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.

This thesis introduces a newly-developed turbulent combustion model, as a next step towards modelling hydrogen combustion in aircraft engines. The proposed model (FGM-ESF) merges the Flamelet Generated Manifold approach's tabulated chemistry with the Eulerian Stochastic Field method's statistical treatment of flame-turbulence interactions at the subgrid scales, which are not resolved in LES. This hybrid model excels in managing complex combustor dynamics, high turbulence, and both premixed and non-premixed combustion modes, all while maintaining computational efficiency. Validated with a lifted turbulent H2/N2 jet flame in vitiated coflow, reflecting typical combustor conditions, the FGM-ESF model produces accurate predictions of mean velocity, temperature, and mixture in close agreement with the experiments. Comparatively, its performance matches the more costly, fully transported chemistry ESF model, showing limited sensitivity to the number of stochastic fields. The balance between computational efficiency and precision in the FGM-ESF model highlights its importance in the advancement of hydrogen-powered aircraft engines.

To achieve the emission goals set out by the International Maritime Organization in 2018. Low or zerocarbon fuels will have to be used. Ammonia is considered to be a possible candidate since it doesn’t contain carbon. This thesis will attempt to study two methods that characterize the closed-cylinder process of an internal combustion engine; the Seiliger approach and Wiebe function. Two things are the main focus of this thesis. Namely, the application of these methods and how this process will be different for ammonia-diesel combustion compared to diesel combustion. The application will be done for a two-stroke compression ignition engine. The operating conditions that are considered are four load points 20%, 40%, 60%, and 100% at a constant engine speed. The application of this method means building an anti-causal and causal simulation model using Matlab Simulink. Both models simulate what happens in one cylinder during the closed-cylinder process, require the engine parameters as input, and produce the same results. The anti-causal model processes the pressure as a function of the crank angle to determine the combustion reaction rate. The causal model simulates the combustion reaction rate using a Wiebe function to determine the pressure. The Wiebe function is determined based on the reaction coordinate produced by the anti-causal model. By using the Wiebe function, the causal model produces smoother results than the anti-causal model. The Seiliger parameters are determined by using a Newton-Rhapson solver with the maximum pressure, maximum temperature, indicated work, and heat input as equivalence criteria. The results produced by this thesis generally show that the constructed method can produce accurate results. However, this accuracy is correlated to the operating conditions of the engine. As for the changes necessary for ammonia-diesel combustion. These changes have been provided on a conceptual level, with conceptual meaning in terms of equations and assumptions. These changes have not been implemented into a computer model that has been verified and validated. The fundamental difference for the constructed method according to this thesis is the fact that the combustion parameters; start and end of combustion for the two fuels have to be incorporated in the combustion model used for the anti-causal and causal model. This change has to be made, along with assumptions that the injected fuel evaporates and combusts almost simultaneously. This assumption is considered to be highly questionable for ammonia.

