An experimental and numerical investigation of CO2 diluted, oxy-fuel combustion in a reciprocating engine using mixtures of natural gas and hydrogen

Promovendus/a: Mauro Daese

Promotor(en): Prof. dr. Joshua Lacey, Prof. Francesco Contino

Decarbonizing internal combustion engines (ICEs) remains a significant challenge in the global effort to mitigate greenhouse gas emissions. Despite the rapid expansion of renewable energy technologies, ICEs continue to supply approximately 25% of global energy demand and remain a substantial source of emissions. Consequently, rather than being entirely displaced, ICEs are increasingly being re-evaluated within the energy transition as flexible systems capable of operating with sustainable fuels.

Within this framework, synthetic e-fuels such as hydrogen and methane present a viable pathway toward carbon-neutral operation. Produced using renewable electricity and captured CO₂, these fuels enable a closed carbon cycle while maintaining compatibility with existing engine infrastructures. This positions ICE-based systems as attractive solutions for applications requiring dispatchable and scalable power generation, particularly in balancing intermittent renewable energy sources.

A key technological approach facilitating this transition is CO₂-diluted oxy-fuel combustion. In contrast to conventional air-based combustion, nitrogen is excluded from the oxidizer and replaced by a mixture of oxygen and carbon dioxide. This configuration inherently suppresses NOₓ formation while generating an exhaust stream with elevated CO₂ concentrations, thereby improving the efficiency of carbon capture processes. Furthermore, oxygen can be supplied as a byproduct of water electrolysis, while CO₂ may be recirculated within the system, enhancing process circularity. However, the introduction of CO₂ fundamentally alters flame characteristics due to its high specific heat capacity and diluent properties, affecting reaction kinetics, flame propagation, and thermal behavior. These effects introduce challenges related to combustion efficiency, stability, and energy conversion, which remain insufficiently understood under practical engine conditions.

Accordingly, integrating CO₂-diluted oxy-fuel combustion with renewable fuels such as hydrogen and methane represents a promising yet technically demanding pathway toward low-carbon ICE operation, requiring deeper insight into the governing combustion phenomena and their impact on engine performance.