Browsing by Author "Pontika, Evangelia"
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Item Open Access Comparison of sodium sulphate deposition rate models based on operational factors influencing hot corrosion damage in aero-engines(American Society of Mechanical Engineers, 2021-01-11) Pontika, Evangelia; Laskaridis, Panagiotis; Nikolaidis, Theoklis; Koster, MaxHot corrosion is defined as the accelerated oxidation/sulphidation in the presence of alkali metal molten salts. It is a form of chemical attack that causes good metal loss. Current lifing models in aircraft engines focus on creep, fatigue and oxidation while hot corrosion damage has been overlooked as being of secondary importance. However, the absence of hot corrosion lifing models for aircraft engines often leads to unexpected and unexplained hot corrosion findings by aircraft engine operators and Maintenance, Repair and Overhaul (MRO) providers during inspections. Although hot corrosion does not cause failure on its own, the interaction with other damage mechanisms can reduce component life significantly, consequently, there is a requirement for including hot corrosion in the damage prediction process of aircraft engines. In both theoretical and experimental studies in literature, deposition of molten salts is identified as one of the primary conditions for hot corrosion to occur and an increased amount of deposited liquid salts accelerates the attack. Currently, most hot corrosion studies are limited to experimental testing of superalloys which are pre-coated with a controlled layer of salts. Such experimental studies are disconnected from gas turbine operating conditions during service. The present paper analyses two deposition rate models applicable to gas turbine operating conditions using Design of Experiments. Design space exploration is presented by taking into account gas turbine operating parameters which vary during a flight as well as temperature ranges where hot corrosion can occur. Analysis of variance is presented for 6 input parameters using Box-Behnken 3-level factorial design. Results from the Analysis of Variance indicate that the deposition rate models are sensitive to pressure and salt concentration in the gas flow. Finally, the saturation point of sodium sulphate has been investigated within the operating range of gas turbine and it was found that it can vary significantly under different conditions.Item Open Access Hot corrosion damage modeling in aeroengines based on performance and flight mission(AIAA, 2024-10) Pontika, Evangelia; Laskaridis, Panagiotis; Nikolaidis, Theoklis; Koster, MaxHot corrosion is a form of chemical damage that causes surface degradation, sound material loss, and reduced component life. A lifing analysis in aeroengines without considering hot corrosion can lead to unexpected damage findings and increased scrap rates due to blade thickness loss beyond repair. This paper presents a novel methodology to predict hot corrosion damage based on aeroengine performance and flight mission analysis while taking into account environmental exposure, fuel quality, and material factors. The participating mechanisms, from salt and sulfur ingestion to deposition and hot corrosion attack, are discussed to explain the phenomenon in aeroengine components. In the investigated engine type, the first stage of the low-pressure turbine is the most affected. The application of the new methodology provides insights into the damage progression during the flight, the most affected components and the importance of capturing variations in the fuel quality, environmental exposure at the flight region, and the thrust derate policy. For a representative 1500 n mile mission, the variations in environmental exposure, fuel quality, and derate policy within typical limits can result in up to +350% damage. The outputs of the new framework can inform the decision making for maintenance, repair, and overhaul contract costing and scheduling.Item Open Access Hot corrosion damage modelling in aero engines based on performance and flight mission analysis(AIAA, 2023-01-19) Pontika, Evangelia; Laskaridis, Panagiotis; Nikolaidis, Theoklis; Koster, MaxLifing models for aircraft engines are mainly focused on creep, fatigue and oxidation, while hot corrosion remains one of the least explored areas. Hot corrosion is a form of chemical damage that causes surface degradation, sound material loss and reduced component life. A lifing analysis for aircraft engines without considering hot corrosion can lead to unexpected and unexplained hot corrosion findings by aircraft engine operators and Maintenance, Repair and Overhaul (MRO) providers during inspections. Although hot corrosion does not cause failure on its own, the interaction with other damage mechanisms can reduce component life significantly. Consequently, there is a necessity for including hot corrosion in the damage prediction process of aircraft engines. This paper presents a new methodology to estimate hot corrosion damage based on aero-engine performance and flight