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.

Given the enduring issues of human-induced climate change, the appeal of strategies aimed at reducing greenhouse gases has never been greater. CO2 is the most concerning greenhouse gas due to the large quantity already emitted into the atmosphere and the ongoing excessive emissions from anthropogenic activities. The transportation sector significantly impacts global warming, as all major transportation modes depend on fossil fuels. The principal fuel used in aviation is kerosene, which is a jet fuel derived from petroleum. Due to the environmental risks associated with petroleum-based fuels, synthetic kerosene is an appealing alternative that could aid the decarbonisation of the aviation sector. This research study aims to conduct a techno-economic analysis of synthetic kerosene, as a potential sustainable fuel for aviation. To address the excessive CO2 concentrations in the atmosphere, the process of extracting CO2 from the air, known as direct air capture, is investigated. A model is developed in Aspen Plus consisting of four main modules, namely direct air capture with NaOH sorbent and calcium looping, syngas production through the reverse water gas shift reaction, Fischer-Tropsch Synthesis and hydrocracking & distillation. There is a substantial gap in the literature concerning the utilisation of direct air capture technologies for synthetic fuel production, and this study aims to narrow this gap.

To meet the goals of the Paris agreement,sustainable aviation fuels, such as hydrogen, need be adopted on a large scale within the coming decades. Hydrogen-assisted combustion of kerosene is investigated as an intermediate step in the transition towards sustainable aviation. This study addresses the gaps in the current understanding of hydrogen blending into kerosene with respect to chemical kinetics and emission of NOx, CO and un burnt hydrocarbons.  A perfectly-stirred chemical reactor model is developed to study the fundamental effects of hydrogen blending into kerosene. Additionally, to focus on a more practical application the single-reactor model is extended to a chemical reactor network which represents a lab-scale lean premixed prevaporized combustor setup supporting multi-fuel combustion. Combustion characteristics and emission profiles are carefully studied for different hydrogen blending fractions using the developed models, as well as the reaction pathways in oxidation of hydrocarbons.  Hydrogen blending is observed to increase the reactivity of kerosene, mainly due to increased availability of OH and H radicals, as well as O to a lesser extent. For 20% of kerosene mass substituted with H2, ignition delay time at 1200 K and 1 bard ecreases by 55%. Peak laminar flame speed increases by up to a factor of 2.2,while peak adiabatic flame temperature rises by 74 K. In rich burning conditions, H2 additions remove hydrocarbon reaction loops, which causes a strong decrease in un burnt hydrocarbon emissions and potentially soot. CO emissions can be greatly reduced from H2 additions at very lean conditions as overall burning rate is increased, which is corresponding to a reduction in lean extinction limit. This limit is reduced in the chemical reactor network combustor model by ∆φ=0.09 already for substitution of kerosene mass by 20%.  For φ>0.6, dissociation of CO2 is enhanced from thermal effects and causes emission of CO to rise with hydrogen blending when normalized to carbon in fuel. This effect is reflected in the combustion efficiency, which is improved with H2 blending only for very lean conditions,φ<0.6. The reaction pathways of aromatics are modified with H2 addition,which results in a chemical inhibition of the mechanism responsible for thema jority of un burnt hydrocarbon emissions at very lean conditions. Furthermore,formation of NOx is increased via the thermal path since flame temperatures rise. The prompt NOx route becomes more efficient due to promotion of CH formation, while the N2O and NNH paths are enhanced from increased radical availability. Despite the increased emission of NOx at constant φ, blending H2under constant combustion power and combustor mass flow leads to decreasedflame temperatures and reduces total emissions of NOx, CO and unburnt hydrocarbons.

