Liquid hydrogen has been identified as a low-emission alternative to hydrocarbon fuel sources for aircraft. Although there has been a notable increase in the number of studies and technology readiness of liquid hydrogen technologies in the recent decade, there is still more research and development necessary to realize commercially viable hydrogen-fueled aviation. Achieving zero boil-off by using active cooling has been identified as a potential method of decreasing the mass and volume of a future liquid hydrogen fueled aircraft. However the lack of literature or data on the thermal performance and specific power of cryocoolers for this application makes it difficult to assess its feasibility. Therefore, a study was performed to develop a reverse turbo-Brayton cryocooler simulation tool, focused on the three heat exchangers of this cooler type. This paper presents the methodology for the development of this tool alongside a case study on a liquid hydrogen fuel tank for TU Delft's flying-V concept. From the case study it has been concluded that the considered RTBC design offers a reduction in the liquid hydrogen mass, however not significant enough to offset the cryocooler's own weight. An improved performance and specific power of the individual components would be required to achieve a net weight reduction.

A significant trend in aero engine design has been the rise in turbine inlet temperatures, as well as the drive to produce raise efficiency. Since the 1960s, turbine inlet temperatures have exceeded turbine material limits, with turbine cooling systems being used to bridge the gap. Modern engines require substantial amounts of cooling air, prompting a need to understand further the impact of turbine cooling on turbine and engine performance in cycle calculations.

Current models employed for performance analysis of cooled turbines are based on technical assumptions that are several decades old. This raises questions about the possibility of adapting models to more accurately represent modern engine technology. As such, this thesis aims to develop a cooled turbine model (CTM) for use in PyCycle, an open-source engine cycle analysis platform. The CTM is based on the cooled turbine blade row model defined by Young and Wilcox, which employs empirical constants to estimate cooling mass flow rates. The CTM can estimate the cooling flow requirements and the associated entropy rise for the turbine, accounting for the irreversibility in the turbine cooling process.

The implemented CTM models a complete turbine stage and multi-stage turbines based on three key aspects: the thermodynamics of a cooled turbine row, the work extraction in an equivalent uncooled turbine stage, and the conversion of thermodynamic properties between an absolute and rotating frame of reference. The CTM was verified and validated using three other cases, and it was found to accurately capture the effects of turbine cooling on bulk flow properties.

Following the implementation of the CTM, a study into the (semi-)empirical parameters and constants was performed to update existing parameters for modern engines. The limited availability of data relating to flow velocities and Mach numbers in aero-engine turbines forms a significant obstacle to the accurate specification of some empirical parameters. An estimation for the average Stanton number over turbine blades based on the gas temperature and Reynold’s number was derived and validated with the Von Karman Institute’s LS-89 turbine cascade results. The impact of updating the empirical parameters used in the CTM
has been assessed by formulating the cooling flowestimation as an optimization problem.
Using the updated ranges for the empirical parameters, the optimization study showed the potential for a significant reduction in the estimated cooling fraction.

Hydrogen Polymer Electrolyte Membrane (PEM) fuel cell technology is becoming increasingly popular in the transportation sector, especially the automotive industry. It can power electric drives by converting hydrogen into electricity in a chemical reaction with oxygen, whose products consist only of water. Therefore, hydrogen PEM fuel cell-based powertrains are free of any harmful emissions, enabling clean propulsion technology. An important part of an automotive fuel cell system is the air processing subsystem, which usually features an electrical air compressor (E-compressor) to supply the necessary oxygen for the chemical reaction. This E-compressor can absorb between 10-30% of the fuel cell gross power. One way to decrease this share is to expand the fuel cell air exhaust flow in a turbine that contributes to power the E-compressor, essentially realizing an electric turbocharger (E-turbocharger). E-turbochargers for fuel cells are still in the development phase, therefore there is a lack of experience and knowledge on their benefit. In this thesis, a model of an existing automotive PEM fuel cell air processing system has been developed using the AVL Cruise M software. In addition, two prototype PEM fuel cell E-turbochargers (ETC1 and ETC2, respectively) have been modeled and integrated into the main air processing system model. Steady-state simulations have been performed for three different power levels. Moreover, the turbine inlet temperature of the ETC1-based model was varied in the range of 60°C to 150°C to quantify what benefits exhaust heating with waste heat brings in addition to the inherent turbocharging performance gains. The results show that compared to the baseline system, the model featuring ETC1 achieved an increase in net power between 3.04-6.78% or a decrease in fuel consumption between 3.19- 7.67%, depending on the power level. For the ETC2-based model, from low to high load, the net power increased between 1.88-2.04%, or fuel consumption decreased between 2.07-3.17% compared to the baseline system. When increasing the turbine inlet temperature to 150°C, the model showed an additional decrease in fuel consumption of 2.1 percentage points at full power. The models could be improved by implementing a first-principle-based model of the E-compressor and E-turbocharger, which could have been developed in this project if more detailed information on the heat flows within these components was available.

