Part Load Conditions Research Articles

In-Situ Efficiency Estimation of Induction Motors Using Whale Optimization Algorithm

Abstract: This paper investigates the in-situ efficiency prediction of induction motors using four optimization algorithms: genetic algorithm (GA), particle swarm optimization (PSO), whale optimization algorithm (WOA), and red fox optimization algorithm (RFO). Experimental evaluations were conducted on three induction motors with power ratings of 22 kW, 30 kW, and 132 kW under varying load conditions (25%, 50%, 75%, and 100%). The performance of the algorithms is tested not only under full load conditions but also under partial load conditions. This is an important requirement, given that motors usually do not run at full load in real-world applications. The algorithms were assessed based on their convergence behavior, accuracy, and experimentally measured efficiency values. The results revealed that the performance of the algorithms varies depending on the motor power and load level. While WOA is more successful at medium and high loads, PSO stands out at low loads. While GA provides higher accuracy, especially at full load on an motor, the performance of RFO varies according to the load level. In general, the performance of WOA and RFO stands out to some extent. The study demonstrates the advantages of non-intrusive methods for motor efficiency prediction that eliminate the need for direct shaft power measurements. It also offers practical benefits in industrial applications, such as reducing downtime and improving energy management. Cite this article as: M. Göztaş, M. Çunkaş, and M.A. Şahman, “In-situ efficiency estimation of induction motors using whale optimization algorithm,” Turk J Electr Power Energy Syst., 2025; 5(2), 114-124.

On the effect of draft tube rod protrusion on runner blade stress fatigue of single-regulated axial turbines

Under off-design and transient operations of hydraulic turbines, these machines are subjected to harmful pressure fluctuations originating from the presence of vortical flow. These oscillations increase stress-induced fatigue damage on the turbine runner, shortening turbine life and reducing its reliability. This study investigates how cylindrical rods in the draft tube affect the runner blade strains and their consequent fatigue damage during transient and off-design steady-state operations. Different part-load conditions of an axial model turbine and two transients between speed-no-load and best efficiency point were experimentally studied using time-resolved pressure and runner blade strain measurements. The proposed adjustable flow control technique effectively reduced the runner damage, particularly at lower loads where reductions as high as 70% were obtained. In addition, draft tube pressure data were used for fatigue estimation, and a correlation with blade stress damage was observed at lower loads where high-amplitude load cycles occurred. The results showed that different protrusion lengths should be used function of the prevailing operating condition to obtain optimal damage reductions with lower efficiency penalties. Therefore, the proposed technique can provide an adjustable solution that mitigates off-design pressure oscillations and their consequent damage while limiting efficiency losses.

Mitigation of Unsteady Excitation in a Large Vertical Centrifugal Pump Under Flow Instability Via Novel Diffuser Configurations

Abstract Hydraulic excitation under flow instability threatens the operational safety of large vertical centrifugal pumps (LVCP), which are crucial in long-distance water transfer systems. This study uses delayed detached eddy simulation (DDES) to examine the unsteady excitation behavior of LVCP with two novel radial vaned diffuser designs, diffuser B and diffuser C. Diffuser B integrates large and small hydrofoil vanes, while diffuser C features a gradually varying hydrofoil layout. Simulation results reveal diffuser B postpones the head drop compared to diffuser A, while diffuser C exhibits the highest and most consistent head under part-load conditions. Diffuser C also reduces pressure pulsation intensity by up to 53.54% and low-frequency pulsations by 57.87%, especially at low flow rates. While diffuser B shows limited improvement in excitation forces, diffuser C not only markedly reduces the pulsation intensity of the excitation force but also mitigates the imbalance of radial excitation force in the circumferential direction, particularly under deep stall conditions with a maximum reduction of ΔFR to 80 N. Internal flow analysis indicates that the nonuniform pressure rise from the inlet to the outlet of diffuser A is the primary cause of pressure pulsation and excessive radial excitation force. The incremental hydrofoil vane assembly in diffuser C significantly reduces velocity variations across different blade spans and enhances the uniformity of pressure distribution. Additionally, diffuser C effectively suppresses large-scale vortex rotational propagation in the flow channel. These improvements collectively contribute to better control of unsteady hydraulic excitation in LVCP under unstable operating conditions.

