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Abstract The prime purpose of this work is to prepare a novel kind of Pickering interfacial solid catalysts for biodiesel production to meet the requirements of highly efficiency and environmental benign. To achieve this goal, the core–shell P[xSPA-yDABCO]@SiO2@Fe3O4 composite materials with a shell of photo-responsive and base catalytic sites were manufactured by means of layer-by-layer fabrication method. The modified materials, entirely characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectra, X-ray powder diffraction (XRD) and magnetization versus magnetic (VSM) techniques, demonstrated sufficient catalytic active sites and photo-responsive sites. Among all the so-prepared catalysts, P[3SPA-2DABCO]@SiO2@Fe3O4 performs extremely well and can stabilize soybean oil-in-methanol Pickering emulsion for 24 h, achieving a biodiesel yield up to 98.2% at a catalyst dosage of 5 wt% after the reaction time of 5 h at 60 °C. Furthermore, the double responsive solid catalyst can be readily separated from the mixture of reaction by an external magnet and UV irradiation, and still presented superior catalytic activity after 6 cycles.

Abstract CBM reservoirs are extremely vulnerable to damage due to their complex pore structure. So, changing pore structures in CBM reservoirs is of vital importance for reducing reservoirs damage. Organic solvents have been considered as additives into fracturing fluids to enhance production because they can enhance the pore connectivity and loosening macromolecular network structure. It is thus of great interests to investigate how organic solvents (ethanol and ethylene glycol ether) change micropore structures and fluid distribution. In this study, samples were selected from different wells completed in No. 3 coal seam, Zhaozhuang minefield. Low-pressure nitrogen adsorption (LP-N2GA) experiments were conducted on coal samples to evaluate the changes in pore-structure parameters including specific surface area (SSA), pore diameter, and pore volume. NMR experiments were conducted on coal samples to evaluate the changes in fluid distribution. Analyzing the LP-N2GA results suggests ethylene glycol ether and ethanol can effectively increase SSA, pore diameter, and opening degree of pores in coal samples. Comparative analysis of NMR results indicates that ethylene glycol ether consistently reduces the irreducible water saturation (Swir) in samples. The average value of Swir of raw samples is 0.8670 and the average value of Swir of samples treated with ethylene glycol ether value is 0.7644. Considering the pore-structure alterations, this study demonstrates that ethylene glycol ether is more preferable for enhancing recovery from CBM reservoirs compared with ethanol.

Abstract Residues from the liquefaction of Black Thunder subbituminous and Illinois No. 6 bituminous coals in an autoclave and a bench unit were examined petrographically. Optical microscopy proved valuable for ranking the samples on the basis of overall coal conversion and presence of vitroplast, granular residue and inertinite. It was observed that in the autoclave that runs on Black Thunder coal, K 2 CO 3 was a superior water gas shift reaction catalyst to NaAlO 2 , or a combination of CS 2 and Fe or Mo catalysts. The amount of vitroplast showing vacuoles and cenospheric morphology in the residues was inversely related to the CO conversion, indicating that the mechanism of vitroplast dissolution is linked to the availability of active CO intermediates (e.g. formate ion, HCOO − ). A CO-steam mixture was more effective than syngas or pure H 2 and N 2 in increasing Black Thunder coal conversion, and resulted in greater morphological changes to the coal particles. In contrast, for Illinois No. 6 coal pure H 2 had a greater effect on coal solubilization and overall conversion than pure CO at the same temperature; this was attributed to the absence of carboxylates to react with the formate ions. Higher mesophase and coke contents were detected in some bench unit runs on Black Thunder coal that were operated in counterflow mode. Higher severity, poorer mixing, longer residence time and a reduction in pressure by almost 3.5 MPa are believed to be responsible for the retrogressive reactions forming mesospheres in these cases.

