Copyright 2000 American Institute of Aeronautics and Astronautics, Inc.; All Rights Reserved Aerospace America
December, 2000
SECTION: THE YEAR IN REVIEW; Propulsion and Energy; Pg. 50
LENGTH: 627 words
HEADLINE: Propellants and combustion
BYLINE: by John Buckmaster and Joseph Powers
BODY: The Dept. of Energy funds several university centers as part of its nuclear weapons stewardship program. Each is addressing a computational problem with a complexity comparable to that of nuclear explosion simulation. The problem being examined by the Center for the Simulation of Advanced Rockets (CSAR) at the University of Illinois at Urbana-Champaign is the simulation of the Space Shuttle's solid rocket boosters. CSAR's combustion and energetic materials group is responsible for modeling the combustion of the heterogeneous propellant and the interaction of the combustion processes with chamber flow events and with mechanical events (such as crack propagation) in the propellant.
An important step was taken this year in defining a packing algorithm that generates a model for the propellant morphology characterized by spherical particles of ammonium perchlorate imbedded in a fuel binder. When size distributions measured by Thiokol are used in the packing algorithm, packing fractions (volume fraction of perchlorate) are generated that agree closely with industrial data.
Model propellants defined in this way support a complex 3D combustion field. Preliminary calculations have dealt with simplified 2D models in which the propellant has the form of either a periodic sandwich or a random pack of various-sized discs. For the first time, such calculations account for complete coupling between the gas phase and the condensed phase, and for the unsteady nonplanar regression of the propellant surface. The ultimate goal is the ab initio prediction of propellant burning rates under a variety of conditions.
The University of Illinois program will be successful only if a sophisticated knowledge of propellant kinetics is acquired. In a cooperative effort by scientists at Yale University, Penn State, and the China Lake Naval Air Warfare Center (a program now formally linked to the University of Illinois effort), fundamental experimental and numerical studies are under way to generate this knowledge. Simple flame configurations, such as that defined when a jet of fuel (methane or ethylene, for example) is blown against a slab of ammonium perchlorate, permit detailed measurement of the flame structure and its numerical simulation using complete kinetic schemes. Excellent agreement between theory and experiment is achieved. The ultimate goal is to study the reactions of HTBP decomposition products with ammonium perchlorate.
Research at the University of Notre Dame, in collaboration with the Los Alamos National Lab, is focused on developing a wavelet adaptive multilevel representation combined with intrinsic low-dimensional manifolds to efficiently address combustion problems that have a large range of length and time scales. The methods have been used successfully to resolve a fully viscous detonation in a hydrogen-oxygen-argon system. They are being applied to model gas-phase kinetics in combustion of solid explosives, as well as other problems. Intrinsic low-dimensional manifold strategies are likely to be of value to CSAR when it exploits the Yale consortium results.
Scientists in the Air Force Research Lab's Propulsion Directorate were awarded U.S. Patent 5919710 for an "Optical Technique for Quantitating Dissolved Oxygen in Fuel." This patent is for a laser-based instrument that provides continuous, noninvasive quantification of dissolved oxygen in aviation fuel.
Engineers at ALSTOM Power in Baden, Switzerland, have developed a new passive combustion control technique that can maintain stable combustion in a laboratory-scale combustor and reduce NO[x] and CO formation. This development has the potential to extend the capability of advanced gas turbines for power generation.
GRAPHIC: Picture, A packing algorithm can be used to generate model propellant packs consisting of ammonium perchlorate spheres of various sizes imbedded in a fuel binder. This simple pack consists of 24-, 20-, and 6-mum spheres.
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