Search Results (43)

A methodology for the development of nonlinear model predictive control for thermal management of a 40-ton fuel-cell heavy-duty truck is presented, using the medium-temperature cooling circuit as a case study. The approach integrates control-oriented modeling, parameter estimation, and experimental validation based on drivetrain test bench measurements under controlled high-temperature ambient conditions. A lumped-parameter model of the medium-temperature circuit, including coolant, oil, electric motors, and power-electronics auxiliaries, is derived and implemented in a Simulink environment, with heat-transfer parameters calibrated from test bench data and radiator air-side resistance and fan characteristics derived from CFD simulations and manufacturer specifications, respectively. Model parameters are identified using a systematic estimation procedure and the resulting model is validated against long-duration roller test measurements, achieving coefficients of determination above R² = 0.9 and normalized RMSE values below 10% for all key temperatures. The validated model is then used as the prediction model in a model predictive controller that manipulates radiator fan and coolant-pump speeds, while treating component heat losses, vehicle speed and ambient temperature as measured disturbances. The controller is evaluated in a model-in-the-loop environment for representative long-haul and urban driving cycles and different ambient temperatures, and its performance is benchmarked against conventional rule-based and PI-based control strategies. Depending on the driving cycle and ambient conditions, the proposed NMPC reduces cooling system energy consumption by up to 39.6% compared to a PI controller (VECTO Urban Delivery cycle, 35 °C ambient), with an average reduction of 16.6% across all investigated driving cycles and ambient conditions, without a significant increase in average or maximum coolant temperature. The proposed methodology provides a transferable workflow for developing predictive thermal management control in fuel-cell heavy-duty vehicles and other complex automotive cooling systems. Full article

Vapor compression refrigeration systems account for substantial global electricity consumption, and improving compressor efficiency offers significant potential for energy conservation and climate change mitigation. Linear compressor technology, particularly moving magnet configurations, has attracted attention for its oil-free operation and reduced friction losses, yet comprehensive experimental data under realistic refrigeration cycle conditions remain limited. This study experimentally evaluates the operational characteristics and performance of a moving magnet linear compressor integrated into a complete R134a vapor compression refrigeration system. The investigation systematically varies compressor load from 65% to 85% and pressure ratio from 2.0 to 3.5 while maintaining a fixed condenser temperature of 45 °C. Key parameters, including resonant frequency, piston offset, matching capacitance, power input, mass flow rate, motor and volumetric efficiencies, refrigerant mass distribution, cooling capacity, and coefficient of performance (COP) were measured and analyzed. Results indicate that piston offset remains nearly constant under varying compressor loads, fluctuating around 0.39 mm, but increases by 36% as pressure ratio rises from 2.0 to 3.5, necessitating careful pressure ratio control to prevent mechanical interference. Motor efficiency decreases from 87.7% to 82.4% as the compressor load increases, suggesting favorable part-load operation for domestic energy consumption reduction. This potential remains to be verified through long-term cyclic tests and a full annual energy assessment. The condenser consistently stores over 70% of the refrigerant charge, with distribution most sensitive to operating condition changes. Cooling capacity reaches a maximum of 434.6 W at 85% load and a pressure ratio of 2.0, while the COP achieves approximately 4.5 under the same conditions and decreases to 2.4 at a pressure ratio of 3.5. Normalized COP remains relatively stable at approximately 0.33 across the tested conditions. These experimental findings provide a robust baseline for the design, integration, and control of moving magnet linear compressors in energy-efficient refrigeration applications. Full article

