Approach to in situ analysis of scramjet combustor behavior

Abstract

Procedures used to assess combustion behavior of scramjet engines in the 1960s were not published at that time, but may be relevant to current scramjet research. This article describes hydrogen-fueled scramjet investigations performed at the General Applied Science Laboratories during the 1966-1970 time period. The analysis procedure, involving fuel-injection tailoring, aided in locating injection sites in the scramjet combustor and in predicting the pressure rises induced by combustion at selected points in the combustor. The method was applied to two geometrically dissimilar engines whose performance levels were measured in similar freejet facilities. One of these engines incorporated a combustor entrance (gap) height of approximately 2.9 in. and an overall combustor/nozzle length of 10 gap heights. The injector placement resulting from this development approach did not induce pressure distributions that one would associate with the higher-process-efficiency, minimumentropy solution. Nevertheless, approximately 80% of the target thrust levels were attained in these engines at fuel-air equivalence ratios of one, without the benefit of isolators and without deleterious combustor-inlet interactions. Agreement between predicted and measured combustion pressure rises was generally good and satisfactory agreement exists between the pressure rise measured and that calculated using a current cycle analysis.