Discussion:
OK, I don't understand this, but it sounds cool: rotating detonation rockets
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Ted Nolan <tednolan>
2020-05-07 19:15:35 UTC
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Permalink
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine

A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.

As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.

"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
--
columbiaclosings.com
What's not in Columbia anymore..
Lynn McGuire
2020-05-07 22:02:35 UTC
Reply
Permalink
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
I read the article in ExtremeTech ???. They were claiming no fuel required.

Lynn
J. Clarke
2020-05-07 22:42:59 UTC
Reply
Permalink
On Thu, 7 May 2020 17:02:35 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
I read the article in ExtremeTech ???. They were claiming no fuel required.
The sciencealert site seems to have been slashdotted if it ever
existed at all.
Scott Lurndal
2020-05-07 23:00:31 UTC
Reply
Permalink
Post by J. Clarke
On Thu, 7 May 2020 17:02:35 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
I read the article in ExtremeTech ???. They were claiming no fuel required.
The sciencealert site seems to have been slashdotted if it ever
existed at all.
Might have been slashdotted. I had no problem reading the page.

It's much more nuanced than Lynn's description. Even Lynn's
excerpt from the article explicitly mentions the fuel that is
required.
Lynn McGuire
2020-05-07 23:37:16 UTC
Reply
Permalink
Post by Scott Lurndal
Post by J. Clarke
On Thu, 7 May 2020 17:02:35 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
I read the article in ExtremeTech ???. They were claiming no fuel required.
The sciencealert site seems to have been slashdotted if it ever
existed at all.
Might have been slashdotted. I had no problem reading the page.
It's much more nuanced than Lynn's description. Even Lynn's
excerpt from the article explicitly mentions the fuel that is
required.
I read another article that suggested a perpetual motion machine. I did
not quote the article.

Lynn
James Nicoll
2020-05-08 15:21:52 UTC
Reply
Permalink
Post by Lynn McGuire
Post by Scott Lurndal
Post by J. Clarke
On Thu, 7 May 2020 17:02:35 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
I read the article in ExtremeTech ???. They were claiming no fuel required.
The sciencealert site seems to have been slashdotted if it ever
existed at all.
Might have been slashdotted. I had no problem reading the page.
It's much more nuanced than Lynn's description. Even Lynn's
excerpt from the article explicitly mentions the fuel that is
required.
I read another article that suggested a perpetual motion machine. I did
not quote the article.
You understand that perpetual motion machines are bullshit and any
article that claims one exists was written by someone who is very
ignorant or a con artist?
--
My reviews can be found at http://jamesdavisnicoll.com/
My tor pieces at https://www.tor.com/author/james-davis-nicoll/
My Dreamwidth at https://james-davis-nicoll.dreamwidth.org/
My patreon is at https://www.patreon.com/jamesdnicoll
Lynn McGuire
2020-05-08 20:00:16 UTC
Reply
Permalink
Post by James Nicoll
Post by Lynn McGuire
Post by Scott Lurndal
Post by J. Clarke
On Thu, 7 May 2020 17:02:35 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
I read the article in ExtremeTech ???. They were claiming no fuel required.
The sciencealert site seems to have been slashdotted if it ever
existed at all.
Might have been slashdotted. I had no problem reading the page.
It's much more nuanced than Lynn's description. Even Lynn's
excerpt from the article explicitly mentions the fuel that is
required.
I read another article that suggested a perpetual motion machine. I did
not quote the article.
You understand that perpetual motion machines are bullshit and any
article that claims one exists was written by someone who is very
ignorant or a con artist?
Yup.

Lynn
m***@sky.com
2020-05-08 04:22:30 UTC
Reply
Permalink
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
--
columbiaclosings.com
What's not in Columbia anymore..
There is a Wikipedia article on the concept - with references - at https://en.wikipedia.org/wiki/Rotating_detonation_engine
Jaimie Vandenbergh
2020-05-08 14:21:06 UTC
Reply
Permalink
Post by m***@sky.com
Post by Ted Nolan <tednolan>
https://www.sciencealert.com/rocket-scientists-have-built-and-tested-an-impossible-engine
A type of rocket engine once thought impossible has just
been fired up in the lab. Engineers have built and successfully
tested what is known as a rotating detonation engine, which
generates thrust via a self-sustaining wave of detonations
that travel around a circular channel.
As this engine requires far less fuel than the combustion
engines currently used to power rockets, it could eventually
mean a more efficient and much lighter means of getting our
ships into space.
"The study presents, for the first time, experimental
evidence of a safe and functioning hydrogen and oxygen
propellant detonation in a rotating detonation rocket
engine," said aerospace engineer Kareem Ahmed of the
University of Central Florida.
--
columbiaclosings.com
What's not in Columbia anymore..
There is a Wikipedia article on the concept - with references - at https://en.wikipedia.org/wiki/Rotating_detonation_engine
The Sciencealert article is honest enough to include the words "If it can be
scaled up", and the Wiki entry says the 3" test rig "may make scaling the
engine design unfeasible". This is a lot more sensibly tentative than I
expect!

