The combustion performance of sustainable aviation fuel with hydrogen addition

Abstract

Hydrogen (H2) aircraft have been proposed for the “Fly Net Zero” target. The combination of jet fuel and H2 was offered to successfully operate the jet engine with H2 without further combustor modification. The current work used hydro-processed renewable jet fuel (HRJ) and experimentally investigated its combustion properties and H2 addition in the constant volume combustion chamber (CVCC). Experiments were performed at the initial temperature (Tini) from 600 K to 818 K, initial pressure (Pini) 10, 15 bar and equivalence ratio (φ) = 0.5. Normal spray ignition (SPI) and direct injection spark ignition (DISI) were studied. Overall, HRJ has a shorter ignition delay (ID) for SPI. At 600 K, adding 10% and 20% H2 to HRJ increased ID to 12.68% and 38.46%, respectively. As Tini rose to 725 K, increment in ID was shortened to 5.96% and 20.47% with 10% and 20% H2 addition, respectively. For DISI, at 600 K, adding 10% and 20% H2 to HRJ shortens ID to 3.56% and 4.92%, respectively. When comparing the ID of DISI with the SPI, ID was shortened to 84.64% and 91.77% for 10% and 20% H2 addition, respectively. Emission results showed that adding H2 reduced CO2, while NOx emissions were increased. Ansys Chemkin-Pro was used to run numerical simulations of a zero-dimensional (0-D) closed homogeneous batch reactor model (CHBR). An existing HRJ mechanism was adopted, and H2 elementary reaction rate constant factors were updated for better model predictions. The updated model was under prediction with the experimental ID periods. The simulation results showed that the reaction H2+OH = H + H2O is the primary cause for consuming OH radicals with H2 addition, leading to an increase in fuel ID. At higher temperatures, two major reactions (HO2 + H2 = H2O2 + H, and HO2+HO2 = H2O2 + O2) followed by H2O2 = OH + OH are accountable for reproducing OH radicals. Thus, the fuel ID was shorter.