Browsing by Author "Sethi, Vishal"
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Item Open Access Abating CO2 and non-CO2 emissions with hydrogen propulsion(Cambridge University Press (CUP), 2024-04-02) Mourouzidis, Christos; Singh, G.; Sun, X.; Huete, Jon; Nalianda, Devaiah; Nikolaidis, Theoklis; Sethi, Vishal; Rolt, Andrew Martin; Goodger, E.; Pilidis, PericlesThis contribution focuses on the abatement with hydrogen of CO2 and non-CO2 emissions. It is agenda-setting in two respects. Firstly, it challenges the globally accepted hydrocarbon sustainable aviation fuel (SAF) pathway to sustainability and recommends that our industry accelerates along the hydrogen pathway to ‘green’ aviation. Secondly, it reports a philosophical and analytical investigation of appropriate accuracy on abatement strategies for nitrogen oxides and contrails of large hydrogen airliners. For the second contribution, a comparison is made of nitrogen oxide emissions and contrail avoidance options of two hydrogen airliners and a conventional airliner of similar passenger capacity. The hydrogen aircraft are representative of the first and second innovation waves where the main difference is the weight of the hydrogen tanks. Flights of 1000, 2000, 4000 and 8000 nautical miles are explored. Cranfield’s state of the art simulators for propulsion system integration and gas turbine performance (Orion and Turbomatch) were used for this. There are two primary contributions to knowledge. The first is a new set of questions to be asked of SAF and hydrogen decarbonising features. The second is the quantification of the benefits from hydrogen on non-CO2 emissions. For the second generation of long-range hydrogen-fuelled aircraft having gas turbine propulsion, lighter tanks (needing less thrust and lower gas temperatures) are anticipated to reduce NOx emissions by over 20%; in the case of contrails, the preliminary findings indicate that regardless of the fuel, contrails could largely be avoided with fuel-burn penalties of a few per cent. Mitigating action is only needed for a small fraction of flights. For conventional aircraft this penalty results in more CO2, while for hydrogen aircraft the additional emission is water vapour. The conclusion is that our research community should continue to consider hydrogen as the key ‘greening’ option for aviation, notwithstanding the very significant costs of transition.Item Open Access Assessment of an energy-efficient aircraft concept from a techno-economic perspective(Elsevier, 2018-04-17) Goldberg, Chana; Nalianda, Devaiah; Sethi, Vishal; Pilidis, Pericles; Singh, Riti; Kyprianidis, KonstantinosAn increase in environmental awareness in both the aviation industry and the wider global setting has led to large bodies of research dedicated to developing more sustainable technology with a lower environmental impact and lower energy usage. The goal of reducing environmental impact has necessitated research into revolutionary new technologies that have the potential to be significantly more energy efficient than their predecessors. However, for innovative technologies in any industry, there is a risk that adoption will be prohibitively expensive for commercial application. It is therefore important to model the economic factors of the new technology or policy at an early stage of development. This research demonstrates the application of a Techno-economic Environmental Risk Assessment framework that may be used to identify the economic impact of an energy-efficient aircraft concept and the impact that environmental policy would have on the viability of the concept. The framework has been applied to a case study aircraft designed to achieve an energy saving of 60% in comparison to a baseline 2005 entry-into-service aircraft. The model compares the green aircraft concept to a baseline conventional aircraft using a sensitivity analysis of the aircraft direct operating cost to changes in acquisition and maintenance cost. The research illustrates an economically viable region for the technology. Cost margins are identified where the increase in operating cost due to expensive novel technology is counterbalanced by the reduction in cost resulting from low energy consumption. Viability was found to be closely linked to fuel price, with a low fuel price limiting the viability of energy-efficient aviation technology. In contrast, a change in environmental taxation policy was found to be beneficial, with the introduction of carbon taxation incentivising the use of an environmentally optimised aircraft.Item Open Access An assessment of high overall pressure ratio intercooled engines for civil aviation(Cranfield University, 2014-01) Camilleri, William; Sethi, VishalAs gas turbine technology matures, further significant improvements in engine efficiency will be difficult to achieve without the implementation of new aero-engine configurations. This thesis delivers an original contribution to knowledge by comparing the design, performance, fuel burn and emission characteristics of a novel geared intercooled reversed flow core concept with those of a conventional geared intercooled straight flow core concept. This thesis also outlines a novel methodology for the characterisation of uncertainty at the conceptual design phase which is useful for the comparison of competing concepts. Conventional intercooled aero-engine concepts suffer from high over-tip leakage losses in the high pressure compressor, high pressure losses in the intercooler installation and increased weight and drag whereas the geared intercooled reversed flow core concept overcomes some of these limitations. The HP-spool configuration of the reversed core concept allows for an increase in blade height, a reduction in over-tip leakage losses and an increase in overall pressure ratio. It was concluded that a 1-pass intercooler would be the lightest and most compact design while a 2-pass intercooler would be easier to manufacture. In the reversed flow core concept the increased length of the 2-pass intercooler could be accommodated. In this concept the mixer also allows for a reduction in fan pressure ratio and a useful reduction in component losses. Both intercooled concepts were shown to benefit from the use of a variable area bypass nozzle for the reduction of take-off combustor outlet temperature and cruise specific fuel consumption. The intercooled cycles were optimised for minimum fuel burn and it was found that the reversed flow core concept benefits from higher overall pressure ratio and lower fan pressure ratio for an equivalent specific thrust. This leads to an improvement in thermal efficiency and more than a 1.6% improvement in block fuel burn. The NOx during landing and take-off as well as during cruise was found to be slightly more severe for the reversed flow core concept due to its higher overall pressure ratio. The contrails emissions of this concept were occasionally higher than for a year 2000 turbofan but only slightly