Cheers - Jaimie
--
Tomorrow (noun) - A mystical land where 99 per cent of all human
productivity, motivation and achievement is stored.
-- http://thedoghousediaries.com/3474
Quadibloc
2020-05-09 02:50:57 UTC
Reply
Permalink
Post by Jaimie Vandenbergh
The Sciencealert article is honest enough to include the words "If it can be
scaled up", and the Wiki entry says the 3" test rig "may make scaling the
engine design unfeasible". This is a lot more sensibly tentative than I
expect!
So I assume the 3-inch diameter test rig does not produce a useful amount of
thrust per square centimeter?

As the article noted, there were a lot of parameters that had to be just right
for the engine to provide thrust instead of blowing up, so indeed scaling it up
won't be trivial. But if the thrust per square centimeter were enough, one could
simply scale the engine up by having *more* 3-inch diameter engines.

So it might already be useful in space, where it would have things like ion
engines competing with it.

John Savard
Peter Trei
2020-05-09 15:04:02 UTC
Reply
Permalink
Post by Quadibloc
Post by Jaimie Vandenbergh
The Sciencealert article is honest enough to include the words "If it can be
scaled up", and the Wiki entry says the 3" test rig "may make scaling the
engine design unfeasible". This is a lot more sensibly tentative than I
expect!
So I assume the 3-inch diameter test rig does not produce a useful amount of
thrust per square centimeter?
As the article noted, there were a lot of parameters that had to be just right
for the engine to provide thrust instead of blowing up, so indeed scaling it up
won't be trivial. But if the thrust per square centimeter were enough, one could
simply scale the engine up by having *more* 3-inch diameter engines.
So it might already be useful in space, where it would have things like ion
engines competing with it.
John Savard
There's a video here.

It has Russian text, no subtitles, and you want to jump forward about a minute. It does
clarify the concept though.

But I still don't understand is how it saves fuel. Perhaps it gets more complete combustion while still within the engine.

Pt
Peter Trei
2020-05-09 15:10:11 UTC
Reply
Permalink
Post by Peter Trei
Post by Quadibloc
Post by Jaimie Vandenbergh
The Sciencealert article is honest enough to include the words "If it can be
scaled up", and the Wiki entry says the 3" test rig "may make scaling the
engine design unfeasible". This is a lot more sensibly tentative than I
expect!
So I assume the 3-inch diameter test rig does not produce a useful amount of
thrust per square centimeter?
As the article noted, there were a lot of parameters that had to be just right
for the engine to provide thrust instead of blowing up, so indeed scaling it up
won't be trivial. But if the thrust per square centimeter were enough, one could
simply scale the engine up by having *more* 3-inch diameter engines.
So it might already be useful in space, where it would have things like ion
engines competing with it.
John Savard
There's a video here.
http://youtu.be/EBcflqPNhCY
It has Russian text, no subtitles, and you want to jump forward about a minute. It does
clarify the concept though.
But I still don't understand is how it saves fuel. Perhaps it gets more complete combustion while still within the engine.
Pt
Hmm....

Scott Manley has a very informative Twitter thread about it.

https://twitter.com/DJSnM/status/1258765021279969281

Pt
Quadibloc
2020-05-09 15:31:14 UTC
Reply
Permalink
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it gets more complete
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just burning. That would
already seem to imply the fuel is engaging in activity more relevant to thrust.

John Savard
Quadibloc
2020-05-09 15:55:16 UTC
Reply
Permalink
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it gets more complete
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just burning. That would
already seem to imply the fuel is engaging in activity more relevant to thrust.
...oh dear, that's just silly. While one doesn't usually think of a gas stove,
say, as providing thrust, when something explodes, that's just expansion due to
heat happening quickly.

John Savard
Peter Trei
2020-05-09 16:20:55 UTC
Reply
Permalink
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it gets more complete
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just burning. That would
already seem to imply the fuel is engaging in activity more relevant to thrust.
...oh dear, that's just silly. While one doesn't usually think of a gas stove,
say, as providing thrust, when something explodes, that's just expansion due to
heat happening quickly.
John Savard
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of conditions. The only thing I can think of that makes this engine more fuel efficient is if more of the combustion products can be directed out the back of the rocket, instead of burning outside the bell in a bright flame.

