Flow and combustion dynamics in a model scramjet are experimentally investigated in Mach-4.5 free streams. A supersonic nozzle is employed to inject the gaseous ethylene fuel into supersonic crossflows. The flow field is visualized using Rayleigh scattering method in airflows seeded with carbon dioxide at stagnant room temperature, in which the laser radiation is scattered by condensed carbon dioxide particles in tens of nanometer diameters. The ethylene jet is auto ignited in high-enthalpy flows of total temperature 2,600 K after compression and deceleration in the scramjet isolator and combustor. The combustion structures of the jet flame are investigated using hydroxyl planar laser-induced fluorescence imaging. An internal beam delivery system is used to project a laser sheet into a scramjet in the counter-streamwise direction, in which the laser sheet is enabled to scan over the entire flow volume in the spanwise direction. The overall ethylene combustion distribution and flame structures are dominated by the flow mixing initiated by the transverse jet injection.