The growing energy demand and climate change poses a need for alternative energy generation in terms of renewable resources. Renewable energy resources are characterised by their intermittent behaviour. A backup power supply is required that can deliver electricity when the supply from the renewables is not sufficient. Gas turbines operating with hydrogen is an attractive option, since hydrogen combustion has zero carbon emissions and can be used as an energy storage when the supply of renewable energy sources are abundant. However, hydrogen combustion poses several challenges. A hydrogen flame has a higher flame temperature than natural gas, leading to more NOe production. To
reduce these NOe emissions, gas turbines operate in lean premixed conditions. This creates a risk of flame flashback, in particular boundary layer flashback, which can lead to severe damage to the gas turbine.
Recent research performed on boundary layer flashback revealed that two flame configurations, i.e. unconfined and confined, showed fundamentally different flashback phenomena. Unconfined flame flashback refers to the situation where an initially stable flame anchored at the burner rim eventually moves into burner tube. When a flame is partially of completely surrounded by walls and propagates and then starts propagation along the wall, it is called confined flame flashback. Previous studies have focused on one of the two flashback processes at a time. However, the transient flashback process between unconfined and confined flame flashback is not well understood. Research has shown that hydrogen is much more prone to flashback compared to natural gas. This has been attributed to the difference in flame speed between natural gas and hydrogen, but the exact reason for the difference in flashback behaviour between natural gas flames and hydrogen flames has yet to be found.
In this study, a quartz Bunsen burner is used to investigate the flashback phenomena of turbulent premixed hydrogen-natural gas-air flames. To gain more insight in the flashback phenomena, three experiments have been performed. First, flashback maps are obtained to determine the flashback limits of the quartz Bunsen burner. Secondly, the influence of a flame on the flow was investigated using turbulent statistics. Finally, both unconfined and confined flashback are visualised, thereby capturing the transient flashback process between these two configurations. This has been done for a stoichiometric natural gas flame and a lean hydrogen flame. Laser diagnostics like Particle Image Velocimetry (PIV) and Miescattering are used to obtain the turbulent flow statistics and to visualize the instantaneous flashback process. The results show that regions with negative velocity fluctuations in the unburned mixture are the predominant physical mechanism for the start of unconfined flashback and for the transient flashback process of the flame propagating into the burner. However, the start of a flashback event depends on the combination of several parameters: the bulk velocity, the position of the flame front before it interacts with a region with negative velocity fluctuations, the magnitude of the negative velocity fluctuations and whether a region with positive velocity fluctuations is absent after interaction of the flame with the region consisting of negative fluctuations. So, unconfined flashback is rather a statistical phenomena, where the chance of the occurrence of a flashback event is increasing for a decreasing bulk flow velocity. Experiments showed that the transient process between unconfined and confined flashback is very short and fast. After a distance of approximately 5 mm upstream of the burner rim, a backflow region starts to develop in front of the flame, which denotes the start of confined flashback. The time needed for a natural gas flame propagating upstream from the burner rim to reach a confined configuration is approximately 17 ms and only 5.6 ms for the hydrogen flame. The suggested physical mechanisms leading from unconfined flashback to confined flashback are the convex shape of the flame towards the reactants during upstream flame propagation and the reduced cross-sectional flow area of the burned gases at the flame tip. Due to the created backflow in front of the flame and the abovementioned mechanisms, the upstream flame propagation is strongly enhanced, which explains why the flashback propensity for confined flames is much higher than for unconfined flames. The experiments showed that the hydrogen flame propagates closer to the wall than the natural gas flame, indicating higher backpressure effects. The hydrogen flame is thermaldiffusive unstable and the convex shape of the flame tip during flashback strongly enhances the local flame speed and thus the upstream propagation velocity. In contrast, the hydrodynamic instability encountered in the natural gas flame only retards the flow in front of the flame tip, but does not affect the flame speed. This might explain the difference in flashback behaviour between natural gas and hydrogen flames.

The decarbonization of the transport sector is a major challenge for the transition towards a sustainable economy. Amongst the different measures to lower the impact of road transportation on the environment is the use of biofuels, especially for heavy duty vehicles. For biofuels to be affordable and well integrated, improvements in the production process in terms of energy performance and economic feasibility need to be made.

Consequently, this thesis aims at the techno-economic assessment of the integration of pyrolysis oil gasification with electrolysis and syngas catalytic upgrading. Oxygen, being a co-product of electrolysis, is used as an oxidizer for entrained flow gasification of biomass derived pyrolysis oil. Hydrogen from the electrolyzer is used to enhance the production of biofuel. The process was designed to have a high-temperature solid oxide electrolysis cell (SOEC) and the biofuel was chosen to be compressed natural gas (bio-CNG). The modeling of the process was performed on Aspen Plus software and calculations of parameters for the gasifier and electrolyzer were done using Fortran and Matlab respectively.
As aimed by the integration of electrolysis, the hydrogen produced is added to the syngas to obtain a feed ratio of 3, required for an optimum methane production. The increase in the feed ratio at the level of the gasifier is mainly limited by the oxygen equivalence ratio (OER), considering the extent of combustion reactions and the operating temperature. The amount of steam inputted was found to increase the molar ratio of H2 to CO without significant change in the feed ratio due to the increase in the concentration of CO2. However, steam was still necessary for adjusting the temperature of the gasifier to values that are in accordance with experimental ones in literature. The obtained final product stream of bio-CNG at 250 bar and 15℃ has a purity of 98.63 mol% and 99.15 wt%.

Moreover, by applying heat integration to the process, the resulting surplus heat was 10.71 MW, which was assumed to be used to generate steam that is inputted to the SOEC for producing hydrogen as an additional product. The process was found to have an overall efficiency of 73.8% (LHV basis) and 78.2% (HHV basis). Heat integration increased the process efficiency by 15% (LHV basis) and 23% (HHV basis), by removing to a great extent the need for external heat and by having hydrogen as an energy output added to CNG.
As a complement to the energy performance, the economic feasibility of the process was assessed. The total capital investment was found to be 889.5 Euros/kWinput, the net present value was 6.0342 million Euros and the rate of return on investment 30.02%.

