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排序方式: 共有5306条查询结果,搜索用时 15 毫秒
31.
G.M. Kosmadakis D.C. Rakopoulos C.D. Rakopoulos 《International Journal of Hydrogen Energy》2021,46(34):17955-17968
The cyclic variability in a spark-ignition (SI) engine is examined fueled with methane/hydrogen blends with the use of an in-house computational fluid dynamics (CFD) code. A recent methodology is followed, which has been developed with the main aim at providing accurate predictions of the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) in a fraction of time. Instead of simulating several tens of engine cycles, the methodology is based on the numerical results obtained from just 5 cycles, which are then processed for developing suitable fitted correlations of the main parameters as a function of a normalized distance. The latter expresses the distance of the spheres of the initial flame within the computational cell at the spark-plug region with the local turbulent eddy, and provides a smooth transition from the laminar burning regime to the fully turbulent one. This sub-model is included in the ignition numerical approach and is applied here in a SI engine with 3 different hydrogen contents, 10%, 30% and 50%, and three equivalence ratios, 1, 0.8 and 0.7, showing that the COV of IMEP is well predicted compared to the available measured data. Other parameters of engine cycle variations are also examined, such as the distribution of the IMEP. The variability of NO (nitric oxide) emissions is also examined, showing that for the stoichiometric cases it follows a distribution similar to a normal (Gaussian) one, while for lower ratios it is positively skewed. Overall, the methodology seems to provide reliable results for the whole range of the operating conditions examined, while the next steps of this activity will focus on similar cases for engine with variable speed and load, with the final goal to include additional mechanisms that contribute to the engine cycle variations. 相似文献
32.
The anaerobic digestion (AD) performance of spent cow bedding was investigated with different hydrothermal pretreatment (HP) conditions. Spent cow bedding was pretreated with low temperatures (50, 70, and 90℃) and different pretreatment times (2-72 h) with ammonia and without ammonia. The results showed that spent cow bedding was a good raw material for AD. After pretreatment, the concentration of volatile fatty acids (VFAs) in the group of hydrothermal pretreatments with ammonia (HPA) was higher than that in the HP group at the same pretreatment temperature and time. The optimal pretreatment condition was achieved with an HPA of 50℃ holding for 72 h. At the optimal condition, the highest concentration of VFAs was 1.58-10.85 times higher than that of the other pretreated groups. The highest hemicellulose and lignin removal rates were 58.07% and 10.32%, respectively. The highest methane yield was 163.0 ml·(g VS)-1, which was 48.9% higher than that of the untreated group. The VFAs, pH, and reducing sugars showed positive relationships with the methane yield. Therefore, HP at low temperature can enhance the AD performance of spent cow bedding. 相似文献
33.
N.A.A. Fatah A.A. Jalil M.L. Firmansyah S. Triwahyono H.D. Setiabudi D.-V.N. Vo 《International Journal of Hydrogen Energy》2021,46(48):24676-24686
In this study, unique fibrous silica ZSM-5 was successfully synthesized by using three type of alcohol possessing different alkyl-chain length as the co-surfactant. The effect of diverse co-surfactant was observed in the changes of physical properties, such as crystallinity, inter-dendrimer distances and pore properties. According to the IR and temperature programmed desorption of ammonia (NH3-TPD) analyses, all catalysts exhibited different acid strengths which could be triggered by the different amount of additional silica species. All catalysts exhibited high catalytic performance in the hydrocracking of 1,3,5-triisopropylbenzene due to the absence of diffusion limitation. However, FZSM5C3 exhibited the highest catalytic activity which corresponded to its high number of Brønsted acid sites. It was observed that different length of co-surfactant alkyl-chain has resulted in different degree of oil penetration into the microemulsion system which subsequently triggered in various inter-dendrimer distances and amount of incorporated silica species. Hence, the altered physicochemical properties led to the difference in catalytic performance due to the presence of different number of Brønsted acid sites. 相似文献
34.
35.
《能源学会志》2020,93(6):2526-2535
The catalytic combustion and non-isothermal kinetics of bituminous coal by CeO2, Fe2O3, and NiO were investigated. The exothermic characteristics during catalytic combustion of bituminous coal were determined. Based on the Coats-Redfern method by introducing the function of kinetics mechanisms, the activation energies and pre-exponential factors of catalytic combustion of bituminous coal were estimated iteratively by regression. It is found that the catalysts promoted the transport of oxygen to the coal or char surface and effectively improved the combustion characteristics of bituminous coal. Under the same experimental conditions, the exothermic values were significantly increased and the catalysts of composite oxides exhibited higher exothermic values than pure metal oxide catalysts. The metal oxides significantly reduced the activation energies of bituminous coal combustion. SEM analysis presented that combustion residues became more porous with the addition of the catalyst. 相似文献
36.
