In this thesis work, we strive to describe and apply the modelling methodology for simulating a turbulent jet diffusion flame stabilized behind a bluff body by applying flamelet generated manifold (FGM) model and steady diffusion flamelet model for predicting the pollutant emissions from the flame. The flame under consideration is a CH4/H2 (1:1) bluff-body stabilized flame known as HM1. The numerical calculations of the flow physics has been completed by using a commercial CFD code namely Ansys Fluent 19-R3, where the computational domain is assumed to be two dimensional and axis-symmetric in nature due to the cylindrical symmetry of the burner with an structured grid for meshing. The turbulence is modelled by using a two equation Reynolds averaged Navier Stokes model, namely the standard k – ϵ model with a modification in the Cϵ1 from 1.44 to 1.60. The chemical mechanism used in the project was the GRI 2.11 mechanism developed by the Gas Research Institute, USA. Next, postprocessing tools like the Reactor Network Model (RNM) and Ansys NOx post-processor were used as an alternative, possibly a better way to obtain the NO species
concentrations. The acquired results from the simulation are thoroughly analysed and were compared to earlier results on the HM1 flame in the literature and validated by using the experimental data documented by the University of Sydney in collaboration with the TNF Workshop. The results showed that the steady diffusion flamelet performed better than the FGM model and was in acceptable agreement with the experimental data, although some under-prediction and overpredictions were reported for NO and OH species. In regard with the post-processing tools the RNM model performed better than the Ansys NOx post processor.

In reacting flows, detailed chemistry computations are usually avoided precomputing the thermochemical quantities as functions of a reduced set of variables such as the Flamelet Generated Manifold (FGM) approach[34]. Although it mitigates the calculations of detailed chemical mechanism, the memory requirement associated to store the lookup table and retrieve the information during numerical simulations is usually large (order of Gigabytes). Thereby, extending the FGM approach in order to include other conditions requires to add
other independent variables which will inevitable lead to increase the size of the lookup table. This will generate that Large Eddy Simulations (LES) cannot be performed such as is the case of the Diluted Air FGM (DA-FGM) approach developed by Xu Huang[9], limiting the simulations to Reynolds Average Navier-Stokes (RANS) approach. In this master thesis, the goal is to use Artificial Intelligence (AI)-Machine Learning (ML) techniques in order to reduce substantially the computational cost of storing lookup tables. In order to achieve this, the Artificial Neural Network (ANN) technique is used. First, a 4D FGM lookup table for hydrogen flames is simplified using the aforementioned AI technique. Then, this technique is used to replace a 6D lookup table generated using the DA-FGM approach. The accuracy and stability of the models provided by ANNs is measured by statistical indicators, providing high accurate and stable AI models. Finally, in the middle of this project, unexpected issues regarding the 4D lookup table were encountered, which lead to recreate the 4D lookup table. After studying carefully how the 4D lookup table was created, a new 4D lookup table is generated, providing excellent results and improving the AI models obtained.

This thesis report discusses the design of a cost-effective and compact electric combustion air preheating for the LSV® burner. The industry has a complex problem to solve and an important role to play during the energy transition, that is needed because of global warming. Many industrial processes use heat generated by the combustion of fossil fuels. An alternative sustainable solution needs to be chosen in the future. Fossil fuels can be replaced by biofuels, hydrogen, electric power or a hybrid solution.

For this study a solution using electric power is investigated, which could also be used in a hybrid solution. Electric combustion air preheating can be used to shift the energy input from fuel energy to electrical energy. This is new since normally combustion air preheating is accomplished in the convective part of the fired heater. A system to heat up the combustion air to a temperature of 300°C is designed using correlations for tube banks and CFD modelling. An experiment is also conducted to investigate the impact of the combustion air preheater on the burner and fired heater performance. It is important that the burner and fired heater performance remain almost unchanged since the whole fired heater is designed around specific performance parameters.

The design includes a staggered and finned tube bank that can reduce CO2 emissions with 3.2 % by using green electricity when operating 3000 hours per year. This method for combustion air preheating will also result in an operating cost reduction and a payback time of less than five years. A drawback of this system is that the NOx emissions will increase by a factor of 2, which is bad for the environment since it is responsible for the formation of smog and the general acidification of soil and water. This could be avoided by improving the burner design or applying other combustion control mechanisms.

The outcome shows that electric combustion air preheater is suitable technology for CO2 emissions reduction in the short term for fired heaters. With the increasing CO2 emissions cost and increasing volatility of the electricity market, this is an attractive grid balancing equipment.

The lifespan of internal reforming solid oxide fuel cells (SOFCs) is not yet sufficient. Among other design challenges, this is due to detrimental carbon deposition formations. This must be mitigated, without compromising the power output and efficiency of the fuel cell for it to become a commercial viable product. The carbon that is deposited originates from a methane/hydrogen mixture, fed to the fuel cell. All failure modes caused either directly or indirectly by carbon formations are explored. A 3D-model representing part of an SOFC is modelled, in order to identify areas specially susceptible to carbon depositing on the anode. The methane is reformed by a surface chemistry mechanism developed with density functional theory. By doing this, it is possible to model both reaction kinetics and reaction equilibrium of the reforming process.
The final model can accurately model local mixture composition, as well as surface site coverage. The reaction rate and activation energy of methane reforming on a nickel catalyst is also calculated by using the output of the simulations. The site coverage observed can lead to further carbon deposition, but this is not yet modelled.