Aviation is an important contributor to anthropogenic climate change. As indirect greenhouse gases, nitrogen oxides (NOx = NO + NO2) add to the Effective Radiative Forcing (ERF) induced by aircraft emissions. This work addresses a better understanding of emission mitigation by investigating dependencies between engine parameters and emitted nitrogen oxides as a part of the campaign VOLCAN. In-flight near field measurements are conducted using the DLR research aircraft Falcon, chasing an Airbus A321neo equipped with CFM LEAP-1A engines featuring lean combustion through staged fuel injection. Nitrogen oxide concentrations are measured applying the well-established chemiluminescence method. Emission indices are quantified for different fuels including Jet A-1, Sustainable Aviation Fuel (SAF) and two SAF blends with different levels of aromatics. Four combustor inlet temperature settings are tested and staged (lean) combustion is compared to unstaged (rich) combustion. Emissions are measured for two different but technically identical engines, deviating in terms of exhaust gas temperature margin. As expected, results indicate no significant differences in emitted nitrogen oxides for the investigated fuels. Measurements confirm that nitrogen oxide emission indices increase exponentially with combustor inlet temperature. Due to the forced nature of the analyzed rich burn mode, a reduction in nitrogen oxide emissions through lean combustion cannot be confirmed. Based on presented data, a relationship between engine degradation and nitrogen oxides is likely. Near field observations agree with well-established far field measurements and lead to lower uncertainties. Preliminary results of the ECO-Demonstrator campaign are in line with VOLCAN measurements. The performed research is a highly valuable contribution to extremely rare empirical in-flight emission data. Established nitrogen oxide dependencies support technical decision making to reduce aviation’s climate impact.

This thesis focuses on simulating the refuelling process for a liquid hydrogen-powered commercial aircraft. The liquid hydrogen is intended to flow from the refuelling truck, through a transfer line, into the aircraft’s tank using pressure feed. The numerical simulation was built upon an existing tank model, however it did not consider the effects of flashing within the transfer line, nor did it account for the thermal mass or imperfect insulation of the transfer line. This tank model was nevertheless not yet been validated against experimental data. In addition, only a small fraction could be filled on top of the receiving tank, as the complex underlying physics of liquid hydrogen droplet evaporation were not included in the model. First, the tank model was modified and validated using recently published experimental data. A sensitivity analysis was performed to identify the process parameters for which the model results aligned most closely with the experimental data. The parameters that exhibited the most significant impact on the results included the loss factor, droplet diameter, heat ingress due to radiation, transmission line delay constant, and vent-closing pressure. A loss factor of 11, droplet diameter of 6mm, transmission line delay constant of 5, and vent-closing pressure of 3bar were found to provide the best match with the experimental data. The considered heat ingress due to radiation also yielded satisfactory results, whereas other parameters did not significantly affect the simulation. The experiment was lacking the last 18 seconds of transient data. When comparing the model with the experimental data at the end of the refuelling process, discrepancies were observed. The model exhibited namely a significantly higher pressure, vapour temperature and mass compared to the experiment. These discrepancies were expected to be caused by the receiving tank’s venting valve in the experiment, which displayed odd behaviour during the last stage of fill. Despite these disparities at the end of the filling process, the transient behaviour throughout the process was found to be well aligned with the model results. As a result, the modified tank model was deemed suitable for simulating the LH2 refuelling process. Then, a case study was conducted to simulate the refuelling process for a commercial aircraft similarto the Airbus ZEROe Turboprop concept. The objective was to calculate the refuelling time and the associated losses resulting from venting the aircraft’s tank during the refuelling process. The refuelling time has been determined to be around 19 minutes, accompanied by venting losses from the aircraft tank totalling 36.7kg, which accounts for approximately 2.2% of the total fuel transferred. This refuelling time is more than three times longer than the refuelling time of the kerosene-powered equivalent, the Bombardier Q400. Nevertheless, the total time taken by the LH2 refuelling process was determined tobe well within the turn-around time if LH2 refuelling is possible while in parallel performing other tasks of the turnaround. However, future research is required to determine whether this is possible. Additionally, the aim was to find what process parameters impact the refuelling time and losses due to venting from the aircraft tank. Therefore, a second sensitivity analysis was conducted to assess the impact of various parameters on the refuelling process of the case study aircraft. This analysis revealed that the venting pressure of the aircraft tank, operational pressure in the trailer tank, transfer line length, and transfer line diameter emerged as crucial factors influencing the refuelling time. A general observation was done were an increase of 25% in transfer line length resulted in a increased refuelling time of 6%. In addition, it was noticed that a decrease in venting pressure by 0.1bar resulted in a decrease in refuelling time of about 1.2%. The percentage of spraying in the aircraft tank was identified as the most significant factor affecting venting from the aircraft tank, for which 100% spraying reduced the amount of venting by 30%. Next, a one-dimensional, homogeneous fluid model was developed to consider the effects of flashing, thermal mass, and imperfect insulation of the transfer line. The transfer line was discretised inn elements with equal length. A linear pressure distribution was considered between the supply and receiving tank, but an option was presented to account for the entrance length. Using the conservation laws for mass and energy, the enthalpy in each node along the axial location of the transfer line was computed. Using REFPROP, the corresponding fluid temperature was determined. The transfer line model was coded in Python using Scipy’s solve_ivp solver. The model was validated using both liquid nitrogen and liquid hydrogen. Discrepancies existed between the model and experimental data, which were expected to be caused by incorrect heat transfer correlations. Finally, the developed transfer line model was integrated into the tank model with the the goal of simulating the effects of flashing, thermal mass and imperfect insulation of an initially warm transfer line to more accurately model the refuelling process for the case study aircraft. However, it was discovered that the liquid temperature in the aircraft tank increased to infeasibly high values, which resulted in a lower liquid density, leading to a decreased mass flow rate in the transfer line, thereby increasing the refuelling time. The dominant factor contributing to these elevated liquid temperatures originated from inaccurately modelling flashing. The incapability of the integrated model to simulate two-phase flow within the liquid phases of the tanks was expected to be the cause behind the lacking capability to capture the flashing phenomenon accurately. As a result, it was concluded that the integration of the tank and transfer line models failed to accurately capture the phenomenon of flashing and so did not provide a more accurate representation of the refuelling process. As a result, the case study results obtained solely from the modified and validated tank model were considered to hold greater credibility.It was nevertheless recommended to perform research on restructuring the integrated model so that the liquid phases are described by temperature and pressure, instead of the saturated states. In addition to this, describing the liquid state by temperature and pressure would allow for simulating subcooling. Since subcooling aids to achieve a vapour-free flow to guarantee a reliable liquid mass flow, implementing the possibility of simulating subcooling is of interest.

