Impact of HEFA Fuel Properties on Gaseous Emissions and Smoke Number in a Gas Turbine Engine

The study aims to establish the behavior of hydro processed esters and fatty acids (HEFA), as a type of alternative fuel with a conventional Jet A-1 as a reference fuel using a GTCP85 aircraft auxiliary power unit (APU). The research evaluates the impact of fuel properties on emissions using HEFA (blends in 18 proportions) and Jet A-1. With increasing HEFA proportions in the fuel, it is observed that reduction of gaseous emissions is not absolute. No specific trend of gaseous emissions reduction, in terms of aromatic and hydrogen content, were observed for the 18 blend ratios tested. For 50:50 blend of HEFA and Jet A-1, which meets current American Society for Testing and Materials (ASTM) specifications D7566 as drop-in fuel to D1655, the average reduction of NOX, CO, UHC emissions in PPM are ∼ 40%, 18%, and 28%, respectively. In contrast, no significant difference observed in CO2 emissions as compared with Jet A-1. Furthermore, the smoke number is proportional to the aromatic fuel content, fuel density (at 15°C), and carbon content irrespective of load condition. Conversely, the smoke number tends to be inversely proportional to the hydrogen, Sulphur, iso-paraffinic, and heat content of the fuel. Finally, these findings will contribute to the knowledge of fuel properties on impact engine performance and emissions as the aviation industry moves towards 100% SAFs.