Search Results (36)

Ensuring proper indoor air quality in high-rise apartment buildings is a crucial challenge, particularly when upgrading ventilation systems during deep energy renovation of existing buildings. This study evaluates the condition of existing ventilation systems and assesses the performance, cost, and energy efficiency of different mechanical ventilation solutions with heat recovery, including centralized and decentralized balanced ventilation with heat recovery, single-room ventilation units, and mechanical extract ventilation with heat pump heat recovery or without heat recovery. An onsite survey revealed significant deficiencies in existing ventilation systems, such as airtight window installations without dedicated fresh air valves, misaligned and decayed exhaust shafts, and inadequate extract airflow in kitchens and bathrooms. SWOT analyses for each system highlighted their strengths, weaknesses, opportunities, and threats, providing valuable insights for decision-makers. The results indicate that while centralized and decentralized mechanical ventilation with heat recovery enhances energy efficiency and indoor air quality in high-rise multifamily apartment buildings, challenges such as high installation costs, maintenance complexity, and architectural constraints must be addressed. Heat recovery with exhaust air heat pumps is a viable alternative for high-rise apartment buildings when more efficient options are not feasible. Full article

With the rapid growth of air travel, reducing carbon emissions in aviation is imperative. Electric aircraft play a key role in achieving sustainable aviation, especially for large civil aircraft, where reducing emissions, improving the fuel efficiency, and enabling flexible power regulation are essential. This study proposes a dual-shaft, separated-exhaust fuel cell hybrid aircraft propulsion system (HAPS), using a solid oxide fuel cell (SOFC) to replace the conventional turbine-driven compressor. The independent speed control of the high- and low-pressure spools is realized via a power distribution system. A thermodynamic model is developed, and performance evaluations, including parametric, exergy, and sensitivity analyses, are conducted. At the design point, the system delivers 36.304 kN thrust, 16.775 g/(kN·s) specific fuel consumption, 15.931 MW SOFC power, and 54.759% SOFC efficiency. The exergy analysis highlights the optimization of components like the heat exchanger and fan to reduce energy losses. The sensitivity analysis reveals that the spool speeds and fuel utilization significantly impact the performance. The findings provide valuable insights into optimizing control strategies and offer a novel, efficient, and low-carbon power solution for aviation, supporting the industry’s transition towards sustainability. Full article

Utilizing the intermediate air shaft for smoke exhaust is one of the crucial emergency ventilation methods in metro tunnel fires. To study the impact of metro tunnel slope on smoke exhaust performance of intermediate air shaft, this paper employs numerical simulation to conduct research from the following aspects: the longitudinal distribution of ceiling smoke temperature, visibility distribution, smoke layer height, and the smoke exhaust efficiency of intermediate air shaft. The results demonstrate that as the tunnel slope increases, the maximum ceiling temperature decreases, and the visibility at dangerous height increases. The smoke layer height on the downhill side of a sloped tunnel is higher than that of a horizontal tunnel, while the smoke layer height on the uphill side is lower. Under single-side smoke exhaust mode, the smoke exhaust efficiency of the 2# intermediate air shaft rises as the tunnel slope increases. However, under air supply plus smoke exhaust mode, the smoke exhaust efficiency of the 2# intermediate air shaft decreases with the growing tunnel slope. Full article

Turbine engines are currently one of the most important and expensive aircraft components. Both for economic and safety reasons, high engine reliability is required. Therefore, sophisticated methods are needed to determine their current condition. Diagnostics of turbine engines allow for the detection of faults before they lead to damage. The article presents methods and results of vibroacoustic diagnostics of a miniature GTM400 jet engine adapted to kerosene and hydrogen fuel supply. During thermal and vibroacoustic tests of engine parameters powered by hydrogen fuel supply, the engine seized up in the initial start-up phase due to improper control and rapid thermal changes in the gas line. The cause of the undesirable technical condition of the engine was a significantly higher temperature of gases (exhaust gases) affecting the working elements of the engine (turbine shaft, rotor, and blades), which consequently led to engine damage. This phenomenon and the results obtained from the unexpected technical condition constitute a valuable premise for considering the issue of proper operation of the turbojet engine during fuel changes, especially following current trends related to the decarbonization of the aviation sector. The obtained research results and the resulting observations and conclusions make it necessary to perform technical analyses and pre-implementation tests each time before allowing the use of a conventional engine if it undergoes the process of reconstruction in terms of using a new fuel (especially if its technical parameters are different from the originally used one). The presented method of conducting tests allows for a detailed determination of the causes of damage to the cooperating elements of the engine structure under the influence of changes in operating parameters. Full article

