CERES :: Browsing by Author "Roumeliotis, Ioannis"

Browsing by Author "Roumeliotis, Ioannis"

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Open Access
Aeroderivative gas turbine back-up capability with compressed air injection
(Elsevier, 2020-08-08) Abudu, Kamal; Igie, Uyioghosa; Roumeliotis, Ioannis; Szymanski, Artur; Di Lorenzo, Giuseppina
The transition to more renewable energy sources of power generation is associated with grid instability and the need for backup power, due to their intermittency. This provides an opportunity for gas turbine engines, especially the aeroderivative (AD) types that generally have higher ramp rates than heavy-duty engines. Nonetheless, higher ramp rates are still necessary to meet more stringent grid requirements, with increased renewables subscription. The study examines ramp rate improvements and performance enhancement through compressed air injection at the back of the high-pressure compressor (HPC). Two configurations of AD engines are considered in the investigation. In-house gas turbine performance simulation software has been used to simulate the steady-state and transient operations for design and off-design performance. Compressed air injection in the study is facilitated by an assumed compressed air storage or an external compressor. The steady-state analysis for power augmentation shows that for the two-spool engine with fixed speed low-pressure compressor (LPC), a 16% increase in power is obtained with 8% of flow injection. The other engine that is intercooled and consists of a variable speed LPC with power turbine shows a 21% increase in power for the same injection amount. Above 8% injection, the HPC of both engines tends towards an adverse rise in pressure ratio. However, up to 15% of flow injection is allowed before the surge point. It is seen generally that the operating point of the LPC moves away from surge, while the opposite is the case for the HPC. For transient simulations focused on ramp rates, the better improvements are shown for the intercooled engine that runs at variable speed. This is a ramp rate improvement of 100% with air injection, while that of the other engine increases by 85%
Open Access
Ammonia for civil aviation: a design and performance study for aircraft and turbofan engine
(Elsevier, 2024-04-06) Sasi, Sarath; Mourouzidis, Christos; Rajendran, David John; Roumeliotis, Ioannis; Pachidis, Vassilios; Norman, Justin
The 2050 net zero targets for aviation to decarbonize the industry means that solutions need to be delivered that can help achieve those targets. Transitioning to zero carbon aviation fuel is an effective solution to achieve those targets. This research article aims to highlight the potential design and performance implications of using Ammonia as a zero-carbon fuel for civil aviation through a retrofit case study conducted for an Airbus A350-1000 equivalent aircraft. The impacts on both turbofan design and aircraft payload-range capability are presented. A feasibility study of using Ammonia as a Hydrogen carrier for civil aviation is also presented. The turbofan design impacts, and payload range capability are assessed using Cranfield University’s in-house gas turbine performance tool TURBOMATCH and NASA FLOPS respectively. A 3-point turbofan cycle design strategy is utilized for redesigning turbofan engine cycles using Ammonia as a fuel. Ammonia fuel conditioning assessment is made using REFPROP to investigate its impact on turbofan design. Utilizing pure Ammonia as an aircraft fuel can provide significant turbofan redesign opportunities. Fuel conditioning assessment revealed that for a 430 kN thrust class engine, 2.1 MW of thermal power is required to condition Ammonia fuel at take-off. As a result, various strategies to condition the fuel and its significant impact on turbofan design are presented indicating fuel conditioning as a major design driver for Ammonia fuelled turbofan engines in the future. Although upon initial preliminary assessment, Ammonia utilized as a Hydrogen carrier showcased potential by providing additional mission range capability when compared to a pure Ammonia burning aircraft, the significant thermal energy required to crack (decompose) Ammonia into Hydrogen highlighted the challenges at aircraft mission level and Hydrogen turbofan design implications. It is found that energy requirement (power) to crack Ammonia into Hydrogen are significant which is approximately an order of magnitude higher than Ammonia fuel conditioning itself.