Meeting the ever-increasing energy demands in our planet where conventional sources of energy are finite and fast depleting, controlling adverse phenomena like climate change, soil erosion, greenhouse gas emission, ozone layer thinning and pollution will remain profound challenges until widespread adoption of sustainable sources of energy is achieved. The shift to a sustainable energy system cannot be complete without the contribution of biomass energy. Within the ecosystem of biomass energy, gasification is a thermochemical conversion process undertaken to obtain a high-quality product gas by increasing the low energy density of solid biomass. The product gas can be used in power applications or be converted to liquid fuels for transportation. Gasification is carried out at high temperatures (700-1500°C) by using a gaseous agent under sub stoichiometric conditions (R.A. Kersten & De Jong, 2015). The main non-condensable permanent gases obtained from gasification are CO, H2, CO2 and CH4. Use of allothermal gasifiers, whose working is based on the separation of combustion and gasification chambers within the gasifier, with heat supply for carrying out endothermic reactions, established via heat carrier or heat exchanger, have shown many advantages compared to the conventional gasifiers (Hofbauer & Materazzi, 2019). The mix-up of product gas and flue gas is avoided in this type of gasification. Secondly, while using air for biomass combustion, the nitrogen present in air reduces the quality of the end product by not participating in gasification, thus resulting in a diluted product gas. A high-quality product gas can be obtained from allothermal gasifiers without the need for establishing an expensive air separation unit, as required in case of conventional gasifiers. The 50 kWth Indirectly Heated Bubbling Fluidized Bed Steam Reformer (IHBFBSR) at Delft University of Technology (TU Delft) represents a new concept of allothermal gasification technology where heat required for the endothermic gasification reactions is provided by two radiant tube burners placed vertically inside the reactor, one at the top and one at the bottom. The aim of this research is to optimize and validate the kinetic model developed for the IHBFBSR by a former student, Maarten Kwakkenbos in Aspen Plus®. The optimization is carried out with the help of the several steps, described in the report. The optimized model is then validated by using the results of the gasification tests performed under various operational conditions by PhD Candidates Mara del Grosso and Christos Tsekos. The optimized model predicts the gas composition obtained from the IHBFBSR quite well. In addition to the yield of permanent gases, N2, H2O and tars concentration in the product gas, along with various gas ratios (CO/H2, CH4/H2, CO/CO2) from the model are compared with the experimental values and found to be in reasonable agreement. Moreover, key performance indicators such as carbon conversion (CC), cold gas efficiency (CGE) and overall efficiency (OE) are also evaluated from both model and experiments and compared. The error ranges for most of the parameters lie within the reported deviations observed in various gasifier models in literature. After the validation of the model, the possibility of recycling a fraction of the product gas to feed the burners in order to make the set up more sustainable is evaluated. Sensitivity analyses is performed by varying steam to biomass ratios (SB*), primary and secondary air flowrate to evaluate the best process conditions under which product gas obtained from the gasifier, after subsequent cleaning, can be used for methanol production based on the H2/CO ratio. The results indicate that a higher SB* and a higher secondary air flowrate can result in a H2/CO ratio closer to the desired value required for optimum methanol production. From the heat analysis performed for the model, a possibility of increasing the overall efficiency of the process by adding a bypass line in the gasifier setup is suggested to be explored. The master thesis concludes by answering the research questions and recommendations to improve the detailing and accuracy of the model.

