# Not Just Another Old Flame

**NASA scientists are studying spiral-shaped flames on Earth to
understand how fire behaves in space.**

May ZZ, 2000 \-- The forms of flames on Earth are familiar to everyone.
We all know what a burning match, candle, fireplace or blowtorch look
like \-- or a burning building, or rocket ignition blast. The presence
of gravity and the effects of air or gas movement, plus the type of fuel
and oxidant, determine everything from a flame\'s shape and temperature
to burn rate, burn pattern, soot deposition and how fast it will or
won\'t be extinguished.

\"But in the microgravity of space, we are not dealing with just another
old familiar flame,\" says Dr. Vedha Nayagam of NASA\'s National Center
for Microgravity Research on Fluids and Combustion at the Glenn Research
Center (GRC) in Cleveland, OH, where the nature of combustion in space
is being studied intently by teams of scientists.

Above: On Earth, gravity-driven buoyant convection causes a candle flame
to be teardrop-shaped (A) and carries soot to the flame\'s tip, making
it yellow. In microgravity, where convective flows are absent, the flame
is spherical, soot-free, and blue (B). \[more information\]

\"The tall spear-shaped flame on a candle, or the \"roaring hearth\"
look of bonfire-type flames, or the forced-air look of a rocket or
furnace flame are very different indeed in the absence of gravity,\" Dr.
Nayagam states. \"Soot deposition, burning rates, completeness of
combustion, exhaust products and other characteristics all change
radically in space.\"

\"The absence of gravity aboard the Space Shuttle, a space station or
other space vehicle makes flames behave in ways that can be either
beneficial \-- as in microgravity manufacturing processes \-- or very
dangerous in the case of a fire in materials, chemicals or electrical
devices. It is vital to know what makes flames start and stop in null
gravity, and how flames behave while burning. The safety of NASA\'s
space crews and vehicles can depend on our knowledge of combustion in
space.\"

## Watching the Flame Go \'Round

Recently, Dr. Nayagam and Dr. Forman A. Williams of the University of
California at San Diego, a co-investigator in NASA/GRC\'s microgravity
combustion science program, came upon some startling discoveries about
flames in microgravity.

In an experiment Nayagam and Williams ignited a plastic disk a little
bigger than a CD with a blowtorch and then spun it slowly (2 to 20 rpm)
in still air. They expected to see flames burning in a horizontal
circle. Instead, the flame burned in a flat spiral pattern, with the
spiral moving in the direction opposite to the disk\'s spin. Further, as
the flames lessened their tips exhibited a meandering motion from side
to side. The shapes and motion were observed by photographing the flames
on the spinning disk at 500 frames per second to produce slow-motion
imaging.

Left: Flames on top of a disk slowly spinning in a clockwise direction
burn in a spiral headed counterclockwise. Vedha Nayagam and Forman
Williams are studying this phenomenon, which occurs both on Earth and in
microgravity, in the hopes of fully explaining the pattern with basic
physics principles.

Starting a fire at the center of a still disk is like dropping a stone
in a quiet pond, says Nayagam. It produces a flame front that moves
outward in a circle, fading as the fuel (the disk) is consumed. If you
spin the disk, then the circular flames become spiral. But the disk
doesn\'t have to be spinning to make spiral flames, Nayagam pointed out.

\"Even in still conditions \... just before circular flames extinguish,
\[the flames\] break symmetry \-- and spirals appear in the center hole
of the flames and propagate outwards in a spiral instead of in a
circular wave front,\" he explained.

\"Spiral burning could be common in the slow, swirling flows that we can
establish in a microgravity environment \-- but these results were very
unexpected in normal Earth gravity,\" added Dr. Williams. \"We want to
understand and explain the flame shapes and behavior in both
environments by using basic principles of physics, which has not yet
been done. We plan to explore further what causes the spiral flame
pattern, and what causes the tips to follow a meandering path.\"

\"It is already known that these dynamic spiral patterns appear in
certain chemical reactions, and in flames where the oxygen and a gas
fuel are pre-mixed, and in slime molds. The spirals are even in the
electrical signals of the beating human heart, and in the electrical
neuron impulses in the brain.\"

Right: The heart\'s pumping action is controlled by an electrical
conduction system comprised of a specialized network of cells within the
heart muscle tissue. Electrical signals within the heart muscle move in
a spiral. Understanding this pattern could result in a better
understanding of arrhythmias, alterations of the heartbeat. \[more
information from cardima.com\]

\"But this is the first we have known of a spiral wave front propagating
through a diffusing system with a so-called \'excitable\' static medium,
varying as changes in some parameter such as temperature pushes the
process forward. A heated surface of oxygen plus fuel (the plastic disk)
supports wave propagation in combustion flames as the oxygen and fuel
molecules diffuse to find one another.\"

Dr. Nayagam adds that all such media exhibit the same phenomena of
stretched diffusion flames in spiral form with moving tips, when the
surface is swirling as combustion occurs (\"Von Karman swirling
flows\"). The swirl speed stretches the flame, and the stretch rate
varies directly with the spin speed of the fuel disk. This
characteristic gave rise to their project\'s name: Stretched Diffusion
Flames in Von Karman Swirling Flows. The flames\' tips follow a
meandering pattern - much like a cloverleaf or flower - which increases
in length and width as the spin of the supporting disk medium increases.
At very slow spin, the spiral flames are small and the meander of their
tips is minimal. But faster spin and an increase in other factors such
as pressure (which increases buoyancy) and oxygen cause the flame
spirals to be greater and to have more tip meander.

Nayagam says it is an advantage to be able to generate the wave
propagation of these flames in the lab under normal gravity, where it is
easier to study the at much less expense than in the expensive and
infrequently available microgravity on the Space Shuttle or KC-135 in
parabolic flight.

Left: At NASA\'s Johnson Space Center, there is a microgravity research
aircraft nicknamed the \"Vomit Comet\" used to fly parabolas to
investigate the effects of \"zero\" gravity. The KC-135 is a predecessor
of the Boeing 707, which is typically used for refueling military
aircraft.

**Why Set A Spinning Disk On Fire?**

\"We need to discover how and why flames propagate in microgravity, and
under what conditions flame propagation changes. Hopefully the studies
will also explain turbulent combustion, as the swirling flow is vital to
understanding the phenomenon *called fire whorl*,\" says Dr. Nayagam.

\"Understanding these surprising phenomenon may enable scientists to
predict flame extinction and to help mitigate fire risks on Earth and in
microgravity,\" states Dr. Nayagam. \"The initial and on-going basic
reason for NASA\'s combustion studies is to learn about spacecraft fire
safety. We need to answer questions such as: what is the worst condition
for fire in a microgravity environment, and under what conditions a fire
will increase its burn rate or be extinguished. Our goals include
learning under what conditions materials in a spacecraft will or won\'t
support fire.\"

\"The bottom line\" Dr. Nayagam says \"is that this simple system of
flames on a spinning disk under variable controlled conditions
illustrates more complex systems on Earth, in spacecraft, and in the
human body.\"