Current design methods for oblique manifolds were first presented in the paper of London et al. in 1968. This method presents a single equation to shape the dividing manifold of several manifold configurations. However, current literature shows a potential to improve the current design method by implementing advanced techniques. This paper aims to bridge this gap by presenting an innovative design methodology incorporating these advanced techniques. The proposed design method integrates free-form deformation and adjoint-based methods within a 1st-order shape optimization framework. The objective function focuses on the minimization of mass flow mal-distribution, evaluated by an incompressible Reynolds-Averaged Navier-Stokes solver. Through three initial tests, this paper demonstrates a consistent improvement in the objective for all obtained designs. Noteworthy is the finding that small changes to the initial design lead to significant enhancements, evidenced by an 82.5\% decrease in the mass flow mal-distribution. Off-design testing further substantiates the effectiveness of the design method, showcasing superior performance under varying initial conditions for the optimized designs. Further testing not only exhibits improved objectives but also reveals common features among results for diverse initial designs. This paper shows a novel and effective design methodology for consecutive manifold systems, laying a robust foundation for an improved design method.

The environmental emergency is one of the most critical challenges of modern times. The exponential increase of industrial activities is the primary cause of anthropogenic climate change, with negative consequences for the environment, society and economy. In the transport sector, decarbonization is the most significant challenge. In aviation, the environmental objectives are to halve international CO2 emissions by 2030, and to reach net-zero carbon emissions by 2050. The achievement of these goals implies a step-change in the traditional practice of aircraft design, with many resources invested in research for promoting the use of fossil fuel-free propulsion systems and electrified auxiliary systems.

In this framework, the research presented in this dissertation is on methods for automated design optimization with applications to a novel electrically-driven Environmental Control System (ECS) for aircraft cabin cooling. The ECS is the main consumer of non-propulsive power onboard aircraft. The founding idea of the project, which has been carried out in collaboration with several companies, is to replace the traditional ECS equipping airliners, which is based on Air Cycle Machine (ACM) technology, with Vapour Compression Cycle (VCC) systems powered by high-speed centrifugal compressors. Work performed within this project demonstrated that such a VCC-based ECS can be more efficient and lighter than an ACM-based ECS in the case of mainstream passenger airplanes. The main goal of the research documented in this dissertation is to provide design methods and guidelines for the optimal design of aircraft ECS whose core is a VCC system powered by novel high-speed electrically-driven compressors and using low-Global Warming Potential (GWP) working fluids in place of the conventional R-134a refrigerant. Additionally, the study encompasses the analysis of the impact of the selected working fluid on the optimal design of the main system components, i.e., the heat exchangers and the centrifugal compressor. For this purpose, a novel integrated design optimization framework has been developed: it allows to perform the multi-objective optimization of the aircraft ECS across different points of the aircraft operating envelope. This method enables the concurrent automated optimization of thermodynamic cycle, preliminary component sizing and working fluid selection. Moreover, the successful application of the method to this complex case demonstrates that the approach is generally applicable to any thermal energy conversion system.

