Mixing fuel particles for space combustion research using acoustics
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INTRODUCTION
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A study of flame propagation and extinction of premixed flames has occupied a position of central interest in combustion science. Microgravity experimentation offers the opportunity to establish uniform quiescent clouds of particulates and to study their roles in two-phase flame propagation and extinction processes. It can be shown m that theoretical representation of the microgravity two-phase flames is far more tractable than those that are required for normal gravitational conditions. Details of combustion experiments planned for microgravity environments have been discussed elsewhere.t2] The important property of a fuel particle cloud, being quiescent and uniformly mixed, has been impossible to realize prior to the space exploration era. Gravity, turbulence properties following mixing, and free convection processes are all present deficiencies that promise to be manageable with present microgravity space laboratory facilities. This paper describes efforts to date to verify that lycopodium fuel can be adequately mixed in a standard flame tube in a near zero-gravity environment prior to proceeding to extensive combustion tests aboard the Shuttle (STS). The science requirements for the STS Particle Cloud Combustion Experiment (PCCE) listed here were used to guide the development test program conducted in the NASA Lewis Research Center microgravity facilities: (1) Distribution of particles along the tube length (concentration uniformity), within -+5 pct (2) Number of particles in given volume (equivalence ratio qb), set point --+5 pct, where qb = actual fuel-air ratio/ stoichiometric fuel-air ratio (3) Set point pressure 1.0 x l0 s Pa -+5 pct (4) Set point temperature 21 -+6 ~ (5) Air composition in tube 21 -+1 pct oxygen; 79 pct nitrogen (6) Gravity level (3 axis). Set point: 5 x 10 -4 g (nominal), stability: -+ I x 10-4 g, and recording frequency: 1 Hz.
ROBERT J. BURNS, JEROME A. JOHNSON, and ROBERT B. KLIMEK are Aerospace Engineers, National Aeronautics and Space Administration, Lewis Research Center, Cleveland, OH 44135. This paper is based on a presentation made in the symposium "Experimental Methods for Microgravity Materials Science Research" presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25-29, 1988, under the auspices of the ASM/MSD Thermodynamic Data Committee and the Material Processing Committee. METALLURGICALTRANSACTIONS A
APPARATUS
A. Experimental Test Package The test package consists of a single flame tube assembly and the instrumentation, controls, and data recorders to collect the data. The STS flight experiment will have eight flame tube assemblies representing eight fuel-air ratios (~P); and the test data will be similarly measured and recorded. Flame tube (see Figure 1). A 75 cm long by 5 cm diameter flame tube was designed to represent a standard 100 cm flame tube because of space limitations on the STS. Lexan was chosen for the tube walls because of its nonfragile properties along with its light transmitting characteristics needed by the l
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