Gas turbines for power generation use lean premixed flames to adhere to the strict pollutant emissions regulations. Unfortunately, this often leads to thermoacoustic instabilities. These instabilities can lead to failure of system components, flame blow-off or flashback and a reduction in efficiency. Especially the high frequency transverse thermoacoustic instabilities can lead to big problems in the successful operation of gas turbines. These instabilities can be reduced by adding damping devices or mitigating the excitation mechanisms. In this work, Large Eddy Simulation (LES) is used to identify the thermoacoustic instability which tends to occur in a specific heavy duty gas turbine combustor design. In order to successfully counteract this instability, identification of the acoustic mode affecting the burner is required. Results from the LES are compared with experiments to test the predictability of LES and research mitigation techniques. The oscillation amplitudes do not match due to numerical damping, but the frequency of the oscillation in LES is within 1% of the experimental value. Furthermore, a coherence between the heat release and pressure oscillations of 80% is achieved and the phase of the oscillations are within 90° of each other. This confirms that the Rayleigh criteria is satisfied and the instability in the simulation is indeed a self-excited thermoacoustic instability. After identifying the mode, Fast Fourier Transform (FFT) of the pressure data at the combustor walls is used to visualize and locate the mode. Its location suggests that fuel supply oscillations could be a possible driving mechanism. However, the frequency of the oscillations in the fuel supply did not match that of the thermoacoustic instability so this hypothesis was rejected. After identifying the mode, the effect of different simulation and operation parameters is researched. First a model coefficient which influences the flame length is changed. Shortening the flame results in a higher amplitude instability, due to the location of maximum heat release moving closer to the location of the source of the instability. Next, the fuel distribution is changed in order to break flame symmetry and reduce the instability amplitude. This is done successfully, as the amplitude of the instability at the peak frequency is reduced to the same level as the surrounding noise frequencies. Finally, the effect of adding Helmholtz resonators specifically designed for the instability of interest is researched. A transfer function is defined to measure the response of the resonators to a pressure fluctuation in front of them. The result is compared to an analytical solution to determine the effectiveness of the resonators. Like the fuel biasing, also the resonators performed well and resulted in a decrease of the instability amplitude.

This study presents the numerical modeling of boundary layer flame flashback in premixed tube burners with turbulent flow and high hydrogen content. The modeling approach is based on a RANS turbulence model and a flamelet combustion model using a flame surface density approach in combination with multiple turbulent flame speed correlations to close the chemical source term. The Zimont turbulent flame speed correlation is used to model flame flashback and gain insight in the relevant mechanisms driving the occurrence of the instability. However, this approach has not let to a method to predict in ad- vance that a flame is near flashback conditions. This implicates that the flashback process (when mod- eled with this specific modeling approach) seems to occur after a certain threshold has been passed. When this threshold has been passed the flashback process is self-amplifying. The ability of the mod- eling approach based on the Zimont correlation to predict flame flashback is compared to experimental data. Based on this comparison it is concluded that the numerical model performs fairly well. The most notable result is the flame regime map which shows that the numerical model is able to capture that an increase in the hydrogen concentration in the fuel leads to an increased flashback propensity, which was also seen in experimental results. Furthermore, high hydrogen concentration fuels are character- ized by high flame speeds and, if sufficiently lean, by a Lewis number lower than 1. In combination with differential diffusion this leads to the thermal diffusive instability. At an attempt to improve the nu- merical model, two turbulent flame speed correlations that account for these effects were selected and implemented in the numerical model. However, these correlations did not lead to an improved ability of the model to predict flame flashback and flame shape. This reinforces the initial findings that the numerical model with the Zimont turbulent flame speed correlation already performed fairly well.

Zero Emission Fuels B.V. (ZEF) is a start-up company developing a fully autonomous methanol synthesis micro-plant that will be energy driven by solar panels. The process implements an alkaline water electrolyzer, which supplies the methanol synthesis reactor with hydrogen. The electrolysis system includes a small-scale stack of cells and is designed to operate at 90 ^oC and the high pressure of 50 bar, with a 30% potassium hydroxide electrolyte. The system is also self-pressurized through the continuous accumulation of the electrolysis gases in the closed flash separation vessels. To control the process, the company has designed a novel system that aims to maintain the gas pressure at 50 bar and the liquid electrolyte level inside the flash separators at a fixed point. 
The present work has two main objectives. The first is to characterize the transient dynamic response of the company's current experimental electrolysis setup under the effect of the operating conditions and control. The second objective is to predict the level of gas crossover that is induced during the system's operation and evaluate the risk of explosive mixtures formation. Two different models were developed to fulfill the research targets.
The first model is based on a 1-d transient hydraulic network analysis. Simulations were conducted using Simulink for a current density range of 500-5000 A/m². The model predicts the electrolyte flow and pressure response in the various elements and locations of the network respectively, indicating also the oscillatory behavior induced by the operation of the valves. A key finding is the high differential pressure between the stack anodes-cathodes that is caused when the valves open, posing a danger for the integrity of the separators between the half-cells.
The second model was developed in MATLAB and uses the predicted flow response of the first model to estimate the crossovers by solving numerically the unsteady 1-d advection-diffusion equation in the corresponding elements. The effect of the supersaturated electrode boundary layer was also considered as an enhancing parameter of the mass transport through the separators of the cells and a sensitivity analysis was conducted. The main finding is that this parameter has an important effect, especially on the hydrogen crossover inducing 1% higher hydrogen impurity when it is increased by a factor of 10. The crossovers of both hydrogen and oxygen are found to gradually increase and reach an almost stable value under the effect of the control system. A comparison of the model with preliminary experimental data indicates a supersaturation intensity between 5 and 15 times higher than the solubility of the components. In this range, the system will safely operate above 2000 A/m² without the formation of explosive mixtures. 