The method was applied to the design of the ECS of two different aircraft to demonstrate its capabilities: a large passenger rotorcraft and a single-aisle short-haul aircraft, i.e., the A320. Results show that it is possible to design an efficient VCC system for aircraft ECS that is powered by an electrically-driven centrifugal compressor and uses low-GWP refrigerants as working fluids. In particular, in the case of a small-capacity ECS for large rotorcraft, it was demonstrated that the use of high-molecular complexity refrigerants, such as haloolefins, enables the design of lighter and more efficient VCC systems if compared to the state-of-the-art. The test case of the airliner ECS provided the specifications to further develop and test the methodology: a so-called physics-based equation of state model was adopted for the computation of the thermodynamic properties of the working fluid. Molecular parameters allow to define the fluid, therefore they can be optimized as part of the global optimization of the design of the system. Parameters are constrained so as to define a realistic molecule, though non-existing, called pseudo-fluid. Actual working fluids whose molecular parameters are similar to those of the optimal pseudo-fluid}are selected in a following step of the design procedure. Optimal working fluids are therefore natural refrigerants. The use of these working fluids with null GWP would reduce the environmental footprint of the considered environmental control systems, while enabling an (albeit small, in the considered case) reduction of specific fuel consumption.

Complementary to the numerical investigation, a novel experimental setup called IRIS (Inverse organic Rankine cycle Integrated System) was designed, realized and successfully commissioned at the Propulsion & Power laboratory of Delft University of Technology. The setup was conceived to enable testing and performance analysis of VCC-based aircraft ECS and to validate in-house software for system and components design. The setup hosts two main test sections: one to test compressors and another to test air-cooled condensers. The results of the commissioning show that it is possible to continuously operate the IRIS setup in steady-state conditions at temperature levels which are very close to those at the design point, thus achieving a Coefficient of Performance (COP) equal to 3.76±0.48. @en

Hydrogen fuel cells are set to play an important role in decarbonizing the aviation sector. They operate at higher efficiencies than turbine engines, but their low operating temperature requires a dedicated thermal management system. The added drag, weight and parasitic power of such a system has a high impact on aircraft performance and its design must be integrated with overall propulsion system development. Among cooling options, flow boiling has the potential of increasing the cooling system performance, but design methods are lacking in the literature. To address this problem, this thesis presents preliminary design methods able to size both conventional single-phase and novel two-phase cooling systems and tests them on a reference regional turboprop aircraft. Sizing results show that pumped multi-phase systems result in lower system mass and drag than conventional single-phase cooling while vapour compression systems are a less attractive option due to their high power demand.

The need for more efficient aircraft has led to the conception of innovative engine configurations, such as the combined-cycle engine proposed by Delft University of Technology or the Water-enhanced turbofan developed by MTU and Pratt & Whitney. The evaluation of the potential benefits of these novel engine concepts requires detailed performance studies considering weight and drag penalties as figures of merit. At present, no weight estimation tools with sufficient level of accuracy and flexibility are publicly available, apart from WATE++, a tool developed by NASA. However, this software is subject to export control restrictions and cannot be used outside the USA. For this reason, the development of a new component-based preliminary engine design tool, "Weight EStimation of gas Turbine engines" (WEST), was started. The goal of WEST is to predict the weight of novel engine architectures with a reasonable level of accuracy, accounting for design parameters like turbine inlet temperature, overall pressure ratio, mass flow rate, and turbomachinery configuration, with a minimal set of geometry inputs specified by the user. A previous work demonstrated that WEST can effectively predict the weight of turbofan gas generators. As only the main components are modeled, the WEST estimates account for approximately 70-90% of the actual engine weight.

The capabilities of WEST were expanded in this study to allow for the design of small-scale turboshaft engines. To this purpose, a methodology to design radial compressor disks was implemented, and successfully verified against FEM results. Regarding the modeling of the complete turboshaft, it was found that the predictions of the tool account for only 60-70% of the actual engine weight. Such result was, however, expected, as WEST does not take into account the particle separator and the integrated gearbox, which may account for up to $30\%$ of the engine's total weight.

