Comparison of supersonic combustion between impulse and vitiation-heated facilities

A comparison has been made between supersonic combustion in two commonly us ed, but fundamentally different, facilities for scramjet research, a vitiat ion-heated blowdown tunnel and a free-piston shock tunnel. BS passing the s hock-tunnel freestream Row through a normal shock and then expanding it to Mach 2.5, combustor inlet conditions and geometries were nominally replicat ed between the two facilities. A constant-area rectangular duct and a diver ging duct, both employing central-strut hydrogen injection, were used. Boun dary-layer separation and choking in the constant-area duct limited superso nic combustion comparisons up to a fuel equivalence ratio of the order of 0 .3. The experimental results also show that the onset of boundary-layer sep aration occurs at the same combustor pressure loads and that it behaves sim ilarly in the different facilities. With the diverging duct, comparisons we re made up to an equivalence ratio of 1.05. Agreement between the results o btained in the two facilities is within experimental error when the differe nt freestream and boundary layers are accounted for.