Transport sector CO2 emissions are on the rise and responsible for nearly 30% of the EU’s total CO2 emissions (European Parliament,2019). An attractive way to reduce the CO2 emissions by transport is by changing the fuel used. Hydrogen is expected to play a key role in a clean, secure and affordable energy future (IEA). However, a clean, widespread use of hydrogen in global energy transitions faces several challenges. Currently, the global hydrogen production is approximately 7.2 EJ per year, 96% of which comes from fossil fuels. To harness the potential of hydrogen on the way to a clean energy future requires the capture of CO2 from hydrogen production from fossil fuels and greater supplies of hydrogen from renewable energy sources. This study focuses on assessing the techno-economic potential of the membrane technology coupled with carbon capture technology, to produce decentralized bio-hydrogen in realizing a low carbon society in The Netherlands. A literature survey was performed to determine the performance of the membrane reactor & cryogenic capture technologies and expected technological advancements. With the information obtained,a basic process of membrane reforming with carbon capture was modeled in Aspen Plus. Different configurations of the basic process were developed. In the first stage, thermodynamic key performance indicators were used to compare the performance of the different configurations developed. Secondly, one promising configuration was chosen and the levelized cost of hydrogen was used to optimize the process parameters like sweep ratio, permeate pressure, feed pressure etc. Finally, the optimum configuration was used to determine its economic and CO2 emissions potential compared to the conventional steam methane reforming process. Exergy analysis for the optimum configuration was also performed.The optimum levelized cost of hydrogen of the decentralized hydrogen production system developed in this work is calculated to be 4.19 €/kg H2. The levelized cost of hydrogen for the equivalent centralized steam methane reforming system is 5.98 €/kg H2. Therefore, the decentralized system developed is more attractive than the centralized system. The higher costs of the centralized system are due to the hydrogen transportation costs. Furthermore, the carbon capture unit costs 0.68  €/kg H2 and an additional dehydration unit at 0.4 €/kg H2 is required to meet the PEM fuel-cell hydrogen specifications. The efficiency and carbon capture rate of the developed configuration is 66.07% and 72.13% respectively,higher than the conventional process. The exergy efficiency of the developed process is 65.1%. The CO2 emissions for the decentralized system across the value chain are calculated to be 1.4 kg CO2/kg H2. Future scenarios with renewable energy in the electricity mix result in negative CO2 emissions, making the system attractive to limit the climate change and also benefit financially from the EU-ETS. The CO2 emissions of the centralized system are 5.45 kg CO2/kg H2 with post-combustion carbon capture and 10.14 kg CO2/kg H2 with state-of-the-art reforming. With a carbon tax to be implemented soon,the costs of this system will rise making the decentralized system even more attractive. However, uncertainties in the development of an integrated hydrogen transport infrastructure, fuel-grade hydrogen demand, technological advancements in membrane reactors etc. may affect the comparative attractiveness of the systems.