Open Access
Application of model based systems engineering for the conceptual design of a hybrid-electric Atr 42-500: from system architecting to system simulation
(American Society of Mechanical Engineers, 2021-01-11) Cappuzzo, Federico; Broca, Olivier; Vouros, Stavros; Roumeliotis, Ioannis; Scullion, Calum
The progress in aerospace technology over the recent years led to the development of more sophisticated and integrated systems. To cope with this complexity, the aerospace industry is seeing a progressive trend towards adopting Model-Based Systems Engineering (MBSE) in various stages of the product development cycle. The ability to capture emerging behavior, mitigation of risk and improved communication among different stakeholders are some key benefits that MBSE provides over traditional methods for complex systems and processes. This paper attempts to bridge the gap between system architecting and system simulation activities by proposing a methodology to facilitate seamless flow of information between the two development aspects. This methodology was applied to the development of a parallel hybrid-electric version of the ATR 42–500. The use case was designed for a regional mission of 400 nautical miles with the ability to meet regulation requirement of carrying enough reserves for landing at an alternate airport. An integrated systems model, consisting of gas turbine engine, electric powertrain, and flight dynamics, was developed with Simcenter Amesim to analyze the dynamics performance of the aircraft throughout the whole mission. The key metrics evaluated were fuel consumption, take-off weight and the Energy Specific Air Range (ESAR) of the aircraft. As environmental regulations are becoming more stringent, pollutant and noise emissions were considered in the study. The most promising hybrid configurations are recognized, the potential benefits are quantified highlighting the strong potential of System Architecting and System Simulation to provide valuable insights early in the development cycle, reducing the time and cost of product development.
Open Access
Assessment of engine operability and overall performance for parallel hybrid electric propulsion systems for a single-aisle aircraft
(American Society of Mechanical Engineers, 2021-09-16) Kang, Sangkeun; Roumeliotis, Ioannis; Zhang, Jinning; Pachidis, Vassilios; Broca, Olivier
This paper aims to assess the gas turbine operability and overall hybrid electric propulsion system performance for a parallel configuration applied to a 150 passenger single-aisle aircraft. Two arrangements are considered: one where the low pressure shaft is boosted and one where the high pressure shaft is boosted. For identifying limits in the hybridization strategy steady state and transient operation are considered and the hybridization effect on compressor operability is determined. Having established the electric power on-take limits with respect to gas turbine operation the systems performance at aircraft level is quantified for the relevant cases. Different power management strategies are applied for the two arrangements and for different power degrees of hybridization. The results indicate that despite the fact that pollutant emission and fuel consumption may improved for hybrid propulsion, this comes at the cost of reduced payload and operability margins. Boosting the low pressure shaft may give the highest engine performance benefits but with a significant weight penalty, while the low pressure compressor system operability is negatively affected. On the other hand boosting the high pressure shaft provides lower engine performance benefits but with smaller weight penalty and with less operability concerns.
Open Access
Assessment of engine operability and overall performance for parallel hybrid electric propulsion systems for a single-aisle aircraft
(American Society of Mechanical Engineers, 2022-01-04) Kang, Sangkeun; Roumeliotis, Ioannis; Zhang, Jinning; Broca, Olivier; Pachidis, Vassilios
This paper aims to assess the gas turbine operability and overall hybrid electric propulsion system (HEPS) performance for a parallel configuration applied to a 150 passenger single-aisle aircraft. Two arrangements are considered: one where the low-pressure (LP) shaft is boosted and one where the high-pressure (HP) shaft is boosted. For identifying limits in the hybridization strategy, steady-state and transient operation are considered, and the hybridization effect on compressor operability is determined. Having established the electric power on-take limits with respect to gas turbine operation, the systems performance at aircraft level is quantified for the relevant cases. Different power management strategies (PMS) are applied for the two arrangements and for different power degrees of hybridization. The results indicate that despite the fact that pollutant emission and fuel consumption may improve for hybrid propulsion, this comes at the cost of reduced payload and operability margins. Boosting the LP shaft may give the highest engine performance benefits but with a significant weight penalty, while the LP compressor system operability is negatively affected. On the other hand, boosting the HP shaft provides lower engine performance benefits but with smaller weight penalty and with less operability concerns.
