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Visual characterization of the spatial and temporal distribution patterns of displacing fluids and CH₄ within the pore space and exploration of the differences in sweep effect on CH₄ are key to predicting the scale of CO₂ geological sequestration and production capacity within the reservoir. There are large differences in the displacement efficiency of CH₄ in the pore space by different components of the displacing fluid. In this study, the more cost-effective displacing fluid injection scheme is explored on the basis of CO₂ sequestration and enhanced gas recovery. Thus, the displacement behavior and dispersion characteristics of CO₂, gas mixture (50 % CO₂ + 50 % N₂) and N₂ at the pore scale are investigated. N₂ has the highest overall sweep efficiency during displacement, but it also causes the greatest degree of mixing. In contrast, liquid and supercritical CO₂ has the weakest diffusion ability and the lowest overall sweep efficiency on CH₄, but cause the least mixing. In addition, it is found that the dispersion coefficients of all three displacing fluids become smaller with increasing pressure, with the entrance/exit effect causing the CO₂ dispersion coefficients to increase by 11.3 % to 23.4 %.

In the present study, influence of different anode and cathode materials including carbon felt, carbon cloth, and several metal electrodes with or without carbon cloth covering on sediment microbial fuel cell (SMFC) performance was investigated. Results suggested that stainless steel poorly performed as cathode electrode whereas it exhibited reasonable performance as anode. In SMFCs with carbon felt cathode, anodes including 400 series stainless steel mesh and 300 series stainless steel plate, both covered with carbon cloth, led to higher maximum power densities of 88 and 87 mW/m⁻², respectively, compared with carbon felt, carbon cloth, 400 series stainless steel mesh, 300 series stainless steel mesh covered with carbon cloth, and copper plate covered with carbon cloth (power densities of 40, 74, 53, 68, and 47 mW/m⁻², respectively). They also resulted in higher loss on ignition (LOI) removals of 9.4 % and 8.7 %, respectively. Cyclic voltammetry results showed that stainless steel plate covered with carbon cloth produced the highest redox current that was two times that of the carbon cloth. In addition, electrochemical impedance spectroscopy indicated lower charge transfer resistance in the SMFC with anodes including 400 series stainless steel mesh (20.6 Ω) and 300 series stainless steel plate (25.7 Ω), both covered with carbon cloth, compared to other anode materials. These findings suggest that stainless steel electrodes covered with carbon cloth provide SMFCs with improved electrochemical characteristics that enhance their electricity production and organic matter removal.

Higher-molecular-weight gases (HMWGs), which have not received much attention, also contain invaluable information about the coal spontaneous combustion (CSC) development process. In order to investigate the formation mechanism of HMWG, the emission behaviors of HMWG from coal oxidation and pyrolysis experiments were compared, and FTIR and ESR were used to analyze the microstructural evolution of the coal sample. The results show that the volume fractions of most HMWGs increased regularly with increasing temperature. The contribution of the pyrolysis process to the yield of most hydrocarbon HMWGs was close to 100 %, while it was below 89 % for C₄ ∼ C₆ n-alkanes and benzene and less than 10 % for acetaldehyde and acetone. The decomposition of active structures could produce free radicals, the concentration of which increases with increasing temperature. The formation mechanism of HMWGs was proposed based on the experimental results: HMWGs came from both the thermal reaction and the coal-oxygen reaction process. The thermal reaction process would release the majority of hydrocarbon HMWGs from room temperature. Some active structures began participating in the coal-oxygen reactions to produce oxygen-containing HMWGs at 90 ℃. After reaching 170 ℃, the coal-oxygen reactions were further intensified to release minority n-alkanes, benzene, and small amounts of C₄ olefins.

Biomass oxidative pyrolysis introduces restricted oxygen into the reaction zone, realizing autothermal pyrolysis to address the heat supply challenges inherent in large-scale applications. However, heavy components (＞200 Da) in bio-oil are critical precursors that lead to coke formation upon heating, which hinders the utilization of bio-oil. In this study, the conventional and oxidative pyrolysis experiments of cellulose, hemicellulose, and lignin in a fix-bed reactor were conducted at temperatures ranging from 300 °C to 800 °C, aiming to investigate the evolution of heavy components in bio-oil during biomass oxidative pyrolysis. The results showed that the addition of oxygen promoted the generation of bio-oil. Compared to conventional pyrolysis, the addition of oxygen mostly increased the yields of cellulose-oil, hemicellulose-oil, and lignin-oil by 28.21 %, 10.94 %, and 16.84 %, respectively. Further comprehensive analysis revealed that oxygen promoted the depolymerization of three components at a lower temperature range (＜ 500 °C). With increasing temperatures, oxygen enhanced the polymerization of volatiles from cellulose and lignin, where oxygen, acting as a binder, promoted the generation of phenolic compounds of heavy components in lignin-oil. Conversely, as the temperature increased, oxygen enhanced the oxidative decomposition of volatiles from hemicellulose, inhibiting the generation of heavy components in hemicellulose-oil. To sum up, this study presented a global evolution route of heavy components in bio-oil during oxidative pyrolysis of three components.