Lean premixed flames are being used in gas turbines to reduce the emission of NOx. Unfortunately, it results often in thermoacoustic instabilities. These instabilities are high amplitude pressure oscillations which cause damage to the combustion system, reduce efficiency, flame blow-off or flashback. While the cause for instabilities due to longitudinal modes is known, the cause for transverse thermoacoustic instabilities is still not fully understood. Currently, transverse thermoacoustic instabilities are avoided by damping devices that consume considerate amounts of cooling air, thus raising the flame temperature and NOx emissions. Therefore, a good understanding of the feedback cycle that cause transverse thermoacoustic instabilities is crucial in predicting and avoiding combustion instabilities. In this work, Large Eddy Simulations (LES) is used to study processes involved by the driving of instabilities in a small scale burner. Additionally, different dampening alternatives are designed and validated. Experiments have shown that a small scale burner becomes unstable with decreasing flame lengths, due to the addition of hydrogen to the fuel. To research the impact compact flames have on combustion instabilities, simulations of methane flames with decreasing lengths is performed. It is found that decreasing the flame length, increased the amplitude of the pressure oscillations. Similar as to the experiment, both longitudinal, as well as transverse instabilities, is observed in the LES. Unfortunately, to study the transverse thermoacoustic instabilities, the longitudinal modes must be avoided. Hence a modification is designed to dampen the longitudinal mode without affecting the transverse modes. Ultimately an orifice plate was designed that reduced the pressure amplitude of the longitudinal mode by 92 %, while hardly influencing the transverse modes. The sufficient suppression of the longitudinal modes enabled the research into the transverse thermoacoustic instabilities feedback cycle. The research found two driving mechanisms for transverse instabilities. First of all, flames located at pressure anti-nodes are excited by pressure-induced flow oscillations from the premixing ducts. Consequently, the flame’s heat release positively coupled with the acoustic pressure. Additionally, the lateral movement of the flame towards regions of higher pressure, due to transverse acoustic velocity, is observed. Especially at pressure nodes, where acoustic velocities are most potent, the flame movement was substantial. While both mechanisms are found and agree to the driving criteria, it is difficult to say what their actual contribution to the instabilities are. Finally, the actual driving of transverse thermoacoustic instability by flow oscillations inside the premixing duct is studied. At first, a modification is designed to deliberately cause a quarter-wave resonance that forces the pressure anti-node away from the flames. This way, the unsteady heat release is not able to couple with acoustic pressure oscillations. Secondly, a modification inspired by a muffler is aimed at dampening all acoustic waves travelling through the premixing duct. Unfortunately, the quarter-wave resonance created new unstable modes as well as increased the strength of the other instabilities. Also, the muffler modification is not able to dampen the transverse instabilities. Moreover, a resonant mode arose inside one of the muffler elements causing a new instability inside the combustion chamber.

The effort to reduce global anthropogenic carbon dioxide emissions has caused a growing interest in the use of sustainable energy sources. One of the potentially sustainable energy sources considered as an alternative for the currently used fossil sources is biomass. Biomass is organic matter that originates from plants or animals which can be used as chemical energy carrier for fuels or for the production of chemical feed stock[Basu, 2010]. Gasification is a thermochemical process that converts materials like biomass into useful convenient gaseous fuels or chemical feedstock[Basu, 2010]. Gasification takes place at high temperature in the presence of a gaseous agent. Gasification is aimed at increasing the overall energy density of biomass by producing gaseous energy carriers with a higher energy density than the original biomass feed. Conventional gasifiers combust a fraction of the biomass or char in order to provide heat to the reduction reactions. This has two disadvantages. First, the flue gasses are mixed with the product. Secondly, the air that is used for partial biomass combustion mainly consists out of nitrogen. The nitrogen dilutes the gasification product significantly. The Indirectly Heated Bubbling Fluidized Bed Steam Reformer [IHBFBSR] set-up at the TU Delft is a novel indirectly heated gasifier or allothermal gasifier. The combustion of natural gas takes place in a separate combustion chamber inside the reactor chamber. Steam gasification can therefore be performed in the absolute absence of oxygen. A radiant tube facilitates heat transfer from the combustion to the reaction chamber. The radiant tubes are installed at the top and bottom of the IHBFBSR and work according to the heat from inside to outside principle. The aim of this study is to assess the performance of the IHBFBSR set-up at the TU Delft and compare its performance with other existing allothermal gasifiers. The main research question of this study is stated as: "How does the Indirectly Heated Fluidized Bed Reactor perform in terms of product yield, product quality and energy efficiency and how does its performance compare to other indirectly heated gasifiers?". In order to answer this question, both an equilibrium model and a kinetic model have been designed. Sub-optimal conditions for the IHBFBSR take place at a reactor temperature of 850 degrees C, which is the maximal controlable temperature of the reactor. At this temperature, the carbon limit is reached for an equivalent ratio of 0.23. The CGE at the carbon limit equals 69.7%. Optimal process conditions are where the particle size of the bed material is maximized without losing the fluidization behaviour of the bed. The maximum particle size equals 600 micron. The overall efficiency of the system can be increased by heat transfer between the inlet and outlet gasses of the burners and by the separation and combustion of tars and char to add heat to the process. This study shows that the pyrolysis step in the IHBFBSR is rate limited by internal heat transfer. In addition, the char oxidation reaction is limited by mass transfer of oxygen to the char particle.