higher than for the straight core concept. This dissertation shows that in spite of input uncertainty the reversed flow core intercooled engine is a promising concept. Further research should focus on higher fidelity structural and aerodynamic modelling.Item Open Access CFD investigation of a core-mounted-target-type thrust reverser, Part 1: reverser stowed configuration(ASME, 2017-12-25) Mahmood, Tashfeen; Jackson, Anthony J. B.; Sethi, Vishal; Khanal, Bidur; Ali, FakhreDuring the second half of the 90's, NASA performed experimental investigations on six novel Thrust Reverser designs; Core Mounted Target Type Thrust Reverser (CMTTTR) design is one of them. To assess the CMTTTR efficiency and performance, NASA conducted several wind tunnel tests at Sea Level Static conditions. The results from these experiments are used in this paper series to validate the CFD results. This paper is part one of the three-part series; Part 1 and 2 discusses the CMTTTR in stowed and deployed configurations, all analysis in the first two papers are performed at SLS conditions. Part3 discusses the CMTTTR in the forward flight condition. The key objectives of this paper are: first, to perform the 3D CFD analysis of the reverser in stowed configuration; all analyses are performed at SLS condition. The second objective is to validate the acquired CFD results against the experimental data provided by NASA[1]. The third objective is to verify the fan and overall engine net thrust values acquired from the aforementioned CFD analyses against those derived based on 1-D engine performance simulations. The fourth and final objective is to examine and discuss the overall flow physics associated with the CMTTTR under stowed configuration. To support the successful implementation of the overall investigation, full-scale 3DCAD models are created, representing a fully integrated GE90 engine, B777 wing, and pylon configuration. Overall a good agreement is found between the CFD and test results; the difference between the two was less than 5%.Item Open Access CFD investigation of a core-mounted-target-type thrust reverser, Part 2: reverser deployed configuration(ASME, 2017-12-25) Mahmood, Tashfeen; Jackson, Anthony J. B.; Sethi, Vishal; Khanal, Bidur; Fakhre, AliCMTTTR design was proposed by NASA in the second half of the 90's. NASA carried out several experiments at static conditions, and their acquired results suggested that the performance characteristics of the CMTTTR design falls short to comply with the mandatory TR performance criteria, and were therefore regarded as an infeasible design. However, the authors of this paper believe that the results presented by NASA for CMTTTR design require further exploration to facilitate the complete understanding of its true performance potential. This Part2 paper is a continuation from Part1and presents a comprehensive three-dimensional (CFD) analyses of the CMTTTR in deployed configuration; the analyses at forward flight conditions will be covered in Part 3. The key objectives of this paper are: first, to validate the acquired CFD results with the experimental data provided by NASA: this is achieved by measuring the static pressure values on various surfaces of the deployed CMTTTR model. The second objective is to estimate the performance characteristics of the CMTTTR design and corroborate the results with experimental data. The third objective is to estimate the Pressure Thrust (i.e. axial thrust generated due to the pressure difference across various reverser surfaces) and discuss its significance for formulating the performance of any thrust reverser design. The fourth objective is to investigate the influence of kicker plate installation on overall TR performance. The fifth and final objective is to examine and discuss the overall flow physics associated with the thrust reverser under deployed configuration.Item Open Access Civil aircraft trajectory analyses - impact of engine degradation on fuel burn and emissions(Cranfield University, 2013-05) Venediger, Benjamin; Sethi, VishalCommercial aviation and air traffic is still expected to grow by 4-5% annually in the future and thus the effect of aircraft operation on the environment and its consequences for the climate change is a major concern for all parties involved in the aviation industry. One important aspect of aircraft engine operation is the performance degradation of such engines over their lifetime while another aspect involves the aircraft flight trajectory itself. Therefore, the first aim of this work is to evaluate and quantify the effect of engine performance degradation on the overall aircraft flight mission and hence quantify the impact on the environment with regards to the following two objectives: fuel burned and NOxemissions. The second part of this study then aims at identifying the potential for optimised aircraft flight trajectories with respect to those two objectives. A typical two-spool high bypass ratio turbofan engine in three thrust variants (low, medium and high) and a typical narrow body single-aisle aircraft similar to the A320 series were modelled as a basis for this study. In addition, an existing emissions predictions model has been adapted for the three engine variants. Detailed parametric and off-design analyses were carried out to define and validate the performance of the aircraft, engine and emissions models. The obtained results from a short and medium range flight missions study showed that engine degradation and engine take-off thrust reduction significantly affect total mission fuel burn and total mission NOx emissions (including take-off) generated. A 2% degradation of compressor, combustor and turbine component parameters caused an increase in total mission fuel burn of up to 5.3% and an increase in NOx emissions of up to 5.9% depending on the particular mission and aircraft. However, take-off thrust reduction led to a decrease in NOx emissions of up to 41% at the expense of an increase in take-off distance of up to 12%. Subsequently, a basic multi-disciplinary aircraft trajectory optimisation framework was developed and employed to analyse short and medium range flight trajectories using one aircraft and engine configuration. Two different optimisation case studies were performed: (1) fuel burned vs. flight time and (2) fuel burned vs. NOx emitted. The results from a short range flight mission suggested a trade-off between fuel burned versus flight time and showed a fuel burn reduction of 3.0% or a reduction in flight time of 6.7% when compared to a “non-optimised” trajectory. Whereas the optimisation of fuel burn versus NOx emissions revealed those objectives to be non- conflicting. The medium range mission showed similar results with fuel burn reductions of 1.8% or flight time reductions of 7.7% when compared to a “non- optimised” trajectory. Accordingly, non-conflicting solutions for fuel burn versus NOx emissions have been achieved. Based on the assumptions introduced for the