Operation of a Compression-Ignition Kerosene Aviation Engine with Sustainable Aviation Fuel: An Experimental Study

Abstract

The aviation industry is undergoing environmental scrutiny due to its significant greenhouse gas emissions. Sustainable aviation fuels (SAFs) are a vital solution for reducing carbon emissions and pollutants, aligning with global efforts for carbon-neutral aviation growth. SAFs can be produced via multiple production routes from different feedstock, resulting in significantly different physical and chemical fuel properties. Their suitability in a compression-ignition (CI) aircraft engine was evaluated through test bench investigations at TU Wien - Institute of Powertrain and Automotive Technology in partnership with Austro Engine. ASTM D7566-certified fuels like Hydrotreated Vegetable Oil (HVO), Fischer-Tropsch-Kerosene (FTK) or Alcohol to Jet (AtJ), but also an oxygen containing biodiesel have been tested extensively. Gaseous emissions, soot emissions, indication measurement data, efficiencies, and the like were acquired and comprehensively analyzed for engine operation with different fuels and fuel blends. Operation with all investigated fuels could be demonstrated successfully at three representative operating points with the original engine setup. At constant boundary conditions, neither maximum permitted in-cylinder pressure, pressure gradient, or exhaust gas temperature were exceeded (nevertheless, an adaption of the injection strategy is recommended). Ignition delay and combustion duration - dependent on fuel properties - greatly influence the formation of incomplete combustion products like HC and CO as well as NOx and soot emissions. Especially the extremely low cetane number of AtJ leads to a substantial increase in premixed combustion, which significantly influences NOx and soot emissions, depending on operating conditions. A low aromatic content (as found in HVO) is beneficial for reducing HC, CO, and soot due to the absence of ring-like molecule structures. Also, a reduced adiabatic flame temperature contributes to a decreased NOx concentration. The high oxygen content of the biodiesel is known to be beneficial for reducing HC, CO, and soot, while it contributes to increased NOx emissions. At comparable air/fuel ratios within a specific operating point, all tested fuels and fuel blends exhibit comparable CO2 emissions