Composite technologies developmentstatus for scramjet applications

C. BOUQUET - R. FISCHER - J.M. LARRIEUG. UHRIG - J. THEBAULT

Snecma Propulsion SolideBP37 – 33165 – Saint Médard en Jalles -

FRANCE

AIAA-6917- Dec 2003 - Norfolk

ABSTRACT

Through the UTC and SNECMA initiated JointComposite Scramjet (JCS ) program, the potentialusing of carbon – carbon and carbon – siliconcarbide composite materials in a scramjetcombustor demonstrated weight savings andincreased thermal margins relative to an all –metallic scramjet.

The fi rst appli cations selected for use of SNEC MA– produced composite materi al was for the air –breathing pilots, used for ignition and stabilizationin the combustor, and a panel representative of anuncooled wall. These components were jointlydesigned by the team, produced by SNECMA andtested successfully at Mach 7 flight conditions atthe UTRC scramjet test facility in June of 2001.

In parallel to the system studies carried within theframe of the JCS program, a USAF-DGAcooperation, the AC3P (Advanced CompositeCombustion Chamber Program), funded thedevelopment of a C/SiC actively cooled technologyas a potential future replacement for the currentHySET metallic design. Several panels weremanufactured and tested in parallel to a materialand structural development study. The final test inApril 2003 at the USAF AFRL radiant facilitydemonstrated a SNECMA manufactured totallyleak-free composite heat exchanger in relevantconditions.

This paper presents the technological developmentstatus of scramjet applicable technologies atSNECMA and the foreseen future developments.

INTRODUCTION

From the initial development of C/Cmaterial for Solid Rocket Motor nozzles, SnecmaPropulsion Solide has developped a family ofC/SiC materials to be compatible with the more andmore stringent requirements for the propulsion andexternal structure of future aerospace vehicl es.Since 1984 SNECMA is proposing its carbonsilicon carbide (C/ SiC) NOVOLTEX material forramjet and scramjet application.After succesful tests demonstration with Onera ofRamjet composite structure, a new cooperation wasstart ed with the UTC group for demonst ration ofC/SiC use in Scramjet .The Joint Composite Scramjet (JCS) program is aninternally funded technology development anddemonstration program between Pratt&Whitney(P&W), the United Technologies Research Center(UTRC), and SNECMA. The goal of this programis to develop an all-composit e version of the P&Wcooled metallic scramjet combustor, includingrelated components, from composite materialproduced by SNECMA..

In CY 2000, an 18-month period of workwas initiated on the design, fabrication, assembly,and testing of three types of components. The firstwere leading edges samples, to determine materialperformance and durability. Second, were uncooledversions of the UTRC-developed airbreathingpilots. Third, was the fabrication of a passivelycooled panel . designed (thermal and thermal-structural analyses) for operation at Mach 8/1500psf dynamic pressure fli ght conditions.

In parallel, a USAF-DGA cooperation, theAC3P (Advanced Composite Combustion ChamberProgram), funded the development of a C/SiCactively cooled technology as a potential futurereplacement for the current HySET metallic design.Several panels were manufactured and tested inparallel to a material and structural developmentstudy.Radiant tests at USAF-AFRL were performed in2002 and 2003 using nitrogen then kerozene ascoolant to evaluate the potential of the AC3concept. The final test were performed in April2003 using hot kerozene as coolant anddemonstrated a SNECMA manufactured totallyleak-free composite heat exchanger in relevantconditions at the maximum capacity of heat flux ofthe AFRL radiant facility.

12th AIAA International Space Planes and Hypersonic Systems and Technologies15 - 19 December 2003, Norfolk, Virginia

AIAA 2003-6917

Copyright © 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

CARBON-CARBON & CERAMICCOMPOSITES BACKGROUND

Snecma Propulsion Solide. ( formerly SEP,Société Européenne de Propulsion ). began thedevelopment of C-C in 1969 as throat materials toimprove the performances and the reliability ofSolid Rocket Motor nozzles.

