An investigation on the flame characteristics of sustainable aviation fuels and their blends near lean ignition limit

With the increasing adoption of SAFs in aero-engines, ignition performance and flame stability are critical for achieving reliable combustion over a wide operating range. This study investigates the transient flame evolution of RP-3, HEFA-SPK, and their equal-volume blend near the lean ignition limit under 273 K–101 kPa, 253 K–80 kPa, and 233 K–60 kPa conditions. High-speed imaging, centroid tracking, and POD analysis are employed to characterize flame trajectories and spatial modal evolution. Results show that RP-3 exhibits stable radial contraction, while HEFA-SPK undergoes faster initial contraction but more pronounced axial retraction and re-development. The blend inherits the radial behavior of HEFA-SPK, whereas its axial evolution shows nonlinear coupling between RP-3 and HEFA-SPK. POD reveals that RP-3 transitions from RECM to APM with reduced stability; HEFA-SPK transfers energy to higher-order modes while maintaining low-order stability; the blend resembles RP-3 but exhibits enhanced asymmetry under severe conditions. APM promotes early radial convergence with greater trajectory contribution and deflection, whereas RECM dominates axial stretching. These findings clarify the effects of fuel composition on transient flame dynamics and provide guidance for SAF-blend ignition evaluation and combustion optimization.