Flowfields and combustion dynamics of sequential-dual fuel injection schemes are investigated in a circular, direct-connect combustor in the arc-heated hypersonic wind tunnel ACT-II. The fuel injection scheme includes variations of fuel injector Mach number (Mach 1 and Mach 3) and fuel nozzle quantity (single jet and dual jet). Flow structures are visualized using high-speed (10 kHz) planar laser Rayleigh scattering (PLRS) in supersonic freestreams with stagnation temperature 300 K, whereas combustion dynamics of ethylene flame are investigated using hydroxyl (OH) chemiluminescence and planar laser induced fluorescence (PLIF) imaging at high-enthalpy freestreams. Instantaneous and time-averaged images of large-scale coherent structures and jet inner structures reveal that flow mixing of fuel and freestream benefits from the unsteadiness of flow separation and bow shock-jet interactions. The non-premixed jet flame shape in high-enthalpy flow shows similarity at various jet momentum and jet nozzle Mach number. Dual transverse jet injection has increased penetration depth compared to single jet injection due to the flow blockage from the first jet and there exists an optimum jet distance to maximize the jet penetration. The second jet injection breaks up the smooth flame front originating from the first jet, promotes flame front transition to the corrugated flame regime, and enhances the combustion efficiency through better mixing. A second bow shock from the second jet may act as a continuous ignition source. The combustion enhancement by the hot radical supply from the first jet resides inside the thin flame front only in the non-premixed combustion.