From these initial products, newapplication were developped at nozzle level ofdifferent motor using solid or liquid propellant andnew areas of C-C applications appeared soon suchas brakes or equipment for indust rial furnaces.

All these parts permitted to develop, onone hand all the design methodology withcomputation tools and data base issued fromcharact eri zation work, and on the other hand all theproduction facilities to manufacture large sizeelements or large quantities of small parts.

In the seventies, the development ofchemical vapor infiltration (CVI) of silicon carbide(SiC) opened another field of application in strongoxidative environment or a long durationrequirement. Then Snecma Propulsion Solide workscontinuously to increase the lifetime underoxidative environment required for reusableaerospace systems or for high energy applications.

These developments permitted tomanufacture significant parts for the EuropeanHERMES project (Cf fig 1) and have now serialapplication for parts in nozzle of jet engines ortactical missiles

Fig 1. C- SiC parts for HERMES project

The Snecma group has now 3 mainProduction sites, 2 in France , 1 in Kentucky ,representing more than 30 furnaces for carbon orsilicon carbide chemical infiltration, up to 2.5mdiameter in size , which mean a capacity of morethan 300 metric tons of C-C and C-SiC parts.

Fig2 - Large size C-C and SiC CVD furnaces

To improve the quality of the C-C material SnecmaPropulsion Solide developed and use various 2 to 4Dimension preform constructions. Most of theproduction of the Snecma group is based onNOVOLTEX , a 3D carbon non-woven preformconstruction made by an automatic technology .Needling consists in attaching fabric layers to eachother with carbon fibers carried by needles .Needling is carried out after each layer so that,at the end, each part of the preform, through thethickness, has received the same amount oftransferred fibers as shown in the fi gure 3this provides Novoltex its good through-the-thickness homogeneity, and .its 3D characteristics.

Fig 3. Novoltex Carbon preform technology

Bell-shaped nozzle extension preforms are nowproduced with dedicated automatic tape-wrappingand needling machines.

Fig 4. Novoltex bell shaped preform

.

SNECMA RAMJET COMBUSTORSBACKGROUND

Early in the eighties the interest of usinguncooled C/ SiC to replace metallic parts insulatedwith ablative materials was clearly identified forlong duration missions in ramjet combustors:

SNECMA participated, in cooperationwith ONERA, to several demonstration programs,

In a first program , tests were made at Onera todemonstrate long duration performances of a 1mlong ramjet combustion chamber using SnecmaPropulsion Solide winding and infiltrationtechnologies

Fig 5 –ramjet combustion chamber during longduration firing.

In an other program , the developmentmade lead to the test of the front part of a ramjetcombustion chamber including:

- A front dome.- The fore cylindrical part of the

chamber.- Two air inletsAll these parts were exposed to a high

temperature oxidative swirling flow which isimposed in this zone to stabilize and improvecombustion efficiency (see air inlet temperaturefi eld in fig 3)

Parts were manufactured using 2D fabricsfor dome and cylinder and NOVOLTEX carbonpreforms for air inlets. The parts were SiCinfiltrated using the CVD process.

Fig 6 – Ramjet air inlet temperature at steady state.

No significant erosion or mass loss wasobserved after 1300 s at temperatures as high as2250 K.

Fig 7 – Head end of ramjet combustion chamberafter firing.

Several other tests contributed to demonstrate theexcellent behavior of this material not only inramjet combustion chambers environment but alsofor hot gas valves. It is manufactured at industriallevel since 15 years and a large data base ofmechanical properties is available in a wide rangeof temperatures.

So it was naturally sel ect ed to manufacturethe composite parts of the JCS program.

JCS PRELIMINARY LEADING EDGESTESTS

Preliminary design activities performed inan integrated team ( UTC/SNECMA) have shownthe high potential payoff of uncooled compositeparts to reduce mass and complexity of a scramjetcombustor. Airbreathing pilot injectors anduncooled chamber wall demonstrators wereselected as a first st ep.