Biodiesel fuel produced through transesterification is mainly used in blends with conventional diesel fuel (D100). The analysis of the combustion process parameters for each specific biodiesel fuel represents the basis for a rational approach to the utilization of available motor fuel quantities. In this study, the differential and cumulative heat release laws during the combustion of D100 and blends of biodiesel fuel made from waste grape seed oil and D100 were analyzed. In addition, the engine efficiency and economy for the cases of using the aforementioned fuels were analyzed. The tests were conducted on a single-cylinder, air-cooled diesel engine with direct fuel injection. The engine testing was conducted for two engine loads; that for which the brake was a mean effective pressure of 4.2 bar, and for the full load, that for the brake was a mean effective pressure of 5.6 bar at engine speeds of 1635 rpm, 1937 rpm, and 2239 rpm. All experimental work was conducted for conventional diesel fuel D100 and for biodiesel diesel blends B7 and B14. The combustion rates of D100, a blend containing 7% of biodiesel by volume (B7), and a blend containing 14% of biodiesel by volume (B14) were examined. However, the higher combustion rate of the B14 blend, particularly during the combustion of the first 50% of the fuel mass per cycle, could have a positive impact on the fuel economy of the working cycle and the brake thermal efficiency (BTE). The maximum heat release rates for D100, B7, and B14 at full load and an engine speed of 2239 rpm are 115.65 J/deg, 148.01 J/deg, and 152.99 J/deg, respectively. At full load and engine speeds of 1635 rpm and 2239 rpm, the brake thermal efficiencies (BTEs) for D100, B7, and B14 were 0.301, 0.285, and 0.296 and 0.281, 0.273, and 0.277, respectively. Under other tests, the highest BTE was observed for the B14 blend. Therefore, from the perspective of brake thermal efficiency (BTE), the most favorable blend for application is B14. Full article

Potato harvesters operating in hilly and mountainous areas are often subjected to harsh working conditions such as high temperature, sun exposure, and high torque excavation. Due to the fluid sealing characteristics, closed loop hydraulic systems are prone to high temperatures during long-term continuous operation, resulting in a decrease in fluid viscosity, poor lubrication, severe wear, and power attenuation. This study investigates the hydraulic system of potato harvesters in hilly terrain, systematically analyzing its energy transfer process and identifying key heat-generating components. Based on an optimization strategy that extends the flow path of high-temperature fluid within the tank, four distinct tank designs were proposed. Computational fluid dynamics (CFD) and thermodynamic simulations were conducted to evaluate their heat dissipation performance, followed by full-machine validation testing. Results indicate that the walking and lifting systems are the primary heat sources. The dual pump contributes the highest proportion of heat (52.07%), followed by the walking motor (20.54%). The heat exchanger dissipates 72.91% of the heat, while the hydraulic oil tank accounts for 14.93%. Among the four tank designs, Tank 0 exhibited the fastest temperature rise, reaching a thermal equilibrium of 83.27 °C, whereas Tank 1 had the lowest equilibrium temperature (78.62 °C). Heat dissipation efficiencies for the tanks were 7.8%, 12.9%, 10.1%, and 11.6%, respectively. The residual gas volume fraction decreases significantly as the bubble diameter increases, due to the higher buoyancy and faster rise velocity of larger bubbles, which leads to shorter residence times and more effective precipitation. Tank 1 achieved the lowest equilibrium temperature, indicating the best thermal efficiency. Tank 3 showed the best overall degassing performance, particularly for medium-to-large bubbles. Tank 1 was selected as the optimal final design because it could offer an excellent balance, with very good cooling and competitive degassing (especially for small bubbles). Field tests confirmed a 14.8% reduction in thermal equilibrium temperature for Tank 1 (75.6 °C) compared to Tank 0 (88.7 °C). Simulation and experimental data showed strong agreement, with maximum errors of 9.2% for return fluid temperature, 12.7% for cooling return fluid temperature, 9.7% for pressure, and 8.5% for flow rate. Average errors remained below 8.4% for pressure and 7.6% for flow rate. These results validate the accuracy of the simulation model and the effectiveness of the tank optimization method. Full article

Efficient cooling systems are crucial for achieving high efficiency and power density in electric vehicle motors. To enhance motor cooling performance, a novel oil spray cooling system was developed, referred to as the centripetal-inclined oil spray (CIOS) cooling system. The CIOS cooling system features axial oil channels evenly distributed on the surface of the stator core, with each channel connected at both ends to stepped oil channels. This configuration allows for direct oil spraying towards the center at specific inclined angles without the need for additional components such as nozzles, oil spray rings, and oil spray tubes, which reduces costs, minimizes the risk of oil leakage, and enhances motor reliability. Electromagnetic and computational fluid dynamic simulations were conducted on the motor with the CIOS cooling system. The results indicated that the CIOS cooling system adversely impacted core losses and torque, while these effects were minimized after optimization, with losses increasing by up to 0.29% and torque decreasing by up to 0.45%. The CIOS cooling system achieved stable oil spraying, forming oil films on the end-winding with a maximum formation rate of 49.4% and an average thickness of 1.56 mm. Compared to the motor with oil spray rings, the motor with the CIOS cooling system exhibited lower temperatures across all components and more uniform cooling. Finally, the cooling performance of the CIOS cooling system was verified through experiments, and the results showed that the measured temperature closely matched the simulated results, with a maximum error of 5.9%. The findings in this study are expected to provide new insights for optimizing oil cooling systems in electric vehicle motors. Full article

