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Direct-Connect Supersonic Combustion Test Facility
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Purpose:

The purpose of the Direct-Connect Supersonic Combustion Test Facility is to test scramjet combustors in flows with stagnation enthalpies duplicating that of flight at Mach numbers from 4 to 7.5 in direct-connect, or connected-pipe, fashion so that the entire facility test gas mass flow passes through the combustor. The flow at the exit of the facility nozzle simulates the flow exiting an inlet and entering the combustor of a scramjet in flight. Scramjet nozzle geometric simulations can also be added to the scramjet combustor exit. The stagnation enthalpy necessary to simulate flight Mach number for the combustor test is achieved through hydrogen-air combustion with oxygen replenishment to obtain a test gas with the same oxygen mole fraction as atmospheric air (0.2095).

[DCSCTF heater] During facility heater operation, oxygen is injected into the airstream from instream injectors and premixed before hydrogen is injected. The hydrogen is injected into the air/oxygen mixture from instream injectors centered in holes located in a baffle plate upstream of the water-cooled combustor section. Ignition of the gas mixture is achieved using an electric-spark-activated hydrogen/oxygen torch igniter.

Calculated test gas compositions for the standard operating conditions of the DCSCTF are tabulated in the table at the bottom of the page. The data are listed only if the species mole fractions are 0.0001 or greater. These calculations were made with finite-rate chemistry during the expansion through the facility nozzle. The primary contaminant in the test gas is water vapor which varies from 0.083 mole fraction at Mach 4 conditions to 0.358 at Mach 7.5 conditions. A small amount of nitric oxide (0.004 mole fraction) is also present in the test stream at the Mach 7.5 condition.

Various facility nozzles can be attached to the facility combustion heater to simulate scramjet combustor entrance conditions. Two nozzles currently are available for use in the DCSCTF; both are two-dimensional (rectangular) contoured nozzles. The first is a Mach 2 nozzle with throat dimensions of 0.846 x 3.46 inches and exit dimensions of 1.52 x 3.46 inches; the second is a Mach 2.7 nozzle with throat dimensions of 0.356 x 6.69 inches and exit dimensions of 1.5 x 6.69 inches. Vacuum for altitude simulation is provided by a 70-foot diameter vacuum sphere/steam ejector system (requiring up to 25,000 lbm/hr of steam).

Gaseous hydrogen (at ambient temperature) is the primary fuel used in the scramjet combustors tested in the DCSCTF, although test using other types of fuel are conducted occasionally. The hydrogen fuel for the scramjets comes from the same trailers as the hydrogen for the facility heater and is regulated to 720 psia before entering the scramjet fuel manifolds. A 20/80-percent mixture of silane/hydrogen (by volume) is supplied from K-size cylinders (maximum storage pressure of 2400 psia) for use as an igniter/pilot of the primary fuel in the scramjet combustor.

Data Acquisition:

The data acquisition system for the DCSCTF, which has recently been updated, consists of a commercially available software package (AutoNet) running on a Pentium processor. The new system incorporates a NEFF 300 signal conditioner and NEFF 600 amplifier/multiplexer capable of supporting 128 channels. In addition to the A/D capabilities of the NEFF, up to 512 static pressure measurements can be recorded using a Pressure System Incorporated (PSI) 8400 electronic sensing pressure (ESP) system and sixteen 32 port modules. Nonintrusive laser-based diagnostics are commonly used in the DCSCTF and the combustor test section can be mounted on a thrust-measuring system.

Test Capabilities

The DCSCTF normally operates at heater stagnation pressures between 115 and 500 psia and at heater stagnation temperatures between 1600 and 3800 R. Test gas mass flow rates range from 1 to 30 lbm/s. The Mach number/altitude map for the DCSCTF is shown in the figure below. The left boundary is the lower temperature limit of stable operation of the heater (~ 1600 R) and the right boundary represents the maximum operational stagnation temperature (~ 3800 R). The lower (diagonal) boundary reflects the maximum allowable heater pressure (~ 500 psia) and the upper boundary reflects the lowest pressure for stable heater operation (~ 115 psia); however, these pressures translate into higher simulated stagnation pressures on the flight envelope when typical scramjet inlet and aircraft bow shock losses are included. (An inlet kinetic energy efficiency of 0.985 was assumed.) The standard operating conditions of the DCSCTF are shown by the symbols on the figure and are tabulated in the adjacent table. The normal test schedule is 2 or 3 test days per week. Tests average 20 to 30 seconds duration with multiple tests (5 to 10) per day.

[HAPB facilities test conditions] [DCSCTF simulation map]

JP-7 Fuel Heater

Recently, an ~1MW electrically-powered JP-7 fuel heater was added to the DCSTF to allow testing of scramjet flowpaths with heated hydrocarbon fuels.

Research performed using the DCSCTF

  • ISTAR JP-7 fueled Injector Characterization Rig, (Current), ICR

  • Recent work with Coherent Anti-Stokes Raman Spectroscopy and the SCHOLAR combustor model, SCHOLAR

  • Research with rocket based combined cycle engines, (1996-1998), RBCC

  • Research with ramp injectors, (1989-1992), RAMPS

  • Non-intrusive measurements within the hot flowfield of a scramjet combustor using Coherent Anti-Stoke Raman Spectroscopy, (1989/1990), CARS

See a brochure of the DCSCTF

Questions or Inquiries
Questions or inquiries about this facility should be directed to: Kenneth E. Rock
HAPB

 

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Last updated: Thursday, August 14, 2008 14:48