The present work aims to develop a simple theoretical model to study the propagation of flames in closed or half-open ducts in the early stages of the process including the onset of flame front inversion. It is known from previous studies that flame propagation in these configurations is characterized by four stages, namely the spherical flame stage, the finger flame stage, the flat flame stage, and the flame front inversion stage. The fourth stage is also called the tulip flame stage. The instant at which the flame skirt region touches the side walls of the duct (or tube) is here considered the onset of the flame front inversion phenomenon. In order to accurately represent the early stages of flame propagation and the onset of flame front inversion, a theoretical model was developed that takes into account the effects of compressibility. It was also possible to obtain an analytical solution for this model. The effect of compressibility was incorporated into the model through a parameter that depends on the initial Mach number of the mixture and on the expansion ratio of the flame. The results obtained with the model were compared with experimental results from the literature concerning mixtures of hydrogen, carbon monoxide and air in different compositions and equivalence ratios, in closed and half-open ducts. The model was shown to be adequate to represent the early staged for flames propagating in closed or half-open ducts. The model for determination of the time at which the flame skirt touches the side walls of the duct showed an average value of the relative errors of 1.84% when compared to available experimental data for H₂/CO/air.

This work investigates the self-excited thermoacoustic parametric instability of downward propagating laminar premixed ammonia flames in an open-closed combustion tube. NH₃/O₂/N₂ flames were propagated at different laminar burning velocities at equivalence ratios of ɸ = 0.8 and ɸ = 1.2. Different unstable flame regimes were observed through pressure fluctuation measurements and synchronized high-speed imaging capturing the lateral and longitudinal perspectives of flame propagation. The observed propagation speed of quasi-planar flames showed a strong correlation with the calculated laminar burning velocities of NH₃/O₂/N₂ mixtures. For the first time, the cellular structures of laminar premixed ammonia flames at the onset of parametric instability were clearly observed from the present experimental approach. The experimental cellular flame wavenumbers and acoustic velocity fluctuation amplitudes at the onset of parametric instability are in qualitative agreement with the theory of stability of laminar flames under acoustic excitation. Experiments have shown that NH₃/O₂/N₂ flames are more unstable than CH₄/O₂/N₂ flames at the same laminar burning velocity independent of Lewis number within the range of tested conditions. The influence of activation energy on parametric instability is investigated through a comparative thermoacoustic analysis between two different fuels at varied equivalence ratios. Ammonia flames are characterized by large overall activation energy and Zeldovich numbers compared to hydrocarbon flames. This work elucidates how this unique property characterizes the acoustic instability of downward propagating premixed ammonia flames in a tube based on classical theories on acoustic instability of laminar premixed flames.

In the context of carbon neutrality, the widespread application of waste heat recovery systems in steel production is crucial for energy conservation and emission reduction. This study investigates the formation and combustion removal mechanisms of carbon deposits in coke oven risers during waste heat recovery by analyzing the physicochemical structure, combustion behavior, and kinetics of different layers. The results revealed that lower temperatures near the tube wall produced higher volatile content in the lower layer. Over time, the carbon deposits gradually graphitized from bottom to top. Under long-term heating and iron catalysis, the lower carbon deposits showed a higher order degree and poorer combustion performance. The middle layer, characterized by more pores formed during polycondensation, exhibited a larger specific surface area than other samples and burned slightly faster than the upper layer. Increasing heating and airflow rates could linearly enhance the combustion efficiency of carbon deposits. The random pore model accurately described the combustion process of the upper and middle layers, whereas the multi-stage weight loss in lower deposits aligned better with a multi-stage reaction random pore model. This research could further strengthen the understanding of carbon deposits in the riser and improve the removal effect, thereby promoting waste heat recovery from coke oven gas.