This paper presents the design and development of a proof of concept (PoC) open-source data logger system for wireless data acquisition via Wi-Fi aimed at bench testing and fault detection in combustion and electric engines. The system integrates multiple sensors, including accelerometers, microphones, thermocouples, and gas sensors, to monitor critical parameters, such as vibration, sound, temperature, and CO₂ levels. These measurements are crucial for detecting anomalies in engine performance, such as ignition and combustion faults. For combustion engines, temperature sensors detect operational anomalies, including diesel engines operating beyond the normal range of 80 °C to 95 °C and gasoline engines between 90 °C and 110 °C. These readings help identify failures in cooling systems, thermostat valves, or potential coolant leaks. Acoustic sensors identify abnormal noises indicative of issues such as belt misalignment, valve knocking, timing irregularities, or loose parts. Vibration sensors detect displacement issues caused by engine mount failures, cracks in the engine block, or defects in pistons and valves. These sensors can work synergistically with acoustic sensors to enhance fault detection. Additionally, CO₂ and organic compound sensors monitor fuel combustion efficiency and detect failures in the exhaust system. For electric motors, temperature sensors help identify anomalies, such as overloads, bearing problems, or excessive shaft load. Acoustic sensors diagnose coil issues, phase imbalances, bearing defects, and faults in chain or belt systems. Vibration sensors detect shaft and bearing problems, inadequate motor mounting, or overload conditions. The collected data are processed and analyzed to improve engine performance, contributing to reduced greenhouse gas (GHG) emissions and enhanced energy efficiency. This PoC system leverages open-source technology to provide a cost-effective and versatile solution for both research and practical applications. Initial laboratory tests validate its feasibility for real-time data acquisition and highlight its potential for creating datasets to support advanced diagnostic algorithms. Future work will focus on enhancing telemetry capabilities, improving Wi-Fi and cloud integration, and developing machine learning-based diagnostic methodologies for combustion and electric engines. Full article

Vertical shaft natural ventilation is a common smoke exhaust method in highway tunnel fires. This study investigated the vertical shaft natural smoke exhaust work in highway tunnel fires with the effect of multiple factors through numerical simulation. Using the analysis of the flow field of smoke in nearby areas of the vertical shaft and the quantitative calculation of the gas exhausted through the vertical shaft, considering the impact of shaft division and board height, an optimal vertical shaft arrangement was proposed, and the working conditions of this arrangement in low-pressure environments were discussed. The results show that dividing a single large vertical shaft into multiple small vertical shafts and appropriately adjusting the board height can reduce the incidence of vertical shaft plug holes and significantly enhance the vertical shaft smoke exhaust performance. Meanwhile, the board-coupled shaft (BCS) has excellent working ability in low-pressure environments, and when pressure drops, smoke exhaust efficiency will improve. This research offers a foundation and reference value for improving the vertical shaft smoke exhaust system in highway tunnels. Full article

High-temperature smoke generated by tunnel fires is the most important factor causing casualties. To explore the influence of natural wind on fire smoke movement in an extra-long highway tunnel based on the Taihang Mountain Tunnel, the distribution law of natural wind in the tunnel was obtained by on-site monitoring of the meteorological conditions at the tunnel site. A three-dimensional fire dynamics tunnel model considering an inclined shaft smoke exhaust was established, and the influence of natural wind on tunnel temperature distribution, smoke spread and smoke exhaust efficiency was studied. The results show that the natural wind speed of the Taihang Mountain Tunnel is mainly concentrated at 0~3 m/s. The main wind direction of the natural wind on the left tunnel is opposite to the driving direction, and the distribution probability of the main wind direction in each section is 81.27% and 72.15%, respectively. The main wind direction of the right tunnel is the same as the driving direction, and the distribution probability of the main wind direction in each section is 56.78%, 69.73%, 67.32% and 64.65%, respectively. The negative natural wind can inhibit the smoke spread downstream of the smoke exhaust port, but it is not conducive to the smoke exhaust. The positive natural wind promotes the smoke spread to the downstream of the smoke exhaust port, and the larger the natural wind speed, the longer the spread length. Natural wind reduces the smoke exhaust efficiency. For positive or negative natural wind with a guaranteed rate of 70%, the smoke exhaust efficiency is reduced by 27.76% and 15.59%, respectively, compared with the condition without natural wind. The research results can provide a useful reference for the design of fire smoke exhausts and smoke control schemes in extra-long highway tunnels. Full article