Rising carbon dioxide concentrations in the air increase the global temperature since the industrial revolution. Today, there exists a great need to limit global warming, and an energy transition is vital to do so. With the upcoming changes in our energy system, bioenergy is widely discussed, resulting in a heated debate on including or excluding bioenergy in the energy transition. This study aims to identify the least controversial feedstocks out of 40 different ones and if they will help to resolve the controversies around bioenergy. Before a feedstock is deemed controversial, a background of bioenergy was established to see what role bioenergy has in today's energy system and in the future. A literature analysis identifies the role of bioenergy today. Using the 'IAMC 1.5C Scenario Explorer' hosted by IIASA the role in the future is identified. To determine the least controversial feedstocks, a multi-criteria decision analysis (MCDA) is performed. The PROMETHEE II method is used to perform the MCDA and the entropy weight method for weighting the criteria. The ranking and weighting make use of MATLAB. Since the aim is to classify feedstocks as the least controversial, the criteria are deduced from a literature analysis and represent the controversies of bioenergy. The first part of the report indicates a significant role in today's renewable energy system and a shift towards more modern bioenergy implementations like biofuels and bio-electricity. According to the scenario analysis, for the five different shared socio-economic pathways, bioenergy will be used. Besides the identification of a clear use of bioenergy in the future energy system, the scenario analysis of TFE of bioenergy indicated a shift towards modern bioenergy use. It was observed that the solid biomass use reduced and a strong increase in liquid biofuels in the transport sector will happen. These findings are in line with the predictions made by the IPCC. Also, this is in accordance with the observed growth rates and development trends found for today and in the recent years. This all results in the conclusion that bioenergy is important for the energy transition. Due to the observed research and development into biofuels and bio-electricity, traditional bioenergy will be phased out and replaced by modern bioenergy types. The next part of the report considers the controversies around bioenergy. The following controversies are identified and considered the most discussed ones: chain emissions, removal of carbon sinks, the carbon debt, land-use, competition with the food industry, and biodiversity. Identification of the controversies and with that the criteria are necessary for the feedstock ranking. The MCDA ranking shows that residues and wastes feedstocks are the least controversial, followed by alfalfa. The top eight high-scoring crops are alfalfa, oil palm, kenaf, mustard, cotton seeds, prairie grasses, camelina, and hemp. For this top eight, an additional ranking that included water use is done. This ranking shows that incorporating such a detail does not significantly change the results. It was seen that the top four was kept constant except when the simplest form of an MCDA is applied. Cotton seeds drops two to three places in rank. Prairie grasses replace cotton seed at place five when water use is considered. The most remarkable contradiction with literature is that oil palm ranks very high, and miscanthus is not present in the top eight. Oil palm is, in literature, considered a very controversial feedstock, and miscanthus shows promising features. These results indicate that either the data is not specific enough, or the criteria are not detailed enough. Another explanation is that the choice for an objective weighting method is not the best choice since it excludes opinions of the decision makers (the scientist participating in the debate). The debate is opinion and preference driven, which makes that a data based weighting method might not be ideal. Nevertheless, the rank of the waste streams is following the expectations. The results indicate that waste streams are to be used as primary feedstocks when controversies need to be resolved. The PROMETHEE II ranking shows this solution, and a sensitivity analysis supports the results. Reflection of the data for the feedstocks and the controversies shows that the use of residues and waste feedstocks can resolve several controversies with a relatively high degree of certainty (controversy of land use and competition with food industry) and others with some degree of certainty (controversy of chain emissions and biodiversity). Due to the global scope and simplifications, the data used could be improved. Therefore, further research is necessary to back-up the findings. Nevertheless, this research gives insight into the controversiality of several feedstocks and takes a first step in tackling the bioenergy debate.

Efficient combustion processes are indispensable in limiting the temperature increase to 1.5 deg C as set by Intergovernmental Panel on Climate Change (IPCC) before 2030 to curtail the effects of global warming. As for the emissions, the main task lies in controlling the air-fuel ratio in the lean regime as to control the emissions of NOx since they reach maximum discharge at the stoichiometric ratio whereas improper mixing can lead to an increase in CO emissions. Thus, the air and fuel interactions need to be studied to achieve control over emissions. To that end, good computational models are necessary to supplement the design process to control both the emissions and combustion instabilities. The latter can severely damage the combustion chamber. Therefore, the proper modeling of the fuel-air interfaces in high-pressures is pivotal as they differ significantly from the low-pressure injection. Various numerical droplet evaporation models are studied in trans/supercritical environments, the fluid is called supercritical when it's above the critical states whereas it is called transcritical when it passes the critical state. As for the droplets, two components were selected namely n-heptane and n-dodecane. The former for 0-D and 1-D models and the latter for 3-D models, the cases were dictated by the availability of experimental works. As for the 0-D and 1-D models, various correlations based on the Nusselt and Sherwood numbers were utilized. The Prandtl number and other non-dimensional numbers were computed by thermophysical property models based on the 1/3 rd rule rather than fixed values. In comparison, the developed 0-D and 1-D models conform to the experimental results and other computational studies ranging from perfect-gas to real-gas against the experimental work available in the literature. It is hypothesized that the differences in the computation of the latent heat of vaporization are more pronounced in the accuracy of the lifetime of the droplet rather than the density of the components. In 3-D models, the liquid-vapor interface is modeled by level-set and phase-field methods. Thermodynamic closure is achieved by the Peng- Robinson equation of state. Prandtl number assumption model is invoked for the computation of the liquid thermal conductivity, Chung model for the calculation of viscosity of mixtures, and Firoozabadi model for the Maxwell-Stefan diffusion coefficient. A basic model is used for the computation of surface tension coefficient for the phase-field 3-D models. A qualitative agreement was observed between the 3D model under this study, numerical work, and the experimental campaign of microscopic droplets for all the three vaporization regimes namely classical, translational and diffusive mixing. All the models yielded olive-shaped droplets. Effects of mesh resolution on the phase-field quantities were studied and contrasted with the same mesh size for the level set method in a 2-D configuration. Recommendations include better surface tension models, thermal conductivity for gaseous mixtures, the inclusion of PC-SAFT equation of state, cross-diffusion terms, and high mesh resolution of the O(-7) m in the droplet region coupled with adaptive meshing based on the gradient of the phase-field parameter.

