Alternative Fuels for General Aviation Piston Engines: A Comprehensive Review

This review synthesizes recent research on alternative fuels for piston-engine aircraft and related propulsion technologies. Biofuels show substantial promise but face technological, economic, and regulatory barriers to widespread adoption. Among liquid options, biodiesel offers a high cetane number and strong lubricity yet suffers from poor low-temperature flow and reduced combustion efficiency. Alcohol fuels (bioethanol, biomethanol) provide high octane numbers suited to high-compression engines but are limited by hygroscopicity and phase-separation risks. Higher-alcohols (biobutanol, biopropanol) combine favorable heating values with stable combustion and emerge as particularly promising candidates. Biokerosene closely matches conventional aviation kerosene and can function as a drop-in fuel with minimal engine modifications. Emissions outcomes are mixed across studies: certain biofuels reduce NOx or CO, while others elevate CO2 and HC, underscoring the need to optimize combustion and advance second- to fourth-generation biofuel production pathways. Beyond biofuels, hydrogen engines and hybrid-electric systems offer compelling routes to lower emissions and improved efficiency, though they require new infrastructure, certification frameworks, and cost reductions. Demonstrated test flights with biofuels, synthetic fuels, and hydrogen confirm technical feasibility. Overall, no single option fully replaces aviation gasoline today; instead, a combined trajectory—biofuels alongside hydrogen and hybrid-electric propulsion—defines a pragmatic medium- to long-term pathway for decarbonizing general aviation.