This study investigates ignition enhancement strategies for a dual strut/cavity scramjet combustor under simulated Mach 2 flight conditions. To address the low-Mach-number combustion instability challenge, we employ a methane/oxygen rocket’s tail flame as a pilot flame combined with plasma jet activation. Experimental results reveal two critical findings: (1) Engine ignition failed without rocket assistance, confirming the necessity of external ignition support at low Mach numbers; (2) Flame flashback occurred in the secondary cavity when local equivalence ratios reached 0.5, correlating with amplified 100Hz pressure oscillations. While plasma injection enhanced kerosene combustion efficiency by intensifying the pilot flame, it simultaneously exacerbated flame flashback and pressure oscillation amplitudes, demonstrating the inherent trade-off between combustion enhancement and stability control in cavity-stabilized systems.