In recent years, the energy transition has led to increasingly higher installed capacities of intermittent renewable energy sources. This has sparked the interest in power-to-fuel technology to store excess renewable energy in the chemical bonds of synthetic fuels. As a highly reactive, turn-key process, plasma-chemical conversion offers a promising approach to power-to-fuel technology. However, recent studies have shown limitations in either energy efficiency, conversion or flow rate. The novel Spinning Arc Plasma Reactor (SAPR) developed by J. van Kranendonk stabilises the plasma by mechanical rotation with the potential to contain a liquid film for in-situ product removal. The aim of this thesis is to characterise this reactor by studying the effect of rotational confinement on the reactor performance. To this end, the prototype initially built by J. van Kranendonk was further developed. A wealth of recent studies on the plasma-chemical conversion of CO2 as a step in the formation of synthetic fuels serves as a benchmark to compare reactor performance of the SAPR concept against. A series of experiments with argon were performed to establish the relationship between the system variables (pressure, power, flow rate and rotational speed) and the plasma parameters (electron temperature and electron density). Based on this knowledge, a series of experiments with CO2 were performed to establish the relationship between the reactor performance measured by the conversion and energy efficiency and the system variables: pressure, power and flow rate. The maximum conversion of about 30% to 55% was obtained at an energy efficiency of approximately 0.25% and the maximum energy efficiency of about 3% was achieved at a conversion of approximately 8.5% conversion. Similarly to other studies, improvements to either one came at the expense of the other. The performance of the SAPR proved comparable to dielectric barrier and other glow discharges but was outperformed by microwave and gliding arc discharges. Especially energy efficiency was inferior to these configurations. Further analysis of the discharge emission spectra suggested that CO2 dissociation mainly occurred through electron impact excitation. This explains the large difference in energy efficiency as microwave and gliding arc configurations are able to exploit more energy efficient dissociation channels. Nonetheless, this study was able to further develop the concept and has laid the ground work to explore the potential effect of a liquid film and in-situ product removal on the reactor performance.

The turbulent lifted Dutch natural gas jet diffusion flame in cold co-flowing air is widely used in gas turbine operation and subject of the current investigation. In striving to clean and sustainable combustion, adding hydrogen to the Dutch natural gas (DNG) fuel and CO2 in the coflow is promising. Objective of this investigation is to study the effect of hydrogen fuel-addition and CO2 coflow-dilution on the stability of a turbulent lifted DNG jet diffusion flame in cold co-flowing air. OH* chemiluminescence and particle image velocimetry (PIV) are applied simultaneously at a low sampling frequency of 50 Hz to determine time-averaged statistics of the lift-off height and stabilization point location of the flame. PIV measurements at a sampling frequency of 2.5 kHz are performed to determine the transient behaviour of the stabilization point, the flow conditions at the stabilization point and the burning velocity. Hydrogen fuel-addition leads to increased flame stability. With more hydrogen in the fuel, the lift-off height reduces and the stabilization point location shifts upstream and radially inward. The burning velocity at the stabilization point increases with increasing hydrogen fuel-concentration. A significant difference is observed in the burning velocity conditioned on upstream or downstream stabilization point motion. Hydrogen enables the flame to stabilize in a region of the flow that is characterized by high gas velocity and high vorticity. CO2 dilution of the coflow leads to decreased flame stability. With increasing CO2 coflow-dilution, the lift-off height increases and the stabilization point position shifts downstream and radially outward. The burning velocity at the stabilization point increases with increasing CO2 coflow-dilution and the flame stabilizes in a flow region with significant lower vorticity.
Additionally, this report provides useful statistics of the investigated quantities and presents a description for the transient behaviour of the stabilization point.

The present study aims to assess and advance the prediction skill of solar radiation in high resolution weather forecasts by large-eddy simulations (LES). The GPU-Resident Atmospheric Simulation Platform (GRASP) was used to simulate the atmosphere around the Cabauw experimental site for atmospheric research (CESAR) in the Netherlands. Large-scale boundary conditions were provided by coupling the simulation to a general circulation model (GCM). Radiative tendencies were calculated using two di_erent implementations of the Rapid Radiative Transfer Method for GCMs (RRTM-G): one runs in advance of the simulation using pre-calculated atmospheric _elds, the other employs dynamically updated _elds during the simulation. Both con_gurations generated simulations of every day in 2016, which were compared to each other and validated using observations from the Baseline Surface Radiation Network (BSRN). This study revealed that the implementation of interactive radiation altered cloud representation in the simulations, in most cases causing clouds to rise. This process correlated with an increase in turbulence kinetic energy of up to 2 m2/s2 locally. The clouds that were raised tended to break up more often between 5 and 7 km altitude, leading to a decrease in average cloud fraction and increase in short-wave down-welling radiation. The results suggest that the implementation of interactive radiation enabled the development of cloud top entrainment instabilities, which could be responsible for the cloud breakup in these cases. Regardless of the chosen implementation of the radiative transfer method, large errors are made in the prediction of surface solar radiation. GRASP produced root mean squared errors (RMSE) of 122.4 W/m2 and 115.7 W/m2 using prescribed and interactive radiation, respectively, while the large-scale model used to provide the initial and boundary conditions to the simulation produced an RMSE of 87.3 W/m2. The large error in GRASP's prediction of surface solar radiation can partly be attributed to conversion errors made during GRASP's initialization of the thermodynamic state, which lead to erroneous diagnoses of the liquid water content in the atmosphere.