In the present era of environment-friendly and clean combustion systems, there is an increasing demand for fast and accurate tools for emission predictions. The best choice is the CFD-CRN method which is a combination of computational fluid dynamics (CFD) and chemical reactor network (CRN) for decoupled simulation of fluid flow and detailed chemical kinetics. This thesis describes an improved solver implementation for resolving a constructed CRN using only global resolution methods and debunks the notion of needing any form of sequential resolution. This research focuses on further improving the Python based computational tool AGNES, developed at the Delft University of Technology. AGNES can automatically cluster CFD cells into reactors, solve the network and visualise the results [?][?]. This project aims at boosting the performance by reducing computation time and selecting a PETSc [1] based global resolution approach using time integration and Newton’s method. Sandia flame D, a piloted methane-air jet flame (Re=22400) [2], is chosen as the test case. The CRN results for species concentration, mainly NO and CO, are validated with the experimental data and CFD simulation results to ensure no compromise on the accuracy. The solution time and convergence ratewere compared for pre-research AGNES (AGNES v1.1) and the current version (AGNES v1.2). Results show that opting for an entirely global resolution approach is computationally feasible at higher reactor count (more than 500 reactors) and proves superior to the pre-research version. The achieved speedup is around 13% and with smart Jacobian evaluation, this is risen up to 21%. The potential reason for the improved performance is identified as the capability of the global time integration method (in place of local sequential resolution approach) to provide sufficient convergence with an increasing number of reactors and increased complexity. Moreover, the solver can be further augmented by selecting an efficient way for Jacobian calculations either by using automatic differentiation or simplifying the current Python loop approach.

In the future, fossil fuels will be replaced by renewable sources. Hydrogen seems to be a promising energy carrier (fuel). A lot of research has been conducted on the combustion of hydrogen, but the effect of the high diffusivity of hydrogen compared to other species (differential diffusion) was often not included in simulations of turbulent flames because turbulent mixing is expected to suppress strong influence of differential diffusion. Nevertheless effects of differential diffusion have been reported in experiments. The main purpose of this thesis is to include the effect of differential diffusion in a CFD model of turbulent non-premixed hydrogen flames and to validate the models with available experimental data. The validation data set used in this study is a non-premixed turbulent jet flame of hydrogen diluted with nitrogen on 50/50 volume ratio. This flame is interesting because the role of differential diffusion in this flame has been a matter of discussion in the literature.

A review is given of previous work on turbulent non-premixed hydrogen flames and effects of differential diffusion. It is concluded that the Flamelet Generated Manifold (FGM) model and the Transported Probability Density Function (PDF) model are both promising turbulent combustion models for these flames. Next, a new comparative study is made of several turbulence and combustion models using Reynolds-averaged Navier Stokes simulations in Ansys Fluent, and focusing on FGM as turbulent combustion model. It is concluded that the standard k-e with a correction as suggested by Pope is the best choice for the turbulence model. The ANSYS Fluent implementation of FGM does not have the option to include differential diffusion. Therefore it is added in a separate way. To do this, flamelets are created with the help of CHEM1D, a tool developed by TU Eindhoven. These flamelets are combined to an FGM table also including the effect of turbulence via a PDF and this table is imported into Fluent with the help of a user-defined function overwriting the default Fluent FGM table.

In order to clearly see the effects of differential diffusion, simulations with and without differential diffusion are made. Good agreement is obtained between experimental results and the numerical simulation for the models without differential diffusion. This confirms that turbulence can suppress strong influence of differential diffusion. In experiments effects of differential diffusion have been observed at the base of the flame, close to the burner nozzle. The model simulations with differential diffusion included, provide a slightly more accurate prediction of the mean temperature close to the nozzle but still large discrepancies remain.

The work presented in this report investigates the effect of replacing natural gas fuel in a radiant tube burner in an industrial furnace with hydrogen fuel. The flue gas is fully contained inside the radiant tube burner and does not come into contact with the iron products inside the furnace. The burner interacts with the process side of the furnace only by heat transfer. Therefore, the investigation could be divided into a study of two separate systems: the burner and the furnace systems. In the first part, the burner system was evaluated. The impact of changing the fuel of the burners from natural gas to hydrogen on heat-, flow- and radiation of the existing burner was studied. Moreover, the NOx generation has been considered. The investigations were performed using Reynolds Average Navier Stokes (RANS), Computational Fluid Dynamics (CFD) approach using detailed chemistry. Natural gas combustion was simulated as the basis for comparison. The result shows that the CFD model could estimate the NOx emission of the base case well. Next, the combustion with hydrogen was compared. The result suggests that the thermal efficiency of the burner is slightly higher with hydrogen fuel. On the other hand, the NOx emission is significantly higher. A modified burner including internal flue gas recycle was proposed and studied. The result shows that the modified burner can be operated at the same power and the same level of NOx emission as the existing system. Furthermore, different burner power could be applied in order to comply with the NOx emission limit or to increase processing speed. In the second part, a heat transfer analysis of the furnace has been performed. The model agrees well with measured data of furnace atmosphere temperature. The result suggests that having a higher burner power could increase the processing speed and reduce the energy requirement per ton of iron products.