In the present work, a direct oil cooling strategy using a multi-nozzle configuration is proposed for the thermal management of high-power density electric machines. The stator and winding temperatures, heat transfer coefficient, injection pressure, and power consumption are investigated for different nozzle types, nozzle numbers, heights of nozzle combinations, and oil flow rates. In addition, an artificial neural network (ANN) model based on two algorithms is developed for predicting thermal performance under various operating conditions. The flat jet nozzle shows the lowest maximum winding temperature of 120.3 °C and a superior heat transfer coefficient of 3028.6 W/m²-K compared to both full cone nozzles. The power consumption for the flat jet nozzle is higher at 123.9 W compared to other nozzle types. The combination of four flat jet nozzles shows improved oil spray distribution and enhanced cooling compared to combinations of two and six flat jet nozzles. Further, the thermal performance of oil spray cooling with four flat jet nozzles improves when height and oil flow rate are increased. Oil spray cooling with the best configuration shows a winding temperature, heat transfer coefficient, and injection pressure of 98.9 °C, 3408.6 W/m²-K and 4.86 bar, respectively, at a flow rate of 20 LPM. The proposed neural network model with a Levenberg–Marquardt (LM) training variant and logarithmic–sigmoidal (Log) transfer function shows the lowest prediction error within ±2%. Full article

The continuous pursuit of power density, efficiency, and miniaturization poses significant challenges to the heat dissipation and temperature-rise control of permanent magnet synchronous motor (PMSM) for new energy vehicles. This paper proposes a novel S-shaped axial return passage in the motor casing and a combined oil-cooling scheme integrating S-shaped and end-spraying passages. The geometric structure and parameters of the S-shaped passage and end-spraying passage were designed and optimized, and a finite-element temperature-field model of a PMSM equipped with the combined oil-cooling system is established. The results show that, compared with a traditional right-angle axial returning passage, the pressure loss of the new S-shaped returning passage is reduced by 50%, while the wall heat transfer coefficient remains comparable. At a cooling oil flow rate of 12 L/min, the highest temperature of the end winding is 92.6 °C, only 1.5 °C higher than that of the stator core under rated operating conditions. An experimental prototype was fabricated, and the measured results indicate that the simulated end-winding temperature shows close agreement with the experimental values, with a maximum deviation of only 3.8 °C. The proposed combined oil-cooling scheme efficiently enhances the cooling of both the stator core and end winding and significantly improves the temperature uniformity of the PMSM. Full article

This study investigates the thermal performance of an oil-jet-cooled permanent magnet synchronous motor (PMSM), with a particular focus on end-winding heat dissipation. A high-fidelity numerical model that preserves the full geometric complexity of the end-winding is developed and validated against experimental temperature data, achieving average deviations below 7%. To facilitate efficient parametric analysis, a simplified equivalent model is constructed by replacing the complex geometry with a thermally equivalent annular region characterized by calibrated radial conductivity. Based on this model, the effects of key spray ring parameters—including orifice diameter, number of nozzles, inlet oil temperature, and flow rate—are systematically evaluated. The results indicate that reducing the orifice diameter from 4 mm to 2 mm lowers the maximum winding temperature from 162 °C to 153 °C but increases the pressure drop from 205 Pa to 913 Pa. An optimal nozzle number of 12 decreases the peak winding temperature to 155 °C compared with 162 °C for 8 nozzles, while increasing the oil flow rate from 2 L/min to 6 L/min reduces the peak winding temperature from 162 °C to 142 °C. Furthermore, a non-uniform spray ring configuration decreases maximum stator, winding, spray ring, and shaft temperatures by 5.6–9.2% relative to the baseline, albeit with a pressure drop increase from 907 Pa to 1410 Pa. These findings provide quantitative guidance for optimizing oil-jet cooling designs for PMSMs under engineering constraints. Full article