Long-chain ethers have been proposed as promising biofuels for advanced combustion methods, yet their low-temperature oxidation (LTO) characteristics remain poorly understood. In this study, the LTO reactivities of n-heptane and five long-chain ethers with different structures, including dibutyl ether (DBE), diethylene glycol dimethyl ether (DGM), polyoxymethylene dimethyl ethers (PODE), 1,2-dimethoxyethane (1,2-DME), and dipropyleneglycol dimethyl ether (DPGDE) are investigated using a cooperative fuel research (CFR) engine, which is closer to the actual internal combustion engine operating environment. Products formed from LTO of ethers and n-heptane are investigated over a wide range of compress ratios (CRs), and their relationship to the global oxidation reactivity is suggested based on the quantum chemistry calculation. The presence of oxygen atoms in long-chain ethers significantly enhances oxidation reactivity, with the global oxidation reactivity ranking as follows: DGM > DPGDE > 1,2-DME > DBE > PODE > n-heptane. The key intermediate species generated during the LTO of n-heptane include aldehydes, ketones, and cyclic ethers, while oxygen atoms in ethers facilitate the formation of acids. The species pathway analysis and quantum chemistry calculations reveal that (1,5) and (1,6) H-transfers of alkylperoxy radical ($\text{R}\text{O}\dot{\text{O}}$) are critical chain-propagation channels, playing pivotal roles in the LTO process. The impact of oxygen on oxidation reactivity can be attributed to two primary factors: accelerating the H-abstraction of $\dot{\text{O}}\text{H}$ and H-transfer of $\text{R}\text{O}\dot{\text{O}}$ by weakening the neighboring C-H bonds, and enhancing the branching ratio of H-transfer of $\text{R}\text{O}\dot{\text{O}}$. The arrangement of two oxygen atoms between every two carbon atoms (–OCH₂CH₂O–) is optimal for oxidation reactivity, while the arrangement of oxygen and carbon (–OCH₂OCH₂–) weakens the oxidation activity due to fewer available hydrogens for H-transfer. The methyl group in branching-chain, exhibit reduced oxidation reactivity due to the strength of C-H bonds. Additionally, for ethers with the same structure, a longer carbon chain allows for more available hydrogens, resulting in stronger oxidation reactivity.

In this work, a 0D/1D model of a single-cylinder pre-chamber spark ignition (PCSI) engine is extensively validated with experimental data in terms of performance, combustion, and emissions by varying the pre-chamber geometry and operating conditions.

In the first stage, an experimental study is carried out on the PCSI engine at 1600 rpm and wide-open throttle, exploring different pre-chamber (PC) designs and various relative air/fuel (A/F) ratios, λ, in the main chamber.

In the second stage, a phenomenological combustion model for PCSI engines is coupled with additional user-defined sub-models of in-cylinder turbulence, heat transfer, and pollutant emissions. These are integrated into a 1D engine model and used to reproduce a set of 16 measured data for a reference PC geometry. The model adequately describes the performance, pollutant production, and burn rate in both the pre- and main-chamber considering the effects of jet-induced turbulence and distributed multiple flame kernels in the main chamber.

The predictive capability of the 1D model is further tested on an extended dataset composed of 163 points, including variations in the PC geometry, proving to satisfactorily reproduce experiments in terms of performance, combustion, and emissions. This last aspect represents the novelty of the present work, demonstrating the reliability of the physical background included within the in-cylinder sub-models.

This study investigated the role of microwave-assisted synthesis in enhancing green hydrogen (H₂) production via thermochemical water splitting (TWS) using Ni-based nanocatalysts on an Al₂O₃ support. H₂-TPR analysis showed that the microwave-assisted synthesized (MW) catalysts exhibited stronger peaks at lower temperatures, indicating improved Ni dispersion on the Al₂O₃ support. Moreover, higher H₂-uptake values were observed with increasing Ni concentration for both synthesis methods, indicating the presence of more accessible reducible sites crucial for catalytic activity. The MW-prepared catalysts displayed smaller particle sizes, narrower pore size distributions, and higher hydrogen adsorption capacities than those synthesized via impregnation. Additionally, they demonstrated superior catalytic activity and efficiency for hydrogen generation, with yields (∼55.42 %). Overall, our research underscores the potential of microwave-assisted synthesis as a promising method to develop efficient catalysts for hydrogen production applications.