trajectory optimisation analyses, the identified optimised trajectories represent possible solutions with the potential to reduce the environmental impact. In order to increase the simulation quality in the future and to provide more comprehensive results, a refinement and extension of the framework also with additional models taking into account engine life, noise, weather or operational procedures, is required. This will then also allow the assessment of the implications for airline operators in terms of Direct Operating Costs (DOC). In addition, the degree of optimisation could be improved by increasing the number and type of optimisation variables.Item Open Access Comparison of hydrogen micromix flame transfer functions determined using RANS and LES(ASME, 2019-11-05) McClure, Jonathan; Abbott, David; Agarwal, Parash; Sun, Xiaoxiao; Babazzi, Giulia; Sethi, Vishal; Gauthier, Pierre Q.Hydrogen has been proposed as an alternative fuel to meet long term emissions and sustainability targets, however due to the characteristics of hydrogen significant modifications to the combustion system are required. The micromix concept utilises a large number of miniaturised diffusion flames to improve mixing, removing the potential for local stoichiometric pockets, flash-back and autoignition. No publicly available studies have yet investigated the thermoacoustic stability of these combustion systems, however due to similarities with lean-premixed combustors which have suffered significant thermoacoustic issues, this risk should not be neglected. Two approaches have been investigated for estimating flame response to acoustic excitations of a single hydrogen micromix injector element. The first uses analytical expressions for the flame transfer function with constants obtained from RANS CFD while the second determines the flame transfer function directly using unsteady LES CFD. Results show the typical form of the flame transfer function but suggest micromix combustors may be more susceptible to higher frequency instabilities than conventional combustion systems. Additionally, the flame transfer function estimated using RANS CFD is broadly similar to that of the LES approach, therefore this may be suitable for use as a preliminary design tool due to its relatively low computational expense.Item Open Access Comparison of tabulated and complex chemistry turbulent-chemistry interaction models with high fidelity large eddy simulations on hydrogen flames(American Society of Mechanical Engineers, 2021-01-11) Zghal, M.; Sun, Xiaoxiao; Gauthier, Pierre Q.; Sethi, VishalHydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. The EU H2020 ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3. The micromix combustor comprises thousands of small diffusion flames where air and fuel are mixed in a crossflow pattern. This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and low-temperature small diffusion flames in lean overall equivalence ratios. In order to mature the hydrogen micromix combustion technology, high quality numerical simulations of the resulting short, thin and highly dynamic hydrogen flames, as well as predictions of combustion species, are essential. In fact, one of the biggest challenges for current CFD has been to accurately model this combustion phenomenon. The Flamelet Generated Manifold (FGM) model is a combustion model that has been used in the past decades for its predicting capabilities and its low computational cost due to its reliance on pre-tabulated combustion chemistry, instead of directly integrating detailed chemistry mechanisms. However, this trade for a lower computational cost may have an impact on the solution, especially when considering a fuel such as Hydrogen. Therefore, it is necessary to compare the FGM model to another combustion modelling approach which uses more detailed complex chemistry. The main focus of this paper then, is to compare the flame characteristics in terms of position, thickness, length, temperature and emissions obtained from LES simulations done with the FGM model, to the results obtained with more complex chemistry models, for hydrogen micromix flames. This will be done using STAR-CCM+ to determine the most suitable numerical approach required for the design of injection systems for ultra-low NOx.Item Open Access Development and application of a preliminary design methodology for modern low emissions aero combustors(SAGE, 2020-04-23) Liu, Yize; Sun, Xiaoxiao; Sethi, Vishal; Li, Yi-Guang; Nalianda, Devaiah; Abbott, David; Gauthier, Pierre Q.; Xiao, Bairong; Wang, LuIn this article, a preliminary design framework containing a detailed design methodology is developed for modern low emissions aero combustors. The inter-related design elements involving flow distribution, combustor sizing, heat transfer and cooling, emission and performance are coupled in the design process. The physics-based and numerical methods are provided in detail, in addition to empirical or semi-empirical methods. Feasibility assessment on the developed work is presented via case studies. The proposed combustor sizing methodology produces feasible combustor dimensions against the public-domain low emissions combustors. The results produced by the physics-based method show a reasonable agreement with experimental data to represent NOx emissions at key engine power conditions. The developed emission prediction method shows the potential to assess current and future technologies. A two-dimensional global prediction on liner wall temperature distribution for different cooling systems is reasonably captured by the developed finite difference method. It can be of use in the rapid identification of design solutions and initiating the optimisation of the design variables. The altitude relight efficiency predicted shows that the method could be used to provide an indicative assessment of combustor altitude relight capability at the preliminary design phase. The methodology is applied and shows that it enables the automatic design process for the development of a conceptual lean staged low emissions combustor. The design evaluation is then performed. A sensitivity analysis is carried out to assess the design uncertainties. The optimisation of the air distribution and cooling geometrical parameters addresses the trade-off between the NOx emissions and liner wall cooling, which demonstrates that the developed work has potential to identify and solve the design challenges at the early stages of the design process.Item Open Access Development of gas turbine combustor preliminary design methodologies and preliminary assessments of advanced low emission combustor concepts(Cranfield University, 2012-07) Khandelwal, Bhupendra; Singh, R.; Sethi, VishalIt is widely accepted that climate change is a very serious environmental concern. Levels of carbon dioxide (CO2) and other emissions in the global atmosphere have increased substantially since the industrial revolution and now increasing faster than ever