Performance and combustion characteristics of Heavy-Fuel aircraft piston engines at high altitudes: Comparison between conventional fuels and HEFA sustainable aviation fuel

The use of sustainable aviation fuel (SAF) in heavy-fuel aircraft piston engines (HF-APE) has significant implications for reducing carbon emissions in general aviation. However, current research on the combustion characteristics of SAF in HF-APE primarily focuses on ground conditions, and a comprehensive understanding of high-altitude combustion has yet to be fully developed. This study examines the high-altitude performance and combustion characteristics of a HF-APE using conventional fuels and HEFA-SAF through experiments conducted in a high-altitude environmental simulation. The power and fuel consumption performance, as well as the in-cylinder combustion process of diesel, RP-3 kerosene (RP-3), and SAF at altitudes ranging from 0 to 5500 m, are compared and analyzed.The experimental results reveal a consistent trend of power loss for all three fuels (diesel, RP-3, and SAF) at varying altitudes. At an altitude of 5500 m, power losses compared to sea level are 23.4% for diesel, 22.8% for RP-3, and 22.1% for SAF. The specific fuel consumption (SFC) increases significantly at low speeds but varies little at high speeds, with RP-3 and SAF exhibiting an SFC 8.3% higher than that of diesel at low speeds. The in-cylinder pressure and heat release rate (HRR) trends are similar under varying loads, with RP-3 and SAF exhibiting longer ignition delay times (IDTs) compared to diesel, but higher HRR peaks under highload conditions. The high-altitude environment causes a reduction in peak pressure and HRR for all fuels, while also prolonging ignition delay and combustion duration. Specifically, at an altitude of 5500 m, peak pressure and HRR are reduced by an average of 12% to 23%. HEFA-SAF demonstrates enhanced power performance and lowtemperature fluidity in high-altitude environments, providing a crucial experimental foundation for the use of SAF in general aviation and unmanned aerial vehicle propulsion.