Flameless combustion is a combustion regime which results in drastically lower ABe emissions. ABe has been found to influence global warming through its interactions with ozone chemistry and, exposure to this gas has been found to have adverse health effects on humans. The jet-in-hot-coflow design is well suited for studying flame morphology and the coflow composition can easily be changed. In most of these setups in literature, the reaction zone is uncontained, allowing ambient air to enter the region of interest. Furthermore, there is currently a lack of emissions data over a wide range of operating conditions.

This project included the engineering, design, and development of an enclosed jet-in-hot-coflow setup as well as an analysis of the flow field and combustion characteristics through experiments. Measurements were done using PIV, suction probe gas analyzer, thermocouples, and chemiluminescence imaging. Experiments were done with methane-air mixtures in the central jet and the coflow consisted of hot burnt products of methane-air combustion with the addition of external diluents such as 6B2 and A2. One of the most interesting results was that ABe reburning was observed in the reaction zone produced by the central jet, which was found to be correlated to the 6B concentration in the combustion chamber. The addition of 6B2 and A2 as diluents in the coflow resulted in a longer combustion zone and reduced temperatures in the combustion chamber, leading to decreased ABe production, and increased reburning. Further, the impact of oxygen concentration, equivalence ratio, and coflow temperature on product species formation was also analysed. The results indicate that combustion zone growth and temperature effects are balanced for lower jet speeds, while for others, the effects of increasing combustion zone size and distribution with increasing equivalence ratio result in reburning becoming more dominant. Improvements are recommended, such as redesigning the central jet cooling assembly, integrating a secondary burner inside the mixing duct, implementing a pre-heating system for temperature control, and using high-speed imaging techniques for capturing flame development and ignition behaviour.

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.

The validity of current prediction methods for the formation of contrails from modern turbofan engines is investigated. A modelling framework has been developed for estimating the impact of engine configurations on contrail formation by analyzing the physics of the mixing between core and bypass flow. Within this framework, Engine Performance Modelling yields the flow conditions at exhaust nozzle exits. A 2D axisymmetric CFD Flow Field Solver then determines the flow parameters behind the engine. Water vapour dispersion is simulated using a species transport model, after which contrail locations are determined by a set of criteria for homogeneous ice crystal formation. Finally, particles are tracked to determine mixing lines, which are compared to those from current prediction methods. From a Leap-1A engine case study using this framework, it can be concluded that assumptions of instantaneous mixing underlying current methods are not valid, resulting in their overestimation of the mixing line gradient.

