Abstract: In response to the demand for aviation carbon neutrality, the effects of hydrogen addition on flame propagation, autoignition, and autoignition-assisted flame propagation for surrogate jet fuel were numerically investigated at engine conditions. Results show that for fuel-rich conditions, the normalized flame speed increases nonlinearly with increasing hydrogen ratio and can reach over 20, which poses great challenges for avoiding flashback. For fuel-lean mixtures, the flame speed enhancement due to the flame temperature can be ignored, while cannot be for fuel-rich mixtures. For autoignition, there exists kinetic coupling for n-dodecane/hydrogen mixtures. Based on this, the diagram for autoignition risks is constructed, which indicates that hydrogen suppresses autoignition under subsonic cruising conditions, while it may suppress or promote autoignition under supersonic cruising conditions, depending on the hydrogen mixing ratio and the combustor inlet temperature. For the coupling of flame propagation and autoignition, the one-dimensional calculations of autoignition-assisted flames demonstrate that, for the complex fuel with two-stage ignition, the first-stage ignition assistance can be eliminated when the mass fraction of hydrogen reaches 50%.