before. There is a thought that this has already led to dangerous warming in the Earth’s atmosphere and relevant changes around. Emissions legislations are going to be stringent as the years will pass. Hydro carbon fuel cost is also increasing substantially; more over this is non- renewable source of energy. There is an urgent need for novel combustor technologies for reducing emission as well as exploring alternative renewable fuels without effecting combustor performance. Development of novel combustors needs comprehensive understanding of conventional combustors. The design and development of gas turbine combustors is a crucial but uncertain part of an engine development process. At present, the design process relies upon a wealth of experimental data and correlations. Some major engine manufacturers have addressed the above problem by developing computer programs based on tests and empirical data to assist combustor designers, but such programs are proprietary. There is a need of developing design methodologies for combustors which would lead to substantial contribution to knowledge in field of combustors. Developed design methodologies would be useful for researchers for preliminary design assessments of a gas turbine combustor. In this study, step by step design methodologies of dual annular radial and axial combustor, triple annular combustor and reverse flow combustor have been developed. Design methodologies developed could be used to carry out preliminary design along with performance analysis for conventional combustion chambers. In this study the author has also proposed and undertaken preliminary studies of some novel combustor concepts. A novel concept of a dilution zone less combustor has been proposed in this study. According to this concept dilution air would be introduced through nozzle guide vanes to provide an optimum temperature traverse for turbine blades. Preliminary study on novel dilution zone less combustor predicts that the length of this combustor would be shorter compared to conventional case, resulting in reduced weight, fuel burn and vibrations. Reduced fuel burn eventually leads to lower emissions. Another novel concept of combustor with hydrogen synthesis from kerosene reformation has been proposed and a preliminary studies has been undertaken in this work. Addition of hydrogen as an additive in gas turbine combustor shows large benefits to the performance of gas turbine engines in addition to reduction in NOx levels. The novel combustor would have two stages, combustion of ~5% of the hydrocarbon fuel would occur in the first stage at higher equivalence ratios in the presence of a catalyst, which would eventually lead to the formation of hydrogen rich flue gases. In the subsequent stage the hydrogen rich flue gases from the first stage would act as an additive to combustion of the hydrocarbon fuel. It has been preliminary estimated that the mixture of the hydrocarbon fuel and air could subsequently be burned at much lower equivalence ratios than conventional cases, giving better temperature profiles, flame stability limits and lower NOx emissions. The effect of different geometrical parameters on the performance of vortex controlled hybrid diffuser has also been studied. It has been predicted that vortex chamber in vortex controlled hybrid diffuser does not play any role in altering the performance of diffuser. The overall contribution to knowledge of this study is development of combustor preliminary design methodologies with different variants. The other contribution to knowledge is related to novel combustors with a capability to produce low emissions. Study on novel combustor and diffuser has yielded application of two patent applications with several other publications which has resulted in a contribution to knowledge. A list of research articles, two patents, awards and achievements are presented in Appendix C.Item Open Access Effect of steam addition on gas turbine combustor design and performance(Elsevier, 2016-05-12) Xue, Rui; Hu, Chunbo; Sethi, Vishal; Nikolaidis, Theoklis; Pilidis, PericlesAdding steam influences the combustion process inside the combustor, which should be taken into account during combustor design. The design of combustor has long been the most challenging process. This study integrated the gas turbine performance with the combustor design, and formulated a detailed procedure for single annular combustors with steam addition consideration in particular. To accomplish this, a computer code has been developed based on the design procedures. The design model could provide the combustor geometry and the combustor performance. The inlet parameters for combustor design are obtained and validated through the calculation of gas turbine engine performance provided by our own home code. The model predictions are compared with operational and configuration data from two real engines and show reasonably good accuracy. The influence of steam addition on combustor design is investigated and results showed the variation of geometrical size is highest for components where intense combustion takes place while the design is almost kept the same for components where only pure flow exists. After conforming the feasibility of the combustor design code, we investigated the effects of steam addition on combustor performance. It revealed that steam injection is an effective way to reduce the temperature in the burner while other performance like the total pressure loss would be slightly deteriorated.Item Open Access Emissions modelling for engine cycle and aircraft trajectory optimisation(Cranfield University, 2013-06) Pervier, Hugo; Sethi, VishalThe aviation industry is currently experiencing a growth rate of about 4% per annum and this trend is expected to continue into the future. One concern about this growth rate is the impact it will have on the environment particularly in terms of emissions of CO2, NOx and relatively recently also cirrus clouds induced by contrails. The ACARE has set emissions reduction targets of 50% reduction of CO2 and noise and 80% reduction of NOx by 2020 relative to Y2000 technology. Clean Sky and other large EU collaborative projects have been launched in an effort to identify new, more efficient, aircraft and engine technologies, greener operational and asset management practices and lower life cycle emissions. This PhD research was funded by and contributed to the Systems for Green Operations Integrated Technology Demonstrator (SGO-ITD) of the Clean Sky project. The key contribution to knowledge of this research is the development and application of a methodology for simultaneous optimisation of aircraft trajectories and engine cycles. Previous studies on aircraft trajectory optimisation studies, published in the public domain, are based on relatively low fidelity models. The case studies presented in this thesis are multi-objective and based on higher fidelity, verified aircraft, engine and emissions models and also include