A first task was done, in order to verifythat SNECMA C/ SiC material was able towithstand the very high heat fluxes encounteredunder Mach 8 condition. One of worst condition tocheck for the injector design was at the leadingedge of the ai rbreathing pilot cowl. A set of leadingedges was then designed and built to check theircapacity to withstand the high flux withoutsubstanti al erosion and then sel ect the lowest radiuscompatible with this goal within the manufacturingconstraints.

Three wedge samples with radii ranging from0.75mm to 1.25 mm were manufactured and testedby fitting them at the location of the injectors.

Fig 8 – LE samples 0.75, 1, 1.25 mm radius

The two first samples (radius 1.25 and 1mm) were tested in UTRC scramjet rig at Mach 7,q= 750 psf mounted at the location of the pilotcowl. Each sample was test ed for 90s 7 times.

Mass loss was below 1% after 7 cycleswithout significant regression of the LE.

The third sample (radius 0.75 mm) wastested at General Applied Sciences Laboratory(GASL) facility at Mach 8/1500psf for 150s andshowed the same behavior : see fig 9 (after test)

Fig 9 – Leading edge samples (0.75 mm radius )after test

These tests have demonstrated the abilityof the material to withstand the very severeconditions of the pilot cowl cumulating 7 thermalcycl es for the two fi rst and 150s at M8/1500psf forthe third.

JCS COMPOSITE INJE CTORS DESIGN ANDMANUFACTURING

Airbreathing pilot injector engineeringanalysis was performed in common to take thehigher benefit of using SNECMA material :

- The baseline design for the pilots was theUTRC-developed water-cooled airbreathing one,adapted to fit with the C-SiC manufacturingconstraints.

- A two p arts design (cowl and body )assembled by a clevis-tang was selected forthermomechanical and manufacturing reasons(thanks to NOVOLTEX technology for real 3Dbehavior and machining capability : see fig 10).

Fig 10 – Airbreathing pilot – Cowl and body

- Metallic tubes, embedded in groovesmachined in the composit e parts, were sel ected forfuel injection inside the pilot chamber and on thecowl. Body was adapted to fit with test rig interfaceand thermal insulation needed to preserve metallicframe from hot composite part.

Thermomechanical analysis of the parts wasperformed by SNECMA using in house analysistool MARC.and P&W thermal analysis results asinput .

Maximum predicted temperatures were :M=7/750psf :T = 2230°K on cowl trailing edgeM=8/1500psf :T= 2550 °K on cowl leading edge

Fig 11 – Thermal analysis at M=7

Thermomechanical analysis wasperformed for the airbreathing pilot for bothMACH 7 and 8 including transi ent phases (ignitionand cool down). They have shown positive marginsin all conditions. The design in two sliding partsand SNECMA C/ SiC properties permitted to limitstresses to acceptable limits at the junction betweencowl and body ( see fig 12)

Fig 12 – Stresses at cowl/body junction

Four pilots were produced by SNECMA and sent toUTRC for final assembly on test bench.

JCS COMPOSITE 6"x8"PANEL DESIGN ANDMANUFACTURING

A 6"x8" panel with a wall thickness of 3mm was designed and machined in a NOVOLTEXICVI SiC densified preform. Edges are thi ckened tofit in the metallic frame of the test rig (see fi g 7)Equivalent thermomechanical analyses wereperformed to consolidate the design

Fig 13 – Uncooled Panel with thermocouples in thecenterline.

PILOTS AND PANEL INTEGRATION INTEST RIG

UTRC have ensured the integration of compositepilots and panel in the rig.

Pilots have been pl aced in a metallic frameable to support both metallic or composite versionand providing water cooling for the metallic oneand thermal insulation of the frame for thecomposite one. The location of the two pilots waskept strictly identical to that of the original setup.

The uncooled panel was placeddownstream on cowl side of the combustorenabling visualization through an existing windowon the upper wall side.

Fig 14- Integration in UTRC test rig

pilot block

location of JC Spanel

air-breathingpilots panel

viewingisolator

inlet air

° F

TEST PLAN AND MEASUREMENTS

Test planAll testing was conducted at Mach

7/750psf in the UTRC scramjet test rig, whichresulted in combustor entrance conditions of Mach3.3, or gas velocity of 5870f/s (1790 m/s). The gasconstituents of the inl et airfl ow consisted of air andwater vapor (hydrogen/oxygen vitiator withmakeup oxygen). Once the last test configurationwas made, testing has been continued to obtain themaximum number of cycles on the installedhardware. Each cycle was 25 to 30 s long.

