Sonderforschungsbereich/Transregio 40 Annual Report 2016 311

Characterization of a Multi-Injector GOX-GCH4Combustion Chamber

By S. Silvestri , H. Riedmann , O. Knab and O. J. Haidn Lehrstuhl fr Turbomaschienen und Flugantriebe Extraordinariat Raumfahrtantriebe, Technische

Universitt MnchenBoltzmannstr. 15, 85748 Garching b. Mnchen

Todays high performance liquid propellant rocket engines for transfer into orbit andspace exploration are mostly based on well-established cryogenic propellant combina-tions like liquid oxygen/liquid hydrogen (LOX/LH2), due to their high specific impulse.The potential of using hydrocarbon as propellant, in particular methane instead of hy-drogen, is under active consideration since it could be a solution for the high operationalcosts. In the context of the national research program Transregio SFB/TRR-40, sub-project K1, the Institute of Flight Propulsion (LFA) of the Technische Universitt Mnchen(TUM) and the Combustion Devices Department of Airbus Safran Launchers carry outexperimental and numerical investigations on heat transfer and injector characterizationat application-relevant combustion pressures and temperatures. In the current studyresults from an experimental investigation on an oxygen/methane multi-injector com-bustion chamber are presented. They provide detailed information about the thermalloads at the hot inner walls of the combustion chamber at representative rocket engineconditions and pressure ranges up to 40bar. The present study aims to contribute to theunderstanding of the thermal transfer processes and of interacting behavior betweenthe injectors and injector-wall. Due to the complex flow phenomena linked to the useof cryogenic propellants, like extreme variation of flow properties and steep tempera-ture gradients, in combination with intensive chemical reactions, the problem has beenpartially simplified by injecting gaseous oxygen and gaseous methane. Numerical sim-ulations performed by the Combustion Devices Department of Airbus Safran Launcherswill accompany the experimental work and help for a better understanding of the testresults.

1. IntroductionHydrocarbon propellants are attractive in the space propulsion field due to their ease

in handling and low operational costs. In particular, oxygen/methane is one of the mostpromising hydrocarbon propellant combination since it features high specific impulse,low coking tendency and good performance. The design and optimization of liquid rocketengines using methane require a detailed knowledge and understanding of the dominat-ing physical phenomena of propellant injection, combustion and heat transfer. Already

Institute of Turbomachinery and Flight Propulsion Division Space Propulsion, Technische Uni-versitt Mnchen (TUM), Germany

Airbus Safran Launchers, Mnchen, Germany

312 S. Silvestri, H. Riedmann, O. Knab & O. J. Haidn

in the 80s, oxygen/methane propellants have been examined for high chamber pres-sure boost phase engine applications [1] and this fluid combination has been studied byseveral research teams in the US Space program [2] as well in Russia [3] and in Eu-rope [4]. Recently, the interest for this propellant combination has arisen. European andRussian industries cooperate to conceive a LOX/CH4 engine for booster applications.Jaxa [6] conducts hot-firing test on a LOX/CH4 rocket engine for an upper stage system.Perdue University [7] focuses the attention on LOX/CH4 expander cycle engines. How-ever, the new propellant combination brings new challenges and the knowledge in oxy-gen/methane combustion, flame stabilization and injector design criteria need a wide-range of experimental and analytical database. Because the combustor performance ofliquid rocket engines is strongly influenced by both the geometry of the injector and theinjector interactions, the injector design is very crucial in the rocket engine development.In the context of the national research program Transregio SFB/TRR-40 on Technolog-ical Foundation for the design of thermally and mechanically high loaded componentsof Future Space Transportation System, a multi-injector combustion chamber has beendesigned for gaseous oxygen (GOX) and gaseous methane (GCH4) focusing on highpressure (up to 100bar) and film cooling behavior. One of the key aspects of the projectis to improve the knowledge on heat transfer processes and cooling methods in the com-bustion chamber, which is mandatory for the engine design. The attention is focused, inparticular, on injector-injector and injector-wall interaction. In order to have a first char-acterization of the injectors behavior, the multi-element combustion chamber is testedat low combustion chamber pressures and for a wide range of mixture ratios.