Open Access
Assessment of hydrogen fuel for rotorcraft applications
(Elsevier, 2022-09-19) Saias, Chana Anna; Roumeliotis, Ioannis; Goulos, Ioannis; Pachidis, Vassilios; Bacic, Marko
This paper presents the application of a multidisciplinary approach for the preliminary design and evaluation of the potential improvements in performance and environmental impact through the utilization of compressed (CGH2) and liquefied (LH2) hydrogen fuel for a civil tilt-rotor modelled after the NASA XV-15. The methodology deployed comprises models for rotorcraft flight dynamics, engine performance, flight path analysis, hydrogen tank and thermal management system sizing. Trade-offs between gravimetric efficiency, energy consumption, fuel burn, CO2 emissions, and cost are quantified and compared to the kerosene-fuelled rotorcraft. The analysis carried out suggests that for these vehicle scales, gravimetric efficiencies of the order of 13% and 30% can be attained for compressed and liquid hydrogen storage, respectively leading to reduced range capability relative to the baseline tilt-rotor by at least 40%. At mission level, it is shown that the hydrogen-fuelled configurations result in increased energy consumption by at least 12% (LH2) and 5% (CGH2) but at the same time, significantly reduced life-cycle carbon emissions compared to the kerosene counterpart. Although LH2 storage at cryogenic conditions has a higher gravimetric efficiency than CGH2 (at 700 bar), it is shown that for this class of rotorcraft, the latter is more energy efficient when the thermal management system for fuel pressurization and heating prior to combustion is accounted for.
Open Access
Assessment of hydrogen gas turbine-fuel cell powerplant for rotorcraft
(Elsevier, 2023-12-11) Baena Mejıas, Rafael; Saias, Chana Anna; Roumeliotis, Ioannis; Pachidis, Vassilios; Bacic, Marko
Conventional turboshaft engines are high power density movers suffering from low efficiency at part power operation and producing significant emissions. This paper presents a design exploration and feasibility assessment of a hybrid hydrogen-fueled powerplant for Urban Air Mobility (UAM) rotorcraft. A multi-disciplinary approach is devised comprising models for rotorcraft performance, tank and subsystems sizing and engine performance. The respective trade-offs between payload-range and mission level performance are quantified for kerosene-fueled and hybrid hydrogen tilt-rotor variants. The effects of gas turbine scaling and fuel cell pressurization are evaluated for different hybridization degrees. Gas turbine scaling with hybridization (towards the fuel cell) results in up to 21% benefit in energy consumption relative to the non-scaled case with the benefits being more pronounced at high hybridization degrees. Pressurizing the fuel cell has shown significant potential as cell efficiency can increase up to 10% when pressurized to 6 bar which translates to a 6% increase in overall efficiency. The results indicate that current fuel cells (1 kW/kg) combined with current hydrogen tank technology severely limit the payload-range capability of the tilt-rotor. However, for advanced fuel cell technology (2.5 kW/kg) and low ranges, hybrid powerplant show the potential to reduce energy consumption and reduce emissions footprint.
Open Access
Assessment of performance boundaries and operability of low specific thrust GUHBPR engines for EIS2025
(American Society of Mechanical Engineers, 2022-04-25) Mo, Da; Roumeliotis, Ioannis; Mourouzidis, Christos; Kissoon, Sajal; Liu, Yixiong
This paper aims to develop a robust design process by approaching the performance boundaries and evaluating the operability of the pursued geared turbofan engine with low specific thrust for EIS 2025. A two-spool direct-drive turbofan (DDTF) engine of EIS 2000 was improved according to aircraft specifications and technology boundaries in 2025. A series of optimized engines with consecutive fan diameters were established to seek the ideal engine by balancing SFC, weight and mission fuel burn. The fan diameter was proved to be a decisive factor for lowering SFC and energy usage. The cycle design optimization process achieved a thermal efficiency of approximately 52%, and a propulsive efficiency of 79.5%, which is 8.19% increase in propulsive efficiency by enlarging fan diameter from 1.6m to 1.9m. Meanwhile, the 1.9m-fan diameter engine achieved a reduction in SFC and fuel burn of 7.47% and 6.58% respectively which offers an overall reduction of 30.82% in block fuel burnt and CO2 emission compared to the DDTF engine. A feasibility check verified the viability of the designed optimum engine in terms of fan tip speed, stage loading and AN2. Dynamic simulation offered a deep understanding of transient behaviour and fundamental mechanism of the geared turbofan engine. An important aspect of this paper is the use of advanced CMC materials, which led to an improvement of 4.92% in block fuel burn and 2.93% in engine weight.
