Scramjet Tests in the ONERA F4 Hotshot Wind Tunnel

Within the LAPCATII European project and within collaboration between ONERA, JAXA and DLR, scramjet models have been tested in 2013 in representative conditions and combustion processes have been evidenced and characterized. Two campaigns, on the HyShot II and HyShot IV combustor, were done in representative Mach 8 flight conditions. The HyShot combustor has been extensively ground studied in several impulse facilities such as HEG (DLR), HIEST (JAXA) and T4 (UQ). The arc-jet F4 wind tunnel appears then as a complementary facility with regards to classical impulse facilities with typical available test time greater by an order of magnitude. Runs were carried out for several hydrogen injection conditions leading to different equivalence ratio levels and evolutions. Together with pressure measurements on the intake ramp and along the internal flow path, schlieren and OH* chemiluminescence visualizations were used to characterize combustion. Several steady and unsteady processes were observed, steady combustion, flame blow-out, combustor choking, and ignition with fuel-on during the run. The choking development can be analyzed from both pressure distributions and visualizations. During a typical run performed in F4, flow conditions decrease through a wide range of total pressure and enthalpy. At the same time, the equivalence ratio evolution can be adjusted from the injection parameters. The analysis of the combustion process is therefore possible over a wide range of enthalpy / equivalence ratio domain. Moreover, choking or blow-out limits can be determined in this domain. The HyShot IV configuration features the same geometry than the HyShot II combustor. The only difference lies in the presence of the JAXA hypermixer injection scheme. Measurements done on the two configurations shows the effect of the hypermixer injection parallel to the incoming flow used for HyShot IV, compared to the simple injection normal to the flow used for HyShot II. Pressure distributions show the clear differences in the shock pattern all along the combustor. The combustion domain is extended to higher equivalence ratio range.