This document describes the development and outcomes of a comprehensive analysis to quantify the climate impact reduction of Sustainable Aviation Fuels (SAFs). Firstly, it is shown that existing Life Cycle Analyses (LCAs) exclude or do not properly model pump-to-wake (PtW) non-𝐶𝑂2 effects resulting from 𝑁𝑂𝑥 & 𝐻2𝑂 emissions and contrail formation, of both Conventional Jet Fuel (CJF) as well as SAF. To this end, a method is developed with which these PtW emissions are thoroughly quantified and incorporated into an existing LCA.

The method is designed to answer the following research question: ”What is the potential climate impact reduction of SAF in aviation?” and is divided into a well-to-pump (WtP) and a pump-towake (PtW) analysis. The WtP values are taken from literature (the CORSIA default values [3]) and indicate how much 𝐶𝑂2-equivalent (𝐶𝑂2𝑒) emissions are made for the production & transport of 1 𝑀𝐽 (unit of energy) of CJF and SAF, in gram: [𝑔𝐶𝑂2𝑒/𝑀𝐽]. For the PtW values, the 𝐶𝑂2 emissions released during the combustion of 1 𝑀𝐽 of SAF or CJF of 70.2 & 73.3 [𝑔𝐶𝑂2 /𝑀𝐽] respectively, are multiplied with a 𝐶𝑂2𝑒 factor for both SAF as well as CJF. This 𝐶𝑂2𝑒 factor is a ratio that evaluates the climate impact caused by all aviation emissions & effects (𝐶𝑂2, 𝑁𝑂𝑥, 𝐻2𝑂 & contrails) relative to that of 𝐶𝑂2. The climate impact is quantified using the Global Warming Potential (GWP) and Average Temperature Response (ATR) climate metrics over a given time horizon (20, 50 & 100 years), which analyze a radiative forcing (RF) and a temperature change (Δ𝑇) response respectively. The RF & Δ𝑇 responses are generated for a baseline CJF scenario as well as a SAF scenario using the non-linear climate chemistry model AirClim. All important aspects of SAF relative to CJF are accounted for: the dissimilar energy density and thus fuel flows, the different 𝐸𝐼𝐻2𝑂 & 𝐸𝐼𝐶𝑂2 , the different 𝐸𝐼𝑠𝑜𝑜𝑡 and thus contrail characteristics, and the similar 𝐸𝐼𝑁𝑂𝑥 . Finally, the WtP part is added to the PtW part to be able to quantify SAF’s well-to-wake (WtW) climate impact reduction potential. The results of this new analysis indicate that:
• Uponinclusion of PtW non-𝐶𝑂2 effects into the CORSIA SAF LCA from Prussi et al. (2021), the lifecycle 𝐶𝑂2𝑒 emissions per 𝑀𝐽 of CJF increase from 89 to 257.2 [192.3-334.9] 𝑔𝐶𝑂2𝑒/𝑀𝐽. Similarly, for all paraffinic CORSIA eligible SAFs [3], the 𝐶𝑂2𝑒 emissions per 𝑀𝐽 increase by 147.7 [88.4-223.3] 𝑔𝐶𝑂2𝑒/𝑀𝐽. The values in the brackets indicate a 5%-95% confidence interval range based on a Monte Carlo uncertainty analysis with 1000 simulations.
• As aresult of the previous point, a hypothetical SAF that is able to reduce lifecycle GHG emissions by 100% (with 0 WtP emissions), only has a climate impact reduction of 42.5% [33.5%-54.1%] when using ATR100, and58%[53.3%-66.7%]when using GWP100 as the climate metric. Nevertheless, the absolute WtW reduction in climate impact increases from 89 𝑔𝐶𝑂2𝑒/𝑀𝐽 to 109.5 [99.2-118.3] 𝑔𝐶𝑂2𝑒/𝑀𝐽 (using ATR100), meaning that SAF’s climate impact reduction potential actually increases when PtW non-𝐶𝑂2 effects are included. This is explained by the fact that SAF not only reduces 𝐶𝑂2 emissions, but also contrail climate impact, which strongly outweighs the increase in SAF’s 𝐻2𝑂 climate impact.
• When adding the CORSIA default WtP values [3] to the PtW values derived in this analysis, SAF’s climate impact reduction potential ranges from 3% or 8.9 𝑔𝐶𝑂2𝑒/𝑀𝐽 (for corn grain EtJ) to 47% or 121.1 𝑔𝐶𝑂2𝑒/𝑀𝐽 (for Herbaceous Energy Crops-FT)- depending on the exact feedstock and conversion process used.