Lead recycling is very important for reducing environmental pollution risks and damages. Liquid lead is recovered from exhaust batteries inside stirred batch reactors; the process requires melting to be cleaned. Nevertheless, it is necessary to establish parameters for evaluating mixing to improve the efficiency of the industrial practices. Computational fluid dynamics (CFD) has become a powerful tool to analyze industrial processes for reducing operating costs, avoiding potential damages, and improving the equipment’s performance. Thus, the present work is focused on simulating the fluid hydrodynamics inside a lead-stirred reactor monitoring the distribution of an injected tracer in order to find the best injection point. Then, different injected points are placed on a control plane for evaluation; these are evaluated one by one by monitoring the tracer concentration at a group of points inside the batch. The analyzed reactor is a symmetrical, vertical batch reactor with two geometrical sections: one cylindrical body and a semi-spherical bottom. Here, one impeller with four flat blades in a shaft is used for lead stirring. The tracer concentration on the monitoring points is measured and averaged for evaluating the efficiency inside the tank reactor. Hydrodynamics theory and a comparison between the concentration profiles and distribution of tracer curves are used to demonstrate both methods’ similarities. Then, the invariability of the tracer concentration on the monitoring points is adopted as the main parameter to evaluate the mixing, and the best injection point is found as a function of the shortest mixing time. Additionally, the influence of the impeller rotation speed is analyzed as an additional control parameter to improve industrial practices. Full article

This study investigates the behavior of air supply in tunnels with multiple vertical shafts during fire incidents, focusing on natural ventilation dynamics. Numerical simulation is utilized to analyze the effect of different variables on air supply within vertical shafts. The findings reveal that the position of the smoke front significantly influences the direction and flow rate of gases during fire development. The mass flow rate of air supply during the stable fire development stage is influenced by the geometric size and positioning of vertical shafts, with shafts closer to the fire source exhibiting higher air flow rates. To address this issue, this study introduces a predictive model for estimating air flow rates in vertical shafts. This model exhibits a high level of accuracy when compared to simulations, offering a reliable method for predicting air flow rates based on the geometric characteristics of vertical shafts. Overall, this research contributes to understanding the complexities of air supply in tunnels with multiple vertical shafts, aiding in the improvement of natural ventilation strategies during fire incidents. Full article

This scientific article presents the results of computational fluid dynamics (CFD) simulations conducted using OpenFOAM to evaluate the effectiveness of a jet fan ventilation system in managing the dispersion of smoke resulting from a car fire incident within an underground car park spanning a total area of 21,670 m², situated in Tabriz, Iran. The primary objective of the study is to determine the velocity fields and evaluate visibility conditions within a 10 m radius to gauge the efficiency and effectiveness of the system. The study employs a smoke concentration production rate of 5.49 × 10⁻⁴ kg/m³s for simulations involving fire scenarios. A total of 17 fire scenarios are examined, each extending 30 m in all directions from the initial location. The research findings demonstrate that the placement of jet fan components plays a significant role in the system’s efficiency, with fans positioned near the ceiling leading to back-layering. To mitigate this issue, the recommended design solution involves the strategic installation of multiple jet fan arrays in specific zones with the addition of 10 extra jet fans, effectively curbing lateral smoke dispersion. Furthermore, the analysis of air flow rates shows that when jet fans direct an excessive airflow towards the exhaust shafts (which have a designated flow rate of 22.5 m³/s), recirculating flows occur, leading to the dispersion of smoke throughout the car park. Consequently, the utilization of low-velocity jet fans (11.2 m/s) proves to be more effective in clearing smoke compared to high-velocity jet fans (22.3 m/s). The study also emphasizes the importance of optimal positioning of supply and exhaust shafts to achieve effective smoke control, highlighting the need for placing them on opposite walls or minimizing airflow turns. Additionally, the research underscores the significance of fire resistance in jet fan units, as their failure during fire incidents can have severe consequences. Full article

