Experimental Study of Vitiation Effects on Scramjet Mode Transition

摘要

MANY ground test facilities for studying dual-mode scramjetn(DMSJ) propulsion rely on stagnation enthalpy simulation viancombustion of hydrogen or hydrocarbon fuel. This heating processnresults in levels of vitiates in the test flow, such as water and carbonndioxide, that are not present in atmospheric air. The effects of thesenvitiates on DMSJ performance and operability must therefore benunderstood if accurate extrapolations to flight can be made. ThenSupersonic Combustion Facility [1] provides a unique opportunity tonstudy such effects since the facility is electrically heated and suppliesna test gas that is free of combustion generated vitiates. However,nwater vapor, in the form of steam, and carbon dioxide can be added tonthe flow to examine the effects these vitiates have on a DMSJ.nPrevious work to study vitiation effects has been performed using upnto 7% H2O and 2.5% CO2, both by mole [1]. However, these resultsnwere only obtained over a limited range of fuel equivalence ratios andnthe study did not fully investigate mode-transition with anprecombustion shock train due to the lack of a flowpath isolator.nThe present study was conducted with vitiate levels closer to thosenencountered in combustion heated facilities and with an isolatorninstalled. Reference [2] provides details of the new configuration.nBasically it consists of the DMSJ of [1], a rectangular, direct connectncombustor with a single ramp fuel injector, and a new constant area,nrectangular isolator that is ten duct heights long. This Note reports onnexperimental pressure measurements in the scramjet combustor atntwo vitiated conditions and compares the results with that of clean air.nWater and carbon dioxide levels are examined such that the effects ofnwater vapor vitiation can be isolated for conditions that are representativenof a methane combustion heated facility operating at Mach 5nsimulation. Trends in the data are examined, particularly with respectnto the effect vitiates have on the mode-transition characteristics ofnthe DMSJ.