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.