Tech Briefs Magazine - August 2022 - 35

result is an aircraft with increased performance
and fuel efficiency.
NASA is actively seeking licensees to
commercialize this technology. Please
contact NASA's Licensing Concierge at
Agency-Patent-Licensing@mail.nasa.gov
or call at 202-358-7432 to initiate licensing
discussions. For more information, visit
https://technology.nasa.gov/patent/DRCTOPS-1.
Analyses
Find Cause of Fatal Problem
in Rocket Engine Combustors
Advanced analyses shed light on the mechanism of a deadly
problem plaguing combustion chambers in rocket engines.
Tokyo University of Science, Japan
A
vital piece of gas engines, combustors
- the chambers in which the combustion
powering the engine occurs - break
down due to fatal high-frequency oscillations
during the combustion process. Using
advanced time-series analyses based on
complex systems, researchers have found
what causes them, opening up novel paths
to solving the problem.
Rocket engines contain confined combustion
systems that are essentially combustion
chambers. In these chambers, nonlinear
interactions among turbulent fuel and
oxidizer flows, sound waves, and heat produced
from chemical reactions cause an
unstable phenomenon called combustion
oscillations. The force of these oscillations
on the body of the combustion chamber
- the mechanical stress on the chamber
- is high enough to threaten catastrophic
failure of the engine.
The researchers revealed the physical
mechanism behind the formation and sustenance
of high-frequency combustion oscillations
in a cylindrical combustor using
analytical methods inspired by symbolic dy90
81
Fuel
72
63
54
Oxidizer
Fuel
namics
and complex networks. The combustor
the team picked to simulate is one of
model rocket engines. They were able to
pinpoint the moment of transition from
the stable combustion state to combustion
oscillations and visualize it. They found that
significant periodic flow velocity fluctuations
in a fuel injector affects the ignition
process, resulting in changes to the heat
release rate. The heat release rate fluctuations
synchronize with the pressure fluctuations
inside the combustor and the whole
cycle continues in a series of feedback loops
that sustain combustion oscillations.
Additionally, by considering a spatial network
of pressure and heat release rate fluctuations,
they found that clusters of acoustic
power sources periodically form and collapse
in the shear layer of the combustor
near the injection pipe's rim, further helping
to drive the combustion oscillations.
These findings provide reasonable answers
for why combustion oscillations occur, albeit
specific to liquid rocket engines.
For more information, contact the Media
Office at mediaoffice@admin.tus.ac.jp.
ω [m/s]
300
200
100
-100
-20 -10 01020
Z [mm]
30 40
50
Representation of instantaneous flow velocity field during combustion oscillations in the combustion
chamber of a model rocket engine. The figure shows that large-scale vortex rings are produced
from the injector rim during combustion oscillations. (Image: Satomi Shima, Kosuke Nakamura,
Hiroshi Gotoda, Yuya Ohmichi, and Shingo Matsuyama)
Tech Briefs, August 2022
www.techbriefs.com
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Tech Briefs Magazine - August 2022

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