Energy Science & Engineering最新文献

In this study, nonaxisymmetric endwall contouring technology is employed as a passive control strategy to enhance the stable operating range of a centrifugal compressor with an asymmetric volute. The endwall contouring method is applied to the hub-side wall of the vaned diffuser within a centrifugal compressor stage. Instead of utilizing a flat hub as the baseline diffuser, various diffuser configurations featuring hub-side contoured endwalls are explored, with adjustments in the peak radial position and peak height of the convex and concave profiles. Numerical simulations are conducted to evaluate the performance of the centrifugal compressor stage with both the baseline and contoured vaned diffusers. The investigation explores the underlying flow control mechanisms and establishes the effective endwall contouring guidelines. The findings highlight the effectiveness of endwall contouring in enhancing the stable operating range of centrifugal compressors. Notably, a substantial enhancement of 15.1% in the stable operating range is achieved by employing the contoured diffuser with the peak radial position near the vane leading edge (LE) and the peak height at 20% of the vane height. The endwall contoured diffusers reduce the positive LE incidence angles to direct the fluid toward the suction side (SS), and increase the radial velocity near the SS to suppress the hub-suction corner separations in the diffuser passages near the volute tongue. These improvements collectively contribute to the enhancement of diffuser flow characteristics. Finally, a set of effective endwall contouring guidelines is proposed to guide the endwall contouring design for enhancing the stable operating range of centrifugal compressors.

Hybrid oils ensure multifaceted technological (self-lubricating and favorable fatty acid properties), and sustainable (environmental, economic, and societal) benefits towards biodiesel conversions. The hybrid oils (Hydnocarpus wightiana oil and waste cooking oils [40:60 v/v]) were synthesized to methyl ester with alkaline catalyst sodium hydroxide through the base-transesterification process. The resulting hybrid oil methyl ester (HOME) is 96.68%. The crude oil (CO) and its HOME underwent characterization using gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, and hydrogen-1 nuclear magnetic resonance spectroscopy. The physicochemical properties of crude oils and hybrid biodiesel were analyzed and compared to pure diesel. Different blends of biodiesel–diesel, including binary (20% HOME + 80% diesel [D]), ternary (60% D + 20% HOME + 20% heptanol [H]), and quaternary (20% HOME + 20% H + 10% CO + 50% D) blends, were tested in a single-cylinder compression ignition (CI) engine under various load conditions to assess their performance, emissions, and combustion properties. Experimental findings indicate that the addition of heptanol to diesel or hybrid biodiesel (ternary blend) enhances brake thermal efficiency, reduces brake-specific fuel consumption, and leads to longer ignition delays, resulting in higher internal combustion pressure and thermal energy release rates compared to the quaternary blend. Additionally, compared to pure diesel, the ternary blend exhibits decreased emissions of carbon monoxide (CO) and hydrocarbon (HC), with a slight increase in nitrous oxide (NO_x) and carbon dioxide (CO₂). Notably, the ternary blend emerges as a distinct alternative biodiesel blend suitable for direct use in CI engines without requiring any engine modifications.

To solve the problem of controlling the stability of small coal pillars under the mining disturbance of the adjacent working face, the fourth panel 403 and 404 working faces of the Gaojiabao coal mine with two mining roadways is taken as the object of this research. The comprehensive research method of combining mechanical theory analysis, coal dynamic disturbance experiments and field engineering practice was adopted. First, the analysis determined the magnitude and frequency of fracture-related disturbance loading on the overburden roof of the working face; next, the strain and stress threshold indicators of the coal body, sensitive to the external disturbance load of 10³ J magnitude (continuous disturbance deformation), were tested and obtained through a self-developed rock creep disturbance experimental system, and the stress threshold indicators of coal body specimens sensitive to creep disturbance were defined as the long-term strength. Then, a coal pillar-roof mechanics structure model was established in the premining and postmining areas of the working face, and the overlying support pressure on the coal pillar body was analysed. Finally, a small coal pillar composite reinforcement support technology with ‘two-way buttressing anchor cable for pressure reinforcement + steel pipe concrete pier column + overhead roof break’ was designed to ensuring that the coal pillar body would not be destabilised by cumulative disturbance and large deformation under disturbance. According postmining area support capacity calculations, the support loading acting on the coal pillar is approximately 17593 kN, with the stress being 2.93 MPa; and the factor of safety is approximately 1.23. After engineering practice application of this approach, the vertical deformation of the small coal pillar body and side heave disturbance deformation were effectively controlled during the working face mining disturbance, the vertical deformation of the reinforced coal pillar was only 187 mm, and the side heave deformation was finally stabilised at approximately 124 mm, which maintained good stability.