The aviation industry is shouting out its aim to reach ”net-zero carbon” by 2050. Nevertheless, air traffic is expected to grow up until then, and if fuel consumption is reduced by new technologies and aircraft, other sources of global
warming such as N Ox emissions and contrails are less considered. Therefore, the climate impact improvement of new technologies compared to older ones is not straightforward and requires a deep analysis. This work performs such an analysis via three steps: The selection of a new fleet to be compared with the actual fleet (2019), a comparison between the two fleets emissions via an Aviation Emission Inventory code, and a climate impact assessment with the tool AirClim. The new fleet analysed consists of the replacement of 14 old (entry in service before 2002) Airbus and Boeing aircraft with their new versions (entry in service between 2011 & 2018). The results show a reduction of 8.7% of fuel consumed by total aviation just by replacing the 14 old aircraft with the new ones. On the other hand, it leads to an 8.0% N Ox emissions increase. Nevertheless, the climate impact assessment concludes that this N Ox emissions increase lowers the surface temperature change due to aviation. This is explained by the strong influence of N Ox emissions location on its climate impact. Overall, this new fleet leads to a decrease in temperature change due to aviation in 2050 of 5.3 mK (-5.2%). This work gives important conclusions on the priorities that need to be set for the development of ’greener’ aviation technologies.

In this thesis, a modelling approach to model soot emissions for a Rich Burn-Quick Quench- Lean Burn (RQL) type aero engine combustion chamber will be presented. The sot emissions will be modelled by coupling Chemical Reactor Network (CRN) approach with Method of Moments with Interpolative Closure (MOMIC), a detailed soot formation model. The developed approach will be first validated by comparing it with well-established experimental cases that include progress of multiple species along with soot concentrations. After the validation, a sensitivity study on the developed modelling approach will be conducted to investigate the model’s behaviour for extended combustion conditions. Lastly, the developed modelling approach will be applied to estimate the soot emissions along with other major emissions of a RQL combustion chamber for various power settings.

This thesis covers the experimental characterisation of a multi-nozzle research combustor capable of achieving flameless combustion (FC). The combustor is operated with methane as fuel and air as the oxidiser, under an overall lean equivalence ratio ranging from 0.6-0.9. The work focused on designing and applying different experimental techniques under varying operating conditions. Particle Image Velocimetry (PIV) is used to characterise the flow field for reacting and non-reacting conditions. Local gas temperature and gas composition measurements are performed to characterise the formation of NOx in the combustor. Emission data and local gas temperatures are further reported as a function of the equivalence ratio, thermal power input, and oxidiser's oxygen concentration. PIV revealed the flow field structures to be very similar between non-reacting and reacting flow conditions; the location of the recirculation zones remained unaffected. Significant differences exist in the axial flow velocities and turbulence levels in the central recirculation zone (CRZ). Radial temperature measurements near the reaction zone revealed the temperature profiles to flatten for a decrease in equivalence ratio, indicative of distributed combustion. Gas composition measurements are performed near the exhaust of the combustor. The measurements showed the combustor to perform very well from an emission standpoint. Measurements showed the NOx on the centreline to be ultra-low (<10ppm) for all cases investigated. The N2O and NNH mechanisms are identified as the major contributors to the production of NOx and not the thermal pathway, as the gas temperature is consistently below the thermal NOx threshold of 1800K. A reduction in the equivalence ratio and a reduction in the oxygen concentration both reduce NOx emissions. The measured levels of CO and CH4 were negligible near the exhaust for all operating conditions investigated, confirming that combustion is fully completed at this location. Measurements of CO and CH4 near the reaction zone indicate distributed combustion, where a reduction in the equivalence ratio below 0.7 resulted in elongation and widening of the reaction zone. Oxygen measurements near the exhaust and close to the reaction zone indicate the entrainment of cooling air into the combustion chamber, which would locally influence the equivalence ratio. It is recommended to redesign the exhaust duct connection to eliminate the entrainment of cooling air.

An accurate estimation of gas turbine nozzle guide vane metal temperature locally on its surface is crucial for predicting vane lifetime. The stagnation region at the vane leading edge is, typically, exposed to the highest thermal load, thus, the showerhead configuration of film cooling is often applied on the leading edge. Widely used lean-­burn combustors implement swirlers, leading to a complex flow field over the nozzle guide vane as the swirling profile is often preserved at the inlet of the guide vane. The nozzle guide vane external heat transfer coefficient in the industry is often computed either with boundary layer codes or RANS methods. However, higher accuracy hybrid RANS­LES models are of interest since such models are becoming more and more available due to improved capabilities to facilitate the increase of computational resource demands. This study aims at introducing hybrid RANS-­LES modelling to investigate swirling inflow effects on showerhead film cooling performance.