Open Access
Assessment of the performance boundaries of very low specific thrust direct-drive turbofan engines at aircraft level for EIS 2025
(GPPS Chania20, 2020-09-07) Kissoon, Sajal; Zhang, Fan; Mourouzidis, Christos; Roumeliotis, Ioannis; Pachidis, Vassilios
Within the past decade, concerns over the environmental impact of civil aviation have pushed the research community towards the development of more efficient propulsion technology, which delivers a lower carbon and NOx footprint. The current progress achieved in the various specialised disciplines creates the need to redefine the performance barrier achievable by 2025 state-of-the-art aero-engines. This paper summarises some of the latest advancements within the gas turbine research community on the performance modelling and analysis of very low dspecific thrust direct-drive turbofan engines for EIS 2025. Engine and aircraft performance models were used to predict the extent of fuel burn reduction at aircraft level that could be achieved by reducing the engine specific thrust level , increasing operating pressure and temperature levels and applying technology factors representing a step beyond current state-of-the-art. The models represented modern three-spool direct-drive turbofans powering a typical A350XWB-type aircraft. The outputs of the engine design of experiments (DoE) exercise resulted in three most promising candidates. Targeting EIS in 2025, the final optimum design showed 14.81% block fuel improvement for a representative long (7000nm) range mission, accompanied by 30.9% penalty on engine weight. These results propose that with current technology level, at the lower end of the specific thrust range, there is still available design space for the direct-drive turbofan architecture
Open Access
Assessment of thermo-electric power plants for rotorcraft application
(ASME, 2019-10-01) Roumeliotis, Ioannis; Mourouzidis, Christos; Zafferetti, Mirko; Deniz, Unlu; Broca, Olivier; Pachidis, Vassilios
This paper assesses a parallel electric hybrid propulsion system utilizing simple and recuperated cycle gas turbine configurations. An adapted engine model capable to reproduce a turboshaft engine steady state and transient operation is built in Simcenter Amesim and used as a baseline for a recuperated engine. The transient operation of the recuperated engine is assessed for different values of heat exchanger effectiveness, quantifying the engine lag and the surge margin reduction which are results of the heat exchanger addition. An oil and gas mission of a twin engine medium helicopter has been used for assessing the parallel hybrid configuration. The thermo-electric system brings a certain level of flexibility allowing for better engine utilization, thus firstly a hybrid configuration based on simple cycle gas turbine scaled down from the baseline engine is assessed in terms of performance and weight. Following the recuperated engine thermo-electric power plant is assessed and the performance enhancement is compared against the simple cycle conventional and hybrid configurations. The results indicate that a recuperated gas turbine based thermo - electric power plant may provide significant fuel economy despite the increased weight. At the same time the electric power train can be used to compensate for the reduced specific power and potentially for the throttle response change due to the heat exchanger addition.
Open Access
A characteristic-based 1D axial compressor model for stall and surge simulations
(American Society of Mechanical Engineers (ASME), 2023-09-09) Kissoon, Sajal; Righi, Mauro; Pawsey, Lucas; Pachidis, Vassilios; Tunstall, Richard; Roumeliotis, Ioannis
A low-order unsteady one-dimensional axial compressor and combustor model has been developed at Cranfield University as part of a larger unsteady gas turbine engine model, with the ability to simulate compressor stall and surge. The flow is resolved using the 1D unsteady Euler equations and source terms are used to model bleed extraction (and addition), pressure losses, and heat and work exchange. Species tracking is used in the combustor part of the model, using a semi-coupled approach, to keep track of the combustion products and unburnt fuel in the main gas path. The equations are solved using a Roe Approximate Riemann Solver, modified to handle the high magnitude, transient source terms necessary for this simulation. The performance of the compressor during the transient surge event is described by a set of compressor characteristics, including reverse flow and rotating stall regions, obtained from a validated 3D throughflow code, ACRoSS. To replicate the exact response of multi-stage compressors, stage-by-stage characteristics are used during reverse flow. The low-order method presented is successfully verified against ACRoSS for a high-power surge event of a coupled IPC and HPC configuration. The rate at which the total pressure at the outlet of the HPC collapses was calculated to be within 1%. This approach presents a faster alternative to high-fidelity CFD and can be used to investigate the compressor stall behaviour within minutes during the early design phase.