assessments of conceptual engines with conceptual LPP combustors. The first task involved the development of reactor based NOx emission prediction models for a conventional aero gas turbine combustor and a novel conceptual lean pre-mixed pre-vaporised combustor. A persistent contrails prediction model was also developed. A multi-disciplinary framework comprising a genetic algorithm based optimiser integrated with an engine performance, an aircraft performance and an emission prediction model was then developed. The framework was initially used to perform multi-disciplinary aircraft trajectory optimisation studies and subsequently both aircraft trajectory and engine cycle optimisation studies simultaneously to assess trade-offs between mission fuel burn, flight time, NOx production and persistent contrails formation ... [cont.].Item Open Access Enabling cryogenic hydrogen-based CO2-free air transport: meeting the demands of zero carbon aviation(IEEE, 2022-06-02) Sethi, Vishal; Sun, Xiaoxiao; Nalianda, Devaiah; Rolt, Andrew Martin; Holborn, Paul; Wijesinghe, Charith; Xisto, Carlos; Jonsson, Isak; Grönstedt, Tomas; Ingram, James; Lundbladh, Anders; Isikveren, Askin; Williamson, Ian; Harrison, Tom; Yenokyan, AnnaFlightpath 2050 from the European Union (EU) sets ambitious targets for reducing the emissions from civil aviation that contribute to climate change. Relative to aircraft in service in year 2000, new aircraft in 2050 are to reduce CO2 emissions by 75% and nitrogen oxide (NOx) emissions by 90% per passenger kilometer flown. While significant improvements in asset management and aircraft and propulsion-system efficiency and are foreseen, it is recognized that the Flightpath 2050 targets will not be met with conventional jet fuel. Furthermore, demands are growing for civil aviation to target zero carbon emissions in line with other transportation sectors rather than relying on offsetting to achieve “net zero.” A more thorough and rapid greening of the industry is seen to be needed to avoid the potential economic and social damage that would follow from constraining air travel. This requires a paradigm shift in propulsion technologies. Two technologies with potential for radical decarbonization are hydrogen and electrification. Hydrogen in some form seems an inevitable solution for a fully sustainable aviation future. It may be used directly as a fuel or combined with carbon from direct air capture of CO2 or other renewable carbon sources, to synthesize drop-in replacement jet fuels for existing aircraft and engines. As a fuel, pure hydrogen can be provided as a compressed gas, but the weight of the storage bottles limits the practical aircraft ranges to just a few times that is achievable with battery power. For longer ranges, the fuel needs to be stored at lower pressures in much lighter tanks in the form of cryogenic liquid hydrogen (LH2).Item Open Access Enhancing aero engine performance through synergistic combinations of advanced technologies.(2019-07) Rolt, Andrew Martin; Sethi, Vishal; Nalianda, DevaiahBy 2050 the evolutionary approach to aero engine research and development will no longer be able to maintain historic rates of performance improvement. Future geared fan and open rotor engines promise increased propulsive efficiency and reduced noise, but will need to incorporate new technologies to improve core thermal efficiency in order to meet the ambitious fuel-burn and emissions targets set by ACARE in Flightpath 2050. In the face of increasing air traffic, radical new approaches will be needed to minimize the impact of aviation on the environment. A long-term vision is required. This PhD project investigates the potential of innovative propulsion technologies for civil aviation. Candidate technologies include topping and bottoming cycles, secondary combustion, intercooling and recuperation. The reported research investigates potential synergies between these advanced core technologies that when integrated together should give a significant fuel burn reduction relative to a more-conventional year-2050 ‘reference’ Brayton-cycle turbofan. Spreadsheet models have been used to quantify performance and estimate the weight and fuel burn savings for each new engine cycle. Further models were created to investigate preferred topping and bottoming cycle arrangements. NOx emissions are estimated for engines with rich-quench-lean (RQL) or lean-direct-injection (LDI) combustors. The correlation for future LDI combustor NOx emissions was selected following a review of recent LDI combustor research and a detailed study of alternative options. Increasingly aerodynamically efficient and lighter weight aircraft with more efficient engines will have lower thrust requirements. Advanced engine cycles also generally increase core specific power and reduce core mass flow, so future engines will have smaller turbo-machines that will tend to have lower component efficiencies. Therefore a preliminary study investigated the effects of thrust-scaling on the efficiency of the reference turbofan and possible high-OPR intercooled engines, since these could have very small core components. Novel core-component designs and engine architectures can minimize these penalties. Positive-displacement topping-cycle machines and reverse-flow-core engine layouts should help to maintain component efficiency and improve SFC, but low weight and low drag are also essential to minimize fuel burn. Therefore weight assessments of the advanced engine designs were made, and fuel-burn exchange rates used to quantify expected mission-level CO₂ reductions. Following a qualitative assessment of synergies between potential advanced technologies, an engine that combines intercooling, a topping cycle, secondary combustion and an open-air-cycle bottoming cycle was selected for detailed study. While each of these technologies has been researched previously, the contribution and value that each advanced core technology could bring to the whole in a large geared turbofan has not so far been reported. The approach initiated was to model a series of engines omitting each technology in turn and this scheme has been partially realized. The modelled topping-cycle technology uses six nutating-disc modules as a replacement for conventional combustors, high pressure compressors and turbines. A nutating-disc core module concept design led to the creation of a display model that was shown on the ULTIMATE project stand at the 2018 Farnborough International Air Show. The selected cycle combining all four technologies should reduce SFC by about 15% relative to the reference year-2050 turbofan and is assessed to reduce fuel burn by up to 18.5% in a long-range aircraft. An engine with intercooling, intra-turbine combustion and a bottoming cycle reduces SFC by about 6%, and an engine that is simply intercooled reduces SFC by about 3%. The topping cycle gives the biggest potential thermal efficiency improvement, but nutating-disc technology presents