State-of-the-art developments in fuels, combustors, and combustion technologies for low-emission aero gas turbine engines

Global aviation demand is expected to continue its strong long-term growth, with passenger traffic projected to increase by approximately 4.2% annually, leading to a doubling of air traffic by 2044. As aviation currently accounts for about 2.5% of global Carbon Dioxide (CO₂) emissions, this growth underscores the urgent need for low-emissions aero gas turbine technologies. Consequently, substantial research efforts have focused on advances in alternative fuels, combustor architectures, and combustion concepts to mitigate aviation’s environmental impact. This review provides a concise synthesis of recent developments in low-emission aero gas turbine engines, emphasizing their implications for emissions reduction, operability, and technology readiness. It first examines emerging and transitional aviation fuels—including hydrogen, ammonia, sustainable aviation fuels (SAFs), and fuel emulsions—highlighting their combustion-relevant properties, integration challenges, and emissions characteristics. The evolution of practical combustor architectures, such as Rich-Quench-Lean (RQL), Double Annular Combustor (DAC), Twin Annular Premixing Swirler (TAPS), Lean Direct Injection (LDI), Axially Staged Combustor (ASC), and Variable Geometry Combustor (VGC), is then reviewed, assessing their emissions mitigation potential and operational trade-offs under representative flight conditions. Recent progress in advanced combustion concepts, including lean premixed and micromixer-based systems, water or steam injection, and pressure-gain combustion, is also discussed, with particular attention to stability, flashback, auto-ignition, and thermoacoustic constraints. Finally, specific focus is given to hydrogen-blend combustion technologies, synthesizing fuel–combustor–technology interactions and demonstrating that aerodynamic control, staged fueling, and the degree of premixing must be co-designed to achieve stable operation, low-Nitrogen Oxides (NO_x) emissions, and flashback resistance in hydrogen-capable aero and micro gas turbine combustors.