The maritime sector faces major challenges with increasing regulations from the International Maritime Organization (IMO) and national regulations for CO2, SOx and NOx. Innovative fuel types for maritime use are now under development by various stakeholders. Methanol shows considerable potential as one of the most promising for implementation in the short to medium term, based on the potential availability, emission reduction, and energy density. The Green maritime methanol (GMM) project is Netherlands based collaboration of important stakeholders such as shipbuilders, engine manufacturers and universities. Within this project, methanol is researched as a potential alternative combustion fuel for maritime vessels. For this purpose, the ”Dutch Caterpillar engine dealer” PON Power provided a G3508A engine available as a retrofit option. The engine is a turbocharged spark-ignited natural gas (NG) engine with 8 cylinders and a rated power of 500 kWe at 1500 rpm. After six months of rebuilding the engine, the spark-ignited (SI), port fuel injected (PFI) engine runs on 100% methanol. Tests with stable engine operation were achieved with 100% methanol at 25%, 50%, and 75% engine loading and a constant engine speed of 1500 rpm.
In this research, experiments and modelling have been performed to study combustion using 100% PFI methanol. Measurements are realized with varying: ignition timings, NOx emission settings, and manifold temperatures. Data collected during these measurements such as in-cylinder pressures, emissions, and temperatures, provided a comparison between running the engine on methanol or natural gas. In this comparison combustion stability is determined with the coefficient of variation (COV) of Pmax and of imep, optimum ignition timing is determined and engine efficiency is calculated and compared to NG. Modelling is accomplished with a TU Delft model of the G3508A SI engine adjusted for the use of 100% methanol as a fuel. A modified sub-model for the PFI and vaporization of methanol has been developed. These engine data will be used to validate the methanol engine model and to optimise the engine performance for further experimental runs and better understanding the use of methanol as a fuel.
The effect on the performance and the combustion when 100% methanol is used as fuel for a SI PFI engine compared to premixed injection of natural gas is shown in this work. The engine operates stably on methanol at 50% and 75% load within ignition timings of 16-24 °CA BTDC, but less stable than with NG. Heat release indicates an almost similar combustion duration, but shorter combustion duration is shown for methanol. Also with methanol, the crank angle where 50% of fuel is burnt (CA50) is shown earlier compared to NG. The faster premixed combustion, combined with a better found fuel consumption operating point, resulted in higher efficiencies for methanol compared to NG for the tested 50% and 75% load at comparable operating conditions.

The CFD modeling based on the two-fluid model (TFM) was used on studying the novel indirectly heated bubbling fluidized bed steam reformer (IHBFB-SR). This is a collaborative project between Petrogas and TU Delft for testing the advance’s reactor configuration, which indirectly supplies the heat via radiant burner on the center toward the surrounding bed, thereby improving heat transfer efficiency and reduced the losses. The present work aimed to observe the hydrodynamic and heat transfer of the reactor by first employing air as the fluidizing gas and corundum (Geldart B size) as the bed material. The minimum fluidization condition, bubbles development, and voidage profile are the main objectives for the hydrodynamic simulation. In the heat transfer study, the effect of radiative heat transfer, bubbles and voidage profiles, and different radiative models (P1 and DO) on the heat transfer mechanism were examined. The 2D and 3D models were built, and three drag models: Gidaspow, adjusted Syamlal, and EMMS/Bubbling was employed. The simulation results were then compared to the experimental data obtained, such as minimum fluidization flowrate, pressure drop, bed expansion, and temperature profile on a specific flow rate.

Initially, a grid independency test was conducted using five different grid sizes. It is concluded that the appropriate grid size for simulating the IHBFB-SR with a bed material particle size of 0.496 mm should be at least 7.5 mm or 15 times the corundum particle size. The present research used 2.5 mm or five times dp. The minimum fluidization obtained was in the range of 14-16 kg/h based on both 2D and 3D simulation. Nonetheless, if primarily refers to the 3D model results, the minimum fluidization condition should lie around 14 kg/h. Three drag models have also been compared. It was found that the adjusted Syamlal gives the closest result compared to the experimental data. Nevertheless, the drag modification, based only on minimum fluidization conditions like modified Syamlal, tends to overpredict the drag coefficient on the entire range of solid volume fraction. There are also no significant differences in the bubbles or voidage profiles among those three drag models. Adjusted Syamlal has a slightly larger bubble while Gidaspow and EMMS bubbling has a bit smaller one. The expected better result of using the EMMS bubbling drag model does not appear to have a considerable impact on the case of Geldart B or larger particles. There was also an underprediction of pressure drop and bed expansion on the simulation. Two major factors were the absence of proper particle shape representation through a sphericity factor and the lack of precise simulation of particle size distribution. Only a perfect rounded sphere of corundum with a sphericity factor of one and one uniform size of the particle was assumed.

In the case of heat transfer simulation, bubbles and voidage effect firstly studied. It was found that the increase of the bubbles frequency and size, as represented on the voidage profile, would improve the heat transfer process indicated by the increase of the heat flux. The bubbles’ occurrence on the bed plays a critical role in the mass transfer’s improvement from and to the vicinity of the radiant burner wall, thus increasing heat transfer. In contrast with the voidage, the increase of superficial gas velocity does not directly influence the heat flux. It was also proved that the radiative heat transfer improved the overall heat flux in this bubbling fluidized bed reactor by about 16.11 %. Though it appears small, this contribution fits the range of other proven works, with a similar operating environment and particle size used. There are two different radiative models performed in the simulation: first-order spherical harmonics method (P1) and discrete ordinate method (DO). Both models presented a similar trend, with P1, has a slightly higher magnitude. However, the P1 model shows a peculiar result of having a strange lower temperature lower on the bottom part of the bed. On the contrary, that is not the case for the DO, which is well known for its accuracy but a higher computational cost demand. It is then concluded that for the present setup, the DO model could perform better. Lastly, the overall heat transfer process was investigated. Since no specific experimental data available for validating the heat transfer properties, only the final steady temperature values of five different thermocouples were used. Comparing these two, it was found that the present model did not give satisfactory results due to overprediction of air temperature above the bed and underprediction of bed temperature at the same time. Some improvements are required, as will be presented in the recommendations section.

