Combustion of composite propellants studied at microscopic level

November 30, 1999

CHAMPAIGN, Ill. - Researchers at the University of Illinois are investigating the microscopic combustion behavior of composite propellants, an important step in improving the performance and reliability of solid-fueled launch vehicles and high-speed interceptors.

The workhorse of solid rocket motors, composite propellants consist of a heterogeneous mixture of fuel and oxidizer - generally with the oxidizer as a crystalline material surrounded by a fuel-polymer matrix. A common example is ammonium perchlorate and hydroxyl-terminated polybutadiene binder.

"Ammonium perchlorate has been used in solid propellants for decades, and hydroxyl-terminated polybutadiene binder has been phased into production in the last decade, but fundamental questions remain about their combustion behavior," said Quinn Brewster, a professor of mechanical engineering at the U. of I. "Our work investigates the microscopic behavior of the propellant in a simplified geometry that allows easier measurement and comparison with theory."

To study combustion chemistry at the microscopic level, Brewster and his students first form a small propellant sandwich consisting of a layer of fuel between layers of oxidizer. The sandwich is then ignited in a laser-augmented, high-pressure combustion chamber, and the resulting reaction recorded with an intensified CCD (charge-coupled device) camera.

"An optical chopper permits the sequential acquisition of two nearly simultaneous images - one of the flame emission alone, the other with the sample backlit with an ultraviolet source," Brewster said. "A narrowband filter rejects most of the light except that given off by excited hydroxyl molecules."

By studying the CCD images, the researchers were able to examine how the combustion behavior of propellant sandwiches varied with pressure and oxidizer width. "We found that the burning rate increased and the flame enlarged at high pressures," Brewster said. "Increased pressure and wider oxidizer layers also tended to cause the flame to split."

Through parallel computational simulation studies, the researchers further explored the flame structure and energy-transfer characteristics of the combustion reaction. "We used a two-reaction model where the oxidizer is allowed first to react and form an intermediate species which then combines with the fuel in the second reaction," Brewster said. "This double-reaction sequence provides a simple approximation of the complex flames seen in our laboratory experiments."

The simulation shows an initial flame and two leading-edge flames forming over the oxidizer portion of the propellant. "The initial flame splits due to the influence of these two edge flames, which are anchored close to the surface," said Brewster, who presented his team's findings at the Joint Army, Navy, NASA, Air Force (JANNAF) meeting in Cocoa Beach, Fla., on Oct. 22. "The edge flames provide additional heat which raises the reaction rate of the initial flame."
-end-


University of Illinois at Urbana-Champaign

Related Mechanical Engineering Articles from Brightsurf:

Best practices for mechanical ventilation in patients with ARDS, COVID-19
A team from pulmonary and critical care medicine at Michigan Medicine outlines 20 evidence-based practices shown to reduce time spent on a ventilator and death in patients with acute respiratory failure and acute respiratory distress -- conditions that have many overlaps with severe COVID-19.

How cells use mechanical tension sensors to interact with their environment
In a painstaking experiment, scientists suspended a single protein filament between two microscopic beads.

Mechanical forces of biofilms could play role in infections
Studying bacterial biofilms, EPFL scientists have discovered that mechanical forces within them are sufficient to deform the soft material they grow on, e.g. biological tissues, suggesting a ''mechanical'' mode of bacterial infection.

How mechanical forces nudge tumors toward malignancy
Researchers studying two forms of skin cancer identified a long-overlooked factor determining why some tumors are more likely to metastasize than others: the physical properties of the tissue in which the cancer originates.

Building mechanical memory boards using origami
Origami can be used to create mechanical, binary switches, and in Applied Physics Letters, researchers report the fabrication of such a paper device, using the Kresling pattern, that can act as a mechanical switch.

Not just light: The sensitivity of photoreceptors to mechanical stimuli is unveiled
''We thought we knew almost everything about photoreceptors, but we have proved that is not the case''.

A mechanical way to stimulate neurons
Magnetic nanodiscs can be activated by an external magnetic field, providing a research tool for studying neural responses.

Cell removal as the result of a mechanical instability
Researchers at Kanazawa University report in the Biophysical Journal that the process of cell removal from an epithelial layer follows from an inherent mechanical instability.

Researchers demonstrate transport of mechanical energy, even through damaged pathways
Researchers from the University of Illinois at Urbana-Champaign's Grainger College of Engineering have experimentally demonstrated a new way to transport energy even through wave-guides that are defective, and even if the disorder is a transient phenomenon in time.

Tissues protect their DNA under mechanical stress
Nuclei and genetic material deform.

Read More: Mechanical Engineering News and Mechanical Engineering Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.