In the field of combustion systems, methods and tools are under development to fulfill the need for fast and accurate prediction of emissions such as NO and CO. CFD-CRN is a hybrid approach that utilizes a combination of computational fluid dynamics (CFD) and a chemical reactor network (CRN) to simulate the flow field and chemical kinetics of a combustion system in detail. This thesis describes the research into the effect of applying the energy equation to update the temperature whilst solving the CRN. The objective is to quantify the effect of the common assumption that the temperature generated by CFD is sufficiently accurate and can be kept fixed to reduce the nonlinearity of the system of equations to be solved in the CRN. This research uses and modifies the computational tool AGNES, that was developed at the Delft University of Technology and is able to automatically cluster, solve and visualise the results of a CRN based on results form CFD. The test cases used are the Sandia Flame D, which is a piloted methane-air jet flame with a Reynolds number of 22400, and the Verissimo et al. test case, which is a flameless combustion burner. The CRN was clustered with the zones and tolerances set by Monaghan et al. The results were validated using experimental data of temperature and species mass fractions and the sensitivity of the clustering method was studied.
The results of CFD-CRN simulations were used to evaluate the effect of updating the temperature using the energy equation. The results show that solving the energy equation leads to a progressive overprediction of temperature in the far field of the computational domain, which consequently results in the overprediction of NO and CO concentrations. A potential cause for the overprediction is identified as the heat transfer in the form of conduction and radiation not being accounted for in the solving of the CRN. Unless the diffusion of heat is accurately modeled, the application of the energy equation is not recommended.

The major challenges in the world today is to reduce pollutant emissions from gas turbines while still being able to retain the maximum efficiency in the gas turbine. Especially due to stringent norms on emissions, the research on gas turbines have increased to reduce NOx levels. Most of the gas turbines have been using non-premixed combustion for power generation and since the early 90s research on premixed combustion was sought after. Aircraft engines and many other CHP power plants still currently use non-premixed combustion. Exhaust gas recirculation (EGR) was one of the major part load operations in a gas turbine which was determined to improve part load efficiency and at the same time reduce NOx emission levels.

This thesis research would give an overview on how to model non-premixed combustion in a gas turbine and how different parameters effect NOx emissions. The two main reactors that were used are perfectly stirred reactor(PSR) and a plug flow reactor(PFR). The combustor volume was divided equally between perfectly stirred reactor and plug flow reactor. The half of the combustor where the mixing between the fuel and oxidizer and the combustion reactions occur are modelled by three perfectly stirred reactors which contain flame sheet reactor (FSR), post-flame PSR and PSR recirculation. The volume of FSR was determined by modelling the stoichiometric mixture fraction. This is done by determining the scalar dissipation rate which tells the rate of mixing between the fuel and oxidizer at the stoichiometric interface. The model was then validated using different technical studies on non-premixed combustion.

Parametric analysis was performed with this model using EGR as oxidizer and compared with results that were obtained when using air as oxidizer. It was seen that thermal NOx which was the most amount of NOx released during the combustion was reduced when EGR was used as an oxidizer. It was also found that the CO levels were increased when using EGR but still remained below the level when air was used as an oxidizer. This was due to insufficient residence time inside the combustor. When using EGR as a part load operation and at high pressures in gas turbine, the NOx emissions were lower. The results from the pressure analysis showed that at lower pressures the amount of NOx that was reduced was more when using EGR, but at high pressures the amount of NOx that was reduced was quite less even though it was EGR-oxydizer compositon. It was observed that the NOx and CO levels were still lower while using EGR compared to using inlet guide vanes as a part load operation(IGV). While using a fuel mixture of H2 and natural gas, it appeared that the NOx levels were higher with EGR and air as an oxidizer than just using only natural gas as fuel. At the same time CO emission levels showed that it was low for both EGR and air when fuel mixture of H2 and natural gas was used.

