cars diagnostics of solid propellant combustion at elevated pressure

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  • This article was downloaded by: [Monash University Library]On: 11 September 2013, At: 00:26Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

    Combustion Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/gcst20

    CARS Diagnostics of Solid Propellant Combustion atElevated PressureJohn H. Stufflebeam a & Alan C. Eckbreth aa United Technologies Research Center, East Hanford, CT 06108, USAPublished online: 06 Apr 2007.

    To cite this article: John H. Stufflebeam & Alan C. Eckbreth (1989) CARS Diagnostics of Solid Propellant Combustion atElevated Pressure, Combustion Science and Technology, 66:4-6, 163-179

    To link to this article: http://dx.doi.org/10.1080/00102208908947147

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  • Combust. Sci. and Tech., 1989, Vol. 66, pp. 163-179Reprints available directly from the publisherPhotocopying permitted by license only

    Gordon and Breach Science Publishers. Inc.Printed in Great Britain

    CARS Diagnostics of Solid Propellant Combustion atElevated Pressure

    JOHN H. STUFFLEBEAM and ALAN C ECKBRETH United TechnologiesResearch Center, East Hanford, CT 06108, USA

    (Received March 29, /989; in final form June 29, 1989)

    Abstract-The first CARS measurements of temperature and species concentrations in the exhaust of solidpropellants burning at elevated pressure (,,; 35 atm) are reported. Multiple species data are acquired at hightemporal (10 ns) and spatial resolution from both a homogeneous, double-base and a composite nitraminepropellant. CARS spectra have been obtained from three spectral regions that encompass the signaturesof the major combustion products, CO" CO-N, , and H20. The CARS data are analyzed by comparisonwith computer synthesized spectra generated at various temperatures and species concentrations. Resultsin the postflame zone from nitramine combustion at 23 atm indicate temperatures as high as 2600 K withspecies concentrations of N2 ........ 23%, CO ........ 36%, and H2 ........ 23%. These results compare favorably withpredictions of temperature and concentration from a chemical equilibrium code that simulates thecombustion parameters. Utilization of dual broadband approaches will allow the simultaneous acquisitionof data from the three spectral regions with each laser pulse.

    INTRODUCTION

    Knowledge of combustion species and temperature is necessary for accurate modelingof solid propellant reaction mechanisms and their effect on the macroscopic behaviorof the propellant. Simultaneous, multiple species measurements provide informationon dominant kinetic processes and provide data for comparison with combustionmodels, Diagnostics of solid propellant combustion are extremely difficult because theprocess is transient, the combustion gases are turbulent, often particle-laden and theflame zones are very thin.

    Various approaches have been pursued to circumvent the experimental complexitiespresented by solid propellant combustion. Model flames have been used (Branchet al., 1987; Thorne et al., 1986; Vanderhoff et al., 1986) but they may not preciselysimulate an actual burning solid propellant. Propellants have been burned at lowpressure to expand the reaction zones (Aron and Harris, 1984), but low pressurecombustion may not follow the same routes and branches as at high pressure(Westbrook, 1984), Considerable benefit is likely to be derived from experiments onsolid propellants burning under actual design conditions. Initial diagnostics includedimbedded thermocouples (Kubota et aI., 1974) to measure temperature gradients atfixed points perpendicular to the solid propellant surface. They may perturb the flame,require extensive interpretation to yield valid results (Miller et al., 1984),and moreover,provide no information about the molecular constituents. Optical techniques offer thegreatest potential for these studies, but even their qualities of high spatial resolutionand potential multiple species measurements are strained for applications such as this.Emission (Edwards et al. 1986a; Mal'tsev et aI., 1973) and absorption (Vanderhoff,1988; Bent and Crawford, 1959) experiments are line of sight which makes interpre-tation difficult. Laser-induced fluorescence (LIFS) has been used for identification ofselect radicals (Parr and Hanson-Parr, 1987; Edwards et al., I986b) but generally onlyone species at a time is interrogated. Analysis of LIFS data is difficult becausequenching rates are often not known to sufficient accuracy for the high pressure

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  • 164 J. H. STUFFLEBEAM AND A. C. ECKBRETH

    environments typical of solid propellant combustion. Nevertheless, it is the preferredapproach for measurement of the minor constituents. Of the various laser-opticaltechniques for major species, CARS appears best suited to solid propellant com-bustion and, indeed, has been applied to low pressure solid propellant studies (Aronand Harris, 1984). CARS is not affected by quenching, is fast (10- 8 s), non-intrusive,spatially precise and able to measure temperature and major species concentrationssimultaneously with each laser pulse.

    This paper presents the initial results of experiments that apply CARS diagnosticsto elevated pressure solid propellant combustion and describes measurements oftemperature and species concentrations from such data. The next section brieflyreviews the principles of CA RS, followed by an outline of the experimental arrange-ment. Selected CA RS spectra are presented and estimates of temperature and majorspecies concentration are obtained from comparisons with computer synthesizedspectra. A discussion of the results then follows and future directions for this researchare indicated.

    TECHNICAL BACKGROUND

    Solid Propellant CombustionSolid propellant combustion presents unique experimental challenges. Unlike gas orliquid fuel combustion, there is no control of stoichiometry after ignition, nor is thereany control of fuel or oxidizer flow rate. The sample consumes itself in a relativelyshort time, restricting the data acquisition process. The data are then compared topredictions based on the components used to prepare the propellant formulation.Theoretical mechanisms (Fifer, 1984; Melius, 1988) predict what the products shouldbe and form the basis for experimental design. The propellants investigated in ourexperiments produced equilibrium products such as CO" CO, N" H, and H,O.Additionally chemical mechanisms may be inferred if some intermediate species areobserved and insight is obtained as well, if particular molecules are not observed.Some of the intermediate species that are predicted for the propellants studied hereare NO" NO, HCN, N,O and H,CO. The major Raman resonant frequencies forthese molecules are listed in Table I. The experiment should be designed to observeas many of these species as possible, all simultaneously.'

    It is also necessary to execute the experiments at elevated pressure, for the reasonsalready cited. Chemical equilibrium codes (Gordon and McBride, 1976) are useful forpredicting the temperature and final product distributions at pressures of interest.This has been done for the propellants used in our studies and the results are presented

    TABLE IRaman resonances

    NO, 1320cm- JCO, 1388NO 1876HCN 2097CO 2143N,O 2223N, 2331H,CO 2780H,O 3657H, 4161

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  • CARS DIAGNOSTICS OF PROPELLANTS 165

    TABLE IIEquilibrium calculations of propellant combustion

    Mole fraction (%)Pressure Temperature

    Propellant (atm) (K) CO, CO H, N, H,O

    NOSOL 436 20 2405 8.6 41.2 17.3 11.2 2l.1HMXjTMETN 20 2627 5.0 34.2 18.8 23.9 17.6

    in Table II. The NOSaL 436 is a homogeneous double-base propellant and HMX/TMETN is a composite nitramine. Calculations are presented for just one pressure,close to that of our experiments. The equilibrium values are quite insensitive tovariation of this parameter; changes in pressure by a factor of 2 have little effect(,,; 0.5%) on the results in the table.

    High Pressure CARSCARS results from a laser photon at frequency w, scattering off an excited Ramancoherence, WR, of the probed medium.

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