Unsteady Flow Analysis Inside an Electric Submersible Pump with Impeller Blade Perforation

The electric submersible pump (ESP) is a critical component in subsurface resource extraction systems, yet the presence of gas in the working medium significantly affects its performance. To investigate the impact of impeller perforation on gas–liquid mixing and internal flow characteristics, unsteady numerical simulations were conducted based on the Euler–Euler multiphase flow model. The transient evolution of the gas phase distribution, flow behavior, and liquid phase turbulent entropy generation rate was analyzed under an inlet gas volume fraction of 5%. Results show that under part-load flow conditions, impeller perforation reduces the amplitude of dominant frequency fluctuations and enhances periodicity, thereby mitigating low-frequency disturbances. Under design flow conditions, it leads to stronger dominant frequencies and intensified low-frequency fluctuations. Gas phase distribution varies little under low and design flow rates, while at high flow rates, gas accumulations shift from the midsection to the outlet with rotor rotation. As the flow rate increases, liquid velocity rises, and flow streamlines become more uniform within the channels. Regions of high entropy generation coincide with high gas concentration zones: they are primarily located near the impeller inlet and suction side under low flow, concentrated at the inlet and mid-passage under design flow, and significantly reduced and shifted toward the impeller outlet under high flow conditions. The above results indicate that the perforation design of ESP impellers should be optimized according to operating conditions to improve gas dispersion paths and flow channel geometry. Under off-design conditions, perforations can enhance operational stability and transport performance, while under design conditions, the location and size of the perforations must be precisely controlled to balance efficiency and vibration suppression.

Dynamic mode decomposition based investigation of unsteady flow characteristics and pressure pulsations in centrifugal pumps operating under partial load conditions for scientific advancement

Dynamic mode decomposition based investigation of unsteady flow characteristics and pressure pulsations in centrifugal pumps operating under partial load conditions for scientific advancement

Validation of a Numerical Model for an Axial Hydraulic Turbine Operating at Upper and Lower Part-Load Conditions

Validation of a Numerical Model for an Axial Hydraulic Turbine Operating at Upper and Lower Part-Load Conditions

Development and validation of a quasi-steady-state linear Element-by-Element cooling coil model in wet and dry part-load conditions

Development and validation of a quasi-steady-state linear Element-by-Element cooling coil model in wet and dry part-load conditions

Integrated Control Strategies of EGR System and Fuel Injection Pressure to Reduce Emissions and Fuel Consumption in a DI Engine Fueled with Diesel-WCOME Blends and Neat Biodiesel

A wide experimental campaign was developed on an automotive turbocharged diesel engine, using two blends between diesel oil and waste cooking oil methyl esters (WCOME) and neat biodiesel. A conventional B7 diesel oil was considered as a reference fuel. The two blends, respectively, included 40 and 70% of WCOME, on a volumetric basis. The influence of biodiesel was analyzed by testing the engine in two part-load operating conditions, applying proper control strategies to the exhaust gas recirculation (EGR) circuit and rail pressure, to assess the interactions between the engine management and the tested fuels. The variable nozzle turbine (VNT) was controlled to obtain a constant level of intake pressure in the two experimental points. Referring to biodiesel effects at constant operating mode, higher WCOME content generally resulted in better efficiency and soot emission, while NOX emission was negatively affected. EGR activation allowed for limited NO formation but with penalties in soot emission. Furthermore, interactions between the EGR circuit and turbocharger operations and control led to higher fuel consumption and lower efficiency. Finally, the increase in rail pressure corresponded to better soot emission and penalties in NOX emission. Combining all these effects, the selection of EGR rate and rail pressure values higher than the standard levels resulted in better efficiency, NOX, and soot emissions when comparing blends and neat biodiesel to conventional B7, granting advantages not only with regard to greenhouse gas emissions. Combustion parameters were also assessed, showing that combustion stability and combustion noise were not negatively affected by biodiesel use. Combustion duration was reduced when using WCOME and its blend, even if the center of combustion was slightly shifted along the expansion stroke. The main contribution of this investigation to the scientific and technical knowledge on biodiesel application to internal combustion engines is related to the development of tests on diesel–biodiesel blends with high WCOME content or neat WCOME, identifying their effects on NOX emissions, the definition of integrated strategies of HP EGR system, fuel rail pressure, and VNT for the simultaneous reduction in NOX and soot emissions, and the detailed assessment of the influence of biodiesel on a wide range of combustion parameters.

