Dual-Mode Scramjet Flameholding Operability Measurements

摘要

Flameholding measurements were made in a direct connect combustor facility designed to simulate cavity flameholding in the flowfield of a hydrocarbon fueled dual-mode scramjet combustor where the presence of a shocktrain upstream of the flameholder has a significant impact on the inlet flow to the combustor and on the flameholding limits. A mechanical throttle was installed in the downstream end of the test rig to provide the back-pressurization needed to form the shock train and to decouple the operation of the flameholder from the backpressure formed by heat release and thermal choking, as in a flight engine. Measurements were made primarily with ethylene fuel but a limited number of tests were also performed with heated gaseous JP-7 fuel injection. The flameholding limits were measured by ramping inlet air temperature down until blowout was observed. The test facility used a hydrogen fueled vitiated air heater, Mach 2.2 and 3.3 inlet nozzles, a scramjet combustor rig with a 1.666 by 6 inch inlet and a 0.65 inch deep cavity. Mean blowout temperature measured at the baseline condition with ethylene fuel, the Mach 2.2 inlet and a cavity pressure of 21 psia was 1502 °R. Flameholding sensitivity to a variety of parameters was assessed. Blowout temperature was found to be most sensitive to fuel injection location and fuel flow rates and surprisingly insensitive to inlet Mach number and operating pressure (changed by varying back-pressurization or inlet flowrate). Video imaging through both bottom and side wall windows was collected simultaneously and showed that the flame structure was quite unsteady with significant lateral movements as well as movement upstream of the flameholder.