Swirl-stabilised hydrogen combustion has great potential in the aviation industry since emissions can be significantly reduced compared to fossil fuels. However, a major drawback is a high proneness to flashback. This could be overcome with non-swirling axial air injection (AAI) on the centre-line of the mixing tube. The effect of this concept on the effective Swirl number and flashback propensity was investigated for a radial- and axial swirl generator by Computational Fluid Dynamics (CFD) simulations and cold flow Particle Image Velocimetry (PIV) experiments on a custom-designed combustor model. Acquired results indicate that with increasing amount of AAI the Swirl number reduces due to both inertial and viscous effects. The flashback propensity also reduces as the axial velocity on the centre-line increases by AAI. For equal Swirl numbers the axial swirl generator was found to have a lower flashback propensity compared to the radial swirl generator, suggesting safer operation.

This report covers all major steps to establish an aviation emission inventory for 2019. This emission inventory is set up based on four consecutive steps. The first step is to gather all required data in the information model and this also includes some pre-processing of data to make it as complete as possible. The second step is to estimate the point performance of the aircraft at multiple waypoints along the trajectory based on the Base of Aircraft Data (BADA). This also allows for fuel consumption estimation. The third step uses the point performance data to estimate emissions under the respective flight condition. The last step addresses introduced uncertainties based on the different models. From a first principle perspective the uncertainty on a fleet wide scale (and for short and long haul flights) is found concerning the fuel consumption and various emission species (for example nitrogen oxides and carbon monoxide) using a Monte Carlo simulation. The trajectory data is obtained from flightradar24 in which gaps were identified where the type of aircraft, origin airport or destination airport were missing. Complementing of the database is based around the provided flight numbers and call signs. Based on airline data a variety of assumptions is made relating to payload fraction (69%) and increase in flight distance (8%) compared to the great circle distance. The trajectory is estimated using the rate of climb and descent provided in BADA. The emission model then uses constant emission indices, the boeing fuel flow method 2 (BFFM2) and the DLR method to compute all emissions according to: • Constant emission index: carbon dioxide (corrected for emission index of carbon monoxide), water vapor and sulfur oxide. • BFFM2: carbon monoxide, unburned hydrocarbons and nitrogen oxides. • DLR: black carbon emission. The uncertainty analysis, finally, covers airline operational uncertainty, model uncertainty and engine aging uncertainty to find an average increase in fuel consumption of 4.2%. Due to the influence of fuel flow, other emission species are increased with a different fraction. Due to computational limitations it has been decided to analyze one week, which will be representative of the entire year. Based on this analysis an annual fuel consumption of 272 Tg is simulated with corresponding carbon dioxide emission of 857 Tg. In addition, a nitrogen oxide emission of 5.3 Tg is found. All emission species are mainly emitted on the northern hemisphere on three geographical locations: north America, Europe and south-east Asia. The strongest recommendation is to include military flights and non-jet aircraft in the analysis (mainly turboprop aircraft). In addition, to decrease the dependency on data of a single week, it is advised to obtain more computational power to allow for analysis of multiple representative weeks preferably in both ICAO specified seasons. Finally it is recommended to extend the uncertainty analysis to cover more individual uncertainties such as the uncertainty in cruise altitude (based on airline routing) and to find more research on the uncertainty of sulfur content in kerosene.