Open Access
Design and simulation of eVTOL aircraft Thermal Management System
(ASME, 2025-06) Kang, Sangkeun; Saias, Chana Anna; Roumeliotis, Ioannis; Broca, Olivier
Vertical Take-off and Landing (VTOL) aircraft with hybrid or fully-electric propulsion systems are becoming popular for Urban Air Mobility (UAM) applications. However, they face challenges such as limited power and energy density, stringent operating temperature constraints, and the generation of low-grade waste heat. These issues emphasize the need for effective Thermal Management Systems (TMS) design. In light of the above, this paper aims to design the TMS for a parallel hybrid electric XV-15 aircraft, a widely known civil tiltrotor concept. The TMS is integrated into the aircraft system to assess its impact on energy efficiency and emissions at both aircraft and mission levels. This study considers current state of the art technology and expected advancements over the next two decades to identify the benefits of electrification. In the designed TMS, liquid cooling cold plates serve as the main heat acquisition and cooling system for each electric component. An air-coolant heat exchanger is also incorporated to dissipate the accumulated heat load. The study conducts a comparative analysis to determine the optimal TMS design point. It involves a comparison between two design scenarios: one focused on the cruise condition, which constitutes a significant portion of the flight mission, and another designed specifically for peak heat load conditions. This ensures a holistic evaluation of the TMS's performance across various flight phases, balancing efficiency and resilience to peak demands. Finally, the energy efficiency and emission penalty associated with the TMS integration are quantified and discussed in the study.
Open Access
Design exploration and performance assessment of advanced recuperated hybrid-electric UAM rotorcraft
(American Society of Mechanical Engineers, 2021-11-09) Saias, Chana Anna; Roumeliotis, Ioannis; Goulos, Ioannis; Pachidis, Vassilios; Bacic, Marko
The design of efficient, environmentally friendly and quiet powerplant for rotorcraft architectures constitutes a key enabler for Urban Air Mobility application. This work focuses on the development and application of a generic methodology for the design, performance and environmental impact assessment of a parallel hybrid-electric propulsion system, utilizing simple and advanced recuperated engine cycles. A simulation framework for rotorcraft analysis comprising models for rotor aerodynamics, flight dynamics and hybrid-electric powerplant performance is deployed for the design exploration and optimization of a hybrid-electric rotorcraft, modelled after the NASA XV-15, adapted for civil applications. Optimally designed powerplants for payload-range capacity, energy efficiency and environmental impact have been obtained. A comparative evaluation has been performed for the optimum designs. The respective trade-offs between engine, heat exchanger weight, thermal efficiency, as well as mission fuel burn and environmental impact have been quantified. It has been demonstrated that a recuperated gas turbine based hybrid-electric architecture may provide improvements of up to 6% in mission range capability without sacrificing useful load. At the same time, analyses performed for a representative 100 km mission suggest reductions in fuel burn and NOX emissions of up to 12.9% and 5.2% respectively. Analyses are carried at aircraft and mission level using realistic UAM mission scenarios.
Open Access
Design methodology and mission assessment of parallel hybrid electric propulsion systems
(American Society of Mechanical Engineers, 2022-09-16) Ghelani, Raj; Roumeliotis, Ioannis; Saias, Chana Anna; Mourouzidis, Christos; Pachidis, Vassilios; Norman, Justin; Bacic, Marko
An integrated engine cycle design methodology and mission assessment for parallel hybrid electric propulsion architectures are presented in this paper. The aircraft case study considered is inspired by Fokker 100, boosted by an electric motor on the low-pressure shaft of the gas turbine. The fuel burn benefits arising from boosting the low-pressure shaft are discussed for two different baseline engine technologies. A three-point engine cycle design method is developed to redesign the engine cycle according to the degree of hybridization. The integrated cycle design and power management optimization method is employed to identify potential fuel burn benefits from hybridization for multiple mission ranges. The sensitivity of these mission results has also been analyzed for different assumptions on the electric powertrain. With 1 MW motor power and a battery pack of 2307 kg, a 3% fuel burn benefit can be obtained by retrofitting the gas turbine for 400 nm range. Optimizing the power management strategy improves this fuel burn benefit by 0.2-0.3%. Redesigning the gas turbine and optimizing the power management strategy, provides a 4.2% fuel benefit on 400 nm. The results suggest that a high hybridization by power, low hybridization by energy, and ranges below 700 nm are the only cases where the redesigned hybrid electric aircraft has benefits in fuel burn and energy consumption relative to the baseline aircraft. Finally, it is found that the percentage of fuel burn benefits from the hybrid electric configuration increases with the improvement in engine technology.