A sensitivity analysis has been carried out for the PtW analysis from which it was concluded that the PtW climate impact of both SAF & CJF strongly varied. However, the absolute WtW climate impact reduction potential stayed very similar: the lifecycle 𝐶𝑂2 climate impact reduction remained unaffected, and the PtW non-𝐶𝑂2 climate impact reduction potential varied from 11.75-24.4 𝑔𝐶𝑂2𝑒/𝑀𝐽. Lastly, by allocating SAF to longer flights with higher average flight altitudes, SAF’s non-𝐶𝑂2 climate impact reduction potential is substantially increased from 4.06 to 25.6 𝑔𝐶𝑂2𝑒/𝑀𝐽.

Hydrogen, as a carbon-free fuel, offers a promising solution to reduce CO2 emissions in pursuit of cleaner combustion technologies. However, its combustion poses challenges, including increased NOx production due to high adiabatic flame temperatures, along with risks of flashback and thermo-diffusive instabilities. One approach to addressing these challenges is Moderate or Intense Low-Oxygen Dilution (MILD) combustion, which significantly lowers NOx emissions by reducing reaction temperatures. Techniques like exhaust gas recirculation (EGR) can further support this process. Additionally, blending hydrogen with other fuels, such as ammonia and methane, improves flame stability, safety, and flame speed.

This thesis is part of the ACHIEVE project (Advancing the Combustion of Hydrogen-Ammonia Blends for Improved Emissions and Stability), funded by the European Union under the Horizon European Research and Innovation Actions in collaboration with the Clean Hydrogen Partnership. The project aims to advance Technology Readiness Level 4 technologies that reduce pollutants in unconventional hydrogen blends, such as mixtures of NH3, CH4, and H2. The combustion characteristics of these unconventional blends are studied numerically and experimentally in high-stability combustors, with a focus on MILD combustion and the effects of exhaust gas recirculation.

Aligned with these goals, the TU Delft Enclosed-Jet-in-Hot-Coflow (EJHC) burner, designed for MILD combustion, is used to experimentally investigate premixed and non-premixed methane-hydrogen and pure hydrogen flames. The research examines flame morphology, temperature, emissions profiles, and the effects of exhaust gas recirculation on NOx emissions. This serves as a foundational step for future research into ammonia-hydrogen blends. The burner features a central flame auto-ignited by a hot vitiated coflow produced by a secondary burner. Design modifications were implemented to improve coflow uniformity near the jet exit.

The research involved two experimental campaigns. The first, conducted under cold flow conditions using Particle Image Velocimetry (PIV), assessed coflow uniformity at different inlet velocities. The second campaign focused on reactive flow experiments, using thermocouples, chemiluminescence, and gas analyzers to study methane-air coflow and methane-hydrogen blends in premixed and non-premixed conditions. Hydrogen concentration was varied from 0% to 100%, with different power ratios between the central jet and coflow.
The study showed that using a perforated plate as a secondary burner enhanced coflow uniformity, with PIV results showing reduced radial variations of the vertical velocity component. Thermocouple measurements confirmed a uniform temperature profile.
Flame lift-off height and shape in both premixed and non-premixed conditions were influenced by jet velocity, laminar flame speed, and hydrogen content. Hydrogen addition reduced lift-off height. In premixed conditions, flames were compact and narrow, while in diffusion conditions, higher hydrogen content increased mixing with the coflow at greater radial distances. NO emissions remained stable in premixed cases but were affected by coflow composition in diffusion flames, with lower oxygen levels enhancing NO reburning.

This study provides a versatile system for investigating exhaust gas recirculation and hydrogen blends over a wide range of power and equivalence ratios. It lays the foundation for future studies on ammonia-hydrogen combustion.