As a response to a socio-economic framework which demands lower fuel consumption and CO2 emissions, gas turbine manufacturers strive to attain higher thermal efficiency and specific work output in their engines. The enhancement of these two performance parameters is linked to higher turbine inlet temperatures (TIT), which explains the increasing trend in TIT accompanying aero engines industrial development.  Turbine cooling technology is one of the disciplines strongly contributing to this aim, enabling operational hot gas temperatures to be higher than the melting temperature of the material. This study deals with film cooling: an external type of turbine cooling. Coolant air, bled from the compressor, is injected into the turbine blades and vanes and discharged through small holes into the airfoil´s external boundary layer, creating a thin insulating layer that reduces convective heat transfer from the hot gas to the surface. However, this gain in thermal capability brings along an aerodynamic penalty.  The purpose of this work is to understand the aerodynamic performance of a NACA 0012 airfoil with four rows of holes on the pressure side, as a follow-up experimental study of a previous one using the same model but with suction side injection (Lanzillotta, et al., 2017). A configuration with angle of attack α=0º, freestream velocity V∞=15m/s and air as secondary flow is tested as a baseline to understand the effect of blowing ratio BR∈(0,2) on flow field characteristics. Then, other configurations are tested to analyse the effect of angle of attack, freestream velocity, single row injection and density ratio by using CO2 as secondary flow, to simulate the temperature ratio existing in real gas turbine applications. Pointwise pressure measurements at a location downstream of the airfoil (x= 1.25c) and planar and stereo PIV are used as flow measurement techniques. Wake velocity profile characteristics and aerodynamic losses are retrieved from pressure measurements. Results for the baseline configuration show how the wake velocity profile displaces towards the pressure side when blowing is introduced. For low blowing ratios, the low momentum of the coolant induces high mixing losses whereas for high blowing ratios, the energizing effect of the high momentum coolant outweighs the mixing losses. Maximum losses are found for BR=0.5 and they decrease for higher blowing ratios. For BR=1.4, a shift from wake to jet local behaviour is observed in the wake velocity profile. The high and low velocity regions in the 2D average velocity fields computed from planar PIV measurements show the same trend with blowing ratio and provide further information about the mixing shear layer at a location close to the cooling holes. Finally, 3D average velocity fields computed from stereo PIV display the evolution of the mixing shear layer and jet in crossflow in the streamwise direction.

The Process and Energy department of the Mechanical, Maritime and Materials faculty of TU Delft and the Dutch company Petrogas Gas-Systems B.V. are working together on the commissioning of a small 50 kW (th) Indirectly Heated Bubbling Fluidised Bed Steam Reformer (IHBFBSR) which will be used to gasify the energy crop Miscanthus. However, the new feature is that this fluidised bed will be heated indirectly using radiant tube heaters installed in the reactor. These heaters are made by assembling radiant tubes with self-recuperative burners fired using Dutch Natural Gas. All tubes and burners have been manufactured by the German company WS Warmeprozesstechnik GmbH. This thesis consists of the study of two such distinct burner-tube assemblies, both of different heating capacity. The smaller capacity is of the C80 burner assembled with C100 tube while the larger is of the C100 burner assembled with C150 tube. The heat transfer and fluid dynamics inside both the tubes have been numerically modelled using CFD techniques. The models of the burners have been done using the commercially available software ANSYS Fluent version 18.2. The main objective of this thesis has been to analyse the heat transfer from both the assemblies and calculation of their respective efficiency. To this end, the temperature, velocity, species and turbulence fields have been calculated for inside both the tubes. Also, the total heat output from the radiant tubes has been calculated. However, the mechanism of heat transfer from the radiant tube to the fluidised bed was not known at the time of these calculations. Hence, appropriate boundary conditions have been used to simulate the outer environment. The total heat transfer from the combusting flow to the inner surface of the radiant tube has been calculated. This total heat input has been equated to the heat transfer from the outer surface of the tube to the fluidised bed, assuming steady state condition. The variation of all these parameters has been studied with air factor and preheat temperature. The air factor has been varied from 1.0 to 1.5 for both tubes, by reducing the fuel inlet keeping the air inlet constant. The air preheat temperature has been varied from 300 C to 700 C for C80-C100 assembly and from 300 C to 800 C for C100-C150 assembly. This has been done to calculate an optimum operating condition for both the burner-tube assemblies in terms of maximising heat transfer and radiant tube efficiency and minimising fuel wastage. It has been found that operating at lean condition of 20% excess air by mass at highest air preheat temperature would be the optimum operating condition. The last part of this thesis is the analysis of the robustness of calculations. Three grid sizes have been chosen other than the main grid and all the parameters have been checked for variations, if any. The variation is found to be within scientifically acceptable limits. Hence, it is concluded that the calculations are robust at this level.

