This study investigates the use of a non-pre-mixed resonance igniter for liquid propellant rocket engines, using oxygen and methane. Resonance heating at varying nozzle gap spacing for both oxygen and nitrogen is investigated both experimentally and numerically. High frequency microphone data is used to experimentally determine the operating mode of the igniter. Temperature measured on the outside of the resonator tip is used to evaluate heating performance at specific set points. The Open Source CFD software SU2 is used to create a numerical model, capable of accurately predicting the switch in igniter operating point, as well as the operational parameters leading to the highest rates of thermo-acoustic heating. Ignition attempts show that the separate injection of methane into the combustion chamber causes severe disruption of resonance heating, preventing the mixture from igniting.

This master thesis explores the potential of hydrogen-enriched fuel blends in improving the performance and reducing emissions of lean premixed swirl-stabilized combustors in the aerospace sector. As industries face increased pressure to decarbonize amidst global energy crises and climate change, alternative fuels like hydrogen are being considered due to their lower carbon emissions compared to traditional hydrocarbon fuels.

By employing a high-speed solenoid flow valve to induce controlled fluctuations in the air-fuel mixture, the study investigates how these changes influence the overall behavior of the combustion process. The experimental setup for this thesis involved a swirl-stabilized multi-fuel combustor at the TU Delft Sustainable Propulsion Lab, capable of operating with methane and up to 100% hydrogen enrichment. The experimental analysis used a range of techniques, including Particle Image Velocimetry, SPOD and various acoustic and pressure measurements, to examine the impacts on the combustor’s operation across different power settings and levels of hydrogen enrichment.

The findings reveal that adjusting the equivalence ratio through precise airflow modulation can significantly alter the unsteady combustion dynamics. Notably, this modulation enhances the stability of the flame by dampening the damaging thermoacoustic instabilities commonly associated with lean premixed combustors. Additionally, the research demonstrates that these adjustments can lead to changes in emission levels, notably in how nitrogen oxides and carbon dioxide are produced under varying conditions of hydrogen content and power settings.

A comprehensive numerical model was also developed to support and extend the experimental results, providing insights into the potential scalability and application of these findings to larger, real-world combustion systems. This model underscores the practical implications of the experimental findings, suggesting that such controlled fluctuations can be a viable method to optimize the design and operation of next-generation combustors.

The demand for commercial aviation is growing at an annual rate of 4%, posing significant environmental challenges. Large-capacity aircraft designed for long ranges are often used on short-to-medium range routes, leading to inefficient fuel consumption and higher emissions. With a future market need for aircraft seating 211 to 300 passengers, there is a clear gap for such a passenger airliner. This report examines the feasibility of the X-300 EcoFlyer, a proposed short-to-medium range aircraft with reduced environmental impact. Designed to carry 300 passengers over 3000 km, the X-300 aims to achieve 25% lower CO2 emissions, 50% lower NOx emissions, and 20% lower noise emissions compared to the Airbus A320neo. The study covers aircraft functions, system design, performance analysis, manufacturing, sustainability, operations, logistics, business viability, and technical risks. The findings confirm the X-300 EcoFlyer's potential to meet future demands with lower environmental impact. Innovations include a noise-shielding fuselage, a water-injected turbofan engine, in-wheel electrical taxing, and an electrical environmental control system. Overall, the X-300 EcoFlyer represents a promising solution to the challenges facing the future of high-capacity air transport.

This report discusses urban air quality measurements carried out in a park in Aigaleo (Athens), located adjacent to a busy road. The measurements were taken using the Sniffer4D Mini 2 sensor box with a drone to investigate how Urban Air Mobility can aid in measuring urban air quality. CO, NO₂, O₃, SO2, PM_2.5 and PM₁₀ concentrations were recorded through point measurements at varying locations, altitudes and times. Several validation measurements were carried out, showing that temperature heavily influenced the outcome of the recordings. Due to the high number of variables, no conclusion has been found on the wind effect. During rush hour, NO₂ and CO concentrations were highest close to the traffic; however, NO₂ concentration showed non-linear behaviour with increase in altitude when further from the traffic or out of rush hour. SO₂ concentration always decreased with an increase in altitude; highest concentrations were observed further from the busy road. Highest O₃ concentrations were obtained in the afternoon at higher altitudes, due to its reaction under sunlight. PM_2.5 and PM₁₀ concentrations had a high variability due to environmental conditions. Additionally, continuous measurements were carried out, in which the drone flew a path through several locations and altitudes. The results from these were interpolated to enable the detection of areas with higher concentrations of air pollutants.

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

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

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

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

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