It is the need of the hour to focus research and development towards curbing emissions due to the growing aviation industry. Employing boundary layer Ingesting(BLI) propellers for development of propulsive fuselage concept(PFC) aircraft while utilizing hydrogen as an alternative energy source, is the idea behind project APPU(Advanced Propulsion and Power Unit). However, the empennage wake is detrimental to the propeller. This study uses chord-wise wake blowing technique to fill the empennage wake in order to mitigate the detrimental effects of the wake on the inflow of the aft mounted BLI propeller. A near complete wake filling was observed for the blown configuration, with a 99.7% uniformity in the velocity profiles for the filled empennage wake. The addition to the overall aircraft drag due to the wake blowing system was less than 2 drag counts and a mass flow rate of 0.91-1.23Kg/s was found to be required in the blown cases.

Large eddy simulation paradigm is employed to analyse the internal flow field of a lean premixed swirlstabilized combustor with axial air injection at both non-reacting and reacting conditions for a methane and a methane-hydrogen fuel mixture. The Thickened Flame combustion model with the kinetic mechanism GRI 3.0 and the detailed chemical kinetics solver SAGE available in ConvergeCFD is employed to simulate the flow. An adaptive mesh strategy is used to maximise the mesh resolution in the flame and boundary layer regions. The numerical results are first validated against in-house experimental velocity measurements obtained via particle image velocimetry, and then leveraged to provide further insights on the flow behaviour. Significant reductions in CO2, CO and NOx emissions are observed when changing the fuel to the CH4/H2 mixture. From a POD analysis is observed that a Precessing Vortex Core is present in both the reacting and non-reacting conditions. Flashback and severe local extinctions are not observed during the simulated time.

A formulation based on the evaluation of power conversions within the system allows to overcome the limitations of conventional momentum analyses to study tightly coupled airframe-propulsion configurations such as Boundary Layer Ingestion. The so-called power balance method is applied in a CFD framework to gain insight about the application of this formulation for a wide range of flow conditions and for complex geometries. Not addressed in detail in previous research, it is quantified in this work the evolution of the distribution of energy in the wake of a body subject to turbulence, compressibility effects and angle-of-attack of the incoming flow. For the first time, a three-dimensional geometry representative of a typical aircraft is investigated with the power balance method. The results of a grid convergence study for the application of the power balance method in a CFD framework highlight the importance of generating a mesh with a fine resolution of the flow field globally, paying special attention to the development of the body wake.

For heavy duty diesel engines, piston temperature control is very important in constructing a successful design that meets the demands of increasing power output and stringent emission regulations. Overheating of piston is avoided with engine oil through spray cooling and gallery cooling processes. In this research project, evolution and disintegration of oil jet used for piston cooling by DAF Trucks N.V., is studied numerically using Large Eddy Simulation (LES) and Volume of Fluid (VOF) methodologies. A robust CFD model is built with major focus on the significance of grid resolution in multi-phase LES, and is used to reproduce two test cases. This is followed by characterization of physics involved in oil jet breakup through qualitative inspection. Parameters relevant to the two types of cooling techniques are estimated to see the impact of jet development at different flow rates. Based on the results obtained, the need for grid refinement is assessed and performed for certain cases. Finally, turbulent atmosphere within the crankcase is estimated through a separate simulation and its effect on oil jet is investigated. Results show that for oil in quiescent atmosphere jet turbulence is the dominant force and is the primary cause for disintegration. A clear transition to turbulence is captured with increase in flow rate, as the jet behavior is more and more chaotic with droplet formation and spreading. Importance of grid resolution on droplet capturing is recognized and an isolated analysis shows more droplets being captured with fine meshes. The level of refinement necessary to capture all the droplets still remains an open question. With turbulent atmosphere, no significant change in the jets is obtained until primary breakup and the inertial force of the liquid phase is found to dominate the surrounding flow effects. However, secondary breakup is found to be affected, as aerodynamic interactions increase disintegration and spreading, impacting both the cooling techniques. Results obtained from this research work will be used as primary inputs for further studies in the company on spray cooling and gallery cooling (sloshing flow) leading towards optimization of the piston cooling process.