Abstract Bitumen recovery by steam-solvent coinjection involves the coupled thermal/compositional mechanisms for reduction of bitumen viscosity. Reliable design of such processes requires reservoir flow simulation based on a proper phase-behavior model so that the oleic-phase viscosity near the steam-chamber edge can be modeled reliably. However, the effect of bitumen characterization (e.g., the number of pseudo components used) on steam-solvent coinjection simulation has not been studied in detail, and can be realized only after running multiple reservoir simulations, which is time consuming. There are two main objectives in this paper. One is to develop a reliable method for bitumen characterization by improving the fluid characterization method that was recently developed based on perturbation from n-alkanes (PnA). The other is to develop a novel analytical method for assessing the sensitivity of a particular coinjection simulation to bitumen characterization without having to perform reservoir simulations. A simulation case study is given to validate this analytical method. A proper number of pseudo components for bitumen characterization cannot be determined without considering the effect of phase behavior on the oleic-phase viscosity at chamber-edge conditions in steam-solvent coinjection simulation. Results show that the analytical method developed in this research can detect the sensitivity of recovery simulation to bitumen characterization without performing multiple flow simulations using different sets of fluid models. The PnA-based method developed for bitumen characterization gives reliable predictions of phase behavior for bitumen/solvent mixtures with a small amount of experimental data.

Abstract The rate of oxygen consumption and the release of CO2 were studied using a low-temperature oxidation simulation system. Six model compounds with different functional groups and pore structures were used in the experiment. The results showed that the oxygen consumption rate of six model compounds was mainly controlled by pore diffusion; the release of CO2 for the carbon nanotube (CNT) model compounds CNTs-Mac and CNTs-Mes was controlled by chemical adsorption of oxygen-containing functional groups, while the CNTs-Mic compounds was by diffusion resistance in channels. The carboxyl group, where CO2 adsorbed, was the main adsorption site; this had a higher oxygen consumption rate than the hydroxyl group. Two different methods were employed in further studies to explore the relationship between CO2 and oxygen-containing functional groups: a quantum chemical simulation for basic structural units of lignite, and measuring the activation energy of two types of lignite pre-treated by different CO2 concentrations. Experimental results revealed that the O H bond of the carboxyl was longer than that of the hydroxyl, and the negative surface potential of the carboxyl was stronger than that of the hydroxyl. The non-covalent bond between the reactive group and coal macromolecule could be weakened due to the presence of CO2. Finally, there was a synergistic effect between 30% CO2 and active functional groups to promote low-temperature oxidation of lignite.

Abstract In the study, a three-dimensional CFD simulating model coupling with reasonable turbulent model and reduced chemical kinetic mechanism was established and validated. The auto-ignition development and knocking characteristics of a downsized spark-ignition (SI) gasoline rotary engine (RE) under different boosted conditions were numerically investigated. Results showed that as inlet pressure increased from 1.12 bar to 1.16 bar, the knocking intensity (KI) of the RE was enhanced gradually, and the knocking onset was advanced. However, with the further augment of inlet pressure, the KI did not further increase due to the larger heat dissipation loss caused by high turbulent kinetic energy in the long and narrow combustion chamber of the RE. This indicated that the structure of the downsized SI RE had a certain ability of knocking suppression when inlet pressure was sufficiently boosted. The KI of the RE was more serious in the trailing part of the combustion chamber as compared to other positions due to the unidirectional flow field, especially on both sides near the end cover in the trailing part of the combustion chamber. Therefore, it was concluded that strengthening the cooling of both sides near the end cover in the trailing part of the combustion chamber may be an effective way to reduce the KI of a downsized boosted SI RE. In addition, the KI is closely related to auto-ignition development processes, e.g. end-gas auto-ignition modes. Under the mass fraction of unburned mixtures at the moment of end-gas auto-ignition, the local KI caused directly by single hot-spot auto-ignition was higher than that caused by multiple hot-spots auto-ignitions, and the local KI caused by homogeneous auto-ignition was higher than that caused by multiple hot-spots auto-ignitions.