Energy Saving in Building Air-Conditioning Systems Based on Hippopotamus Optimization Algorithm for Optimizing Cooling Water Temperature

When traditional HVAC (heating, ventilation, and air-conditioning) systems are in operation, they often run according to the designed operating conditions. In fact, they operate under part-load conditions for more than 90% of the time, resulting in energy waste. Therefore, studying the optimization and regulation of their operating conditions during operation is necessary. Given that the control set point for cooling tower outlet water temperature differentially impacts chiller and cooling tower energy consumption during system operation, optimization of this parameter becomes essential. Therefore, this study focuses on optimizing the cooling tower outlet water temperature control point in central air-conditioning systems. We propose the Hippopotamus Optimization Algorithm (HOA), a novel population-based approach, to optimize cooling tower outlet water temperature control points for energy consumption minimization. This optimization is achieved through a coupled computational methodology integrating building envelope dynamics with central air-conditioning system performance. The energy consumption of the cooling tower was analyzed for varying outlet water temperature set points, and the differences between three control strategies were compared. The results showed that the HOA strategy successfully identifies an optimized control set point, achieving the lowest combined energy consumption for both the chiller and cooling tower. The performance of HOA is better compared to other algorithms in the optimization process. The optimized fitness value is minimal, and the function converges after five iterations and completes the optimization in a single time step when run in MATLAB in only 1.96 s. Compared to conventional non-optimized operating conditions, the HOA strategy yields significant energy savings: peak daily savings reach 4.5%, with an average total daily energy reduction of 3.2%. In conclusion, this paper takes full account of the mutual coupling between the building and the air-conditioning system, providing a feasible method for the simulation and optimization of the building air-conditioning system.

Effect of Stratified Charge Combustion Chamber Design on Natural Gas Engine Performance

This study investigates the performance and combustion behavior of a spark ignition engine retrofitted to operate on compressed natural gas (CNG), with a focus on a newly developed stratified charge pre-chamber design. The engine was modified to include an auxiliary intake valve that enables partial enrichment of the pre-chamber mixture without the need for a dedicated fuel injector. This hybrid approach combines the mechanical simplicity of passive systems with the enhanced combustion control of active pre-chambers. Both experimental tests and computational fluid dynamics (CFD) analyses were carried out under partial load conditions (8 Nm) and engine speeds ranging from 900 to 1700 rpm. The results demonstrate improvements in indicated mean effective pressure (IMEP), combustion stability, and flame propagation speed—particularly at lower engine speeds where stratified combustion effects are more pronounced. However, increasing engine speed resulted in reduced volumetric efficiency and elevated exhaust temperatures, indicating potential for further optimization via turbocharging or advanced scavenging techniques. Overall, the findings validate the effectiveness of the proposed design in enhancing thermal efficiency and ignition stability in CNG-fueled engines, especially under urban driving conditions.

Part-load performance of a pure H 2 /O 2 gas turbine cooled by steam from a bottoming-cycle

Hydrogen energy is one of the most attractive renewable resources for mitigating environmental problems and achieving a zero-emission future. Hydrogen-fueled gas turbine power generation is one of the most promising technologies to utilize hydrogen energy. Due to the peak shaving tasks, hydrogen-fueled gas turbines often deviate from the design operating point. Therefore, in this paper, an analysis of the part load performance of a cooled three-spool pure hydrogen-fueled gas turbine for the R-Graz cycle is implemented. Both the mainstream working medium and coolant are steam. Considering the complex physical properties of steam, a novel equation for the evaluation of the mixing loss caused by film cooling is proposed to improve the accuracy of the assessment. Within the load range of 50% to 100%, the results indicate that the isentropic efficiency is dependent on the uncooled polytropic expansion and cooling process. Coolant consumption analysis under part load conditions reveals that the power turbine consumes more than half the coolant, while the high-pressure turbine uses less than 20%. The coolant consumption proportion of the three rotors basically does not change with the load. At last, the coolant cooling technology is considered to improve the total isentropic efficiency and reduce the coolant consumption.