In the context of this thesis, the effect of various diesel-methanol blends in a diesel engine compared to conventional marine diesel oil is investigated by experiments and in-cylinder simulations. The main differences obtained between diesel and methanol are the lower heating value, heat of vaporization and cetane number. During the experiments, the engine was not able to run on M20 at loads lower than 153 [kW]. Pressure signal comparison between the cylinders showed that cylinder one shows better ignition properties for methanol operation compared to cylinder two, three and four. Higher COV's for IMEP and maximum pressure were obtained by methanol blends. Experiments with F76, M10 and M20 fuel have shown that methanol blends increase the specific fuel consumption and slightly decrease the engine efficiency. Specific NOx emissions decreased with 2.9 up to 14.2 [%] by methanol blends compared to F76. Due to the increased fuel consumption, the CO₂ emissions hardly reduced. Exhaust gas temperatures and CO emissions seems to decrease. The ignition delay of methanol blends increased up to 8 [degrees CA] for M20 while remaining the brake power constant. Moreover, the combustion duration and air excess ratio decreased by using methanol blends. A single droplet evaporation model is built to simulate the evaporation heat losses for methanol fuel during the in-cylinder process. Methanol has a longer evaporation time which is a disadvantage for diesel engine applications. By using the single droplet evaporation model combined with an injection model calibrated for dual fuel direct injection, the fuel spray evaporation heat is calculated for implementation in the single zone model. The results are calibrated by using the droplet diameter as a variable. In this way, the evaporation heat required for evaporation of methanol is simulated in the dual fuel single zone model. Heat release analysis shows that the premixed combustion phase of methanol blends is dominant compared to F76, while the diffusive combustion phase significantly reduces. For methanol blends, the residence time at high temperatures is lower due to the decreased combustion duration and elongated ignition delay. Unfortunately, the results from the dual fuel single zone model are strongly dependent on the position of the pressure signal. Results for the temperature of the mean cylinder two, three and four were not in line with the expectations. Cylinder one showed smoother heat release curves and its temperature result was in line with the expectations based on the exhaust gas temperature. More research to the effects of the fuel injectors on the heat release of methanol/diesel blends is recommended.

Power-to-gas (PtG) technology represents a promising route in providing long-term energy security and involves pairing volatile sources of renewable energy (solar and wind energy) with alkaline water electrolysis (AWE) to create a wide range of products based on intermediate hydrogen gas for end-users across various industries such as in fuels, chemicals and power sectors. However, PtG currently lacks the technical adaptability to match the intermittency of these sources caused by daily and seasonal weather patterns, and suffers from a low turndown ratio (TDR) as a consequence.

Zero Emission Fuels (ZEF) B.V. aim to adapt this process to create an autonomous, dynamically operated solar panel add-on known as a micro-plant that will produce methanol from CO2 and H2O in the atmosphere. In doing so, the company looks to extend the TDR, but requires the micro-plant and by extension, its AWE unit to operate in wider partial load ranges, in which lower current densities dominate. These cause a rise in gas crossover within the electrolyser, creating impure and potentially flammable H2-O2 mixtures in the outlet that hinder the functionality of the micro-plant. Specifically within the AWE unit, the risk of oxygen crossover has been qualitatively identified as a likely safety hazard. Therefore, the focus of this thesis was set on studying the feasible development of a prototype (gas scavenger) that can remove trace O2 within the techno-economic scope of ZEF’s micro-plant and electrolyser.

To determine a viable method that meets ZEF’s constraints on cost, size, weight and efficiency, industry techniques were studied that either purify hydrogen gas streams or destructively remove flammable H2-O2 mixtures. Based on a subsequent numerical estimation on each method’s limiting factors, a local combustion process in the form of a micro-combustor was identified to be the most suitable method.

To quantitatively estimate the safety risk crossover poses, two models were developed: a non-dimensional model to analyse how 50 bar pressure influences crossover during operation, and a two-dimensional, transient diffusion model to analyse the extent of trace O2 contamination overnight. Results indicate that to mitigate dangerous impurity levels, a gas scavenger needs to be implemented: (a) above a 0.1% difference in pressure between electrolyser half cells during operation, and (b) upon start-up to remove overnight gas accumulation that may not pose an immediate severe risk at 0.079 mol% contamination relative to amount of stored hydrogen, but has the potential to build-up on a monthly timescale.