Curved exhaust ducts are used in aero engine applications for different purposes, including thrust vectoring, shielding of parts from the exhaust or improving stealth properties. Their integration, however, regularly represents a design problem due to flow separation and high aerodynamic losses occurring in the bend. Curved duct flows for both compressible and incompressible conditions have been studied extensively in the past. However, no experimental results of a high Reynolds number flow through a turbine exit guide vane (EGV) followed by a curved duct have yet been published. An in-depth CFD analysis of the aerodynamic effects is therefore carried out, using the RANS solvers TRACE (at MTU Aero Engines) and SU2, to analyze the flow field and geometric sensitivities of a high Reynolds number flow through an EGV followed by a 90 degree bent duct. The geometry of interest is investigated at a Reynolds number of Re=10^6 and a ratio of bend radius to duct diameter of one. The inflow conditions are prescribed to closely resemble typical flow conditions at the low pressure turbine exit plane of a turbojet engine. After validating the solver with experimental data using the test case of a 90 degree bent duct, an initial CFD analysis of the combined exit guide vane geometry with curved duct is carried out to identify the dominant flow phenomena and mutual effects of the EGV and the bend. Three zones of flow separations are found, each at the convex and concave sides of the bend and one at the lower side of the plug. Secondary flows caused by the bend are found to have an effect on the flow upstream of the EGV, leading to a non-uniform flow inlet angle and aerodynamic loading of the individual blades. Separation downstream of the EGV is influenced by the presence of low velocity wakes from the EGV. Subsequently, a sensitivity study is carried out to find the effect of different geometrical parameters on the flow field. Main investigated parameters are the ratio of bend radius to diameter (R_c/D) and the distance between EGV and bend (l/D). Additionally, the aerodynamic effects of the circumferential EGV positioning, swirl and the plug shape are investigated. It is found that an increase in both bend radius and distance between bend and EGV improves aerodynamic efficiency, while swirl can decrease pressure losses in the duct for small bend radii of R_c/D<0.8. Improving the plug shape and rotating the EGV allows to further increase the aerodynamic efficiency without weight increase. For further optimization of the geometry, it is recommended to include duct geometries with a non-constant bend radius and outer duct diameter to increase the design space.

Over the last 50 years, the global airline industry has seen resilient growth in the demand for passenger travel; this trend is expected to continue in the coming decades. With kerosene being the predominant source used as jet fuel, this increase in air traffic is expected to result in the depletion of non-renewable fossil fuels and undesired climate changes on a global scale. Therefore, the industry is currently exploring the electrification of aircraft, taking into account advanced concepts such as more electric aircraft (MEA) and hybrid electric propulsion systems (HEPS). This thesis addresses a combination of these two concepts characterised as an electrically assisted propulsion & power system (EAPPS). This system integrates a conventional turbofan engine with a network of electrical components, providing assistance to the aircraft propulsion and non-propulsive power systems. This secondary electrical system can be activated throughout the flight mission to assist the turbofan engine and increase the overall system efficiency. The amount of electrical power relative to the total power is defined as the power split ratio. The objective of this study is to evaluate how gradual modifications in this EAPPS affect the overall performance of an Airbus A320neo (new engine option) aircraft in a short-range mission of 1,000 km. The proposed changes include the conversion to an electrical architecture of the non-propulsive power systems, the implementation of a fuel cell system, the installation of photovoltaic panels on the outer skin of the aircraft and the downscaling of the turbofan engine. To analyse these effects accordingly, two separate simulation models were developed within the MATLAB environment to perform and verify a series of trade studies at two different time frames: near future (2020+) and far future (2040+). The results revealed that each modification has proven to be advantageous in terms of overall fuel and energy consumption; however, turning the A320neo into a MEA is the most effective approach. The inclusion of fuel cell and photovoltaic systems brings minor benefits, but also increases the complexity of the system. Nonetheless, the derived optimal setups for the 2020+ and 2040+ scenarios feature all modifications, but with a different power management strategy and engine scaling. The optimal power management strategy for 2020+ includes fully electric taxiing, a take-off power split of 17%, a climb power split of 9% and a downscaled engine of 90%. Compared to the conventional A320neo, this setup will lower the fuel and energy consumption by 17% and 13%, correspondingly. Also, the CO2 emissions are reduced by 16%. By 2040+, the optimal take-off power split increases to 26% and the climb power split to 43%. This allows the CFM LEAP-1A engine to be scaled down to 85%. The total relative savings of fuel, energy and CO2 emissions equal 28%, 18% and 27%, respectively. The impact of the projected technological development in a time period of 20 years, from 2020+ to 2040+, is witnessed through the increased use of electrically assisted propulsion and significant greater amounts saved with respect to fuel, energy and engine emissions.

