Search Results (622)

This review comprehensively presents the development of energy-efficient pneumatic propulsion systems (PPSs) in road vehicle applications, which are classified as green vehicles. The advantages and disadvantages of PPSs were presented, and PPSs were compared with combustion propulsion systems (CPSs) and electric propulsion systems (EPSs), as well as their power-to-weight ratios (PWRs), energy densities, and CO₂ emissions. The review of compressed air vehicles (CAVs) focuses on their historical development and future prospects. This review discusses the use of PPSs with compressed air engines (CAEs) as an alternative propulsion system in green vehicles, providing a simple, energy-saving, and environmentally friendly solution. This review also discusses hybrid air propulsion, which, when combined with internal combustion engines (ICEs) or electric motors (EMs), offers innovative energy-efficient propulsion systems that are more economical than conventional hybrid propulsion systems. This review focuses on recent advances in lightweight air vehicles that improve vehicle handling, increase efficiency, and reduce propulsion energy consumption. Discussion of the study results concerns the use of PPSs in a three-wheeled rehabilitation tricycle (RTB). A comprehensive computation model of the RTB was presented, and the key performance parameters crucial to its operation were analyzed. The results of the RTB simulation were verified through field tests. Full article

Energy conservation and carbon reduction are critical in energy policies. Therefore, numerous energy-saving methods, such as the introduction of new technologies and the replacement of outdated equipment, have been proposed. To determine whether these methods are effective in energy conservation and carbon reduction, scientific validation is required. The most common validation method is energy baseline. An energy baseline refers to the use of data measured before energy-saving improvements. It is used to construct a mathematical model that describes energy consumption. Using the baseline, the energy consumption during the baseline period after improvements is calculated. By subtracting the measured consumption from the value, the amount of energy saved is estimated. Traditionally, linear regression is used to establish energy baseline prediction. However, linear regression has limitations with complex energy data. Therefore, we used deep learning models to handle nonlinear data in the air compression system for comparative analysis. The developed long-short-term memory (LSTM) model showed superior capabilities for processing nonlinear data, aligning with the actual data distribution, and reducing errors. Compared with linear regression models, the LSTM model reduced uncertainty, risk, and cost by 40.3%. Full article

In tropical regions like sub-Saharan Africa, conventional vapor compression HVAC systems contribute disproportionately to energy use, operating costs, and carbon emissions—particularly in coastal urban areas where humidity-driven cooling demand is extreme. Despite these challenges, viable low-energy alternatives remain largely underexplored for this region. This study presents the first simulation-based assessment of a desiccant indirect evaporative cooling (DIEC) system optimized for the hot–humid coastal climate of Dar es Salaam, Tanzania, addressing a critical gap in sustainable cooling research for coastal Africa. Using OpenStudio (version 3.9.0) and a custom EnergyPlus(version 9.3.0) latent heat removal algorithm, this study models a DIEC-equipped medium office building with 100% outdoor air ventilation and exhaust-air-based desiccant regeneration. The model reflects local construction practices, occupancy profiles, and weather data and is validated with >90% accuracy against experimental benchmarks. Results demonstrate that the DIEC system (1) maintains indoor thermal comfort (23.8–24.0 °C) during peak humidity periods, and (2) reduces annual cooling energy consumption by 10.2% relative to single-speed DX systems. These savings are particularly impactful in a context where electricity prices are rising, and HVAC loads consume 25–40% of building operational budgets. Furthermore, the system’s superior humidity control and stable power demand make it well-suited for integration with decentralized renewable energy sources. By establishing a context-specific benchmark for DIEC performance, this study delivers a novel, regionally tailored strategy for decarbonizing urban cooling in coastal tropical Africa. Full article

This article explores the possibility of diagnosing unwanted pressure drops in pneumatic systems. The proposed algorithm aims to distinguish the causes and location of their occurrence. The diagnostics clearly distinguish pressure drops caused by supply lines from those caused in the main or branch lines of an industrial pneumatic system. Pressure drops in pneumatic systems are one of the main causes of increased energy consumption. For the energy and resource optimization of pneumatic systems, it is essential to detect and locate the causes of pressure drops. This article proposes an approach for using the time diagrams of two measurable variables—flow rate and pressure—at the inlet of the end consumer (machine). Based on constant monitoring and a correlation relationship between the two time series, we determined indicators for detecting and locating unwanted pressure drops. In order to verify the proposed approach and the performed analysis, in general, we made observations of 16 real production machines and lines. Full article