Obtaining the best operating parameters of the internal combustion engine has focused the attention of designers and researchers since the first years of its creation. Initial research focused on increasing engine power and overall efficiency. As time passed, these aspirations became more sophisticated and began to concern other operating parameters of the drive unit. The basic problem, however, remained the improvement of filling the cylinder with the working medium. Turbocharger charging consists in using the energy of the exhaust gases to drive a turbine placed on a common shaft with a compressor supplying air under increased pressure to the cylinders. Over time, the turbocharger became one of the key elements and its technical condition began to play a key role in the operation and performance of modern drive units. Like every element, the turbocharger itself is not without its faults. This procedure is known among manufacturers who, when designing power units and their assemblies, pay special attention to the essence of turbocharger construction. Since it is impossible to predict all the phenomena accompanying a working turbocharger at the design stage, the authors of this paper conducted bench tests of a selected batch of turbochargers, focusing mainly on the vibration measurements of the turbocharger rotating assembly. At the same time, we present a dynamic model of the mentioned system based on the analyses resulting from the solutions of the equations of a numerical model. In order to give the research a practical aspect, the results of the theoretical research were compared with the results of bench tests. It has been shown that the basic problem is to guarantee the correct operating parameters of the bearings in the position of static and dynamic equilibrium. Obtaining such operating parameters requires finding a compromise solution, e.g., between the maximum temperature in oil films and the amplitudes of vibration accelerations in bearing nodes. The research results presented in the article can be used as a field for further discussion in the field of research on the reliability of turbochargers and be helpful in the design process in order to avoid design errors and reduce production costs. Full article

Over the past few years, fuel prices have increased dramatically, and emissions regulations have become stricter in maritime applications. In order to take these factors into consideration, improvements in fuel consumption have become a mandatory factor and a main task of research and development departments in this area. Internal combustion engines (ICEs) can exploit only about 15–40% of chemical energy to produce work effectively, while most of the fuel energy is wasted through exhaust gases and coolant. Although there is a significant amount of wasted energy in thermal processes, the quality of that energy is low owing to its low temperature and provides limited potential for power generation consequently. Waste heat recovery (WHR) systems take advantage of the available waste heat for producing power by utilizing heat energy lost to the surroundings at no additional fuel costs. Among all available waste heat sources in the engine, exhaust gas is the most potent candidate for WHR due to its high level of exergy. Regarding WHR technologies, the well-known Rankine cycles are considered the most promising candidate for improving ICE thermal efficiency. This study is carried out for a six-cylinder marine diesel engine model operating with a WHR organic Rankine cycle (ORC) model that utilizes engine exhaust energy as input. Using expander inlet conditions in the ORC model, preliminary turbine design characteristics are calculated. For this mean-line model, a MATLAB code has been developed. In off-design expander analysis, performance maps are created for different speed and pressure ratios. Results are produced by integrating the polynomial correlations between all of these parameters into the ORC model. ORC efficiency varies in design and off-design conditions which are due to changes in expander input conditions and, consequently, net power output. In this study, ORC efficiency varies from a minimum of 6% to a maximum of 12.7%. ORC efficiency performance is also affected by certain variables such as the coolant flow rate, heat exchanger’s performance etc. It is calculated that with the increase of coolant flow rate, ORC efficiency increases due to the higher turbine work output that is made possible, and the condensing pressure decreases. It is calculated that ORC can improve engine Brake Specific Fuel Consumption (BSFC) from a minimum of 2.9% to a maximum of 5.1%, corresponding to different engine operating points. Thus, decreasing overall fuel consumption shows a positive effect on engine performance. It can also increase engine power output by up to 5.42% if so required for applications where this may be deemed necessary and where an appropriate mechanical connection is made between the engine shaft and the expander shaft. The ORC analysis uses a bespoke expander design methodology and couples it to an ORC design architecture method to provide an important methodology for high-efficiency marine diesel engine systems that can extend well beyond the marine sector and into the broader ORC WHR field and are applicable to many industries (as detailed in the Introduction section of this paper). Full article