In 2015, 30% of the world's energy demand was met through petroleum based sources, whose burning has affected the world's climate. The Paris Climate Agreement, among other policies, has shifted the focus towards usage of renewable energy sources. Currently, the renewable market caters predominantly to meeting the electric demand, which only represents 19% of the world's energy consumption. Zero Emission Fuels (ZEF) aims to create a small-scale chemical plant that uses renewable energy sources to create synthetic methanol. This follows the vision of adapting renewable energy sources for non-electric usage. Methanol is the simplest liquid hydrocarbon at atmospheric condition; it can be used as a fuel or as a base chemical for other products. Presently, the industry reforms syngas obtained from fossil fuels to create methanol, predominantly using large-scale catalytic reactors. For production of methanol from renewable sources, Bos and Brilman developed a small-scale catalytic reactor driven by natural circulation. ZEF adapted the Brilman reactor for their chemical plant, creating a prototype of the modified Brilman reactor (MBR). The present work aims to create a model that describes the steady-state methanol production of the prototype using computational fluid dynamics (CFD) and chemical process models.

The MBR is an innovative design based on a closed loop geometry. The gases are driven by buoyant forces from a temperature difference between the high-temperature catalytic reaction zone and the low-temperature condensation zone. Heat recovery elements are used to exchange heat between the hot and cold streams as they travel in the loop. The CFD model developed on Fluent 18.2, uses a RNG k-e turbulent model, with multicomponent species transport, convective heat transfer and momentum loss effects from the catalytic zone. The boundary conditions are based on the operating conditions of the prototype. The model calculates flow-rate, and the effect of heat recovery elements inside the natural circulation loop. A chemical process model developed in COCO 3.2 is used to calculate a mass and energy balance for the two-phase behavior of the gas mixture inside the MBR.

A study of the effects of a natural circulation loop with a configuration similar to the reactor is performed, observing potential benefits by tilting the system. The combination of effects due to heat recovery and flow blockage in the reactor is studied, and the results are evaluated with experimental measurements. The chemical process model developed closely resembles the experimental characterization of the reactor. The parameters of flow-rate and internal temperatures can not be validated due to limited data available from experimental procedures.

In the GasDrive project, a solid oxide fuel cell and a reciprocating gas engine are used to provide electrical and mechanical power for a ship. One of the goals of the GasDrive project is to broaden the limits between knock and misfire for the gas engine. Extending the operating limit could be achieved by addition of anode-off gas. Before anode-off gas can be used in combustion together with natural gas in the GasDrive project, the combustion characteristics of anode-off gas must be known. In this thesis, a literature review is conducted in order to explore similar gasses. One such gas is producer gas, on which both experimental and numerical studies have been conducted by other researchers. To investigate the performance of anode-off gas, an altered in-cylinder model was used. The model is verified using producer gas as a fuel, with the experimental data from producer gas combustion in an IC engine. The model functions properly and is used to investigate anode-off gas combustion.
In modelling the combustion of anode-off gas, multiple parameters are kept constant and similar to that of producer gas. These parameters include the Vibe parameters, engine geometry, air excess ratio, T1, p1, and stoichiometric gas mass fraction from the previous cycle. The combustion duration relative to producer gas is modelled based on the ratio of turbulent flame speeds. This turbulent flame speed is a combination of laminar flame speed and turbulence intensity. At first the SOC is kept constant as well, only altering the EOC for different combustion durations. The maximum power output is 79 kWe for anode-off gas with a 50% fuel utilization rate. The maximum efficiency is 20%. The peak pressure is 104 bar, which is higher than for producer gas, but falls within the limits of what the engine can handle. The peak temperature is 2847 K, which is more than 700 K higher than producer gas. The engine, it is believed, can not handle this temperature. The lowest peak temperature is reached for anode-off gas with a 85% fuel utilization rate and is 2652 K. This is still outside normal engine operating temperatures. Combustion of anode-off gas under stoichiometric conditions in an IC engine is therefore not feasible. Increasing the air excess ratio could resolve this issue, but can not be done in the current model without having experimental data on anode-off gas. The fuel consumption is 6-18 times higher than conventional fuels, also showing that anode-off gas combustion would not be an advantage over conventional fuels. More power at lower temperatures can be reached when retarding start of combustion, achieving MBT timing. Peak power is achieved using anode-off gas with a 50% fuel utilization rate and is 82 kWe. The corresponding peak temperature is 2822 K, which is also outside normal operating conditions of IC engines. Based on the modelling results, it can be said that combustion of anode-off gas is possible in a IC engine, but power outputs will be lower than conventional fuels and fuel consumption will be higher.

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.