Boundary layer ingestion is a concept that can reduce the power requirement of an aircraft. The ingestion of the boundary layer creates non-uniform fan inflow conditions. This thesis work aims to research the effect of installation in a propulsive fuselage concept on fan performance. On top of this, the effect of fan installation on the propulsive fuselage concept itself is evaluated. Through experimental work, the effect of installation on the fan has been mapped. The effect of fan operation on the propulsive fuselage has been investigated through the use of RANS simulations utilising an actuator volume model. The experimental work has shown that the fan deals with a drop in flow coefficient due to installation with favourable behaviour in the hub region. Numerical data support this finding. Moreover, a momentum excess has a disproportional effect on the kinetic energy deposition rates in the jet wake.

Progressing targets on GHG emission reduction urge the the Netherlands Ministry of Defense (NL MoD) to reduce the use of fossil fuels, as they announced to contribute to the Paris agreement by reducing its dependency on fossil fuels by at least 70% by the year 2050. However, without sacrificing striking power, because future naval combatants need to perform their operations on the highest end of the violence spectrum and need to have sufficient autonomy to perform their operations at sea independent of logistic supply lines. The Royal Netherlands Navy (RNLN) is investigating the replacement of the Air Defense and Command Frigate (LCF) between 2030 and 2040 by a Large Surface Combatant. As it will be impossible to achieve substantial reduction of GHG emissions through energy-saving technologies, sustainable fuels need to be implemented in the design. In this thesis, the impact of sustainable fuel choice on the design of Large Surface Combatants with a displacement of around 6000 tonnes is assessed. In particular, the current and future developments of sustainable methanol and diesel have been reviewed from existing literature and are examined on the replacement Large Surface Combatant: specifically their advantages, disadvantages, production routes, future production cost estimates and availability to give an understanding which pathways can help the NL MoD to achieve their stated GHG emissions reduction goals. Furthermore, three different design concepts are presented with respect to fuel composition from which the impact of the established fuels is quantitatively examined. First, sustainable diesel is a drop-in fuel, which makes blending of sustainable diesel with fossil diesel possible in the existing infrastructure allowing a gradual transfer from fossil diesel to sustainable diesel. However, the production is less efficient in a well-to-wake approach and the cost of Bio-diesel and E-diesel is 5% to 30% more expensive with a mean estimated additional cost of 6 €/GJ compared to methanol. Secondly, operating on methanol has a significant impact on the design of a large surface combatant: the specific energy of methanol is more than twice as low as diesel and the ship needs a longer machinery space to allow for a diesel engine propulsion configuration. This results in a increase in displacement of 20%. Finally, navies could consider a two-fuel strategy: sail on methanol during operations with limited autonomy, typically in peace time, and operate on diesel during operations with high autonomy, during war time operations. In this case the design needs to include both diesel and methanol fuel systems and additional space for methanol safety measures. This results in a increase in displacement of 4%. However, the range when operating on methanol is reduced to 2187 nm compared to a 5000 nm baseline range. Assessing the impact of sustainable methanol and diesel for Large Surface Combatants at this level of detail and considering a two-fuel strategy is novel for the field. The results can be used by the Royal Netherlands Navy to compare the different concepts and serve as an indicative substantiation in the acquisition of a new Large Surface Combatant. Moreover, it can help in forming the strategy to migrate future naval combatants from current fossil fuels to future sustainable fuels.