The environmental impact of cement production is strongly associated with the high clinker content and its corresponding CO₂ emissions. This study examines the performance of low-emission cement mortars incorporating supplementary cementitious materials (SCMs), such as ground granulated blast-furnace slag (GGBFS) and fly ash, which partially replace clinker and contribute to CO₂ reduction. Six cement types (CEM I, CEM II/B-V, CEM II/B-S, CEM III/A, CEM V/A (S-V), and CEM V/B (S-V)) were assessed in 104 mortar formulations using a polycarboxylate-based superplasticizer, under varied curing temperatures (10 °C, 20 °C, 29 °C, and 33 °C). The present study is an experimental analysis of the impact of different plasticising and superplasticising admixtures on the demand for admixtures to achieve high flowability and low air content in cement-standardised mortar for admixture testing. PN-EN 480-1. The results indicate that mortars containing CEM III/A and CEM V/B (S-V) exhibited compressive strengths comparable to or superior to CEM I at 28 days, with strength gains exceeding 60 MPa at 20 °C. Workability retention at elevated temperatures was most effective in slag-rich cements. The plasticizing efficiency of the admixture decreased at temperatures above 29 °C, especially in fly ash-rich systems. The incorporation of SCMs resulted in an estimated reduction of up to 60% in clinker, with a corresponding potential decrease in CO₂ emissions of 35–45%. These findings demonstrate the technical feasibility of using low-clinker, superplasticized mortars in varying thermal environments, supporting the advancement of sustainable cementitious systems. Full article

Air separation units (ASUs) are power-intensive devices on the electricity demand side with significant potential for large-scale energy storage. Liquid air energy storage (LAES) is currently a highly promising large-scale energy storage technology. Coupling ASU with LAES equipment can not only reduce the initial investment for LAES, but also significantly lower the operating electricity costs of the ASU. This study proposes a novel modular-integrated process for coupling an externally compressed ASU (ECAS) with LAES. The core advantages of this integrated process are as follows: the liquefaction unit’s storage capacity is not constrained by the ASU surplus load capacity and it integrates cold, heat, electricity, and material utilization. Taking an integrated system with 40,000 Nm³/h oxygen production capacity as an example, under liquefaction pressure of 90 bar and discharge expansion pressure of 110 bar, the system achieves its highest electrical round trip efficiency of 55.3%. Its energy storage capacity reaches 31.32 MWh/10⁴ Nm³ O₂, exceeding the maximum capacity of existing energy storage systems of the ECAS by 1.7 times. Based on a peak-flat-valley electricity price ratio of 3.4:2:1, an optimal economic performance is attained at 100 bar liquefaction pressure, delivering a 7.21% in cost saving rate compared to conventional ASUs. The liquefaction unit’s payback period is 6.39 years—68.1% shorter than conventional LAES. This study aims to enhance both the energy storage capacity and economic performance of integrated systems combining ECAS with LAES. Full article

Compressed air energy storage in aquifers (CAESA) offers advantages of wide availability and low cost, but natural cracks in aquifers may initiate, propagate, and coalesce under mechanical fields, posing potential security risks for CAESA projects. Most previous research has predominantly addressed straight cracks, while folded cracks, which are commonly encountered in geological formations, remain insufficiently studied. This gap in understanding the mechanical behavior of brittle rocks with folded cracks under wetting conditions presents a critical challenge to ensuring the stability of CAESA operations. In this study, uniaxial compression tests were carried out on sandstone specimens with different crack inclination angles (β) and crack folded numbers (n) under wetting and drying conditions using the MTS 815 testing system combined with an acoustic emission system and digital image correlation system. The deformation behavior, peak strength, crack initiation, and coalescence modes under wetting conditions were comprehensively investigated and compared with those under drying conditions. It can be found that the peak strength increases with β (with the maximum peak strength at 1.59–3.44 times the minimum for the same n), while the effect of n is relatively minor (only 1.09–1.21 times variation); the peak strength under wetting conditions is consistently lower than that under drying conditions (all wet/dry strength ratios < 1). Six distinct crack initiation modes and two coalescence patterns were identified. These findings provide valuable insights into the failure mechanisms of brittle rocks containing folded cracks under varying moisture conditions, offering practical references for anti-cracking design and risk assessment of CAESA cavern structures. Full article

