Current and future energy policies are increasingly aiming to reduce carbon emissions from the propulsion and power sector. The combustion of fossil fuels releases carbon, in the form of carbon dioxide (CO2), and there is consensus that the rapid anthropogenic emission of fossil bound carbon is resulting in global climate change. Co-currently, there is growing awareness of the negative impacts of toxic exhaust pollutants from fossil fuel combustion, such as nitrogen oxides (NOx) and carbonaceous soot or particulate matter (PM), on the health of urban populations. While electrification offers a potential replacement for fossil fuels, the electric powertrain is currently only suitable for light duty applications, such as passenger vehicles. There are several high energy requirement applications (aircraft, off-road vehicles in military and construction, thermal power generation) for which currently no appropriate alternative to combustion engines exists.

Hydrogen (H2) has the potential of emerging as the leading energy carrier for the next generation of zero-carbon emission combustion systems. H2 fuelled gas turbines are potentially capable of providing very efficient energy conversion with no carbon emissions, and will be able to span the power and weight requirements of land-based power generation and aero-propulsion. H2 can offer significant benefits over hydrocarbon fuels; its wide flammability range allows very lean combustion, low ignition energy ensures prompt ignition and high diffusivity facilitates efficient air-fuel mixing. However, the utilisation of H2 for combustion is hindered by considerable challenges. Its high flame speed can intensify risks of flame instability and flashback, adversely affecting operation, and high rates of heat release (leading to high thermal loading), combined with H2's corrosive properties, can lead to combustor damage. This means that current gas turbine combustors are not suitable for pure H2 combustion and will have to be re-designed. Complex reactions, turbulent conditions and complicated geometries means that conventional design techniques (such as simulation tools) need to be revised for H2 combustion. Comprehensive experimental campaigns are required to fulfil the gaps in our understanding of fundamental H2 combustion, and to identify regimes for high efficiency and near-zero emission operation in practical H2 combustion systems.

In order to set out new design and operation principles for H2 combustors, the research proposed will (a) identify strategies for H2 injection and efficient mixing with air to create a uniformly distributed H2-air mixture, (b) identify suitable operating conditions that result in favourable flame behaviour with suppressed NOx emissions, (c) identify suitable materials for use with H2 at elevated pressures and temperatures, (d) understand the influence of acoustic boundary conditions on combustion instabilities and (e) investigate the effects of translating concepts studied in a-d vary from lab-scale to large-scale systems operating at practical conditions. The fundamental principles associated with H2 combustion will be developed and evaluated through rigorous experimentation at laboratory scale, and then implemented in two different types of semi-industrial scale combustion systems, (i) representative of industrial small gas turbine for power generation, and (ii) scaled down version of the pre-burner component of the SABRE rocket engine. The experiments performed on these semi-industrial systems will lay the foundations for the follow-on research (beyond the 4 years of this fellowship) to integrate H2-fuelled combustors in full-scale industrial multi-cannular gas turbines and in full-scale rocket engines. The research outcomes will provide underpinning scientific knowledge on H2 combustion for the project partners, Siemens Industrial Turbomachinery Ltd. and Reaction Engines Ltd. (REL), giving them a direct uptake route for this research.

Potential Impact:
The research proposed in my fellowship spans from fundamental understanding of key processes and mechanisms that influence H2 combustion (mixing, flame stabilisation, flame dynamics) to applied research, including NOx emissions and effects of scaling combustor size. The work aims to de-risk utilisation of H2 in gas turbines through development of design and operational principles that avoid flashback, ensure flame stability and supress NOx formation. The potential impact of my fellowship is far-reaching and includes industry, policy, environment, society and academia.
This research is relevant to both experimentalists and modellers conducting research in the areas of combustion diagnostics and sustainable energy vectors. It is intended that this work will encourage other academic institutions and research laboratories to actively pursue H2 research, keeping the UK at the forefront of academic research in low-carbon technologies. High-fidelity experimental data on H2 mixing, combustion characteristics and emissions performance will be readily available to validate and improve simulation models. The unique H2 test facility, which will be developed at UCL during my fellowship, will encourage further research in this challenging and exciting area. Dissemination of research outcomes will be in the form of publications, conference presentations and workshops.

The fellowship will deliver underpinning knowledge of H2 combustion that is highly relevant to gas turbines, enabling safe, efficient and low-emission operation of gas turbines fuelled by H2. Gas turbine OEMs (Original Equipment Manufacturers) and operators will be able to confidently widen the operating capabilities of current gas turbines to use pure H2 and integrate this emerging technology into their future products. In this fellowship, I have partnered with Siemens (gas turbine manufacturer) and Reaction Engines Ltd. (REL), a rocket engine company. The research outcomes from my fellowship will help Siemens achieve their ambition of H2 gas turbines, and that of REL in developing aspirated H2 rocket engines.

My research is highly influenced by policy and legislation that drive future energy scenarios, and hence I will aim to engage regularly with energy policy representatives to increase the policy impact of my research. The UCL Public Policy office has vast resources (I have engaged with them in the past and have been awarded a Public Policy Small Grant) available to enable my policy impact activities.

I also intend to increase the fluency of my communication with a more general audience by initiating and leading several outreach activities that will expose young people to the stimulating world of academic research, and encourage them to pursue careers in science-relevant fields. To this end, I will develop educational resources related to energy science - science clubs, laboratory activities at UCL and summer internships - so that students to get hands-on experience. I will also participate in training courses and other engagement activities organised by UCL, such as Open Days and science fairs, to showcase my research in H2 fuelled technologies.

Finally, the fellowship will enable me to grow as a researcher and establish myself as a leader in the area of H2 combustion. It will give me the opportunity to broaden my technical expertise as well as my supervisory and management skills through mentorship of researchers (PDRAs and PhD students).