mission analysis while taking into account environmental exposure, fuel quality and material factors. The analysis in the present paper focuses on the hot corrosion progress over the course of the flight mission, while varying the major contamination factors and thrust derate, and the hot corrosion rate over flight time is then used to calculate the damage at the end of the mission. The participating mechanisms, from salt and sulfur impurity ingestion to deposition rate and hot corrosion attack, are analytically presented to explain the progress of the phenomenon in aero-engine components. In the investigated type of engine, the first stage of the low-pressure turbine is found to be the most affected. It is concluded that hot corrosion is favored by a combination of high pressure, high sulfur oxide concentration, and high salt deposition rate within an intermediate temperature range while the gas conditions near the component surface remain below the sodium sulfate saturation point, and these conditions are linked with aero-engine operation. The presented hot corrosion framework captures the effect of mission requirements, component operating conditions, environmental exposure, fuel quality and material on the hot corrosion damage of hot section components. It can be used to inform aero-engine maintenance planning, lifecycle analysis and MRO contract-costing, and can benefit digital twins for predictive maintenance.Item Open Access The impact of electric machine and propeller coupling design on electrified aircraft noise and performance(AIAA, 2023-01-19) Zaghari, Bahareh; Kiran, Abhishek; Sinnige, Tomas; Pontika, Evangelia; Enalou, Hossein B.; Kipouros, Timoleon; Laskaridis, PanagiotisNovel propulsion systems have been studied in literature to reduce aircraft emissions with hydrogen or other electrical energy sources. Hybrid Electric Propulsion (HEP) system consists of electric machines as an alternative way to provide power for propulsion resulting in the reduction of aircraft fuel consumption. While reduction of emission is the main driver of new HEP designs, aircraft noise reduction and performance improvement will also need to be investigated. Much quieter electrified aircraft than conventional aircraft is explored with considering the benefits of coupled design between the propeller and electric machines. In this study, several electric machine designs have been explored and coupled with the propeller design to study the trade-off between the aerodynamic and acoustic performance of the propeller. Aerodynamic optimization is used as a baseline to minimize the energy consumption to find the aerodynamics optimum subject to constraints on the thrust levels during the mission. The propeller aerodynamic optimizer considers the electric machine efficiency map, which is a function of propeller torque and rotational speed, to find the optimum combination of propeller and electric machine designs. The objective function of the acoustic optimizations is to reduce the cumulative noise level over the entire mission. It is shown that a wider envelope of peak motor efficiency in the efficiency map provides acoustics and aerodynamic performance benefits. The trade-offs between reducing noise or increasing aerodynamic efficiency to reduce energy consumption are demonstrated.Item Open Access The impact of multi-stack fuel cell configurations on electrical architecture for a zero emission regional aircraft(AIAA, 2023-01-19) Zaghari, Bahareh; Zhou, Tianzhi; Enalou, Hossein B.; Pontika, Evangelia; Laskaridis, PanagiotisAll-electric aircraft can eliminate greenhouse gas emissions during aircraft mission, but the low predicted energy storage density of batteries (=0.5 kWh/kg), and their life cycle, limits aircraft payload and range for regional aircraft. Proton Exchange Membrane Fuel Cells (PEMFCs) using hydrogen are explored as an alternative power source. As the effort on designing high power density and highly efficient fuel cell systems continues, a trade off study on the effect of fuel cell configurations and the electrical conversion strategy on system efficiency, total weight, failure cases, and reduction of power due to failures, will inform future designs. Introducing viable fuel cell stacks and electrical configurations motivates such a trade off study, as well as concentrated design effort into these components. Currently available fuel cell stacks are designed at lower power (in the range of 150kW) to what is required for regional aircraft propulsion (in the range of 4MW). Hence to achieve the total required power, the fuel cell stacks are connected in parallel and series to create multi-stack configurations and provide higher power. In this study, multi-stack fuel cell configurations and the selected DC/DC converters are assessed. Each configuration is evaluated based on power converter design and redundancy, design for high voltage, degradation of fuel cell stacks, total system efficiency, and controllability of fuel cell stacks.Item Open Access Integrated mission performance analysis of novel