The Prospects and Challenges of Sustainable Aviation Fuels (SAFs) for Clean Combustion in Gas Turbine Engines: A Review

The persistent rise in anthropogenic greenhouse gas (GHG) emissions has intensified concerns regarding long-term climate forcing and its potential to induce irreversible impacts on the Earth’s climate system. Presently, sustainable aviation fuel (SAF) blending of up to 50% by volume is approved, within which significant reductions in net carbon dioxide (CO2) emissions have already been demonstrated. Also, moving beyond the current blending limit, it offers the potential for further reductions in both CO2 and non-CO2 climate impacts, including particulate matter (PM) emissions. However, to enable this transition, SAFs need thorough evaluation in terms of operational performance, compatibility with engine parts, and their influence on gas turbine combustion. Past research suggests that SAFs can reduce emissions, especially CO2 by 80%, sulfur dioxide (SO2) by 100%, and PM by 50–90%, subject to the characteristics of their production pathways. However, the reduction in NOx emission due to SAF combustion is found to be negligible, at up to 10%, compared to conventional jet fuel. Cost is one of the primary challenges that restricts airlines from adopting SAF commercially. However, to make it more streamlined, the production process needs to be optimized, and more subsidies and carbon pricing should be provided. This review systematically assesses the benefit of SAF’s chemical and physical properties on combustion–performance–emission characteristics and engine operability. The key engineering challenges related to fuel compatibility with existing engine components, material degradation, high altitude performance, and different emissions are thoroughly discussed. The effects of different operating parameters, including engine loading conditions, speed, altitude level, types of SAFs, and their blending ratio, on different gaseous and PM emissions are critically reviewed. At the end, the cost implications, compatibility, and technical barriers of SAFs have been discussed.