Impact of a Split-Injection Strategy on Energy-Assisted Compression-Ignition Combustion with Low Cetane Number Sustainable Aviation Fuels

The influence of a split-injection strategy on energy-assisted compression-ignition (EACI) combustion of low-cetane number sustainable aviation fuels was investigated in a single-cylinder direct-injection compression-ignition engine using a ceramic ignition assistant (IA). Two low-cetane number fuels were studied: a low-cetane number alcohol-to-jet (ATJ) sustainable aviation fuel (SAF) with a derived cetane number (DCN) of 17.4 and a binary blend of ATJ with F24 (Jet-A fuel with military additives, DCN 45.8) with a blend DCN of 25.9 (25 vol.% F24, 75 vol.% ATJ). A pilot injection mass sweep (3.5-7.0 mg) with constant total injection mass and an injection dwell sweep (1.5-3.0 ms) with fixed main injection timing was performed. Increasing pilot injection mass was found to reduce cycle-to-cycle combustion phasing variability by promoting a shorter and more repeatable combustion event for the main injection with a shorter ignition delay. For both fuels, dwells between 2.0 and 2.5 ms resulted in the lowest variability. For these dwells, the pilot injection cumulative heat release at the main injection timing is maximized, resulting in more rapid ignition of the main injection. Emissions results suggest that mixing-controlled combustion of the main injection is achievable with higher pilot masses at injection dwells between 2.0 and 2.5 ms as indicated by an increase in filter smoke number at these conditions.