very significant design challenges for large aero engines, particularly with regard to internal sealing and bearing loads. Therefore it is recommended that alternative topping-cycle technologies should be researched for long-term aero engine performance improvements. A further study shows the effect of the target 15% reduction in fuel burn on in-flight CO2 emissions by the civil aviation fleet under various traffic-growth scenarios.Item Open Access Evaluation and optimisation of environmentally friendly aircraft propulsion systems(Cranfield University, 2010-04) Celis, Cesar; Sethi, Vishal; Singh, R.; Pilidis, PericlesIn this globalised world where the efficient transportation of people and goods greatly contributes to the development of a given region or country, the aviation industry has found the ideal conditions for its development, thereby becoming in one of the fastest growing economic sectors during the last decades. The continuing growth in air traffic and the increasing public awareness about the anthropogenic contribution to global warming have meant that environmental issues associated with aircraft operations are currently one of the most critical aspects of commercial aviation. Several alternatives for reducing the environmental impact of aircraft operations have been proposed over the years, and they broadly comprise reductions in the number of aircraft operations, changes in the type of aircraft, and changes in the aircraft operational rules and procedures. However, since the passenger traffic is expected to increase over the next years, only the last two options seem to be the most feasible solutions to alleviate the problem. Accordingly, the general aim of this research work is to develop a methodology to evaluate and quantify aircraft/engines design trade-offs originated as a consequence of addressing conflicting objectives such as low environmental impact and low operating costs. More specifically, it is an objective of this work to evaluate and optimise both aircraft flight trajectories and aircraft engine cycles taking into account multidisciplinary aspects such as performance, gaseous emissions, and economics. In order to accomplish the objectives proposed in this project, a methodology for optimising aircraft trajectories has been initially devised. A suitable optimiser with a library of optimisation algorithms, Polyphemus, has been then developed and/or adapted. Computational models simulating different disciplines such as aircraft performance, engine performance, and pollutants formation, have been selected or developed as necessary. Finally, several evaluation and optimisation processes aiming to determine optimum and ‘greener’ aircraft trajectories and engine cycles have been carried out and their main results summarised. In particular, an advanced, innovative gaseous emissions prediction model that allows the reliable calculation of emissions trends from current and potential future aircraft gas turbine combustors has been developed. When applied to a conventional combustor, the results showed that in general the emission trends observed in practice were sufficiently well reproduced, and in a computationally efficient manner for its subsequent incorporation in optimisation processes. For performing the processes of optimisation of aircraft trajectories and engine cycles, an optimiser (Polyphemus) has also been developed and/or adapted in this work. Generally the results obtained using Polyphemus and other commercially available optimisation algorithms presented a satisfactory level of agreement (average discrepancies of about 2%). It is then concluded that the development of Polyphemus is proceeding in the correct direction and should continue in order to improve its capabilities for identifying and efficiently computing optimum and ‘greener’ aircraft trajectories and engine cycles, which help to minimise the environmental impact of commercial aircraft operations. The main contributions of this work to knowledge broadly comprise the following: (i) development of an environmental-based methodology for carrying out both aircraft trajectory optimisation processes, and engine cycle optimisation-type ones; (ii) development of both an advanced, innovative gas turbine emissions prediction model, and an optimiser (Polyphemus) suitable to be integrated into multi-disciplinary optimisation frameworks; and (iii) determination and assessment of optimum and ‘greener’ aircraft trajectories and aircraft engine cycles using a multi-disciplinary optimisation tool, which included the computational tools developed in this work. Based on the results obtained from the different evaluation and optimisation processes carried out in this research project, it is concluded that there is indeed a feasible route to reduce the environmental impact of commercial aviation through the introduction of changes in the aircraft operational rules and procedures and/or in the aircraft/engine configurations. The magnitude of these reductions needs to be determined yet through careful consideration of more realistic aircraft trajectories and the use of higher fidelity computational models. For this purpose, the computations will eventually need to be extended to the entire fleet of aircraft, and they will also need to include different operational scenarios involving partial replacements of old aircraft with new environmentally friendly ones.Item Open Access Evaluation of optimised flight trajectories for conventional and novel aircraft and engine integrated systems(Cranfield University, 2013-04) Gu, Weiqun; Sethi, VishalToday, the air transport industry has become an essential element of global society by its great contributions to the wide exchanges of cultures/people and to the rapid growth in the world economy. However, on the other hand, the adverse impacts on the environment caused by air transport, such as air pollution, noise and climate change, are drawing, increasingly, growing public concern. In order to address the steady growth in air-travel demand in the next decades through an environmentally-friendly way and realise the ACARE 2020 environmental goals, The Clean Sky programme has been launched by European Union over the period 2008 – 2013. The project research, described in this thesis and sponsored by the Clean Sky programme, aims at evaluating the feasibility of reducing the environmental impact of commercial aviation through the introduction of changes in the aircraft operational rules and procedures, as well as the application of the new-generation propfan (open rotor) engine, based on flight trajectory multidisciplinary optimisation and analysis of commercial aircraft. In order to accomplish the above research objectives, a complete methodology to achieve and realise optimum flight trajectories has been initially proposed. Then, 12 component-level models which function as simulating different disciplines, such as aircraft performance, engine performance, engine gaseous emission, and