Finally, the feasibility of the micro-combustor was preliminarily characterised at 50 bar and 80 ⁰C through flame simulations. The variability in low amounts of trace oxygen content show that the mixture is normally non-flammable. Further studies on geometry design and control strategies of the micro-combustor must consider how to achieve optimal ignition conditions, determined to be at richer fuel mixtures between 휙 = 1.03−1.40, and how to contain the flame within a well-defined region. Initial suggestions include using a small volume to induce ignition and relying on wall effects to promote flame quenching.

As a contribution to the decarbonisation of domestic heating, the graduation project investigates the feasibility of the application of UV sensor technology for flame detection and flame monitoring in hydrogen-powered domestic gas boilers. The research includes empirical studies and an analytical approach to describe influences on the sensor signal strength.

The idea of using hydrogen as a medium for storing excess renewable energy is gathering momentum but to deliver, several technological advances are required. One of the main challenges is boundary layer flame flashback (BLF) as a key operability issue for low NO_x premixed combustion of hydrogen-enriched fuels; thus design of tools to predict flashback propensity is of interest. Extensive research has already been done, and the result is three main BLF models, promise to predict the initiation of boundary layer flame flashback accurately. The first model was developed in the Paul Scherrer Institute (PSI) and was applied to an axial-dump burner operating at elevated pressure and temperature conditions with fuel mixtures of H₂-N₂ and H₂. The second model was developed at the University of California, Irvine (UCI) and was based on the flashback experimental data of 100% H₂ fuel (similar geometry with UCI) at elevated pressure and temperature conditions. Finally, the most recent BLF model was developed at TU Delft based upon the 'generalized' Stratford's turbulent boundary layer separation criterion, which is a further development of the model initially developed in TU Munich (TUM) for atmospheric confined H₂ flames in a horizontal channel burner. In this thesis, the performance of the state-of-the-art BLF models is evaluated in a number of academic burners operating with H₂-rich and pure H₂ fuels at atmospheric and elevated operating conditions. While the TU Delft model showed good agreement with 100% H₂ flashback experiments under atmospheric conditions and simple geometries, further modifications are proposed to perform under conditions relevant for gas turbines (increased pressure and temperature). A new turbulent flame speed correlation to capture the effect of pressure on flashback propensity is applied to the model and validated in high-pressure academic burners. Furthermore, the TU Delft model is validated for a lab-scale size of a gas turbine burner geometry, operating at atmospheric conditions and tested in the TU Delft laboratory. This validation shows that it is essential to review the outcome of the boundary layer flashback model at different locations in the boundary layer, and with minor modifications, the model can capture the test results adequately. The sensitivity of the TU Delft model on different fuel compositions is also investigated. Proper selection of the turbulent flame speed correlation is found to improve the model's performance for fuel mixtures less rich in H₂.

Flameless combustion, or MILD combustion is a technology that enables stable combustion with high efficiency while maintaining very low NOx and soot emissions. It is characterized by uniform heat flux and can be achieved when fuel and preheated oxidant jets are mixed into a strong recirculating flow. It is a complex process which combines multiple physical phenomena such as, heat transfer and reactions in a turbulent flow and is difficult to capture numerically via simple Computational Fluid Dynamics (CFD) simulations. Therefore, appropriate turbulence, chemistry, radiation and turbulence-chemistry interaction models are required to address this combustion regime via computational modeling. The present work tries to tackle this issue by conducting a comparative study of different radiation, turbulence and chemistry models for the simulation of a labscale MILD combustion furnace using RANS CFD simulations. This assessment was conducted in two steps. Firstly, the importance of radiative heat transfer in furnaces was investigated, by simulating an axisymmetric oxycombustion furnace using advanced radiation models. The SLW, Domain-based WSGG and Cell-based WSGG models were evaluated using simple chemistry and turbulence models. The results were validated based on the work of Webb et al and experimental results. It was concluded that detailed simulation of the radiative gas properties is important and directly influences the resulting temperature field, especially in the bulk flow region. Secondly, a detailed evaluation of a Dutch natural gas fired Delft lab-scale furnace that is operating in MILD combustion was conducted. For the turbulence modeling, the Standard, the Modified Standard, the Realizable k − ε and the k − ω SST Models were compared firstly qualitatively, based on velocity and reaction field contours, and secondly, quantitatively, based on available LDA velocity measurements. The influence of the chemistry modeling was evaluated in two parts. Firstly, the qualitative effect of changing the Cξ constant of the EDC model on temperature and reaction zones of the GRI-Mech 3.0, the DRM-19, the KEE58 and Chen mechanisms, was investigated. And secondly, the quantitative effect on the use of the GRI-Mech 3.0, the KEE58, Chen and Lu-30, based on CARS temperature measurements was researched. Lastly, the influence of the radiation model was investigated qualitatively and quantitatively using the standard 1-RTE domain based WSGG, a 4-RTE WSGG, a cell-based WSGG and the SLW model.
Out of the mechanisms coupled with the EDC, the GRI-Mech 3.0 performs well. Of the radiative properties models the domain based WSGG performs worse compared to the other models. The cell based WSGG performs similarly to the more advanced spectral and non-grey (4-RTE) models and has lower computational cost. For these reasons, the best overall combination for the studied flameless furnace is found to be the combination of Standard k−ε model, standard EDC with GRI-Mech 3.0 and cell based WSGG.