2. Test specimen and experimental configurationAll the experiments have been performed at the Institute of Flight propulsions test

facility at the Technical University of Munich (TUM). The test bench allows experimentswith gaseous methane and gaseous oxygen for designed interface pressures up to100bar. In this section a brief description of the multi element rocket combustion cham-ber, the injector geometry, the measurement equipment and data analysis proceduresare presented.

2.1. Hardware description

The multi-element rocket combustion chamber, having an inner diameter of 30mm anda contraction ratio of 2.5, is designed for pressure levels up to 100bar and a maximumcombustion temperature of 3600K. In order to easily scale the chamber with the in-jector dimensions, the distance between the injectors and the injector-wall distance iskept constant and equal to half of the injector diameter, which leads to a pattern ofseven injector elements. The combustion chamber, depicted in Fig. 1, comprises mainlyfour cylindrical water cooled chamber segments, a long and three short segments, foran overall length of 341mm. The long segment, in the first position, is equipped withrectangular cooling channels like in typical rocket engine designs, in order to provide agood comparability to full scale applications. The other segments feature instead roundcooling channels. The modular setup simplifies changes in chamber length or hardwareconfigurations. The maximum L* achieved is 906mm. The chamber sections are tight-ened together by eight tie-rods. Hydraulic nuts are mounted before the injector headand by a compensation reservoir the clamping force adapts to the thermal elongationof the chamber. The injector head of the combustor is designed to allow different injec-tor designs. For the current study, shear coaxial injector elements are integrated. For

Characterization of a Multi-Injector Chamber 313

FIGURE 1. Combustion chamber schematic.

FIGURE 2. Scheme of the injector

GOX diameter Di [mm 4GOX post wall thikness w [mm 0.5GOX post reess R [mm 0GCH4 diameter Do [mm 6Injetor area ratio AGCH4/AGOX [- 0.7

TABLE 1. Injector dimensions.

simplicity as initial configuration the GOX post is mounted flush with respect to the in-jection face. In order to centre the GOX post in the faceplate, the injector is equippedwith four equally-spaced fins. The fins are oriented in a radial direction, pointing towardsthe central injector. Fig. 2 shows a sectional drawing of the injector and Tab.1 gives themain characteristic dimensions. To ensure homogeneous injection conditions, in termsof temperature and pressure, two porous plates are placed in the oxidizer and fuel man-ifold respectively.

2.2. Experimental setup

The experimental setup is equipped with standard instrumentations required to charac-terize the operation of the chamber. A pattern of pressure transducers provides mea-surement of the wall pressure distribution along the chamber axis and gives informationabout the acceleration of the hot gas hence on the heat release. WIKA A10 pressuretransducers are used to record the axial evolution of the static chamber wall pressure(PC101...PC113). The pressure sensors are individually calibrated and operated at adata acquisition rate of 100Hz. KISTLER type 6053BB60 dynamic pressure transduc-ers, installed in the oxidizer feed line, in the fuel injector manifold and in the combus-

314 S. Silvestri, H. Riedmann, O. Knab & O. J. Haidn

FIGURE 3. Thermocouple first segment, azimuthal and axial position.

Thermoouples position A B C D E G

Distane from the hot gas side 0.7 1.5 5 10 1 3

TABLE 2. Injector dimensions.

tion chamber wall near the faceplate, are operated with a sample rate of 20 kHz. Todescribe the injection conditions, temperature and pressure of the injected propellantsare recorded upstream the injector after the porous plates. To determine the tempera-ture field, the chamber segments are equipped with 90 type T thermocouples spring-mounted in the chamber wall. The spring loading of the thermocouples will provide aconstant force to ensure a continuous contact between the thermocouples tip and thebase of the hole [11]. This setup aims to minimize the chance of potential loss of contactcaused by expansion and contraction of the material due to changes in temperature orvibrations during the hot run. In the first segment the thermocouples are mounted onfour azimuthal positions to monitor the behaviour of two adjacent external injectors andthe one positioned at the centre of the chamber. Moreover, a regular pattern along thechamber axis provides information about the progress of combustion, see Fig. 3.

In order to be able to reconstruct the temperature field in the chamber material, ther-mocouples are placed at four different radial positions (A,B,C,D). In the short segmentsthe thermocouples are installed on six azimuthal positions to have a complete map ofthe external injector behaviour, see Fig. 4. The temperature field in the chamber mate-rial is reconstructed by thermocouples posi