-octane in PRF facilitates the production of C3H3.The influences of hydrogen addition on laminar premixed fuel-rich primary reference fuels flames at atmospheric pressure are studied by the detailed kinetic analysis. The chemical effects of hydrogen addition on important intermediate species including radicals are distinguished clearly from the dilution and thermal effects. The results show that the increase of the percent of iso-octane in primary reference fuels makes the mole fractions of CH2O and C2H2 reduce but facilitates the production of C3H3. The dilution and thermal effects of hydrogen can suppress the formation of H, O, and OH radicals and CH2O, C2H2 and C3H3 species, and make the profiles shift to the downstream side. The hydrogen chemical effects can promote the formations of these radicals and intermediate species. The H2 chemical effects on H radical are larger than those on O and OH radicals. The dilution and thermal effects are dominant and the overall mole fractions of H, O, and OH radicals, and CH2O, C2H2 and C3H3 species decrease with the hydrogen addition. Finally, the detailed consumption pathways of primary reference fuels combustion with various levels of hydrogen additions are analyzed.

•Chemical effects of H2 addition on CH4/H2 flames are isolated from other effects.•Chemical effects of H2 addition suppress formations of acetylene and ketene.•H2 dilution and thermal effects reduce CH2O and CH3CHO concentrations.•NO formation is suppressed predominantly by H2 dilution and thermal effects.•H, O and OH concentrations increase due to significant H2 chemical effects.A detailed kinetic analysis of chemical effects of hydrogen addition on laminar premixed stoichiometric methane-air flames was conducted at atmospheric pressure. Flame structures and mole fraction profiles affected by chemical effects of hydrogen addition for major species, free radicals and intermediate species are analyzed with particular emphasis on the formations of soot precursor and oxygenated air pollutants. The results illustrate that chemical effects of hydrogen additive lead the methane profile to move towards the upstream side and suppress the formation of acetylene and ketene. The concentrations of free radical H, O and OH increase as methane is replaced by hydrogen mainly due to its chemical effects. In contrast, although the chemical effects of hydrogen addition facilitate the productions of formaldehyde and acetaldehyde, the hydrogen dilution and thermal effects on reducing mole fractions of both species are more significant. As a consequence, the total effects of hydrogen addition lead to a decrease in formaldehyde and acetaldehyde concentrations. Compared to formaldehyde and acetaldehyde, NO mole fraction diminishes in a similar fashion with increased hydrogen additive that the decrease of NO concentration caused by hydrogen dilution and thermal effects is larger than the increase due to its chemical effects.

The chemical effects of CO2 addition on premixed laminar low-pressure dimethyl ether and ethanol flames were studied by comprehensive numerical analysis from fuel-lean to fuel-rich conditions. Added CO2 is assumed as normal reactive CO2 and fictitious inert CO2 to assess the chemical effects of CO2. The dilution and thermal effects of CO2 addition decrease C2H2 mole fractions in ethanol flames instead of DME flames, but the chemical effects can reduce C2H2 mole fractions in both DME and ethanol flames at all equivalence ratios, which reveals that C2H2 formation can be suppressed chemically by CO2 addition. The chemical effects have a weak influence on formaldehyde formation in both DME and ethanol flames. The CO2 chemical effects only result in a slight decrease of acetaldehyde peak mole fractions in DME flames but not in ethanol flames at all equivalence ratios. Mole fractions of the H radical decrease because of the chemical effects of CO2 addition by shifting the equilibrium of CO + OH = CO2 + H in both DME and ethanol flames at all equivalence ratios, and mole fractions of OH and O radicals also decrease for equivalence ratios of 0.8, 1.0, and 1.2, whereas the chemical effects of added CO2 enhance the productions of OH and O radicals for rich conditions at an equivalence ratio of 1.5.

To better understand potential pollutant formations during combustion of conventional hydrocarbon fuels blended with oxygenated fuels, detailed influences of ethanol as fuel additive on small polycyclic aromatic hydrocarbons (PAHs) precursors, aldehydes, ketene and other important intermediate species in premixed fuel-rich low-pressure ethylene flames are distinguished among dilution, thermal and chemical effects of additives. Dominant effects of ethanol addition on each species are underlined respectively. Ethylene oxidation process is delayed when ethylene is substituted by ethanol. The influence of ethanol dilution and thermal effects on ethylene consumption are larger than chemical effects. CO mole fractions slightly decrease mainly as a result of dilution and thermal effects of added ethanol. The reductions in small PAHs precursors (acetylene and propargyl) are attributed to dilution and thermal effects of ethanol addition instead of chemical effects. The ethanol chemical effects promote formations of hazardous pollutants formaldehyde and acetaldehyde, and especially are responsible for the significant increase of acetaldehyde. C2H6, C4H2 and C4H4 mole fractions decrease in a similar way with acetylene and propargyl as ethanol is added. Ethanol used here only serves as a prototype of oxygenated additive, and identification method in this work is more universal which can be easily extended for analyzing other fuel blends of hydrocarbon and oxygenated fuels.