The need for more efficient aircraft has spawned the conception of a variety of novel engine and aircraft architectures, such as the combined-cycle engine proposed by researchers at Delft University of Technology. To evaluate the potential benefits of these concepts comprehensively, in-depth performance simulations are required. Furthermore, penalties with regard to weight and drag are critical considerations, thus new engine technologies must be evaluated within their full airframe-level integration and mission profile. Accurate weight estimations of a variety of design alternatives are therefore necessary in order to properly assess the validity of such technologies and to reach an optimal design with respect to the tradeoffs between weight, drag, and efficiency. No weight estimation tools with sufficient accuracy are publically available at present, thus a new, component-based preliminary engine design tool, named ‘Weight Estimation of Aeronautical Gas Turbine Engines’ (or WEST), was developed. WEST can be used to predict the weight of novel engine architectures to a reasonable degree of accuracy, all the while accounting for sensitivity to design parameters such as turbine inlet temperature, overall pressure ratio, mass flow rate, power, and choice of turbomachinery configuration. Similar methodologies are able to design components worth between 60 and 110% of the actual weight of an existing engine, whereas WEST was able to account for about 70-90%, thus exceeding initial expectations and improving the reliability of the estimations. This tool can therefore be used to estimate the weight of a variety of existing engines, and is sufficiently flexible to model novel architectures as well, since the results are based on the application-specific design of real engine components. Among the potential uses of WEST, a promising one would be to evaluate the weight of a large set of designs for a particular application. Upon these estimates, single-equation surrogate models could be developed using statistical regression, allowing for these equations to be used as a more computationally-efficient weight estimation methodology in a wide range of aircraft-level design and optimization studies. These equations would build upon the work described in this paper and could be used to accelerate the development and introduction of new aircraft-related technologies.

Solid Oxide Fuel Cell (SOFC) systems for aviation applications have been considered for their use as APUs or powertrains, as standalone systems or in combination with gas turbines, and both fueled by reformed Jet-A or by hydrogen. Most existing studies focus on powertrain performance modelling. In this work, traditional tube-and-wing regional aircraft sizing methodologies are modified to account for liquid hydrogen fuel and SOFC-GT-Battery hybrid electric powertrains. Methodologies for powertrain modelling, power sizing, energy sizing, weight calculation and system integration have been derived, implemented, verified, validated when possible, and used to assess several study cases. Considering state-of-the-art metal-supported planar ITSOFC technology installed in a 50-seat regional aircraft as test case, it is concluded that current SOFC system power density is not sufficient to achieve MTOW values similar to conventional kerosene-powered regional aircraft. This work serves as a baseline for the integration of sizing methodologies for SOFC-GT-Battery powertrains into aircraft conceptual-to-preliminary design tools.

Industrial processes are estimated to be responsible for about 20 % of the total greenhouse gas emissions within the European Union (EU). The majority of the industrial energy demand is related to the thermal energy required for process heating. Thus, there is a need to make radical changes to the industrial heating supply to achieve net-zero CO2 emissions. In this regard, high-temperature heat pump systems are being studied as an alternative to conventional fossil fuel-based systems. This project focuses on the modeling and analysis of thermodynamic characteristics of the two heat pump concepts, namely, reverse Rankine cycle based and reverse Brayton cycle-based systems. Both heat pump concepts are compared for high-temperature applications in terms of performance, design feasibility of the key components, and ease of integration with industrial processes.

Range extended electric vehicles (REEV) are being considered as a possible solution for the electrification of passenger vehicles. The application of a recuperated gas turbine (GT) for REEVs shows potential in terms of power-to-weight ratio, emissions and cost. The recuperator plays a major role in achieving target efficiency, while being a main contributor to cost and packaging. The topology and subsequent design are key factors for the success of the concept.

A topology was selected based on literature research of different recuperator concepts for small gas turbines. A sizing model for this topology was developed to obtain a recuperator geometry for a set of boundary conditions. Furthermore, the influence of different gas turbine cycle design parameters, as well as heat exchanger surface geometries, on the resulting geometry was analyzed. The research shows that an integral GT cycle design can be used to obtain a heat exchanger that fulfills REEV requirements.