Overview
I am a Research Associate at Cardiff University, based at the University’s Gas Turbine Research Centre (GTRC) in Port Talbot. My primary research interest is to improve understanding of the combustion fundamentals and potential cycle efficiencies of low-carbon fuels.
Having completed a degree (in Integrated Engineering) and a masters (in Energy Studies) at Cardiff University in the early 1990s, I later returned to complete two contracts as a research assistant. The first contract enabled me to develop my understanding of solid fuels processing (pyrolysis, gasification and incineration) while producing a master’s module on these topics, funded through the Knowledge Enterprise Fund (KEF).
For the second contract, I was based at the GTRC, where I was charged with developing CPD courses for industry (funded by the Low Carbon Research Institute). It was during this time that I became interested in gaseous combustion, especially of alternative low-carbon fuels. Furthering this interest, from 2017 to 2021 I completed a PhD titled ‘Investigating the potential of industrial waste stream ammonia as a fuel for low carbon, gas turbine power generation’. My PhD involved both numerical modelling and experimental investigations.
I then took my experience to consultancy E4Tech (now part of ERM) where I worked briefly as a Low Carbon Maritime consultant before deciding on a more ‘hands on’ role with Tata Steel R&D (Heavy End) in Port Talbot. At Tata, I contributed to improving process stability and transitioning to lower carbon steelmaking.
In 2023, I returned to the GTRC as a postdoctoral researcher in support of National Gas Transmission's (NGT) nationally significant venture, to include hydrogen in the UK's gas grid. In this role, I have undertaken several projects aiming to understand some of the technical and practical implications of the proposed changes to gas composition in the national grid.
Publication
2026
- Davies, T. et al. 2026. Influence of emissions normalisation methods on H2–CH4 fuel comparisons in generic and NOx-Abated gas turbine combustion. International Journal of Hydrogen Energy 223 154402. (10.1016/j.ijhydene.2026.154402)
- Vivoli, R. et al. 2026. Surface roughness effects on the operability and performance of a hydrogen jet burner. Journal of Engineering for Gas Turbines and Power 148 (1) 011014. (10.1115/1.4069474)
2025
- Vivoli, R. et al. 2025. Surface roughness effects on the operability and performance of a hydrogen jet burner. Presented at: ASME Turbo Expo 2025: Turbomachinery Technical Conference and Exposition Memphis, Tennessee, USA 16-20 June 2025. Proceedings of the Turbomachinery Technical Conference and Exposition. Vol. 3A.Combustion, Fuels & Emissions American Society of Mechanical Engineers. (10.1115/gt2025-151389)
- Hewlett, S. et al. 2025. The effects of secondary air staging location, pressure and humidification on NOx emissions for a high ammonia blend in premixed swirl combustion. Presented at: ASME Turbo Expo 2025: Turbomachinery Technical Conference and Exposition Memphis, Tennessee, USA 16-20 June 2025. Proceedings of the Turbomachinery Technical Conference and Exposition. Vol. 2.Coal, Biomass, Hydrogen & Alternative Fuels American Society of Mechanical Engineers(10.1115/gt2025-151612)
2022
- Alrebei, O. F. et al., 2022. Quantifying CO2 emissions and energy production from power plants to run HVAC systems in ASHRAE-based buildings. Energies 15 (23) 8813. (10.3390/en15238813)
- Alrebei, O. F. et al., 2022. Numerical investigation of a first-stage stator turbine blade subjected to NH3–H2/air combustion flue gases. International Journal of Hydrogen Energy 47 (78), pp.33479-33497. (10.1016/j.ijhydene.2022.07.190)
- Amhamed, A. I. et al., 2022. Ammonia production plants - a review. Fuels 3 (3), pp.408-435. (10.3390/fuels3030026)
- Fawwaz Aalrebei, O. et al., 2022. Ammonia-hydrogen-air gas turbine cycle and control analyses. International Journal of Hydrogen Energy 47 (13), pp.8603-8620. (10.1016/j.ijhydene.2021.12.190)
2021
- Pugh, D. et al. 2021. Emissions performance of staged premixed and diffusion combustor concepts for an NH3/air flame with and without reactant humidification. Journal of Engineering for Gas Turbines and Power 143 (5) 051012. (10.1115/1.4049451)
- Pugh, D. et al. 2021. Emissions performance of staged premixed and diffusion combustor concepts for an NH3/air flame with and without reactant humidification. Presented at: ASME Turbo Expo 2020: Turbomachinery Technical Conference & Exposition Virtual 21-25 September 2020. ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. Vol. 4A.ASME. (10.1115/GT2020-14953)
- Hewlett, S. 2021. Investigating the potential of industrial waste stream ammonia as a fuel for low carbon, gas turbine power generation. PhD Thesis , Cardiff University.