37.
《Ceramics International》2020,46(8):11499-11507
In this study, NiCo2O4 with different morphologies were fabricated using carriers by homogeneous coprecipitation combined with a sintering method. The phase and microstructure were characterized by XRD, SEM, EDS, TEM and BET, and the catalytic performances were investigated by NaBH4 hydrolysis experiments. These studies revealed that the deposition morphology of NiCo2O4 can be adjusted by using different kinds of carrier templates, and the supported NiCo2O4 samples presented the pine-needle-like, network-like, ball-cactus-like and dandelion-like morphologies respectively. The optimal catalytic activity, durability and stability make the network-like NiCo2O4 an appropriate catalyst for hydrogen generation of NaBH4 hydrolysis. It was found that the network-like NiCo2O4 is the most reusable and durable catalyst for ten consecutive cycles and 100% hydrogen generation conversion rate without obvious decrease among these morphologies. 相似文献
38.
Synthesis,Characterization, and Catalytic Activity of Mn‐doped Perovskite Oxides for Three‐Way Catalysis 下载免费PDF全文
Mn‐doped La0.8Sr0.2CoO3 perovskite oxides (La0.8Sr0.2Co1–xMnxO3; x = 0, 0.1, 0.3, 0.5) were synthesized by a modified sol‐gel method. The phase‐pure oxides were obtained. CoO and carbonates were formed on the surface of La0.8Sr0.2CoO3. With increasing doping content, these impurities were reduced while the stability of the perovskite structure was improved. The valence state of B‐site ions and the amount of absorbed oxygen were influenced by Mn doping. The catalytic activity of the perovskite catalysts was investigated for CO oxidation and simultaneous removal of CO, C3H8, and NO. For CO and NO removal, La0.8Sr0.2Co0.9Mn0.1O3 exhibited the best performance. For C3H8 removal, the reactivity was promoted linearly with the doping content. The structure‐activity relationship is also discussed. 相似文献
39.
Combination of Reaction and Separation in Heterogeneous Catalytic Hydrogenation of Ethylformate 下载免费PDF全文
Gerson Martin Carla Pereira Frank Pettersson Henrik Saxén Dmitry Y. Murzin Alírio Rodrigues Tapio Salmi 《化学工程与技术》2015,38(5):804-812
Continuous hydrogenation reaction of ethyl benzoylformate was studied over a (–)‐cinchonidine (CD)‐modified Pt/Al2O3 catalyst. The catalyst showed a good stability, and high enantioselectivity was achieved in the fixed‐bed reactor. Chromatographic separation of (R)‐ and (S)‐ethyl mandelate originating from a post‐continuous hydrogenation reaction of ethyl benzoylformate over the (–)‐CD‐modified Pt/Al2O3 catalyst was investigated in the same reaction mixture. A commercial column filled with a chiral selector resin was chosen as a perspective preparative‐scale adsorbent. Since adsorption equilibrium isotherms were linear within the entire investigated range of concentrations, they were determined by pulse experiments for the isomers present in a post‐reaction mixture. Breakthrough curves were measured and described successfully by the dispersive plug‐flow model with linear driving force approximation. 相似文献
40.
Samia Tássia Andrade Maciel Alexander Andrey Lopes da Silva Yasmin Guimarães Pedro Cristiano Nunes da Silva Leôncio Diógenes Tavares Câmara João Monnerat Araújo Ribeiro de Almeida Emerson Schwingel Ribeiro Gabriel Francisco da Silva Lisiane Santos Freitas Donato Alexandre Gomes Aranda 《化学工程与技术》2020,43(11):2149-2159
The catalytic hydrolysis of soybean oil was used as an alternative for the production of monoglycerides (MG) and diglycerides (DG). The reactions were conducted in a stainless-steel tubular reactor in the temperature range of 240–290 °C, on niobium phosphate (NBP) and niobium oxide (NBO) as catalysts. In the hydrolysis reactions at 270 °C, the maximum selectivities of the products of interest were obtained at 22 % MG and 48 % DG for the reaction with NBP, and 7 % MG and 33 % DG with NBO, for 59 % and 36 % of triglyceride conversion in 10 min, respectively. The proposed kinetic model presented a good fit of the theoretical model with the experimental data, showing that the previous hypotheses considered for the mechanism development are suitable for describing the kinetics of soybean oil hydrolysis. 相似文献