Open Access
Dynamic simulation and aircraft level assessment of CMC implementation on GTF engine
(Springer, 2022-12-16) Mo, Da; Roumeliotis, Ioannis; Liu, Yixiong; Mourouzidis, Christos; Kissoon, Sajal
This paper dynamically simulated the geared turbofan engine with CMC turbine components, including impacts of fuel schedule, shaft inertia, volume packing, BOV schedule. Deliberated comparisons were performed between CMC engine and Inconel engine on aircraft level performance and transient behaviour. Heat load examination is included in flight mission analysis, which lays the basis on the gearbox efficiency map related to torque and rotational speed. Results indicate that IPC surge margin of the CMC case slightly fall 0.15% but maintain steady. The mitigated T4 overshooting phenomenon has offered a 30 K drop and thus extended turbine life. More importantly, Fan shaft inertia dominantly affects engine operability, whereas the blow-off air fraction severely impacts the low power setting operation. Further investigation of heat load reveals that power loss at take-off segment accounts for 1.1% of IP shaft input power, which is 3.98% higher than Inconel case. The thermal management system needs to be redesigned to absorb extra heat. On assessment of aircraft level performance, CMC engine provides superior profits in maximizing airline revenue. The predicted annual fuel cost saving is about 0.08 million dollars coming from block fuel reduction. NOx, noise and CO2 demonstrate obvious decline, approaching 5.9%, 1.0% and 4.9%, respectively.
Open Access
Dynamic simulation of a rotorcraft hybrid engine in Simcenter Amesim
(European Rotorcraft Forum, 2018-09-30) Roumeliotis, Ioannis; Nikolaidis, Theoklis; Pachidis, Vassilios; Broca, Olivier; Unlu, Deniz
This paper assesses a series hybrid propulsion system utilizing a recuperated gas turbine configuration. An adapted engine model capable to reproduce a turboshaft engine steady state and transient operation is built and used as a baseline for a recuperated engine. The recuperated engine presents a specific fuel consumption improvement of more than 15% at maximum continuous rating at the expense of surge margin which is reduced. An Oil and Gas (OAG) mission of a Twin Engine Medium helicopter has been used for assessing the hybrid configuration. The thermo-electric system brings a certain level of flexibility allowing for the recuperated engine to operate for high take-off weight cases. If envisioned 2025 technology is considered the fuel benefit of the series hybrid recuperated configuration for the OAG mission is in the range of 5%. The integrated system models (gas turbine, electric and heat exchanger systems) are built in Simcenter Amesim, a system modelling platform allowing for both steady state and dynamic simulation.
Open Access
Flow field explorations in a boundary layer pump rotor for improving 1D design codes
(MDPI, 2023-02-03) Freschi, Rosa; Bakogianni, Agapi; Rajendran, David John; Anselmi Palma, Eduardo; Talluri, Lorenzo; Roumeliotis, Ioannis
Boundary layer pumps, although attractive due to their compactness, robustness and multi-fluid and phase-handling capability, have been reported to have low experimental efficiencies despite optimistic predictions from analytical models. A lower-order flow-physics-based analytical model that can be used as a 1D design code for sizing and predicting pump performance is described. The rotor component is modelled by means of the Navier–Stokes equations as simplified using velocity profiles in the inter-disk gap, while the volute is modelled using kinetic-energy-based coefficients inspired by centrifugal pumps. The code can predict the rotor outlet and overall pump pressure ratio with an around 3% and 10% average error, respectively, compared to the reference experimental data for a water pump. Moreover, 3D RANS flow-field explorations of the rotor are carried out for different inter-disk gaps to provide insights concerning the improvement of the 1D design code for the better prediction of the overall pump performance. Improvements in volute loss modelling through the inclusion of realistic flow properties at the rotor outlet rather than the detailed resolution of the velocity profiles within the rotor are suggested as guidelines for improved predictions. Such improved design codes could close the gap between predictions and experimental values, thereby paving the way for the appropriate sizing of boundary layer pumps for several applications, including aircraft thermal management.
Open Access
Impact of gas turbine flexibility improvements on combined cycle gas turbine performance
(Elsevier, 2021-02-20) Abudu, Kamal; Igie, Uyioghosa; Roumeliotis, Ioannis; Hamilton, Richard
The improvement of gas turbines flexibility has been driven by more use of renewable sources of power due to environmental concerns. There are different approaches to improving gas turbine flexibility, and they have performance implications for the bottoming cycle in the combined cycle gas turbine (CCGT) operation. The CCGT configuration is favourable in generating more power output, due to the higher thermal efficiency that is key to the economic viability of electric utility companies. However, the flexibility benefits obtained in the gas turbine is often not translated to the overall CCGT operation. In this study, the flexibility improvements are the minimum environmental load (MEL) and ramp-up rates, that are facilitated by gas turbine compressor air extraction and injection, respectively. The bottoming cycle has been modelled in this study, based on the detailed cascade approach, also using the exhaust gas conditions of the topping cycle model from recent studies of gas turbine flexibility by the authors. At the design full load, the CCGT performance is verified and subsequent off-design cases from the gas turbine air extraction and injection simulations are replicated for the bottoming cycle. The MEL extension on the gas turbine that brings about a reduction in the engine power output results in a higher steam turbine power output due to higher exhaust gas temperature of the former. This curtails the extended MEL of the CCGT to 19% improvement, as opposed to 34% for the stand-alone gas turbine. For the CCGT ramp-up rate improvement with air injection, a 51% increase was attained. This is 3% point lower than the stand-alone gas turbine, arising from the lower steam turbine ramp-up rate. The study has shown that the flexibility improvements in the topping cycle also apply to the overall CCGT, despite constraints from the bottoming cycle.