The implemented methodology and various turbulence models are first validated by replicating an experimental case of a linear cascade of blades. The uncooled blade external heat transfer coefficient distribution is compared to the experimental data for cases with turbulence intensities of Tu =1% and Tu =8%. The SST k − ω and lag elliptic blending k − ε turbulence models successfully replicated the HTC distribution but the γ − Reθ transition model was required to capture transition on the suction side for cases with Tu =1%. The showerhead film cooling effectiveness is investigated with both RANS and hybrid RANS-­LES models for a configuration of three rows of staggered cooling holes and blowing ratios of 1.4 and 1.9. Uniform inflow and two profiles of swirling inflow are analysed, with the strongest swirl being coupled with a radial temperature profile. Results indicate that the RANS­-LES hybrid model is promising in capturing the unsteadiness of the horseshoe vortex. Mixing between mainstream and coolant jets, and the inherent unsteadiness of the mixing shear layers can only be captured with a scale resolving simulation. The swirling inflow lead to an altered stagnation line and imposed a radial pressure distribution close to the leading edge, which interfered with the coolant distribution on the
leading edge. The coolant jet contact with the vane surface area is found to be the most important parameter affecting the cooling effectiveness since a coolant lift­off led to a significant reduction in cooling effectiveness. A lift­off was often observed in areas where the swirling velocity component misaligned to the mainstream flow direction. A positive contribution to cooling effectiveness was recorded in regions where the swirl component aligned to the mainstream flow direction. The increase in cooling effectiveness was observed due to locally increased momentum of the main flow that aids coolant staying attached to the surface. The benefits of hybrid RANS-­LES modelling are established, and the
results signify the importance of accounting for an unsteady stagnation line during the design of the showerhead film cooling.

To reduce emissions from civil aviation, research is being conducted in lean premixed hydrogen combustors as part of the APPU project at the TU Delft. Next to mitigating CO2 emissions completely, these technologies have the potential to also reduce NOx emissions greatly, allowing for the future of civil aviation to become sustainable. However, the swirling flow of such combustors and the high reactivity of hydrogen lead to increased flashback propensity which can damage the combustor and the engine all together. To counteract this, a concept called Axial Air Injection (AAI) is under investigation. In this technique, an air jet is injected in the mixing tube on its centreline, in an attempt to push the flame more downstream to prevent flame flashback from occurring. The effect of this concept on flashback propensity has been investigated on an axial swirl-stabilized methane combustor, though a parametric variation of swirl intensity and AAI level. The flowfield inside the combustor of each operating point has been visualized by conducting both non-reacting and reacting PIV, which has given insight in their intrinsic differences on flashback propensity for such a combustion system. The results have shown that the non-reacting flowfields prove to be a good indicator of flashback propensity in reacting flowfields for low and high levels of AAI. For in between AAI values, the interaction of heat release, swirling flow and AAI creates a larger deviation which has been shown to be dependent on the presence of circumferential vorticity in non-reacting conditions. It is envisaged that these experimental results will contribute to the body of knowledge in the hydrogen combustor development as part of the APPU project.

To further advance combustion technology, this thesis analyzes a counter swirler setup and its ability to enhance properties such as shear for droplet breakdown or recirculation. The purpose of this project is to perform a cold flow analysis of a dual axial swirl combustion chamber, with axial air injection. The main aim of the thesis is to determine the effect on the flow field of a secondary counter-rotating swirler on the relevant parameters, such as the stagnation point; shear; recirculation and fuel to air mixing, in a combustor that can operate using either hydrogen or kerosene as fuel. During this research project, the methods of assessment are Computational Fluid Dynamics and Particle Image Velocimetry, which will provide clear and quantitative means of evaluating the flow behavior and its impact on the relevant parameters. The variables of this research project will be the geometric swirl number of the secondary swirler, the mass flow split and mass flow through the axial injection tube. The end result of this research project is to determine the influence these variables have on the relevant aforementioned parameters of combustion for several experimental points. This combustor setup may enable the future of aero engine combustion systems that can operate on different fuels, making it possible to balance some of the advantages and disadvantages of these propellants, while at the same time drastically reducing the CO2 and NOx emissions in order to meet the ACARE 2050 projections.

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.

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.