Pt
Quadibloc
2020-05-10 06:13:36 UTC
Reply
Permalink
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it gets more complete
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just burning. That would
already seem to imply the fuel is engaging in activity more relevant to thrust.
...oh dear, that's just silly. While one doesn't usually think of a gas stove,
say, as providing thrust, when something explodes, that's just expansion due to
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out the back
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.

It could be that the rotating detonation rocket works better because more of the
heat goes into expanding the combustion products, thus providing thrust... and
less into heating up the rocket engine itself instead.

John Savard
p***@hotmail.com
2020-05-12 16:35:51 UTC
Reply
Permalink
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it gets more complete
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just burning. That would
already seem to imply the fuel is engaging in activity more relevant to thrust.
...oh dear, that's just silly. While one doesn't usually think of a gas stove,
say, as providing thrust, when something explodes, that's just expansion due to
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out the back
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because more of the
heat goes into expanding the combustion products, thus providing thrust... and
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.

Among liquid hydrogen/ liquid oxygen rocket engines, the Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.

Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.

Peter Wezeman
anti-social Darwinist
Ted Nolan <tednolan>
2020-05-12 16:46:58 UTC
Reply
Permalink
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno. Any time you can get a double digit percent improvment, it's a
great deal.
--
columbiaclosings.com
What's not in Columbia anymore..
Peter Trei
2020-05-13 04:26:22 UTC
Reply
Permalink
Post by Ted Nolan <tednolan>
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno. Any time you can get a double digit percent improvment, it's a
great deal.
Scott Manley has just posted a video about these


Quadibloc
2020-05-13 04:38:50 UTC
Reply
Permalink
Post by Ted Nolan <tednolan>
Post by p***@hotmail.com
If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
I dunno. Any time you can get a double digit percent improvment, it's a
great deal.
Yes, but he's not saying you can get that, only that only 15% improvement would
result if the engine was _perfect_. What you can get, therefore, can be expected
to be much less.

John Savard
Lynn McGuire
2020-05-14 01:40:17 UTC
Reply
Permalink
Post by Ted Nolan <tednolan>
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno. Any time you can get a double digit percent improvment, it's a
great deal.
The article is claiming a 25% reduction in fuel usage by the Navy:

"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."

Lynn
J. Clarke
2020-05-14 04:21:15 UTC
Reply
Permalink
On Wed, 13 May 2020 20:40:17 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Ted Nolan <tednolan>
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno. Any time you can get a double digit percent improvment, it's a
great deal.
"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."
I finally managed to access the site--there's something hosed on my
main machine but the Raspberry Pi gets in just over the same
connection. It has to be a configuration problem of some kind--I spun
up a Windows server on AWS and it was able to get in just fine too.

Anyway, I suspect that they're trying to get increased chamber
pressure by burning behind a shock wave. The "25 percent reduction"
is compared to a gas turbine, not to a conventional rocket engine.
Lynn McGuire
2020-05-14 18:44:41 UTC
Reply
Permalink
Post by J. Clarke
On Wed, 13 May 2020 20:40:17 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Ted Nolan <tednolan>
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno. Any time you can get a double digit percent improvment, it's a
great deal.
"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."
I finally managed to access the site--there's something hosed on my
main machine but the Raspberry Pi gets in just over the same
connection. It has to be a configuration problem of some kind--I spun
up a Windows server on AWS and it was able to get in just fine too.
Anyway, I suspect that they're trying to get increased chamber
pressure by burning behind a shock wave. The "25 percent reduction"
is compared to a gas turbine, not to a conventional rocket engine.
I suspect that half of the Navy ships are running aero-derivative
(variable speed) gas turbines now (SWAG). Changing the combustion
chambers to self generate pressure would decrease their fuel usage as
the compressor on the gas turbine generally uses about 1/3rd of the
generated power.

So, cutting the compressor usage by over half ? Not buying it. You
have to get the compressed air pressure up over the combustion chamber
pressure already, that can be several hundred psia at full throttle.

Lynn
Alan Baker
2020-05-14 19:05:57 UTC
Reply
Permalink
Post by Lynn McGuire
Post by J. Clarke
On Wed, 13 May 2020 20:40:17 -0500, Lynn McGuire
Post by Lynn McGuire
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the
Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno.  Any time you can get a double digit percent improvment,
it's a
great deal.
"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."
I finally managed to access the site--there's something hosed on my
main machine but the Raspberry Pi gets in just over the same
connection.  It has to be a configuration problem of some kind--I spun
up a Windows server on AWS and it was able to get in just fine too.
Anyway, I suspect that they're trying to get increased chamber
pressure by burning behind a shock wave.  The "25 percent reduction"
is compared to a gas turbine, not to a conventional rocket engine.
I suspect that half of the Navy ships are running aero-derivative
(variable speed) gas turbines now (SWAG).  Changing the combustion
chambers to self generate pressure would decrease their fuel usage as
the compressor on the gas turbine generally uses about 1/3rd of the
generated power.
So, cutting the compressor usage by over half ?  Not buying it.  You
have to get the compressed air pressure up over the combustion chamber
pressure already, that can be several hundred psia at full throttle.
And you've already shown yourself so knowledgeable about this by
imagining they were looking at this for their guided missiles...