- Pugh, D. et al. 2021. An investigation of ammonia primary flame combustor concepts for emissions reduction with OH*, NH2* and NH* chemiluminescence at elevated conditions. Proceedings of the Combustion Institute 38 (4), pp.6451-6459. (10.1016/j.proci.2020.06.310)
2020
- Hewlett, S. G. et al. 2020. Industrial wastewater as an enabler of green ammonia to power via gas turbine technology. Presented at: Turbomachinery Technical Conference & Exposition (TURBO EXPO 2020) Virtual 21-25 September 2020. Proceedings of ASME Turbo Expo 2020 Turbomachinery Technical Conference and Exposition. Vol. 3.Vol. GT2020. ASME(10.1115/GT2020-14581)
2019
- Hewlett, S. et al. 2019. Gas turbine co-firing of steelworks ammonia with coke oven gas or methane: A fundamental and cycle Analysis. Presented at: ASME Turbo Expo 2019 Phoenix, Arizona, USA 17-21 June 2019. ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition: Volume 3: Coal, Biomass, Hydrogen, and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration; Organic Rankine Cycle Power Systems. ASME. , pp.GT2019-91404. (10.1115/GT2019-91404)
Articles
- Davies, T. et al. 2026. Influence of emissions normalisation methods on H2–CH4 fuel comparisons in generic and NOx-Abated gas turbine combustion. International Journal of Hydrogen Energy 223 154402. (10.1016/j.ijhydene.2026.154402)
- Vivoli, R. et al. 2026. Surface roughness effects on the operability and performance of a hydrogen jet burner. Journal of Engineering for Gas Turbines and Power 148 (1) 011014. (10.1115/1.4069474)
- Alrebei, O. F. et al., 2022. Quantifying CO2 emissions and energy production from power plants to run HVAC systems in ASHRAE-based buildings. Energies 15 (23) 8813. (10.3390/en15238813)
- Alrebei, O. F. et al., 2022. Numerical investigation of a first-stage stator turbine blade subjected to NH3–H2/air combustion flue gases. International Journal of Hydrogen Energy 47 (78), pp.33479-33497. (10.1016/j.ijhydene.2022.07.190)
- Amhamed, A. I. et al., 2022. Ammonia production plants - a review. Fuels 3 (3), pp.408-435. (10.3390/fuels3030026)
- Fawwaz Aalrebei, O. et al., 2022. Ammonia-hydrogen-air gas turbine cycle and control analyses. International Journal of Hydrogen Energy 47 (13), pp.8603-8620. (10.1016/j.ijhydene.2021.12.190)
- Pugh, D. et al. 2021. Emissions performance of staged premixed and diffusion combustor concepts for an NH3/air flame with and without reactant humidification. Journal of Engineering for Gas Turbines and Power 143 (5) 051012. (10.1115/1.4049451)
- Pugh, D. et al. 2021. An investigation of ammonia primary flame combustor concepts for emissions reduction with OH*, NH2* and NH* chemiluminescence at elevated conditions. Proceedings of the Combustion Institute 38 (4), pp.6451-6459. (10.1016/j.proci.2020.06.310)
Conferences
- Vivoli, R. et al. 2025. Surface roughness effects on the operability and performance of a hydrogen jet burner. Presented at: ASME Turbo Expo 2025: Turbomachinery Technical Conference and Exposition Memphis, Tennessee, USA 16-20 June 2025. Proceedings of the Turbomachinery Technical Conference and Exposition. Vol. 3A.Combustion, Fuels & Emissions American Society of Mechanical Engineers. (10.1115/gt2025-151389)
- Hewlett, S. et al. 2025. The effects of secondary air staging location, pressure and humidification on NOx emissions for a high ammonia blend in premixed swirl combustion. Presented at: ASME Turbo Expo 2025: Turbomachinery Technical Conference and Exposition Memphis, Tennessee, USA 16-20 June 2025. Proceedings of the Turbomachinery Technical Conference and Exposition. Vol. 2.Coal, Biomass, Hydrogen & Alternative Fuels American Society of Mechanical Engineers(10.1115/gt2025-151612)
- Pugh, D. et al. 2021. Emissions performance of staged premixed and diffusion combustor concepts for an NH3/air flame with and without reactant humidification. Presented at: ASME Turbo Expo 2020: Turbomachinery Technical Conference & Exposition Virtual 21-25 September 2020. ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. Vol. 4A.ASME. (10.1115/GT2020-14953)
- Hewlett, S. G. et al. 2020. Industrial wastewater as an enabler of green ammonia to power via gas turbine technology. Presented at: Turbomachinery Technical Conference & Exposition (TURBO EXPO 2020) Virtual 21-25 September 2020. Proceedings of ASME Turbo Expo 2020 Turbomachinery Technical Conference and Exposition. Vol. 3.Vol. GT2020. ASME(10.1115/GT2020-14581)
- Hewlett, S. et al. 2019. Gas turbine co-firing of steelworks ammonia with coke oven gas or methane: A fundamental and cycle Analysis. Presented at: ASME Turbo Expo 2019 Phoenix, Arizona, USA 17-21 June 2019. ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition: Volume 3: Coal, Biomass, Hydrogen, and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration; Organic Rankine Cycle Power Systems. ASME. , pp.GT2019-91404. (10.1115/GT2019-91404)
Thesis
- Hewlett, S. 2021. Investigating the potential of industrial waste stream ammonia as a fuel for low carbon, gas turbine power generation. PhD Thesis , Cardiff University.
Research
Projects
As a postdoctoral researcher at Cardiff University, I have contributed to the following projects:
2025-26 National Gas Transmission: Blend Variability Study
2024-25 National Gas Transmission: Structural Innovation Fund - Beta Phase HyNTS Compression
2023-24 National Gas Transmission: Structural Innovation Fund - Electrolyser Improvements Driven by Waste Heat Recovery