Prediction of emissions from combustion systems is a complex problem involving the coupling between the flow field and chemistry. CFD analysis is the most commonly employed approach. However, it has the drawback that a very high computational cost prevents the use of detailed chemistry models. This master thesis, which focuses on NOx emissions, uses a more unconventional method of emissions prediction: Chemical Reactor Network (CRN). The advantage of this method is that, as it does not use fine discretisation, closure models nor fluid dynamics equations, it allows the implementation of detailed chemistry mechanisms. A CRN is developed first for a single-element Lean Direct Injection (LDI) combustor and then the CRN is adapted for a Multi-Point LDI (MPLDI) combustor. CFD and experimental results are used to set up the CRN. In the base case scenario, in which kerosene is the fuel choice, the NOx emissions predicted are very close to experimental measurements. This is particularly meaningful given the high uncertainties of modelling this highly complex turbulent combustion process. The developed CRN is also used to predict NOx emissions for the same combustor when the fuel choice is varied. Namely, the alternative fuels considered are kerosene enriched with hydrogen, methane and methane enriched with hydrogen. In comparison to kerosene, higher Lower Heating Values (LHVs) of these fuels lead to lower combustor temperatures for the same power input. Consequently, the thermal NOx pathway is weakened and the NOx mass flow generated is reduced. Nevertheless, these fuels with a higher LHV come with an increased operational risk that must be overcome before their implementation in aviation becomes possible.

The past 70 years has shown an incredible growth in air transport. The increase in flights has resulted in an increased strain on the environment. Climate change is a fact. Designers have been working on improving the aircraft, and in particular, the engine efficiency. By improving the internal components through better materials, new design methods and new fabrication techniques, the engine specific fuel consumption has decreased. A major factor however is the engine bypass ratio. By increasing the bypass ratio the engine specific fuel consumption (SFC) can be drastically reduced. As a consequence the engine weight and size increased with subsequent ramifications. Evaluating the installation penalty is not a new topic. In existing literature, studies on the various aerodynamic effects have been published. The largest contributor to the drag is the friction drag from the nacelle. Interference drag due to wing-pylon-nacelle flow interaction can be reduced with proper engine placement. The increase in drag due to a larger engine can also be minimised by the engine location and the shape of the nacelle. All studies show a change in drag when engine size or location are varied. Consequently all studies have been done using finite volume Reynolds Averaged Navier Stokes (RANS) solvers. Friction drag is relatively easy to predict, but if complex flows and separation areas are present, high fidelity tools are required. An answer to the main research question: For narrow wing/body aircraft, can the installation penalties from an increase in bypass ratio outweigh the gain in specific fuel consumption? is found when a full aircraft redesign is allowed. Using the Initiator toolbox it was found that the lower fuel burn, due to a SFC improvement, results is a lighter aircraft for a given mission. The reduction in fuel burn negates the increase in engine weight, drag, and possible interference. The stability analysis is done for an engine retro-fit scenario, like the 737 MAX. The method used requires several assumptions or estimations based on empirical relations. In order to improve the accuracy the vorticity solver FlightStream was used. It was not possible to validate the A320 design by using both FlightStream and the empirical methods, however the trends observed can be used to evaluate the effect on the c.g. margin and the required tail size. The c.g. margin decreased by max 7.1%, which would nullify a typical stability margin of 5%. The calculated maximum increase in tail size is 18%. Compared to the A320 tail size, it is only a 2% increase, and in most cases the tail becomes smaller. This can be explained because the A320 uses an oversized tail, originally designed for the smaller A318.