Abstract It is demonstrated that the fuel deposit has a significant influence on the NOx and particular matter (PM) emissions, especially with the consideration of the more and more strict emission regulations issued by the governments, which results in that the near-nozzle spray has been received the increased attention, recently. In this study, the near-nozzle spray characteristics at the initial and end stages were investigated by a high-resolution camera with a laser as the light source. At the initial stage, microscopic behaviors of the near-nozzle spray were observed at upstream, midstream and downstream, respectively. Moreover, the injection frequency was changed to check the effect on the near-nozzle spray morphology. Next, the micro spray length, width and angle were obtained from the processed images. While, at the end stage, the near-nozzle spray evolutions were observed and characterized at 0.5, 0.3, 0.2 and 0.1 ms before the end of injection (BEOI), the end of injection (EOI), 0.05, 0.1, 0.15 and 0.2 ms after the end of injection (AEOI), respectively. Furthermore, the droplet area, spray area without droplets, droplet number and averaged diameter were calculated. Results show that three structures of the near-nozzle spray at the initial stage can be classified as mushroom, steeple and cylinder shapes. And the injection frequency has an influence on their formations owing to the residual fuel and sucked air AEOI. Moreover, although more droplets can be identified at the end stage with time, it does not indicate the better atomization. On the contrary, these droplets AEOI are responsible for the injector deposit in the real engine.

Abstract Directed relation graph with error propagation (DRGEP) method combined with extensive validation for 0D, 1D and 2D CFD modeling supported by sensitivity and Rate-Of-Production (ROP) analyses are implemented for comparative study of detailed and reduced kinetic mechanisms for CH4 + H2 combustion. To this end, two detailed kinetic mechanisms, namely AramcoMech 2.0 and recently updated Konnov mechanism, were validated using available measurements of ignition delay times and laminar burning velocities for hydrogen, methane and hydrogen + methane fuel mixtures. For all experimental conditions visited, both detailed mechanisms demonstrated good and close to each other performance. Two-stage DRGEP method and reaction reduction based on computational singular perturbation (CSP) were then implemented to achieve two skeletal models: 25 species and 105 reactions for AramcoMech 2.0 and 27 species and 107 reactions for the Konnov model. The conditions for skeletal models generation cover ɸ = 0.5–2.0, temperature 900–2000 K, and pressure 1–50 bar. Turbulent non-premixed flames of CH4 + H2 in the Jet in Hot Co-flow (JHC) burner for two different oxygen concentrations in a co-flow were modeled using both skeletal models. 2-D RANS simulations with OpenFOAM code of the flame structure using the two skeletal kinetic mechanisms are similar except for the mass fraction of OH and CO. To elucidate the differences between two skeletal mechanisms generated using the same reduction method, extensive validation for 0D, 1D and 2D CFD modeling were supported by sensitivity analysis for detailed and skeletal reaction models. Good agreement between the skeletal and detailed mechanisms was found in top reactions as well as their sensitivity coefficients, which affect auto-ignition process and laminar flame propagation. Further chemical and sensitivity analysis of the structure of laminar flames demonstrate that three important reactions, i.e. CO + OH = CO2 + H, H2 + OH = H + H2O, and CH4 + OH = CH3 + H2O have different rate constants in the Aramco and Konnov models that may contribute to the differences in the prediction of CO concentration profiles. The simulation predictions for CO concentrations are improved for laminar flames and JHC flame by using a 25-species modified version in which these rate constants were taken from the Konnov mechanism. It was noted that DRGEP method applied to different detailed kinetic schemes generate skeletal models with different, non-overlapping lists of retained species. The presence of CH2CHO in the Aramco 25-species skeletal mechanism and its absence in the Konnov 27-species mechanism, and the presence of CH, CH2, CH2CO in the latter and their absence in the former mechanism were analysed and explained using Rate-Of-Production analysis for conditions found in the CFD simulations.