flight noise, have been developed or selected/adopted. Further, nine system-level integration and optimisation models were built. These system-level models simulate flights from Amsterdam Schiphol airport in the Netherlands to Munich airport in Germany flown by different types of aircraft through different flight phases with different optimisation objectives. Finally, detailed investigations into the flight trajectory optimisations were performed, extensive optimisation results were achieved and corresponding description, analysis and comparisons were provided. The main contributions of this work to knowledge broadly comprise the following: 1) the further development regarding the methodology of flight trajectory multidisciplinary optimisation; 2) previous work on aircraft trajectory optimisation has often considered fixed objectives over the complete flight trajectory. This research focused on representative flight phases of a flight mission with different optimisation objectives, namely, noise impact and fuel burn during the departure phase; fuel burn and flight time during en route phase; and noise impact and NOx emission during the arrival phase; 3) this research has extended the current flight trajectory optimisations to turboprop and propfan equipped aircraft. As a result, a relative complete 2D flight trajectory multidisciplinary optimisation spectrum, spanned by primary commercial aircraft types, primary flight phases and primary optimisation objectives of interest, has been built. Although encouraging progress have been achieved, this project research, as with any other research activity, is also only ‘on the way’ rather than coming to the ‘end’ point. There are still many aspects which can be improved further and there is still much new research and exploration which can be investigated further. All these have also been suggested in this thesis.Item Open Access Influence of Airport Factors and Mission Fuel Burn Optimised Aircraft Trajectories on Severity and Engine Life(Cranfield University, 2014-06-20) Khani, Nqobile; Sethi, Vishal; Pilidis, PericlesThe continuous growth of air transport has raised concerns about global aircraft fuel consumption, emissions and noise. Industry’s efforts have identified that to reduce future emissions and the impact of aircraft operations on the environment will require contribution from: a) New technologies with better efficiency b) Improved asset management and c) Greener manufacturing and recycling processes. This research falls under asset management and involves aircraft trajectory optimisation. Most aircraft trajectory optimisation studies concentrate on optimising fuel burn, emissions and noise. Fuel burn is the dominant contributor to operating costs. During the course of this work, no work was found to better understand from an operator’s perspective how the optimal solutions for minimising fuel burn and protecting the environment will impact on engine useful life and the engine operating costs. Also no work was found to understand how engine component degradation will impact on the optimised solutions for fuel burn and engine life. The contribution to knowledge from this research is a) the assessment of the impact of airport severity factors on engine life consumption and aircraft performance and b) the assessment and quantification of the change in engine life usage when optimising for flight mission fuel burn and the change in flight mission fuel burn when optimising for engine life usage; in both cases the effects of engine component degradation are considered and assessed. The trade-offs between mission fuel burn and engine life optimised trajectories are presented here for a clean (new) engine for three routes (London–Madrid, London–Ankara and London–Abu Dhabi). The engine life calculated was the HPT blade life and HPT disc life due to creep, fatigue and oxidation failure modes independent of each other. Mission fuel burn and engine life trajectory optimisation assessments were conducted to incorporate the effects of degradation after 3000, 4500 and 5250cycles of operation. Further assessments were made linking aircraft performance to airport severity factors for the clean engine, after 3000cycles and after 5250cycles. A techno-economic environmental risk assessment approach was used. The results indicate that airports at higher altitudes e.g. Cairo, suffer more severity due to higher operating temperatures, but benefit from less climb fuel burn and lower operating costs. The severity and fuel burn for take-off at airports with higher ambient temperatures was found to be more due to the higher operating temperatures required. The operating cost at these airports was thus higher. The fuel burn optimised trajectories were found to be achieved at higher operating temperatures with reduced blade life (due to creep, fatigue and oxidation). In particular, for London–Madrid, the blade creep and blade oxidation lives were found to reduce by -3.4% and -2.1% respectively. The blade oxidation life optimised trajectories showed increase in fuel burn of +3.6% and +4.9% for London–Madrid and London–Ankara respectively. The blade creep life optimised trajectories for London–Abu Dhabi were found to benefit from less fuel burn during climb. The disc creep life optimised trajectories showed benefit in fuel burn for London–Ankara and London–Abu Dhabi. The conclusions from the study are: High OAT and high altitude airports such as Abu Dhabi require higher operating temperatures which have severe consequences on the engine component life, fuel burn and emissions. Fuel burn optimised trajectories have a negative effect on the blade life due to creep, fatigue and oxidation due to higher maximum operating temperatures. However, the reduction in fuel burn outweighs the drop in life, thus benefitting to the operating costs. Optimising for blade creep life benefits the fuel burn for London–Abu Dhabi due to less fuel burn at climb The blade oxidation life optimised trajectories are detrimental to the fuel burn due to slower cruise speeds and more time spent at cruise and descent The disc creep life optimised trajectories benefit the fuel burn for London – Ankara and London–Abu Dhabi due to flying at higher cruise altitudes and burning less fuel. The recommendations from this research include making improvements to the framework such as a) Integrating the lifing methodologies because in reality the failure modes are not entirely independent of each other but do interact b) Develop and incorporate a diagnostics and prognostics tool to predict levels of degradation c) Using actual waypoints and incorporate horizontal trajectory profiles d) Future studies can include noise as an objective, which though mentioned has not been within the scope of this work. e) A key driver to lower operating costs is a considerable reduction in fuel burn. Maintenance costs will inevitably rise with engine life consumption. Further study of the trade-offs between fuel burn and engine