Tech Briefs Magazine - March 2022 - 40

Propulsion
ry but had not been successful due to the
chemical propellants used or the ways they
were mixed. Previous work by the research
team overcame this problem by carefully
balancing the rate of the propellants
hydrogen and oxygen released into the
engine to create the first experimental evidence
of a rotating detonation.
The short duration of the detonation,
often occurring for only microseconds
or milliseconds, makes them difficult
to study and impractical for use. The
researchers, however, were able to sustain
the duration of a detonation wave
for three seconds by creating a new hypersonic
reaction chamber, known as a
hypersonic high-enthalpy reaction (HyperREACT)
facility. The facility contains
a chamber with a 30-degree-angle ramp
near the propellent mixing chamber that
stabilizes the oblique detonation wave.
Next steps for the research are the addition
of new diagnostics and measurement
tools to gain a deeper understanding of the
phenomena. The team will continue exploring
more experimental configurations
to determine in more detail the criteria
with which an oblique detonation wave can
be stabilized. If successful in advancing this
technology, detonation-based hypersonic
propulsion could be implemented into human
atmospheric and space travel in the
coming decades.
For more information, contact Rachel
Williams at Rachel.Williams@ucf.edu; 321443-3284.
Simple,
Fuel-Efficient Rocket Engine for Cheaper, Lighter
Spacecraft
The engine could make rockets not only more fuel-efficient, but also more lightweight and
less complicated to construct.
University of Washington, Seattle, WA
S
ending NASA's Space Shuttle into orbit
required more than 3.5 million pounds
of fuel, which is about 15 times heavier
than a blue whale. But a new type of engine
- called a rotating detonation engine
- promises to make rockets not only
more fuel-efficient, but also more lightweight
and less complicated to construct.
The engine, however, is too unpredictable
to be used in an actual rocket.
Researchers have developed a mathematical
model that describes how these
engines work. With this information, engineers
can develop tests to improve these
engines and make them more stable.
A conventional rocket engine works
by burning propellant and then pushing
it out of the back of the engine to create
thrust. A rotating detonation engine takes
a different approach to how it combusts
propellant. It's made of concentric cylinders.
Propellant flows in the gap between
the cylinders and after ignition, the rapid
heat release forms a shock wave - a strong
pulse of gas with significantly higher pressure
and temperature that is moving faster
than the speed of sound. This combustion
process is literally a detonation - an explosion
- but behind this initial startup
phase, a number of stable combustion
pulses form that continue to consume
available propellant. This produces high
pressure and temperature that drive exhaust
out the back of the engine at high
speeds, which can generate thrust.
Conventional engines use a lot of maThe
experimental rotating detonation engine (shown here) allowed researchers to control different
parameters, such as the size of the gap between the cylinders. The feed lines (right) direct the propellant
flow into the engine. On the inside, there is another cylinder concentric to the outside piece.
Sensors sticking out of the top of the engine (left) measure pressure along the length of the cylinder.
The camera would be on the left-hand side, looking from the back end of the engine. (Photo: James
Koch/University of Washington)
40
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chinery to direct and control the combustion
reaction so that it generates the work
needed to propel the engine. But in a rotating
detonation engine, the shock wave
naturally does everything without needing
additional help from engine parts.
To describe how these engines work,
the researchers first developed an experimental
rotating detonation engine
in which they could control different
parameters, such as the size of the gap
between the cylinders. Then they recorded
the combustion processes with a highspeed
camera. Each experiment took
only 0.5 second to complete but the researchers
recorded these experiments at
240,000 frames per second, so they could
see what was happening in slow motion.
From there, they developed a mathematical
model to mimic what they saw in the
videos. The model allowed them to determine
whether an engine of this type
would be stable or unstable and allowed
them to assess how well a specific engine
was performing.
For more information, contact Sarah
McQuate at smcquate@uw.edu; 206-543-2580.
Tech Briefs, March 2022
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Tech Briefs Magazine - March 2022

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