Abstract: To explore the practicability of the free-jet experimental study on the scramjet fueled hydrocarbon, several tests of a three-dimensional scramjet were conducted at Ma10 simulated conditions of FD-21 piston-driven high enthalpy shock tunnel. The test article was the scramjet including a curved-surface compression inlet, a nearly constant rectangular-section isolator, a little divergent combustor with a cavity and a nozzle with the cross-section transition of rectangle to circle. The chemiluminescence visualization of the excited OH^*/CH^* radical along with the wall pressure measurement was developed to study the establishing process of scramjet flow and ethylene-burning. The temporal and spatial images of OH^*/CH^* in the combustor, together with the scramjet bodyside wall pressure data, were obtained for the tare without fuel injection and the ethylene injection conditions. For the tare condition, the OH^* and CH^* radicals in the combustor only exist at the first 1 ms period of the scramjet flow setup process, and the wall pressure of all taps tends to a plateau after a sharp increase at the air-flow arrival, revealing that the contamination of the diaphragm ablation can be ignored and a quasi-steady flow can be achieved. For the ethylene injection condition, a large number of OH^* and CH^* radicals emerge at the first 2 ms period of the scramjet flow setup process and then tend to a pseudo constant of a low OH^* and an undetected CH^* radical concentration, in spite of the wall pressure feature almost identical to that for the tare case. Additionally, the dramatic difference was achieved in the scramjet wall pressure distributions for the tare and the ethylene injection conditions, which was several orders of magnitude greater than the pressure fluctuation of the sample time interval. These evolving features of OH^*/CH^* radical and wall pressure data indicate an achievement of ethylene burning in hypervelocity flow, and the freejet experiment of a high Mach number scramjet fueled ethylene can be performed in FD-21 shock tunnel.