TEST RESULTS AND PARTS EXPERTISE

Tests results

As stated previously, the gas conditions forthe Mach 7/750 psf condition resulted in a mach 3.3condition at the combustor entrance. Analysis byP&W and SNECMA indicat ed that a predict ed pilotcowl temperature would be in the 3600 F (1980 C)range.

Fig 15 - Composite pilot photos during JCS testing

Visual observation of the cowl during pilotoperation, since it was not possible to installthermocouples on the cowl, support thistemperature assessment as the cowl was veryradiant in the yellow/yellow-white visible lightspectrum. This in comparison to the panel, whichunder combined observation and thermocouplemeasurement operated in the orange/yellowspectrum and was measured at a maximumtemperature 2250 F (1230 C). ( see fig 16)

Fig 16 - Composite panel photos during JCS testing(UTRC run 55.1)

Parts expertise

Following the completion of 3 thermalcycl es, the pilots were examined for matrix erosionand material loss due to matrix or fiber failure. Itwas not ed that the l eading edge radii for both pilotswere unchanged; there was no damage or erosion ofthis critical area. While thermal insulation was lost(whit e residues) the pilots themselves looked prettymuch unscathed by the envi ronment (see fig 17)

Fig 17 - Pilots after 3 cycles

The panel did not experienced anyproblem whatsoever. The post-test photograph(figure 18) show the condition of this panel after 5thermal cycles.

Fig 18 - Hot side face of the panel after 5 cycles

JCS PROGRAM CONCLUSIONS

The C/ SiC airbreathing pilots and thepassively cooled panel, successfully met allobjectives of the planned JCS test program.

Significant results of this test program are :

- Demonstration of the hardware without failure ina scramjet environment.- Durability of this hardware, manufactured fromC/SiC composite materi al in a scramjet combustionenvironment in terms of no measurable erosion ofpilot cowl leading edges, no loss of subst rat e (fibersor matrix), or cracking of the hardware :

- 3 cycl es for a couple of pilots- 5 cycl es for the uncooled panel

- The C/ SiC pilots facilitate early ignition of thepilot fuel relative to metallic water cooled pilots.- The C/ SiC pilots increase the pressure rise of thecombustor and this is believed due to increasedcombustion efficiency within the pilots due to noactive cooling.

Based on test at Mach 7/750 psf dynamicpressure, and long duration leading edges tests,there is a high degree of confidence that pilots anduncooled panel would maintain structural integrityup to Mach 8/1500 psf (end of acceleration).

JCS program, joining UTC experience inscramjets and SNECMA's in high temperaturecomposites, allowed to make a great step towards alightweight combustor preserving high thermalmargins even at high mach number and dynamicpressure.

AC3 PROGRAM OBJECTIVES

As the JCS program permitted to demonstrate thecapacity of Snecma Sepcarbinox® material towithstand the entrance and exit condition of thecombustion chamber, it was identi fi ed to then focuson the other main technological challenge, the fuelheat exchanger panels of the combustion chamber,where worst thermomechnanical loads occur. Theheat exchanger both cooled down the walltemperature of the chamber and heats and cracksthe kerozene inside the panel to permit an easiercombustion

The AC3 program, a DGA-USAF fundedcooperation between ONERA, P&W, SnecmaPropulsion Solide, USAF-AFRL and UTRC, wasdefined to develop and validate a composite heatexchanger design which would be compatibl e of thescramjet engine requirements.

The chosen design consists of SnecmaSepcarbinox C/ SiC structures, the heat exchangeareas being built by the brazing of two CMC panelstogether : The hot side panel presents machinedgrooves to enable the circul ation of fuel as close aspossible to the combustion chamber, the "cold" sideCMC panel presents integrated mani folds machinedin the cross-direction of the grooves.