Boundary-layer instability induces spiral vortices on rotating cones. As they grow along the cone, the vortices enhance mixing of high- and low-momentum fluid, and subsequently, cause the boundary-layer to transition into a turbulent state. This transition process is scientifically enticing as it is one of the classical problems in fluid mechanics. In practice, the transitions of rotating cone boundary-layer are relevant in several engineering applications, including rotating nose-cones of aero-engines. The instability-induced spiral vortices on rotating aero-engine-nose-cones are expected to influence the aerodynamics at the fan root. This will potentially affect the loss mechanism at junctions between fan blades and the hub (the central rotating body of the engine, including the nose-cone). Accurate assessment of these losses requires knowing the boundary-layer instability behaviour on rotating cones in aero-engine-like flow conditions. The past literature on this classical instability problem has only focused on low-speed (low-Reynolds number incompressible) axisymmetric inflow conditions. In reality, aero-engine-nose-cones often experience high-speed (high-Reynolds number compressible) inflow during a cruise. Moreover, several concepts of future-aircraft feature engines embedded in the airframe, or engines with ultra high bypass ratio with short nacelles. Owing to the associated inflow distortions, the nose-cones of these engines will experience non-axisymmetric inflow. However, limitations of the past experimental techniques pose hurdles in investigating the boundary-layer instability on rotating cones in non-axisymmetric as well as high-speed inflows. This dissertation explores the boundary-layer instability on rotating cones with the inflow conditions pertaining to a typical aero-engine, i.e. non-axisymmetric as well as high-speed inflow. First, an experimental method is developed to measure the coherent flow structures on rotating cones. This method uses infrared thermography (IRT) with proper orthogonal decomposition (POD) to detect the thermal footprints of the spiral vortices on rotating cones. The POD modes are selectively used to reconstruct different instability-induced flow features. For this selection, a new criterion is formulated to determine the physical admissibility of the POD modes for reconstructing the flow-feature of interest. This method overcomes the limitations of the past experimental methods and has allowed quantitative measurements of spiral vortex growth, angle and azimuthal number, for the first time in complex flow environment, i.e. axial as well as non-axial inflow and high-speed inflow. The asymmetry of the non-axial inflow has been found to delay the spiral vortex growth on the investigated case of a rotating slender cone (half-cone angle ψ=15º). Here, the spiral vortex growth appears at higher local Reynolds number Rel and local rotational speed ratio S compared to the axial inflow case at same operating conditions. It is postulated that the azimuthal asymmetry of the flow conditions (local Rel and S) disturbs the azimuthal coherence of the instability characteristics, i.e. angle and wavelength of the dominant mode. This inhibits the spiral vortex growth. However, at high rotational speed ratio S, when the instability characteristics approach the azimuthal coherence, the spiral vortices are found to be growing in the asymmetric flow field. Furthermore, the dissertation extends the axial flow investigations from the most addressed case of a rotating slender cone of ψ=15º to the broader cones of ψ=22.5º, 30º, 45º, and 50º. Here, the boundary-layer instability mechanism changes from the centrifugal instability for slender cones ψ ≤ 30º to the cross-flow instability for the broad cones ψ ≥ 30º. The exact half-cone angle where this change occurs still remains unclear. While the past literature majorly focused on rotating slender cones in axial inflow, theoretical studies expressed the lack of experimental data for the rotating broad cones in axial inflow. This dissertation has provided this experimental data on the instability-induced spiral vortices for the rotating broad cones of ψ=45º and 50º in axial inflow. The experimental method developed in this work has enabled studying the boundary-layer instability behaviour on rotating cones, for the first time in high-speed conditions, i.e. local Reynolds number Rel =0—3 × 106, rotational speed ratio S<1—1.5, and inflow Mach number M=0.5. These conditions are typically expected on the aero-engine-nose-cones during the transonic cruise of a large passenger aircraft (like A320, A350, etc.). These high-speed measurements revealed that the spiral vortices grow on the investigated rotating cones (ψ=15º, 30º and 40º) as expected from the low-speed studies. This confirms that the right circular type nose-cones of the transonic cruise aircraft will experience the spiral vortex growth in transitional boundary-layer. The dissertation also conceptually discusses the potential effects of the spiral vortices on the fan aerodynamics. The spiral vortices are expected to influence the aerodynamics within the blade passage, especially, near the hub. Flow at the hub and fan-blade junction corner often separates on the suction side of the blade. This reduces the total pressure rise and efficiency of the engine. Presence of the spiral vortices is expected to affect the local aerodynamics at the hub, including the hub-corner separation, however, quantifying this effect needs further investigation. Furthermore, the dissertation has also shown a typical asymmetric flow field around the nose-cones when the fan is subjected to an inflow distortion. The fan-driven redistribution of the distorted inflow reduces the flow-field asymmetry near the nose-cone wall in the symmetry plane. This is a favourable condition for the spiral vortex growth. Overall, this doctoral research has presented a new experimental approach to the classical problem of the boundary-layer instability on rotating cones. This has allowed furthering the fundamental knowledge about the instability-induced spiral vortex growth on rotating cones in following parameters: local Reynolds number Rel =0—3 × 106, rotational speed ratio S=0—250, inflow Mach number M=0—0.5, inflow incidence angle α=0º—10º and half-cone angle ψ=15º—50º. @en