This study explores the impact of intake air cooling intensity, defined by heat exchanger effectiveness (HEE) and exhaust gas recirculation (EGR), on the energy and environmental performance of a turbocharged compression ignition (CI) engine. Experimental investigations were conducted on a 1.9-litre CI engine operating at 2000 rpm under three brake mean effective pressure (BMEP) conditions (0.2, 0.4, and 0.6 MPa), which correspond to part-load engine operation. HEE was varied at 0%, 50%, and 100%, in both EGR-on and EGR-off modes. Additional numerical simulations were carried out using AVL BOOST software to analyze combustion dynamics, including engine operating cycle modeling to validate the accuracy of the combustion analysis. The results demonstrate that increasing HEE significantly improves cylinder filling and excess air ratio, leading to enhanced combustion efficiency and lower in-cylinder temperatures. This, in turn, reduces specific NO_x emissions by approximately 40% with EGR and approximately 60% without EGR; however, under EGR-on conditions, the reduced combustion intensity leads to increased smoke and unburned hydrocarbon emissions—particularly at high cooling intensities. This effect is primarily associated with the engine control unit’s (ECU) limitations on intake air mass flow to maintain the target EGR ratio. Integrated control of HEE and EGR systems improves engine performance and reduces emissions across varying conditions, while highlighting trade-offs that inform the refinement of air management strategies. Full article

A brick kiln was experimentally studied to measure the transient temperature of hot gases and the compressive strength of the bricks, using pine wood as fuel, in order to evaluate the thermal performance of the actual system. In addition, a transient combustion model based on computational fluid dynamics (CFD) was used to simulate the combustion of natural gas in the brick kiln as a hypothetical case, with the aim of investigating the potential benefits of fuel switching. The theoretical stoichiometric combustion of both pine wood and natural gas was employed to compare the mole fractions and the adiabatic flame temperature. Also, the transient hot gas temperature obtained from the experimental wood-fired kiln were compared with those from the simulated natural gas-fired kiln. Furthermore, numerical simulations were carried out to obtain the transient hot gas temperature and NOx emissions under stoichiometric, fuel-rich, and excess air conditions. The results of CO₂ mole fractions from stoichiometric combustion demonstrate that natural gas may represent a cleaner alternative for use in brick kilns, due to a 44.08% reduction in emissions. Contour plots of transient hot gases temperature, velocity, and CO₂ emission inside the kiln are presented. Moreover, the time-dependent emissions of CO₂, H₂O, and CO at the kiln outlet are shown. It can be concluded that the presence of CO mole fractions at the kiln outlet suggests that the transient combustion process could be further improved. The low firing efficiency of bricks and the thermal efficiency obtained are attributed to uneven temperatures distributions inside the kiln. Moreover, hot gas temperature and NOx emissions were found to be higher under stoichiometric conditions than under fuel-rich or excess of air conditions. Therefore, this work could be useful for improving the thermal–hydraulic and emissions performance of brick kilns, as well as for future kiln design improvements. Full article

Modern aircraft increasingly utilizes highly integrated electronic equipment, driving continuously increasing heat dissipation demands. Vapor compression refrigeration systems demonstrate stronger alignment with future aircraft thermal management trends, leveraging their superior volumetric cooling capacity, high energy efficiency, and independence from engine bleed air. This paper reviews global research progress on aircraft vapor compression refrigeration systems, covering performance optimization, dynamic characteristics, control strategies, fault detection, and international development histories and typical applications. Analysis identifies emerging challenges under large-temperature-range cooling requirements, with comparative assessment establishing zeotropic mixture auto-cascade vapor compression refrigeration systems as the optimal forward-looking solution. Finally, recognizing current research gaps, we propose future research directions for onboard auto-cascade vapor compression refrigeration systems: optimizing refrigerant mixtures for flight conditions, achieving efficient gas-liquid separation during variable overloads and attitude conditions, and developing model predictive control with intelligent optimization to ensure reliability. Full article

The large-scale integration of volatile and intermittent renewables necessitates greater flexibility in the power system. Improving this flexibility is key to achieving a high proportion of renewable energy consumption. In this context, the scientific selection of energy storage technology is of great significance for the construction of new power systems. From the perspective of life cycle cost analysis, this paper conducts an economic evaluation of four mainstream energy storage technologies: lithium iron phosphate battery, pumped storage, compressed air energy storage, and hydrogen energy storage, and quantifies and compares the life cycle cost of multiple energy storage technologies. On this basis, a three-dimensional multi-energy storage comprehensive evaluation indicator system covering economy, technology, and environment is constructed. The improved grade one method and entropy weight method are used to determine the comprehensive performance, and the fuzzy comprehensive evaluation method is used to carry out multi-attribute decision-making on the multi-energy storage technology in the source, network, and load scenarios. The results show that pumped storage and compressed air energy storage have significant economic advantages in long-term and large-scale application scenarios. With its fast response ability and excellent economic and technical characteristics, the lithium iron phosphate battery has the smallest score change rate (15.2%) in various scenarios, showing high adaptability. However, hydrogen energy storage technology still lacks economic and technological maturity, and breakthrough progress is still needed for its wide application in various application scenarios in the future. Full article