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Impacts of alternative aviation fuels on engine cycle design and aircraft mission capability
(American Society of Mechanical Engineers, 2023-09-28) Sasi, Sarath; Mourouzidis, Christos; Roumeliotis, Ioannis; Nikolaidis, Theoklis; Pachidis, Vassilios; Norman, Justin
Recent 2050 net zero targets for aviation have sparked interest among the industry players to seek alternative aviation fuels as a pathway for the immediate alleviation of its carbon footprint. This paper aims to shed light on the opportunities and challenges that zero & low-carbon alternative fuels can provide from a technical standpoint. To address this aim, candidate fuels for aviation were selected from five broad classes of fuels. Then, a preliminary thermodynamic engine cycle design space exploration of a modern three spool turbofan is conducted to identify the fuel impact on cycle performance. Following that, an integrated Engine-Aircraft mission assessment for a Boeing 787 style aircraft with a three spool turbofan is conducted to assess performance at the mission level and explore opportunities and challenges for both powerplant and aircraft, accounting for fuel storage. Finally, an investigation of the opportunities available for the proposed fuels to be used as a heat sink is presented. The results indicate that zero-carbon fuels expand the design space for the powerplant cycle, allow for higher BPR, lower energy specific fuel consumption, lower peak cycle temperatures compared to the rest of the fuels, and provide significant cycle redesign opportunities. On a mission level, cryogenic fuels are penalized for block energy consumption due to the significant weight and size of the fuel storage system, while liquid alternative fuels are comparable to kerosene in terms of emissions and block energy consumption. Concerning Hydrogen, Methane, and Ammonia, the thermal power requirement for fuel conditioning (pressure and temperature rise) is calculated to be 2.2MW, 1.3MW, and 1MW respectively for a 240kN SLS thrust class engine during take-off.
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Integrated hybrid engine cycle design and power management optimization
(American Society of Mechanical Engineers, 2023-09-28) Ghelani, Raj; Roumeliotis, Ioannis; Saias, Chana Anna; Mourouzidis, Christos; Pachidis, Vassilios; Bacic, Marko; Norman, Justin
A novel integrated gas turbine cycle design and power management optimization methodology for parallel hybrid electric propulsion architectures is presented in this paper. The gas turbine multi-point cycle design method is extended to turboprop and turbofan architectures, and several trade studies are performed initially at the cycle level. It is shown that the maximum degree of electrification is limited by the surge margin levels of the booster in the turbofan configuration. An aircraft mission-level assessment is then performed using the integrated optimization method initially for an A320 Neo style aircraft case. The results indicate that the optimal cycle redesigned hybrid electric propulsion system (HEPS) favors take-off and climb power on-takes while optimal retrofit HEPS favor cruise power on-takes. It is shown that for current battery energy density (250 Wh/Kg), there is no fuel burn benefit. Furthermore, even for optimistic energy density values (750 Wh/kg) the maximum fuel burn benefit for a 500 nm mission is 5.5% and 4% for redesigned and retrofit HEPS, respectively. The power management strategies for HEPS configurations also differ based on gas turbine technology with improvement in gas turbine technology showing greater scope for electrification. The method is then extended to ATR 72 style aircraft case, showing greater fuel burn benefits across the flight mission envelope. The power management strategies also change depending on the objective function, and optimum strategies are reported for direct operating cost or fuel burn. The retrofit case studies show a benefit in direct operating cost compared to redesigned case studies for ATR 72. Finally, a novel multimission approach is shown to highlight the overall fuel burn and direct operating cost benefit across the aircraft mission cluster.