As the popularity of electric vehicles (EVs) continues to increase, the need for effective and efficient driveline lubricants and dielectric coolants has become crucial. Commercially used mineral oils or synthetic ester-based coolants, despite performing satisfactorily, are not environmentally friendly. The fatty esters of vegetable oils, after overcoming their shortcomings (like poor oxidative stability, higher viscosity, and pour point) through chemical modification, have recently been used as potential dielectric coolants in transformers. The benefits of natural esters, including a higher flash point, breakdown voltage, dielectric character, thermal conductivity, and most importantly, readily biodegradable nature, have made them a suitable and sustainable substitute for traditional coolants in electric transformers. Based on their excellent performance in transformers, research on their application as dielectric immersion coolants in modern EVs has been emerging in recent years. This review primarily highlights the beneficial aspects of natural esters performing dual functions—cooling as well as lubricating, which is necessary for “wet” e-motors in EVs—through a comparative study with the commercially used mineral and synthetic coolants. The adoption of natural fatty esters of vegetable oils as an immersion cooling fluid is a significant sustainable step for the battery thermal management system (BTMS) of modern EVs considering environmental safety protocols. Continued research and development are necessary to overcome the ongoing challenges and optimize esters for widespread use in the rapidly expanding electric vehicle market. Full article

The efficiency of electric motors is highly dependent on their operating temperature, with lower temperatures contributing to enhanced performance, reliability, and extended service life. This study presents a comprehensive review of state-of-the-art cooling technologies and evaluates their impact on the thermal behavior of a commercial motor–generator system in high-demand applications. A baseline model of a permanent magnet synchronous motor (PMSM) was developed using MotorCAD 2023^® software, which was supported by reverse engineering techniques to accurately replicate the motor’s physical and thermal characteristics. Subsequently, multiple cooling strategies were simulated under consistent operating conditions to assess their effectiveness. These strategies include conventional axial water jackets as well as advanced oil-based methods such as shaft cooling and direct oil spray to the windings. The integration of these systems in hybrid configurations was also explored to maximize thermal efficiency. Simulation results reveal that hybrid cooling significantly reduces the temperature of critical components such as stator windings and permanent magnets. This reduction in thermal stress improves current efficiency, power output, and torque capacity, enabling reliable motor operation across a broader range of speeds and under sustained high-load conditions. The findings highlight the effectiveness of hybrid cooling systems in optimizing both thermal management and operational performance of electric machines. Full article

One of the challenges of our age is climate change and the ways in which it affects the Earth’s global ecosystem. To face the problems linked to such an issue, the international community has defined actions aimed at the reduction in greenhouse gas emissions in several sectors, including the aviation industry, which has been requested to mitigate its environmental impact. Conventional aircraft propulsion systems depend on fossil fuels, significantly contributing to global carbon emissions. For this reason, innovative propulsion technologies are needed to reduce aviation’s impact on the environment. Electric propulsion has emerged as a promising solution among the several innovative technologies introduced to face climate change challenges. It offers, in fact, a pathway to more sustainable air travel by eliminating direct greenhouse gas emissions, enhancing energy efficiency. Unfortunately, integrating electric motors into aircraft is currently a big challenge, primarily due to thermal management-related issues. Efficient heat dissipation is crucial to maintain optimal performance, reliability, and safety of the electric motor, but aeronautic applications are highly demanding in terms of power, so ad hoc Thermal Management Systems (TMSs) must be developed. The present paper explores the design and optimization of a TMS tailored for a megawatt electric motor in aviation, suitable for regional aircraft (~80 pax). The proposed system relies on coolant oil injected through a hollow shaft and radial tubes to directly reach hot spots and ensure effective heat distribution inside the permanent magnet cavity. The goal of this paper is to demonstrate how advanced TMS strategies can enhance operational efficiency and extend the lifespan of electric motors for aeronautic applications. The effectiveness of the radial tube configuration is assessed by means of advanced Computational Fluid Dynamics (CFD) analysis with the aim of verifying that the proposed design is able to maintain system thermal stability and prevent its overheating. Full article

