Effect of forced equivalence ratio fluctuations combined with hydrogen enrichment in a lean technically pre-mixed (swirl-stabilised) methane combustor

Abstract

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.