Littering in urban areas poses a serious threat across the globe, with direct consequences on human health and climate change. Litter pieces such as soda cans or plastic bags left in the environment destroy nature by, for example, polluting water or contaminating soil. Moreover, animals consume these non-digestible pieces. Once they are washed away into the ocean, both land animals and fish ingest plastic pieces. Not only does this destroy the biodiversity, but toxic microplastics make their entrance in the human food chain as well. In light of these problems, there is a need for a rapid and flexible litter cleanup system.

Littering in urban areas poses a serious threat across the globe, with direct consequences on human health and climate change. Litter pieces such as soda cans or plastic bags left in the environment destroy nature by, for example, polluting water or contaminating soil. Moreover, animals consume these non-digestible pieces. Once they are washed away into the ocean, both land animals and fish ingest plastic pieces. Not only does this destroy the biodiversity, but toxic microplastics make their entrance in the human food chain as well. In light of these problems, there is a need for a rapid and flexible litter cleanup system.

Littering in urban areas poses a serious threat across the globe, with direct consequences on human health and climate change. Litter pieces such as soda cans or plastic bags left in the environment destroy nature by, for example, polluting water or contaminating soil. Moreover, animals consume these non-digestible pieces. Once they are washed away into the ocean, both land animals and fish ingest plastic pieces. Not only does this destroy the biodiversity, but toxic microplastics make their entrance in the human food chain as well. In light of these problems, there is a need for a rapid and flexible litter cleanup system.

Aviation has a significant contribution to climate change, which must be decreased. The A321 APPU could offer a substantial improvement, by introducing a hydrogen-powered Auxiliary Power and Propulsion Unit (APPU). This turboshaft engine is located in the tail cone and powers a boundary layer ingestion propulsor, taking over 10% of the thrust. The Steam Injection and Recovery (SIR) cycle is introduced to improve the efficiency of the APPU. This semi-closed water cycle can reduce fuel consumption and NOx emissions. Both the baseline and SIR APPU are modelled in pyCycle, an open-source gas turbine parametric analysis tool. Water properties and heat exchangers are added so pyCycle can model the SIR cycle. The baseline APPU has a thermal efficiency of 45% and a mass of 502 kg. The SIR cycle can increase the efficiency by 1.54% and decrease the NOx emissions by 33.4%, at the cost of a 15.7% mass increase.