Permanent magnet synchronous motors for electric vehicles (EVs) prioritize high power density and lightweight design, leading to elevated thermal flux density. Consequently, cooling methods and heat conduction in stator windings become critical. This paper proposes a compound cooling structure combining direct oil spray cooling on stator windings and housing oil channel cooling (referred to as the winding–housing composite oil cooling system) for permanent synchronous motors in EVs. A systematic design methodology for oil jet nozzles and housing oil channels is investigated, determining the average convective heat transfer coefficient on end-winding surfaces and the heat dissipation factor of the oil channels. Finite element analysis (FEA) was employed to simulate the thermal field of a 48-slot 8-pole oil-cooled motor, with further analysis on the effects of oil temperature and flow rate on motor temperature. Based on these findings, an optimized oil-cooled structure is proposed, demonstrating enhanced thermal management efficiency. The results provide valuable references for the design of cooling systems in oil-cooled motors for EV applications. Full article

Direct liquid cooling technology has the potential to enhance the thermal management performance of electric motors with continuously increasing energy density. However, direct liquid cooling technology has practical limitations for full-scale commercialization. In addition, the conventionally used indirect liquid cooling imposes higher thermal resistance to cope with the increased thermal management performance of high power density electric motors. Therefore, this study proposes a hybrid direct–indirect oil cooling system as a next-generation cooling strategy for the enhanced thermal management of high power density electric motors. The heat transfer characteristics, including maximum winding, stator and motor housing temperatures, heat transfer coefficient, friction factor, pressure drop, and performance evaluation criteria (PEC), are investigated for different spray hole diameters, coolant oil volume flow rates, and motor heat loss levels. The computational model was validated with experimental results within a 5% error developed to evaluate heat transfer characteristics. The results show that spray hole diameter significantly influences cooling performance, with a larger diameter (1.7 mm) reducing hydraulic resistance while causing a slight increase in motor temperatures. The coolant oil volume flow rate has a major impact on heat dissipation, with an increase from 10 to 20 L/minute (LPM) reducing winding, stator, and housing temperatures by 22.05%, 22.70% and 24.02%, respectively. However, higher flow rates also resulted in an increased pressure drop, emphasizing the importance of the selection of a suitable volume flow rate based on the trade-off between cooling performance and energy consumption. Despite the increase in motor heat loss level from 2.6 kW to 8 kW, the hybrid direct–indirect oil cooling system effectively maintained all motor component temperatures below the critical threshold of 180 °C, confirming its suitability for high-performance electric motors. These findings contribute to the development and commercialization of the proposed next-generation cooling strategy for high power density electric motors for ensuring thermal stability and operational efficiency. Full article

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications. Full article

Electrification has become increasingly common in aerospace due to climate change concerns. After successful applications in general aviation aircraft, electrification is now addressing subregional (up to 19 passengers) and regional aircraft (around 80 passengers). Megawatt-class electric motors are needed both to drive propellers and to act as high-power generators in hybrid–electric propulsion systems. Power levels for this class of aircraft require a proper design of heat management systems capable of dissipating a much higher quantity of heat than that dissipated by traditional cooling systems. The technical solution here explored is based on the addition into a diathermic base liquid of nanoparticles, which can increase (by up to 30%) the thermal conductivity of the refrigerant, also providing large surface area enhancing the heat transfer capacity of base liquids. The Italian Aerospace Research Centre (CIRA), as part of the European research initiative Optimised Electric Network Architectures and Systems for More-Electric Aircraft (ORCHESTRA), developed a thermal management system (TMS) based on impinging jets technology for a 1 MW electric motor. In this work, a numerical verification of the possibility for nanofluids to improve the heat exchange efficiency of a submerged oil impinging jets TMS designed to directly cool the inner components of a 1 MW motor is conducted. Investigations aimed to analyse two nanoparticle types (alumina and graphite) added to diathermic oil with concentrations between 1% and 5% by volume. The application of nanofluids significantly increases final thermal conductivity with respect to conventional coolants, a 60% improvement in heat transfer at a fixed mass flow rate is achieved. Electric motor maximum temperatures are approximately 10% lower than those achieved with solely diathermic oil. This result is significant as a safety margin is needed in all cases where a sudden increase in power occurs. Full article