propulsion systems: analysis of a fuel cell regional aircraft retrofit(AIAA, 2023-01-19) Pontika, Evangelia; Zaghari, Bahareh; Zhou, Tianzhi; Enalou, Hossein B.; Laskaridis, PanagiotisThis paper presents the development and application of an integrated, higher-fidelity framework developed within CHARM (the Cranfield Hybrid electric Aircraft Model) for the design, performance analysis and overall evaluation of novel electrified propulsion systems. The developed framework is used to model and analyze the performance characteristics of a Fuel Cell (FC) regional aircraft system in comparison with a conventional regional aircraft and a hydrogen gas turbine regional aircraft retrofit. The FC propulsion system and the hydrogen gas turbine are retrofitted to the same conventional aircraft platform. Physics-based aircraft performance calculations, propeller maps, gas turbine component maps, off-design cycle analysis, electric component maps, calculations for the electric power management and distribution, and a Proton-Exchange Membrane FC (PEMFC) configuration sized to cover the power requirements of a regional aircraft, are integrated within this framework to capture the performance and interaction of components, sub-systems and aircraft during any flight mission and conditions. The aircraft performance, the propulsion system performance characteristics and the emissions of the three technologies are calculated and discussed to understand the challenges and opportunities of using hydrogen-electric propulsion (FC). The effect of capturing the variable mission parameters and flight phases on the performance of the electric power system and FC is presented and compared against a lower fidelity modeling approach for the electric powertrain. The sensitivity of the FC propulsion system and its attributes to varying mission requirements (island-hopping, range, cruise altitude, ambient conditions), as well as the change in the consumed fuel, are demonstrated. This framework can be used to inform the decision-making for the design of electric components and thermal management systems (TMS), and the importance of capturing the trade-off between mass, efficiency and operational constraints in the design process is highlighted. Also, the off-design performance of the electric power system designs and FC is modeled to decide if the design is within acceptable limits under various conditions, and capture the effect of mission requirements and flight conditions on the energy consumption of the overall aircraft system. Finally, a parametric analysis addresses the effect of power density improvement with future technology on the energy per passenger and feasibility of the FC regional aircraft.Item Open Access Integrated power and thermal management system in a parallel hybrid-electric aircraft: an exploration of passive and active cooling and temperature control(MDPI, 2025-03-13) Ouyang, Zeyu; Nikolaidis, Theoklis; Jafari, Soheil; Pontika, EvangeliaHybrid-electric aircraft (HEAs) represent a promising solution for reducing fuel consumption and emissions. However, the additional heat loads generated by the electrical propulsion systems in HEAs can diminish these benefits. To address this, an integrated power and thermal management system (IPTMS) is essential to mitigate these challenges by optimizing the interaction between thermal management and power management. This paper presents a preliminary IPTMS design for a parallel HEA operating under International Standard Atmosphere (ISA) conditions. The design includes an evaluation of active cooling, passive cooling, and active temperature control strategies. The IPTMS accounts for heat loads from the engine system, including the generators, shaft bearings, and power gearboxes, as well as from the electrical propulsion system, such as motors, batteries, converters, and the electric bus. This study investigates the impact of battery power (BP) contribution to cooling power on required coolant pump power and induced ram air drag. A comparison of IPTMS performance under 0% and 100% BP conditions revealed that the magnitude of battery power contribution to cooling power does not significantly impact the thermal management system (TMS) performance due to the large disparity between the total battery power (maximum 950 kW) and the required cooling power (maximum 443 W). Additionally, it was determined that the motor-inverter loop accounts for 95% of the pump power and 97% of the ram air drag. These findings suggest that IPTMS optimization should prioritize the thermal domain, particularly the motor-inverter loop. This study provides new insights into IPTMS design for HEAs, paving the way for further exploration of IPTMS performance under various operating conditions and refinement of cooling strategies.Item Open Access Mapping the effect of variable HPT blade cooling on fuel burn, engine life and emissions for fleet optimization using active control(AIAA, 2023-01-19) Pontika, Evangelia; Laskaridis, Panagiotis; Montana Gonzalez, Felipe; Jacobs, Will; Mills, AndrewModern aero