The intermittent hole-digging tree-planting machine shows a periodic short-time peak load law in planting operation, and the operation process is “idling” for small loads most of the time, leading to large torque fluctuations in the transmission system, unscientific power matching, and high energy consumption. To solve the above problems, this article proposes to use a series of energy-saving flywheels in the transmission system of the tree planting machine. On the premise of obtaining holes that meet the target young tree planting requirements, the optimal power compensation strategy for the flywheel system of the tree planting machine is studied to reduce torque fluctuations in the power transmission system, use smaller power drive units, and save energy. Firstly, the nonlinear multi-body dynamics simulation model of soil cutting by the hole-digging component is established. The boundary and contact conditions are set to simulate the power consumption of the hole-digging component at three rotating speeds. Based on the simulation results, the flywheel power compensation strategy is discussed, and the torque fluctuation of the flywheel balance system is analyzed. The results showed that the higher the speed, the greater the power consumption. The power value suddenly increased from 17.82 kW (1.28 s) to 27.93 kW (1.43 s) when the speed was 220 r/min. Then, the power value rapidly decreased, and the power consumption presented a short-term peak feature. The transmission system’s maximum input power is determined as 17.82 kW according to the various simulated power consumption characteristics. The part exceeding the power consumption is compensated by the energy storage flywheel. The total compensation energy was 2382.5 J. After the flywheel system was involved, the maximum output power of the tractor power output shaft decreased by 36.2%, and the peak torque decreased from 445.7 N·m to 285.1 N·m. The power consumption obtained from the field test and simulation was similar, but the energy required to overcome peak load was jointly provided by the flywheel and the engine. The actual input power of the power output shaft during the energy release period of the flywheel system was 18.51 kW when the rotating speed of the hole-digging component was 220 r/min, and the relative error with the simulation value was 2.43%. The measured actual speed reduction of the flywheel system was 8.9%. After installing an energy storage flywheel in the transmission system of the tree planting machine, the output power of the power unit can be stabilized. Tree planting machines can be equipped with smaller power units, which can reduce energy consumption and exhaust emissions. Full article

In this study, the aerodynamic performance of the exhaust system of a two-shaft gas turbine was investigated experimentally and numerically. The investigation focused on the system “Turbine Stage-Diffuser—Collector Box” and aimed to examine the impact of inlet conditions and geometry particularities on the efficiency of the exhaust system. The experiments were conducted on the Test Ring ET4 (Experimental Turbine-4) at the Peter the Great St.Petersburg Polytechnic University, which was equipped with a special diversion channel to examine the non-axisymmetric outlet of the exhaust duct. The collector box was designed to rotate by 180 degrees around the turbine axis to investigate its impact on the system’s performance. Flow traversing parameters were measured with the five-channel pneumatic pressure probes, and numerical simulations were performed with CFX 15.0. The RANS (Reynolds-averaged Navier–Stokes) equations were closed with the SST (k-ω) turbulence model (Shear Stress Transport model). The study concluded that the RANS SST model predicts the flow in the diffuser before the struts accurately. However, downstream the struts, the CFD (Computer fluid dynamic) results over-predicted the exhaust diffuser pressure recovery coefficient by 14% due to the complex vortex structure of the turbulent flow, which the Averaged Navier–Stokes equations did not resolve. The study highlights the importance of considering the last stage of the turbine, diffuser, and collector box as an integrated system when investigating the aerodynamics of exhaust ducts. The study also emphasizes the impact of geometry and inlet conditions on the exhaust diffuser’s performance and efficiency. The results of this study can be used to optimize the design of the exhaust system of two-shaft gas turbines and improve their thermal efficiency. The integrated approach of combining experimental and numerical methods can provide a detailed and reliable flow picture and can be used for future research in this area. Full article

Longitudinal ventilation and smoke extraction by shaft are common smoke control methods in road tunnel fires. Tunnels often adopt one of these methods in practical engineering. However, it may have a better effect to adopt the method of mixing the two smoke exhaust methods together, which has not been revealed in the previous literature. Hence, the coupled effects of longitudinal ventilation and natural ventilation with shafts on the smoke control in tunnel fires were studied in this work. Numerical simulation was carried out considering different longitudinal ventilation velocities (0–4 m/s) and 4 kinds of typical shaft arrangements (shaft lengths range of 3–12 m, shaft intervals range of 27–60 m). The smoke spread length and smoke exhaust efficiency were analyzed systematically. Results show that (1) with the increase in longitudinal ventilation velocity, the total smoke spread length firstly decreases (V < 1 m/s) and then keeps almost constant (1 m/s < V < 2 m/s), finally increasing significantly (V > 2 m/s). (2) The length of the dangerous area (over 60 °C) at human height is basically 0 for all cases (except for Scenario 4 of shaft arrangement) when the longitudinal ventilation velocity is less than 2 m/s. (3) The CO smoke flow rate through the shaft is relatively high when the longitudinal ventilation velocity is within the range of 1–2 m/s for 4 kinds of shaft arrangement scenarios. Factors such as smoke spread and smoke exhausted through the shaft are comprehensively considered to judge smoke exhaust performance. The following conclusions can be drawn: when the ventilation velocity ranges from 1–2 m/s, it has a positive impact on the smoke control in tunnel fires with natural ventilation with shafts. When the ventilation velocity exceeds 2 m/s, the total smoke spread length and the length of the danger area increase, and the smoke stratification becomes worse, which brings inconvenience to rescue work. The results can provide reference for the design of fire protection in tunnels. Full article