This design is very flexible, permitting to integrateparietal injection, and permitting to shape thegrooves cross section and route to meet both fuelheating requirements and local thermal constraints.In-pl ane or angular panels could then be assembledtogether or with uncooled CMC panels to form afully composite and weight efficient compositeengine.

Fig 19 – AC3 concept with parietal injection

Validation logic

Prior to the manufacturing of large heat exchangerpanels and to their testing in scramjet facilities, itwas decided to focus on reduced scal e panels and tothermal test them in a radi ant facility.

The reduced scale panel was nevertheless with arepresentative geometry concerning the thickness,and the si ze and shape of the grooves, permitting toreproduce the local behavior of a bigger size panel.The relatively small size of the samples permittedto multiply the number of samples to tune andselect the manufacturing routes, identified aspossibly applicable.

The choice of the USAF-AFRL radiant facilitypermitted to get the maximum security level inusing kerozene with hot envi ronment as all the testswere performed under inert atmosphere.Moreover radiant test beds are abl e to perform longduration, well calibrated and instrumented thermalenvironment testing : (contrary to most scramjetengine test-beds, which only offer short durationcombustion cycles.) Thus they permit the validationof the prediction codes, reaching equilibriumconditions.

15 mini-panels with three grooves weremanufactured to assess and develop the differentroutes envisaged. The tightness of the systemappeared as the most critical point, as commonlyused CMC materi als present important porosity andmatrix cracks. An innovative manufacturing routewas down-selected leak-free route and wassuccessfully tested with circulating fuel at servicepressure under up to 1.21 MW/m² incident heatflux.

Since then, 3 additional leak-free mini-panels weremanufactured, confirming the repeatability of theprocess.

Fig 20 – AC3 C-SiC leak-tight mini-panel

The next phases of the program will be focusing on- tests with increased heat flux, using

- Onera ATD5 scramjet test bed- Odeillo sol ar radi ant test facility

-scaling-up the technology, to manufacture and testbigger parts

Fig 21 – 15"x6" AC3 , C- SiC panel

The phase 2 of AC3 program will be dedicated in2004 to the manufacture and test on ONER A ATD5hypersonic test bed of a section of chamber tovalidate the concept of assembly of 4 activelycooled panels in representative Scramjet conditions

Fig 22 – Scramjet section of combustion chamber

CONCLUSIONS

Snecma Propulsion Solide has demonstrated itscapacity to develop and produce complex thermo-structural parts for aerospace appli cations, using itsC-C or C-SiC materials.The last results were the manufacture of totallyleak-free composite heat exchangers which weretested in relevant conditions for scramjetapplication. This is opening new possibilities forthe design of combustion chambers or nozzles.The developments implemented during the JCS andAC3 programs are giving the different technologykey elements which should permit to build an allC-SiC composite combustion chamber for ascramjet engine , thus giving a significantadvantage in term of weight and efficiencycompared to metallic designs.

REFERENCES

(1) Carbon-Carbon Extendible Nozzles,M. Lacoste, A. Lacombe, P. Joyez SEP &R.A.Ellis, JC Lee, FM. PaynePratt&Whitney IAF-97-S.2.04 Turin Oc t97

(2) Carbon-Carbon Nozzle Extension forthe RL10B-2 rocket Engine, R.A. EllisPratt & Whitney , M. LacosteSNECMA/SEP IAF-99-S.2.06 oct 99AMSTERDAM

(3) Application des matériauxthermostructuraux aux chambres decombustion pour statoréacteursD.CRAPIZ SEP AGARD – 79 th

Symposium of the energetics panel onairbreathing propulsion for missilesand projectiles. May 11-15, 1992

(4) Towards an all composite scramjetcombustor - .G. Uhrig , JM. Larrieu Snecma PropulsionSolide AIAA 2002-3883 Indianapolis Jul2002

(5) Direct Fuel Cooled CompositeStructureD. G. Medwick – J.Castro, Pratt&Whitney,D.R. Sobel UTRC, G. Boyet OneraJ.P. Vidal Snecma Propulsion SolideAIAA SL-233/USA-54