engines have increasingly sophisticated control systems. The aim for next-generation aircraft is to have even more adaptive and flexible control systems to enable the optimization of economic aspects, operational aspects and fleet management. Among others, an engine control variable that has the potential to offer various life and fuel burn benefits at different flight phases is the High-Pressure Turbine (HPT) blade cooling air. The HPT blades have demanding cooling requirements to protect their life and decelerate HPT efficiency degradation. However, any engine bleed has a penalty in efficiency and results in increased fuel consumption. Previous generation aircraft have a fixed relative blade cooling flow based on a design choice for a trade-off between life and efficiency. However, with adaptive control systems, there is an opportunity to extract the maximum potential benefit under different flight phases and scenarios. With this opportunity comes the challenge of increased complexity in engine behavior necessitating detailed modeling to quantify effects on lifing, fuel burn and safety. This paper focuses on modeling the performance, lifing and emission effects of variable HPT blade cooling air at take-off, climb and cruise. First, the effect of variable cooling on the Turbine Entry Temperature (TET), Exhaust Gas Temperature (EGT), fuel flow, lifing and NOx emissions are modeled at operating point level while the thrust requirement is achieved. Subsequently, a Design of Experiment is performed at mission level with the relative cooling flow at take-off, climb and cruise as the independent variables to train surrogate, analytical models. The analytical models are applied in the probabilistic modeling of system failure rates under different cooling flows. Optimization of engine control variables, in this case, the HPT blade cooling, requires analytical expressions that can be used in objective functions. These analytical models will inform fleet optimizers and active control systems to facilitate the implementation of fleet decisions such as reducing direct operating costs (fuel cost, maintenance reserves, NOx taxation), meeting NOx requirements of airports and extending Time-on-Wing (TOW). The findings indicate that take-off offers an opportunity to protect HPT life with increased cooling, but caution should be exercised in regard to the damage increase at the downstream non-cooled hot gas path components. A decrease in cooling flow at cruise, which is less detrimental to engine life, can offer significant fuel savings and climb can be investigated for the optimum economic trade-off between life and fuel burn as a response to economic scenarios.Item Open Access Minimising the effect of degradation of fuel cell stacks on an integrated propulsion architecture for an electrified aircraft(IEEE, 2022-07-07) Zhou, Tianzhi; Balaghi Enalou, Hossein; Pontika, Evangelia; Zaghari, Bahareh; Laskaridis, PanagiotisProton Exchange Membrane Fuel Cells (PEMFC) are receiving interest as an electrical source of energy for aircraft propulsion electrification. However, their implementation challenges such as durability, reliability, and the dynamic behaviour of Fuel Cells (FCs) in an integrated hybrid propulsion system have not been fully explored. Currently, most commercial PEMFC stacks have maximum power close to 150kW. To achieve higher power required for aviation, these stacks can be connected in series and parallel to achieve high voltage required for propulsion. Poor design procedure of cells and stacks can cause variation between the stacks resulting in failure and fast degradation of the connected stacks. In this paper the impact of voltage and current drop of one stack, which could be caused by changes in the fuel cell’s individual axillary parts, degradation of the cells within the stack, or faults in the connections and distribution is explored. Upon exploring different configurations, it is found that the arrangements of FC stacks connections could help in reducing the impact of voltage and current variations due to degradation in each stacks. The imbalance stack performance and its effects on the whole energy storage system performance is not fully explored before. It is important to conduct quantitative analysis on these issues before the PEMFC system can be implemented.Item Open Access Thermal management challenges in hybrid-electric propulsion aircraft(Elsevier, 2023-12-08) Asli, Majid; König, Paul; Sharma, Dikshant; Pontika, Evangelia; Huete, Jon; Konda, Karunakar Reddy; Mathiazhagan, Akilan; Xie, Tianxiao; Höschler, Klaus; Laskaridis, PanagiotisThe utilization of hybrid electric propulsion concept in aviation offers a viable solution to address the limitations posed by the relatively low energy density of batteries in fully electric aviation. These hybrid systems enable the aircraft to achieve a significant range while simultaneously minimizing carbon emissions. While the individual components of a Hybrid Electric Propulsion (HEP) system, such as electric motors and batteries, are designed with