The current economic-development system based on fossil fuels can no longer sustain itself and is incapable of satisfying the needs of the global population. Nearly one third are unable to meet even their most basic needs that involve harnessing energy for everyday essential tasks such as maintaining livable shelter and food preparation. Models of development have exacerbated the problem by promoting and subsidizing fossil fuel-based solutions that require those struggling to survive to do so at the expense of the environment and other species. This is a self-defeating trap, whereby the urgent needs of the most vulnerable are pitted against climate change and the mass extinction of complex life forms. The only way to break this contradiction is through the creation of a new development system that removes incentives for short-term, destructive profit and puts people and other forms of life at its center. Healthy, sustainable development must be rooted in the fair and democratic allocation of resources. Prioritization of truly life-focused progress would allow for human beings to shape their own destinies through the use of locally available, renewable energy resources that do not contribute to mass extinction or climate catastrophe. While the downward spiral towards extinction may seem unstoppable, in reality, the biggest obstacle is simply coming to accept that the old view of what constitutes positive development – an extractive, hierarchical philosophy powered by fossil fuels - must be replaced with the new paradigm based on sustainability and cultural realism. Once that understanding has been reached, it is a matter of targeting key areas for change that will make the most difference in the shortest amount of time. The project outlined herein is a contribution to that new development system. My carefully selected target will address the energy needs for clean cooking and heating for the one third of the world population that relies in low-efficiency biomass combustion technology. Although such technology may at first seem too modest to make a difference, the impacts of making this simple change would have profound, world-wide implications. If that vulnerable one third of the world’s population could access clean domestic technology, there would be enormous improvements in health and environmental conditions. The Kulkan reactor is a biomass gasifier coupled to a burner that optimizes the combustion process and heat transfer by means of heat recovery using an air pre-heater and partially premixed laminar combustion of the syngas. The novel design was founded on three hypotheses that addressed the optimization of efficiency, pollution minimization by flame quenching prevention, and reduction of ultra-fine alkali particle emissions. The first two were investigated using an algebraic model (0-D), and computational fluid dynamics of reacting flow for 1-D, 2-D and 3-D. The algebraic model predicts an efficiency of [60 − 65%] which is 4-8 times higher than traditional cooking technology and 25% higher than the best improved cookstove ever reported. The 1-D and 2-D simulations show reduction feasibility of laminar premixed combustion and a reduction of flame length of up to 50% compared to non-premixed, supporting the idea of more compact combustion chambers and prevention of flame quenching. The 3-D simulations show essential information on the importance of the pressure drop calculations necessary for the design process of a Kulkan reactor, particularly for the burner. Furthermore, arguments for the third hypothesis are presented which invite further investigation to reduce the ultra-fine particles containing highly toxic alkali metals, which are produced during high efficiency biomass combustion.

The convection section of fired heaters consists of finned tubes to enhance heat transfer. However, finned tubes make heat transfer in the convection section of fired heaters considerably more complex. Consequently, engineers depend heavily on correlations to determine heat transfer in the convection section of fired heaters. The problem related to the use of these correlations is twofold. First, these correlations have been developed approximately forty years ago by performing wind tunnel experiments for 1" tubes and 2" tubes, after which the results have been extrapolated to accommodate for 4" tubes. Second, industry developments led to the use of 6" tubes or even 8" tubes in the convection section of fired heaters. As a result, it should be questioned if correlations still provide accurate results for these tube sizes. This study aims to validate an entirely new way of calculating heat transfer and pressure drop in the convection section of fired heaters proposed by a recently developed analytical method. In contrast to correlations, the analytical method provides insight in the working principle of fins, is in theory applicable for large tube sizes, and ultimately has the potential to design convection banks more accurately. The latter would result in a reduction of fuel consumption, and with the focus on reducing emissions to reach climate goals, this would mean a significant improvement over existing correlation methods. Numerical models based on the realizable k-epsilon turbulence model have been developed in ANSYS Fluent to be able to validate the analytical method. The values of the heat transfer and pressure drop coefficient relative to the bare tube area have been compared with the values calculated by the analytical method and the ESCOA correlation method for one tube row and for multiple tube rows to see which method resembles the results calculated by the numerical models the closest.

The conducted study investigates the potential of a newly released multi-phase solver to simulate atomization in liquid rocket injectors. The "VOF-to-DPM" solver was used to simulate primary and secondary atomization in an air-blast atomizer with a coaxial injector-like geometry. The solver uses a hybrid Eulerian/Eulerian-Lagrangian formulation with a geometric transition criteria between the two models. The conducted study assumed isothermal, non-reacting flow at room temperature. The primary focus was predicting Sauter Mean Diameter and droplet velocity data at a sampling plane downstream of the injection site. The results showed that the solver is able to produce the expected data and to predict trends similar to those found in experimental measurements. The accuracy of the produced droplet diameters was roughly a factor 2 off compared to experiment. This is attributed to mesh resolution. Measurements were obtained via a cooperative agreement between TU Delft and The University of Sydney. It was concluded that the solver has the potential to predict atomization at a reasonable computational cost, but further study is needed to confirm its full capabilities.