life is therefore recommended.Item Open Access Injector design space exploration for an ultra-low NOx hydrogen micromix combustion system(ASME, 2019-11-05) Agarwal, Parash; Sun, Xiaoxiao; Gauthier, Pierre Q.; Sethi, VishalThe depletion of fossil fuel resources, as well as the increasing environmental concerns have become the driving forces towards the research and development necessary for the introduction of alternative fuel such as hydrogen into civil aviation. Hydrogen is a suitable energy source primarily because it is free of carbon and other forms of impurities and is also the most abundant element in the universe. The advantages of using Liquid Hydrogen (LH2) for civil aviation extends beyond carbon-free mission level emissions; LH2 combustion can potentially reduce NOx emission by up to 90%, providing long-term sustainability and unrivalled environmental benefits. The paper presents a simplified parametric analysis to investigate the influence of various injector design parameters on a hydrogen micromix combustor reactive flow field. The main characteristics investigated are the flame structure (shape and position), the aerodynamic stabilization of the flame and the resulting NOx emissions. The design parameters include variations in the air-feed dimensions and the hydrogen injection diameter. A suitable numerical model was established by comparing various turbulence modelling approaches, reaction mechanisms and turbulence-chemistry interaction modelling schemes. The predictive capabilities, and limitations, of each of these modelling approaches, are assessed. The numerical challenges and limitations associated with modelling H2/air combustion at high pressure and temperature conditions are detailed. The influence of varying the injector design parameters on the mixing and hence the NOx characteristics is assessed.Item Open Access Investigation of impact of engine degradation on optimum aircraft trajectories(Cranfield University, 2016-04) Navaratne, Rukshan; Sethi, Vishal; Pilidis, PericlesThe continuous growth in flight operations has led to public concern regarding the impact of aviation on the environment with its anthropogenic contribution to global warming. Several solutions have been proposed in order to reduce the environmental impact of aviation. However most of them are long term solutions such as new environmental friendly aircraft and engine designs. In this respect, management of aircraft trajectory and mission is a potential short term solution that can readily be implemented. Therefore, in order to truly understand the optimised environment friendly trajectories that can be actually deployed by airlines, it is important to investigate the impact of degraded engine performance on real aircraft trajectories at multi-disciplinary level. Several trajectory optimisation studies have been conducted in this direction in the recent past, but engines considered for the studies were clean and trajectories were ideal and simple. This research aims to provide a methodology to enhance the conventional approach of the aircraft trajectory optimisation problem by including engine degradation and real aircraft flight paths within the optimisation loop (framework); thereby the impact of engine degradation on optimum aircraft trajectories were assessed by quantifying the difference in fuel burn and emissions, when flying a trajectory which has been specifically optimised for an aircraft with degraded engines and flying a trajectory which has been optimised for clean engines. For the purpose of this study models of a clean and two levels of degraded engines have been developed that are similar to engines used in short range and long range aircraft currently in service. Degradation levels have been assumed based on the deterioration levels of Exhaust Gas Temperature (EGT) margin. Aircraft performance models have been developed for short range and long range aircraft with the capability of simulating (generating) vertical and horizontal flight profiles provides by the airlines. An emission prediction model was developed to assess NOx emissions of the mission. The contrail prediction model was adopted from previous studies to predict contrail formation. In addition, a multidisciplinary aircraft trajectory optimisation framework was developed and employed to analyse short range flight trajectories between London and Amsterdam and long range flight trajectories between London and Colombo under three cases. Case_1: Aircraft with clean engines, Case_2 and Case_3 were Aircraft with two different levels of degraded engines having a 5% and 10% Exhaust Gas Temperature (EGT) increase respectively. Three different multi objective optimisation studies were performed; (1) Fuel burn vs Flight time, (2) Fuel burn vs NOx emission, and (3) Fuel burn vs Contrails. Finally optimised trajectories generated with degraded engines were compared with the optimised trajectories generated with clean engines ... [cont].Item Open Access Life cycle greenhouse gas analysis of biojet fuels with a technical investigation into their impact on jet engine performance(Elsevier, 2015-04-07) Lokesh, Kadambari; Sethi, Vishal; Nikolaidis, Theoklis; Goodger, Eric; Nalianda, DevaiahBiojet fuels have been claimed to be one of the most promising and strategic solutions to mitigate aviation emissions. This study examines the environmental competence of Bio-Synthetic Paraffinic Kerosene (Bio-SPKs) against conventional Jet-A, through development of a life cycle GHG model (ALCEmB - Assessment of Life Cycle Emissions of Biofuels) from "cradle-grave" perspective. This model precisely calculates the life cycle emissions of the advanced biofuels through a multi-disciplinary study entailing hydrocarbon chemistry, thermodynamic behaviour and fuel combustion from engine/aircraft performance, into the life cycle studies, unlike earlier studies. The aim of this study is predict the "cradle-grave" carbon intensity of Camelina SPK, Microalgae SPK and Jatropha SPK through careful estimation and inclusion of combustion based emissions, which contribute ≈70% of overall life cycle emissions (LCE). Numerical modelling and non-linear/dynamic simulation of a twin-shaft turbofan, with an appropriate airframe, was conducted to analyse the impact of alternative fuels on engine/aircraft performance. ALCEmB revealed that Camelina SPK, Microalgae SPK and Jatropha SPK delivered 70%, 58% and 64% LCE savings relative to the reference fuel, Jet-A1. The net energy ratio analysis indicates that current technology for the biofuel processing is energy efficient and technically feasible. An elaborate gas property analysis infers that the Bio-SPKs exhibit improved thermodynamic behaviour in an operational gas turbine engine. This thermodynamic effect has a positive impact on aircraft-level fuel consumption and emissions characteristics demonstrating fuel savings in the range of 3-3.8% and emission savings of 5.8-6.3% (CO2) and 7.1-8.3% (LTO NOx), relative to that of Jet-A.