•H2 chemical effects on DME and ethanol flames are comparatively studied.•Chemical effects of H2 addition are isolated from thermal and dilution effects.•H2 chemical effects promote the production of CH4, C2H6 and CH2O in DME flames.•H2 chemical effects suppress formations of C2H2 and C2H4 in DME fuel-rich flames.•C2H2, C2H4 and CH3CHO concentrations in ethanol flames reduce with H2 addition.The influences of hydrogen addition on laminar premixed ethanol/O2/Ar and DME (dimethyl ether)/O2/Ar flames under fuel-lean (Ф = 0.8) and fuel-rich (Ф = 1.7) conditions at 1.0 atm are studied by the detailed kinetic analysis. The comparisons are conducted to illustrate the characteristics of these two isomers affected by H2 addition. The chemical effects of H2 addition on ethanol and dimethyl ether flames are distinguished and separated from its dilution and thermal effects respectively. The results show that the mole fractions of CH4, C2H6 and CH2O in DME flames are larger than those in ethanol flames. The influences of hydrogen addition on CH4, C2H6 and CH2O in ethanol flames are weakly. The chemical effects of H2 addition promote the production of CH4, C2H6 and CH2O and shift the profiles to the upstream side in DME flames. The dilution and thermal effects which decrease the mole fractions of these species and shift profiles to the downstream side are more dominant for DME flames. Meanwhile, the mole fractions of C2H2, C2H4 and CH3CHO in DME flames are less than those in ethanol flames. The H2 chemical effects which mainly promote the formation of C2H2 and C2H4 in ethanol flames suppress the production of these species in DME flames slightly for the fuel-rich condition. The dilution and thermal effects of hydrogen on these species are more dominant in ethanol flames than those in DME flames.

•H2 chemical effects on CH2O/H2 flames are isolated from thermal/dilution effects.•H concentrations increase due to significant H2 chemical effects.•H2 dilution and thermal effects reduce O, OH, HCO and HO2 concentrations.•CO2 formation is suppressed predominantly by chemical effects of H2 addition.The influences of hydrogen addition on laminar premixed fuel-rich formaldehyde flames at the atmospheric pressure are studied by the detailed kinetic analysis. The chemical effects of hydrogen addition on flame structures, mole fractions of major species and free radicals are distinguished clearly from the dilution and thermal effects. The results show that the H2 chemical effects can promote the oxidation of formaldehyde and make the mole fraction profile of formaldehyde move toward the upstream side. The increase of H radical concentration is mainly due to the chemical effects of hydrogen addition. The reaction OH + H2 = H + H2O plays a major role in the productions of H and OH radicals. The productions of O, HCO and HO2 radicals are enhanced by the H2 chemical effects. However, the hydrogen dilution and thermal effects on decreasing these radicals' concentrations are more dominant. The mole fractions of CO and CO2 decrease with H2 addition. The H2 chemical effects facilitate the formation of CO, but suppress the production of CO2.

•H2 chemical effects on butanol flames are isolated from thermal/dilution effects.•Differences of important species among four butanol isomers are analyzed.•C2H2 is promoted by H2 chemical effects and is lowest for t-butanol.•H2 chemical effects increase C3H3 concentration which is lowest for 2-butanol.•CH3CHO is suppressed by H2 dilution/thermal effects and is highest for 2-butanol.Butanol is thought to be a promising alternative biofuel for fossil fuels, which has four different isomers, i.e., 1-butanol, 2-butanol, iso-butanol and tert-butanol. Detailed kinetic analysis of H2 effects on laminar rich premixed flames of these four butanol isomers are performed at atmospheric pressure and the H2 chemical effects are emphasized. The detailed chemical mechanism for high-temperature oxidation and combustion of butanol isomers developed by Sarathy et al. [Combust Flame 2012;159:2028-55] which consists of 286 species and 1892 reactions was used in this study. The equivalence ratios for all the flames are kept constant to be 1.5. The chemical effects of H2 additions on the four butanol isomers flames are separated from the H2 dilution and thermal effects. The effects of H2 addition on major species, intermediate stable species and radicals are analyzed and compared in details for different butanol flames. The rates of production of acetylene, formaldehyde, acetaldehyde, and key radicals are given to obtain the responsible reactions during the butanol combustion with and without H2 additions. In addition, the pathway analyses for these flames are presented and discussed.