The worldwide need for energy as well as environmental challenges have promoted the creation of sustainable power solutions. The combination of different working fluids is used for an organic Rankine cycle-powered vapor compression cycle (ORC-VCC) to deliver cooling applications. The selection of an appropriate working fluid significantly impacts system performance, efficiency, and environmental impact. The research evaluates possible working fluids to optimize the ORC-VCC system. Firstly, Artificial Neural Network (ANN)-derived models are used for exergy destruction ( E d t o t ) and heat exchanger total heat transfer capacity ( U A t o t ). Later on, multi-objective optimization was carried out using the acquired models for E d t o t and U A t o t using the Genetic Algorithm (GA) followed by the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The optimization results showcase Decane ORC-R600a VCC as the best candidate for the ORC-VCC system; the values of E d t o t and U A t o t were found to be 24.50 kW and 6.71 kW/K, respectively. The research data show how viable it is to implement biogas-driven ORC-VCC systems when providing air conditioning capabilities. Full article

Rail transit as a high-energy consumption field urgently requires the adoption of clean energy innovations to reduce energy consumption and accelerate the transition to new energy applications. As an energy-saving fluid machinery, the ejector exhibits significant application potential and academic value within this field. This paper reviewed the recent advances, technical challenges, research hotspots, and future development directions of ejector applications in rail transit, aiming to address gaps in existing reviews. (1) In waste heat recovery, exhaust heat is utilized for propulsion in vehicle ejector refrigeration air conditioning systems, resulting in energy consumption being reduced by 12~17%. (2) In vehicle pneumatic pressure reduction systems, the throttle valve is replaced with an ejector, leading to an output power increase of more than 13% and providing support for zero-emission new energy vehicle applications. (3) In hydrogen supply systems, hydrogen recirculation efficiency exceeding 68.5% is achieved in fuel cells using multi-nozzle ejector technology. (4) Ejector-based active flow control enables precise ± 20 N dynamic pantograph lift adjustment at 300 km/h. However, current research still faces challenges including the tendency toward subcritical mode in fixed geometry ejectors under variable operating conditions, scarcity of application data for global warming potential refrigerants, insufficient stability of hydrogen recycling under wide power output ranges, and thermodynamic irreversibility causing turbulence loss. To address these issues, future efforts should focus on developing dynamic intelligent control technology based on machine learning, designing adjustable nozzles and other structural innovations, optimizing multi-system efficiency through hybrid architectures, and investigating global warming potential refrigerants. These strategies will facilitate the evolution of ejector technology toward greater intelligence and efficiency, thereby supporting the green transformation and energy conservation objectives of rail transit. Full article

In this study, the thermal effectiveness of thermally conductive concrete pavements (TCPs) using silicon carbide (SiC) as a fine aggregate replacement was investigated, compared with that of ordinary Portland cement pavements (OPCPs). The most important purpose of this study is to improve the thermal performance of concrete pavement. Additionally, this study utilized improved thermal properties to enhance the efficiency of pavement heating to prevent icing and snow stacking. Both mixtures met the Korean standards for air content (4.5–6%) and slump (80–150 mm), demonstrating adequate workability. TCP exhibited a higher mechanical performance, with average compressive and flexural strengths of 42.88 MPa and 7.35 MPa, respectively, exceeding the required targets of a 30 MPa compressive strength and a 4.5 MPa flexural strength. The improved strength was mainly attributed to the filler effect and partly due to the van der Waals interactions of the SiC particles. Thermal conductivity tests showed a significant improvement in the TCP (3.20 W/mK), which was approximately twice that of OPCP (1.59 W/mK), indicating an enhanced heat transfer efficiency. In winter field tests, TCP effectively maintained high surface temperatures, overcoming heat loss and outperforming the OPCP. In the site experiment, thermal efficiency was clearly shown in the temperature at the center of the TCP, which was 3.5 °C higher than at the center of the OPCP at the coldest time. These improvements suggest that SiC-reinforced concrete pavements can be practically utilized for effective snow removal and ice mitigation in road systems. Full article

In recent years, pneumatic stages have attracted attention as stages for semiconductor manufacturing equipment due to their low cost and minimal maintenance requirements. However, pneumatic stages include nonlinear elements such as friction and air compressibility, making precise control challenging. To address this issue, this paper aims to achieve high-precision positioning by applying a nonlinear position control method to pneumatic stages. To achieve this, we propose a control method that combines filtered right coprime factorization and Prescribed Performance Control–Sliding Mode Control (PPC-SMC). Filtered right coprime factorization not only stabilizes and simplifies the plant but also reduces noise. Furthermore, PPC-SMC enables safer and faster control by constraining the system state within a switching surface that imposes limits on the error range. Through experiments on the actual system, it was confirmed that the proposed method achieves dramatically higher precision and faster tracking compared to conventional methods. Full article