Finding the cause of a fatal problem in rocket engine combustors

Date:
August 2, 2021
Source:
Tokyo University of Science
Summary:
A vital piece of gas engines, combustors -- the chambers in which
the combustion powering the engine occurs -- have the problem of
breaking down due to fatal high-frequency oscillations during the
combustion process. Now, through advanced time-series analyses
based on complex systems, researchers have found what causes them,
opening up novel paths to solving the problem.



FULL STORY ========================================================================== Rocket engines contain confined combustion systems, which 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. What
causes these oscillations? The answer remains to be found.


==========================================================================
Now, in a breakthrough, published in Physics of Fluids, a team including
Prof.

Hiroshi Gotoda, Ms. Satomi Shima, and Mr. Kosuke Nakamura from Tokyo
University of Science (TUS), in collaboration with Dr. Shingo Matsuyama
and Dr. Yuya Ohmichi from the Japan Aerospace Exploration Agency (JAXA),
have used advanced time-series analyses based on complex systems to
find out.

Explaining their work, Prof. Gotoda says, "Our main purpose was to
reveal the physical mechanism behind the formation and sustenance of high-frequency combustion oscillations in a cylindrical combustor using sophisticated analytical methods inspired by symbolic dynamics and complex networks." These findings have also been covered by the American Society
of Physics in their news section, and by the Institute of Physics on
their news platform Physics World.

The combustor the scientists 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 fuel injector
affect 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, the researchers 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 drive
the combustion oscillations.

These findings provide reasonable answers for why combustion oscillations occur, albeit specific to liquid rocket engines. Prof. Gotoda explains, "Combustion oscillations can cause fatal damage to combustors in rocket engines, aero engines, and gas turbines for power generation. Therefore, understanding the formation mechanism of combustion oscillations is
an important research subject. Our results will greatly contribute to
our understanding of the mechanism of combustion oscillations generated
in liquid rocket engines." Indeed, these findings are significant and
can be expected to open doors to novel routes of exploration to prevent combustion oscillations in critical engines.

========================================================================== Story Source: Materials provided by Tokyo_University_of_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Satomi Shima, Kosuke Nakamura, Hiroshi Gotoda, Yuya Ohmichi, Shingo
Matsuyama. Formation mechanism of high-frequency combustion
oscillations in a model rocket engine combustor. Physics of Fluids,
2021; 33 (6): 064108 DOI: 10.1063/5.0048785 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210802140154.htm

--- up 12 weeks, 3 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)