The combustion cycle-to-cycle variations (CCV) are the typical combustion phenomena in the internal combustion engine, which will not only affect the combustion efficiency, heat-work conversion process, and emission formation in the cylinder, but also cause the output torque and power fluctuation, resulting in unstable and even misfire. These phenomena are particularly evident in the spark ignition (SI) engine, especially at idle, acceleration, and high exhaust gas recirculation conditions. Consequently, it is quite important to explore the internal relationship and correlation mechanism between the CCV and the affecting factors. This paper comprehensively reviewed the fundamental reasons and mechanisms of CCV of the SI engine. In addition, the characteristic parameters and characterization methods of the CCV, the laws and influencing factors of the CCV, and the numerical simulation methods of the CCV were introduced in detail to quantitatively analyze the performance, combustion, and emissions characteristics of the SI engine. Each research direction is discussed in detail in various sections. The research status of the CCV of the SI engine from the experimental and numerical simulation aspects was also presented and discussed. Lastly, effective methods and strategies were proposed to improve the combustion process and fuel economy, and reduce exhaust emissions of the SI engine for high efficiency and clean combustion.

In recent years, as the energy market continues to change, an emerging business model is gradually emerging as an energy provider (EP). The participation of EP as an independent entity in the distribution network investment model not only helps realize a win–win situation for multiple stakeholders but also promotes the innovation and sustainable development of the energy industry. However, in the energy system, EPs, grids, microenergy grids (MEGs), and shared energy storage service providers usually belong to different stakeholders, and their respective pursuit of profit maximization can easily lead to uncontrolled competition, which greatly reduces market efficiency. To address the varying ownership structures within the energy system, a refined bilevel coordinated optimization operation model is introduced, rooted in the master–slave game theory. In this model, the EP assumes the role of the master, while the MEG operator and the shared energy storage operator (SESO) act as slaves. A peer-to-peer energy-sharing mechanism between MEGs and an energy trading mechanism between MEGs and shared energy storage is used to further increase the local consumption rate of new energy. Simulation results demonstrate that the proposed method not only boosts the revenues of an EP, SESO, and MEG operators but also effectively accounts for the MEG's energy storage needs and SESOs' profitability.

This study presents a strategy for preventing and controlling rockbursts in deep and vast seams during the mining operation. We analyzed the main factors influencing rockburst by combining the geological structure of the rock mass with field-collected microseismic monitoring data. Determined the disturbance strain sensitive threshold through mechanical experiments on coal's antidisturbance characteristics, the indoor pull-out test of the supporting bolt was carried out. Studied the rockburst support technology and the antirockburst capability of the support system based on the energy method. The key governing variables of regional impact risk in the big buried deep coal seam operating face include high tectonic stress, goaf effect, fault, and fault protection coal pillar. The uniaxial compressive strength of the coal sample in the 3308 working face is 15.11 MPa, the antidisturbance strength is 10 MPa. When the extreme stress is 86.03%, the specimen fails; the ultimate failure strength under disturbance is 13 MPa. The support system's antishock ability is analyzed based on its energy absorption, under the premise of ensuring the support quality and support strength, the antiscour ability of 3308 Tailentry support meets the anti-impact requirements. It is believed that the system offers adequate lateral confining pressure for the internal creep disturbance-sensitive area, enhancing the area's resistance to disturbance. This is crucial in preventing and managing rockburst incidents.

Huff-n-puff (HnF) is a crucial technology for effectively enhancing the oil recovery (EOR) of tight oil reservoirs. Soaking period is the primary platform for injection medium interacting with formation fluid and reservoir rock in HnF. Elucidating the micro-percolation mechanism of the soaking period is immensely significant for guiding oilfield production practices. The present study established a physical simulation method combining HnF experiments with nuclear magnetic resonance to reveal the microscopic percolation mechanisms, including water, fracturing fluid, and surfactant. Furthermore, the impacts of soaking time, HnF cycles, wettability, and pore structure on oil recovery degree were quantified. The results demonstrate the crucial significance of wettability and pore structure in the soaking period. The dominant mechanism during water HnF in reservoirs characterized by well-connected pore networks and minimal clay pores is micropore imbibition, while conversely, macropore displacement plays a predominant role. The oil recovery degree of fracturing fluid HnF primarily relies on mitigating solid-fluid forces within macropores. The surfactant HnF in preferential water- and oil-wet reservoirs is primarily governed by oil films stripped from macropore walls and micropore imbibition, respectively. Specifically, water and fracturing fluid HnF are suitable for shorter soaking time and fewer HnF cycles, whereas the surfactant HnF exhibits an inverse relationship.