Thermodynamic Evaluation of the Hybrid Combined Cycle Power Plant in the Valley of Mexico

Modern power generation aims to maximize the extraction of thermal energy from fossil fuels to produce electricity. Combined cycle power plants, leaders in efficiency, sometimes require an additional steam generator to compensate for insufficient exhaust gas energy in the heat recovery steam generator (HRSG), leading to hybrid combined cycles. This study presents a comprehensive thermodynamic analysis of the hybrid combined cycle power plant located in the Valley of Mexico, operating under both full-load and partial-load conditions. The investigation begins with an energy analysis evaluating key performance parameters under real operating conditions, including the power generation, heat flow supply, thermal efficiency, fuel consumption rates, steam flow, and specific fuel consumption. Subsequently, the analysis examines the performance of the steam cycle using the β factor, which quantifies the relationship between heat flows in the steam generator and the HRSG, to maintain a constant steam flow. This evaluation aims to determine the potential utilization of exhaust gas residual energy for partial steam flow generation in the steam turbine. The study concludes with an exergy analysis to quantify the internal irreversibility flows within the system components and determine the overall exergy efficiency of the power plant. The results demonstrate that, under 100% load conditions, the enhanced utilization of exhaust gases from the HRSG leads to fuel savings of 33,903.36 tons annually and increases the exergy efficiency of the hybrid combined cycle power plant to 54.08%.

Off-design performance control and simulation for gas turbine engines with sequential combustors

A gas turbine engine with a sequential combustion system has the potential to offer high cycle efficiency at moderate turbine entry temperatures. Consequently, it has one more degree of power setting control, which offers more flexible but also more complex control of engine off-design operations. In this paper, a novel simulation method for off-design thermodynamic performance of sequential combustion gas turbines has been introduced and a novel performance control schedule for part-load operations at various ambient conditions have been proposed aiming to keep the relative workloads between the two turbine sections constant. The proposed control schedule is simple and can be adapted easily. By applying the off-design performance control schedule to a model industrial gas turbine engine with two sequential combustors, the performance of the model engine is simulated at different part-load and at different ambient conditions. The results show that by applying the proposed off-design performance control schedule, the model sequential combustion gas turbine engine could operate effectively at different part-load operating conditions and at different ambient conditions with both turbine sections keeping nearly constant workload distributions.

Numerical analysis of pollutant formation and exhaust emission in a short annular combustor under part load operation

Abstract Emission characteristic of a single annular gas turbine combustor has been studied at engine part-load conditions from idle to max power setting. Under fuel-rich condition. The temperature field and pollutant formation at different power settings are studied in detail. The equivalence ratio varies from 0.35 corresponding idle power setting to maximum 1.1 at max power setting at take-off condition. Concentration of major pollutant species at combustor exit such as NOx, CO, CO2, soot, unburned hydrocarbons and water vapor are analyzed for varying inlet conditions and primary zone equivalence ratios at different power settings using model in ANSYS CFX. The pollutant concentrations are found to be increased at combustor exit with increase in power setting as equivalence ratio and flame temperature increase. The numerical predictions at low regime of power setting are validated against gas sampling data obtained from actual combustor testing in aerothermal test facility. The numerical analysis based on satisfactory validation with limited experimental data is very reasonable and provides input for prediction of pollutant emissions of the intended derivative engine during the landing-takeoff (LTO) cycle prior to engine test.