high efficiency, their integration presents a significant challenge in the realm of thermal management. Designing an efficient system for managing the substantial waste heat generated by heat sources and effectively transferring it to heat sinks during various flight phases is a complex task. This challenge becomes even more critical as the design must adhere to system weight limits and prioritize aviation safety considerations. In this review article, we performed a systematic review of the challenges related to the key elements in a thermal management system. These elements encompass every component or subsystem that contributes to the thermal management of a generic hybrid-electric propulsion system. This includes electric motors and generators, batteries, heat exchangers, power transmission systems, power distribution systems, storages, fuel cells, cooling fluids and pipes, control system, pumps and fans. Following the identification of the challenges, the paper provides a comprehensive summary of the existing solutions that have been offered and pursued by the community to address the challenges. Furthermore, the paper also discusses emerging technologies related to each element, highlighting their potential in overcoming these challenges.Item Open Access Toward net zero: an engine electrification strategy approach of fuel cell and steam injection(American Society of Mechanical Engineers, 2024-08-24) He, Zhengfei; Pontika, Evangelia; Laskaridis, PanagiotisThe turbofan engine electrification is a promising element in the global effort to achieve the 2050 net-zero emission target. This transformative shift embraces alternative energy sources and amplifies system efficiency. Power injection, using the electric motor to provide power assistance for the gas turbine, is a promising concept. Batteries and fuel cells are emerging as prime candidates for replacing traditional fossil fuel power requirements, offering compelling advantages, particularly with electric powertrains offering superior efficiency compared to conventional gas turbines. This direct power injection assistance reduces the power requirement from the combustion, thus reducing the fuel flow and Turbine Entry Temperature (TET). As an outcome, this alteration yields favourable consequences, notably in the form of diminished Carbon Dioxide (CO2) and Nitrogen Oxide (NOx) emissions and lower engine fuel consumption. However, this transition comes at the cost of a potential thermal efficiency penalty, impacts engine stability, and adds extra weight. These drawbacks compromise the power injection’s benefit, highlighting the necessity for introducing electrification strategies in future engine designs. This paper presents an innovative electrification strategy using fuel cells as the power source for engine electrification. The strategy highlights the collection of water as a by-product, followed by treatment processes involving condensation, pressurisation, and superheating. In this configuration, the fuel cell is designed to provide power to the electric motor, which injects power into the low-pressure shaft of the engine and provides assistance. Additionally, steam injection, leveraging the by-product water, enhances the benefits derived from electrification by recovering and redirecting the waste heat from exhaust gases into the combustor. To evaluate the potential impact of this electrification strategy, this research selected and modelled three representative engines, each representative of typical thermodynamic cycles. Two different approaches to steam management were considered, including instantaneous injection with production and storage of steam during production for release during specific flight segments. This research established the synergy between steam injection and different engine thermodynamic cycles, providing a visualised evaluation method. The impact of fuel cell electrification on fuel consumption has been quantified. An estimation of the weight penalty, including fuel cells, hydrogen storage and heat exchanger, is also provided. Furthermore, the sizing of the superheating heat exchanger is analysed to assess its influence on the electrification strategy. This research discovered the impact of steam injection on different engine cycles, established the benefits and constraints, and explained the physics. This research has captured the physics of recovering the waste heat from exhaust pipes, which could compromise fuel consumption benefit and impose a penalty on electrification. This research also indicated under what conditions and phases it is better to use the fuel cell with steam injection. The results and assessments reach the conclusion that the electrification strategy of fuel cell and steam injection is preferable for high-temperature, low-specific thrust engines. An improper deployment could lead to a penalty instead of a benefit. The temperature of the steam is the dominant factor in bringing fuel consumption benefits. Thus, the preferable steam management approach is to inject during T/O and climb.