Anaerobic digestion of abundant feedstock from biomaterials is a good innovative fossil fuel alternative approach for the synthesis of green fuel (biogas). Rotatable central composite design (CCD) and machine learning (ML) via Python coding were successfully used to design, optimize, and predict the rate of biogas production from stew-rice and eggs digestate with Udara seeds in an anaerobic unit. Two-input parameters, such as inoculation ratio (S/I) and hydraulic reaction time (HRT) were considered, resulting in 13 experimental setups under mesophilic surroundings of 25–34°C. Mixture ratios of substrate/inoculum (S/I) of 0.98:1, 1.5:1, 2.75:1, 2.75:1, 4:1, 1.5: 1, and 4.52:1 were used against 30, 20, 44.14, 15.86, 40, 40, and 30 days HRT as modeled by CCD rotatable to optimize biogas production from crushed Udara seeds with spoilt stew-rice and eggs digestate. From the results, it was observed that the coefficient of determination (R²) of 0.9573 was generated via CCD rotatable whereas, the R² of 1 was generated from the multivariate regression of ML approach. Also, the data and graphs derived via ML were superior to the ones derived from CCD rotatable. However, the maximum output of 4.84 L at 4 mixing ratio and 40 days HRT from CCD rotatable is close to the ML value of 4.89 L under the same input factors, yet ML yielded more. Thus, it is clear that the Python-based ML algorithm approach has the potential to predict biogas output better than CCD rotatable. However, the Gas Chromatography Mass Spectrometry analysis of the highest output produced generated 63.29% biomethane and 26.71% CO₂ by volume and produced a flashpoint of −167°C which is flammable. Thus, the generated biogas via an anaerobic unit can be transmitted into large-scale commercial applications for the betterment of mankind.

Hydrogen, as an energy carrier, is attractive to many stakeholders based on the assumption that the extensive global network of natural gas infrastructure can be repurposed to transport hydrogen as part of a zero-carbon energy future. Therefore, utility companies and governments are rapidly advancing efforts to pilot blending low-carbon hydrogen into existing natural gas systems, many with the goal of eventually shifting to pure hydrogen. However, hydrogen has fundamentally different physical and chemical properties to natural gas, with major consequences for safety, energy supply, climate, and cost. We evaluate the suitability of using existing natural gas infrastructure for distribution of hydrogen. We summarize differences between hydrogen and natural gas, assess the latest science and engineering of each component of the natural gas value chain for hydrogen distribution, and discuss proposed solutions for building an effective hydrogen value chain. We find that every value chain component is challenged by reuse. Hydrogen blending can circumvent many challenges but offers only a small reduction in greenhouse gas emissions due to hydrogen's low volumetric energy density. Furthermore, a transition to pure hydrogen is not possible without significant retrofits and replacements. Even if technical and economic barriers are overcome, serious safety and environmental risks remain.

An improved method of clutch coordinated control based on the Kalman filter was proposed to solve the problem that the existing mode switching strategy of hybrid electric vehicles could not adapt to engine temperature changes and clutch wear. First, taking advantage of the relationship between the torque transmitted by the clutch and the starting resistance of the engine, combined with the characteristics of the clutch, the clutch wear was roughly calculated. Accordingly, the control strategy of the clutch in the existing mode switching was improved to adapt to the clutch wear. The adaptive control strategy proposed for clutch wear included the fuzzy control module of the initial engagement pressure, the fuzzy inference module of the clutch engaging pressure change, the clutch wear estimation module and so on. Second, the Kalman filter was used to process the results to improve the estimation accuracy of clutch wear. The engine starting resistance related to starting speed and temperature was modeled to enhance the adaptability of the control strategy to engine temperature. Finally, the designed control strategy was verified in simulation. The results show that the improved control strategy can complete the mode switching when the engine temperature is variable and the clutch is worn. The maximum impact degree increased from 5 m/s³ without wear to 8.5 m/s³ with wear, but it is still less than the index limit, and it can be considered that the proposed strategy can achieve the desired control effect. The fuzzy control algorithm proposed enhances the vehicle's ride comfort during mode switching from pure electric driving to hybrid driving.