Numerical study on pressure fluctuations in a variable speed pump-turbine with head variations

Abstract Grid regulation capacities of Pumped Storage Hydropower Plants (PSHPs) are of great importance for today’s and future power supply systems. In this context, variable speed technologies provide solutions for enhanced operational flexibility of PSHP units. Especially for turbine operation with variable head and part load conditions, the adaptation of the rotational speed offers benefits in terms of hydraulic efficiency, mitigation of pressure fluctuations and accordingly the fatigue behavior of hydromechanical components. The present work deals with numerical assessments of the pressure fluctuations on the runner of a 5 MW reversible Francis pump-turbine prototype equipped with a Full Size Frequency Converter (FSFC). The study aims to asses the impact of head and rotational speed on the pressure fluctuations at different load levels. Three power levels with a speed variation of ± 12% are investigated by single phase unsteady CFD simulations considering two different net head values with a variation of 20%. The numerical results give some insights on the scalability of the pressure fluctuations on the runner at the different operating conditions. It is demonstrated that rotor-stator interaction (RSI) related fluctuations are well scalable. Important transposition errors are found for low frequency fluctuations and stochastic content which is partially explainable by the limited statistical information provided by the numerical results. Finally it is shown that important mitigation of the pressure fluctuations can be achieved at deep part load conditions thanks to variable speed.

Performance analysis and flow loss mechanisms in large vertical centrifugal pumps: Effects of guide vane wrap angles and blade number configurations

This study investigates the flow characteristics and energy loss mechanisms in large vertical centrifugal pumps through entropy production theory and Q-criterion analysis, focusing on the effects of guide vane wrap angles and blade numbers. Numerical simulations reveal that optimal hydraulic performance occurs at a guide vane configuration of nine blades with a 48° wrap angle. Entropy production analysis demonstrates that turbulent entropy production and wall entropy production are dominant in the pumps, with the turbulent entropy production significantly exceeding the wall entropy production. The wrap angle significantly influences guide vane and volute performance, while showing limited impact on impeller efficiency. Increasing the wrap angle enhances flow control within the guide vane, reducing flow separation, and local turbulent entropy production. Conversely, reducing blade numbers induces flow channel blockage, increasing turbulence intensity in the downstream volute and elevating hydraulic losses in the guide vane, volute, and impeller under partial load conditions. Higher blade numbers improve flow rectification and enhance impeller–volute interaction, albeit at the cost of increased turbulent kinetic energy and frictional losses in the guide vane. These findings provide critical insight into flow-energy loss mechanisms and establish a theoretical foundation for optimizing guide vane structural design in large vertical centrifugal pumps, with potential applications in energy-efficient pump system development.

Analytical approach for Francis turbine part load resonance risk assessment

Abstract Francis turbines operating at part load conditions experience cavitating vortex rope in the draft tube resulting from the swirling flow at the runner outlet. This cavitating vortex rope induces convective and synchronous pressure fluctuations at the rope precession frequency. The pressure fluctuating synchronous component, comprised between 0.2 and 0.4 times the turbine rotational speed, can be addressed as a draft tube pressure source forced excitation of the entire hydraulic system including the turbine itself. The synchronous component propagates through the entire hydraulic circuit and may lead to hydroacoustic resonance if the part load excitation frequency matches with one of the hydraulic system natural frequencies or even the natural frequencies of the synchronous generator. The paper presents a simplified analytical method to assess the resonance risk of the hydraulic system at early stage of a project. This method is based on a first estimation of the hydraulic system natural frequencies which is achieved from hydroacoustic properties of the hydraulic system such as pipe length, cross section area and wave speed. The cavitating draft tube is modelled with equivalent wave speed representative of the cavitation compliance and with a hydraulic inductance representative to the draft tube water inertia. The accuracy of this method is evaluated by comparison with a detailed 1D SIMSEN software frequency analysis, enabling to determine the eigen frequencies and eigen mode shapes of the hydraulic system, considering 3 different Francis turbine hydraulic layouts in terms of tailrace tunnel’s length and diameter. The simplified methodology provides reasonably good results to identify potential risk of resonance at early stage of the project. The proposed analytical method for the assessment of the Francis turbine part load resonance risk is nowadays included as ANNEXE E.3 of the technical specification of the new IEC Technical Specification 62882 ED1 entitled “Hydraulic machines – Francis turbine pressure fluctuation transposition” which was issued in 2020-09.