The graduation project was conducted at the upper stage liquid propulsion department of ArianeGroup at the facilities of Airbus DS, Bremen. Based on a series of past flights of Ariane 5 launcher, the aim is to analyze the fluid motion and the pressure fluctuations in the cryogenic propulsion upper stage Liquid Hydrogen (LH₂) and Liquid Oxygen (LO_x) tanks during the ascent phase. Pressure fluctuations (drops or rises) during the ascent phase are undesirable due to the need for relief or re-pressurization of the fuel tanks. Tank relief is obtained through relief valves, while re-pressurization is done using on-board gaseous Helium; both cases increase the failure probability of the system and/or the total weight of the launcher.The objective of the project is to find out why these pressure fluctuations occur, what are the parameters that affect the pressure evolution and at what extend the liquid fuel motion (sloshing) is responsible for this behavior.According to the literature several parameters affect the pressure evolution during sloshing. These parameters are further investigated through flight data analysis. The approach also involves CFD simulations of the kinematic behavior of the liquid fuel focusing on the sloshing angle. Finally, a statistical model is built attempting to predict the pressure change inside the tanks. Higher sloshing angles match with higher pressure rise inside the LO_x tank. The magnitude of the pressure rise appears to be directly connected to the kinematic profile of the launcher as well as to the ullage volume of the tank. The maximum predicted ullage pressure is below the tank's sizing pressure limit. Regarding the LH₂ tank, no strong correlation of flight parameters to the pressure change is identified; no sufficient statistical model is built. The CFD simulation shows that relatively higher sloshing angle magnitude and duration exists near the pressure drop periods and that strong breaking waves are likely to be formed in the case of a sudden pressure drop behavior. The LH₂ tank is more prone to the formation of breaking/splashing waves. The effect of vibrations, which is not included in the CFD study, is also important for the explanation of the pressure drop magnitude.

Supercritical CO2 (sCO2) is considered as a working fluid in future Concentrating Solar Power (CSP) applications
to increase the efficiency of the power cycle. Due to the limited experience, the turbine of an sCO2 power cycle is in literature referred to as the component with the highest risk. In this thesis, a design methodology will be established and used to gain knowledge in sCO2 turbine design by designing and analysing a turbine concept which can be used to generate sCO2 turbine experimental data for validation purposes. The high density of the fluid in combination with the low power output of the turbine results in small turbine dimensions, a high rotational speed and a large axial load when using existing design wisdom. Therefore, the effect of limiting the rotational speed and axial load on the turbine design is evaluated.

The turbine design methodology includes a preliminary design module, an aerodynamic design module and a mechanical design module. The aerodynamic design module consists of a steady-state and transient solver to evaluate the importance of taking into account transient effects when estimating the aerodynamic performance. According to literature, pressure loads can have a significant effect on the stresses in sCO2 turbines. Therefore, the mechanical design module is able to take into account the pressure loading from the steady-state and transient aerodynamic design.

The low power in combination with the limited rotational speed pushes the turbine design away from the desired specific speed range. During the preliminary design, the radial inflow turbine was found to give the best performance while meeting the turbine requirements. The degree of reaction of the turbine is close to
0, to limit the axial load due to the pressure difference across the rotor. As a result of the low specific speed, the turbine efficiency of 74% is lower than usually seen for radial inflow turbines. As no sudden peaks in entropy generation are seen across the rotor channel, it can be concluded that the high curvature of a low reaction radial inflow turbine does not seem to have a detrimental effect on the turbine performance. The main contribution to the losses can be found in the rotor channel as a result of the tip clearance losses and high flow velocities compared to reference turbines, while the stator losses are comparable. A good agreement is found between the steady-state and transient aerodynamic analysis. Based on this, it can be concluded that a steady-state analysis can give a good approximation of the turbine performance, but evaluating more designs would be required to generalise this statement to all small-scale low reaction sCO2 turbomachinery. Due to the low degree of reaction of the turbine, the stresses originating from the pressure load are found to be less than 1% of the total stresses. Based on this, it can be concluded that only taking into account centrifugal loads for a low reaction sCO2 turbine gives a good estimation of the stresses in the turbine during operation.

As this research focuses to a large extend on establishing the methodology, for future research it is recommended to perform a more thorough optimisation of the turbine shape, in particular to reduce the losses in the rotor channel by for example introducing a shrouded design. Moreover, it is recommended to analyse the turbine in combination with the other subsystems in the power block to also take into account the interaction between the subsystems.