Abstract: Experimental investigations on the combustion process of a liquid hydrocarbon fueled scramjet, ignited by hydrogen pilot flame, and with four different inlets, were conducted in free-jet tests, which simulated the fly conditions of Ma=6 and H=25km. Ignition failed with inlet of geometry internal contraction ratio R_C=3, which was comprised of two sweep side compression walls with a contraction of 6° and without horizontal compression surface, due to low static pressure at inlet exit. Stable combustion was sustained in scramjet and positive thrust was measured with inlet of R_C=3, comprising an additional part of horizontal external compression surface. Adapting inlet of higher R_C=5.35, comprising a whole horizontal compression surface, would result in severely distorted airflows at inlet exit, which deteriorated the behavior of isolator, decreased combustion performance, at some cases, even leaded to extinction. Two isolators with different length-to-hydraulic diameter ratios (2.5 and 5) were contrasted, and it was shown that longer isolator increase the ability of isolating the interaction between inlet and combustor and part fuels can be injected about downstream of isolator to improve combustion efficiency.

Key words: scramjet, supersonic combustion, hydrocarbon fuel, inlet, free-jet