Comparative Evaluation of the Effect of Exhaust Gas Recirculation Usage on the Performance Characteristics and Emissions of a Natural Gas/Diesel Compression-Ignition Engine Operating at Part-Load Conditions

The use of natural gas as an alternative fuel in dual-fuel compression-ignition engines can lead to a substantial reduction in the majority of pollutant emissions compared to fossil fuels, while the thermal efficiency of the engine can be maintained at adequate levels. Its usage has increased widely in recent years, and significant efforts have been made to investigate the inherent physical and chemical processes that take place during this engine’s combustion, as well as the parameters that affect the operation of the engine and use natural gas as energy source. The scope of this study is to investigate the effect of EGR temperature (cold and hot) and rate (10% and 20%) on the performance characteristics and emissions of a dual-fuel compression-ignition engine operating at a specific engine operating point under dual-fuel (diesel–natural gas) conditions. For this reason, a phenomenological two-zone combustion model was developed. The results of the model were validated against the experimental data obtained from a single-cylinder direct-injection, turbocharged compression-ignition dual-fuel research engine operated under part-load conditions (IMEP = 0.52 Mpa and engine speed = 1500 rpm) and at various replacement percentages of diesel using methane (which was treated as a natural gas surrogate). The model results were in good agreement with the experimental results, revealing the ability of the model to be used in the aforementioned EGR analysis. The results of the study revealed that engine operation with 10% cold EGR does not significantly affect the engine performance characteristics, and combined with the addition of 80% gaseous fuel energy, can lead to a substantial reduction in NO and soot emissions, with a moderate increase in CO emissions. On the other hand, a significant finding of the present work is that engine operation with hot EGR under the investigated operating conditions, even though it had a beneficial effect on NO-specific emissions, led to a reduction in engine efficiency and may raise issues regarding the mechanical strength of the engine.

Large-eddy simulations of Francis turbine flow control by radial jets

Francis turbine operation often experiences part load conditions, at which precessing vortex core (PVC) and double-helix structures can occur, limiting the stable operation range. The study investigates the mitigation of these flow instabilities in a Francis turbine air model by implementing radial jet injection. This approach is based on linear stability analysis and its adjoint formulation, revealing sensitive flow areas. Manipulating these zones can significantly impact instability dynamics. We perform large-eddy simulation of turbulent swirling flow in the Francis turbine model and employ radial injection through 12 circularly distributed holes on the runner crown tip with an injection flow rate of 2% of the inlet flow rate. A comparison with experimental data and a convergence study demonstrated good agreement in velocity fields and pulsation characteristics. Flow control was conducted for a wide range of hole positions and different angles between radial jets and the base flow. Spectral analysis of wall-pressure fluctuations revealed an optimal hole position, coinciding with the experimental results. However, flow control in simulations was less effective, reducing pressure pulsations of azimuthal flow modes m = 0, 1, 2 × 64, 33, and 17%, accordingly. Variation of the jet angle orientation demonstrated the highest pressure variance suppression for 90°. In pressure variance contours, PVC diminishing was observed near the runner crown, but that was amplified downstream.

Effect of compression ratio and hydrogen addition on performance and different phases of hydrogen/diesel combustion in reactivity controlled compression ignition engine

Abstract Reactivity controlled compression ignition (RCCI) engines use a minimum of two fuels with dissimilar reactivities. The current experimental study examined the effects of compression ratio (CR), hydrogen flow rate, and load on performance, knocking tendency, emissions, and different phases of co-combustion in a hydrogen–diesel RCCI engine employing conventional diesel in-cylinder injection and hydrogen induction into the manifold, which reduces the system cost. A constant-speed stationary engine was selected for this study because it has rarely been studied. Compared with the existing literature, wider ranges of hydrogen flow rates (up to 30 slpm) and CRs (15–20) were investigated in this study. The results indicate that the maximum brake thermal efficiency was obtained at low hydrogen flow rates (3–5 slpm). Under part-load conditions, the maximum heat release rate and cylinder pressure decreased with an increase in the hydrogen flow rate. At high loads and high CRs, a second peak was observed in the heat release curve, the magnitude of which increased with the hydrogen flow rate owing to H2 + air-premixed combustion. The knocking tendency increased with an increase in the hydrogen flow rate and a decrease in the CR. These findings can potentially help in identifying the best operating conditions for stationary constant-speed compression ignition engines adapted for H2–diesel RCCI operations, as these engines find wide application in rural economies for powering electric generators, water pumps, and agricultural equipment.