Alan Baker
2020-05-14 05:09:00 UTC
Reply
Permalink
Post by Lynn McGuire
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the
Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno.  Any time you can get a double digit percent improvment, it's a
great deal.
"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."
You cannot read for comprehension.

The ARTICLE doesn't make that claim.

The article quotes the NAVY making that claim.

And just so you know:

The US Navy doesn't use rocket engines, so what fuel efficiencies they
can achieve literally has NOTHING to do with what efficiencies might be
achieved...

...against the most efficent ROCKET ENGINES.
Robert Carnegie
2020-05-14 15:22:30 UTC
Reply
Permalink
Post by Alan Baker
Post by Lynn McGuire
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the
Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno.  Any time you can get a double digit percent improvment, it's a
great deal.
"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."
You cannot read for comprehension.
The ARTICLE doesn't make that claim.
The article quotes the NAVY making that claim.
The US Navy doesn't use rocket engines,
I did wonder about that.

But they use rockets on 4th of July, right?
Lynn McGuire
2020-05-14 18:36:46 UTC
Reply
Permalink
Post by Robert Carnegie
Post by Alan Baker
Post by Lynn McGuire
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the
Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120 megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno.  Any time you can get a double digit percent improvment, it's a
great deal.
"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."
You cannot read for comprehension.
The ARTICLE doesn't make that claim.
The article quotes the NAVY making that claim.
The US Navy doesn't use rocket engines,
I did wonder about that.
But they use rockets on 4th of July, right?
Hmmm. I wonder what those missile guided cruisers are firing then ?

Lynn
Scott Lurndal
2020-05-14 18:55:34 UTC
Reply
Permalink
Post by Lynn McGuire
Post by Robert Carnegie
But they use rockets on 4th of July, right?
Hmmm. I wonder what those missile guided cruisers are firing then ?
I'm pretty sure they fire missiles.

Which often have rocket engines (but in the future may have
scramjets instead as they persue mach5+).
Alan Baker
2020-05-14 19:04:36 UTC
Reply
Permalink
Post by Scott Lurndal
Post by Lynn McGuire
Post by Robert Carnegie
But they use rockets on 4th of July, right?
Hmmm. I wonder what those missile guided cruisers are firing then ?
I'm pretty sure they fire missiles.
Which often have rocket engines (but in the future may have
scramjets instead as they persue mach5+).
And which have nothing to do with what the Navy is looking at rotating
detonation for:

'With its strong dependence on gas-turbine engines for propulsion, the
U.S. Navy is always looking for ways to improve the fuel consumption of
these engines. At the Naval Research Laboratory (NRL), scientists are
studying the complex physics of Rotating Detonation Engines (RDEs) which
offer the potential for high dollar savings by way of reduced fuel
consumption in gas-turbine engines, explains Dr. Kazhikathra
Kailasanath, who heads NRL's Laboratories for Computational Physics and
Fluid Dynamics.'

<https://www.nrl.navy.mil/news/releases/navy-researchers-look-rotating-detonation-engines-power-future>
Alan Baker
2020-05-14 19:03:09 UTC
Reply
Permalink
Post by Robert Carnegie
Post by Alan Baker
Post by Lynn McGuire
Post by Peter Trei
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
But I still don't understand is how it saves fuel. Perhaps it
gets more complete
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
Post by Peter Trei
combustion while still within the engine.
One thing is that the fuel actually explodes instead of just
burning. That would
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
Post by Quadibloc
already seem to imply the fuel is engaging in activity more
relevant to thrust.
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
...oh dear, that's just silly. While one doesn't usually think of
a gas stove,
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
say, as providing thrust, when something explodes, that's just
expansion due to
Post by Quadibloc
Post by Peter Trei
Post by Quadibloc
heat happening quickly.
2 H2 + O2 -> 2H2O yields a fixed amount of heat pretty much regardless of
conditions. The only thing I can think of that makes this engine more fuel
efficient is if more of the combustion products can be directed out
the back
Post by Quadibloc
Post by Peter Trei
of the rocket, instead of burning outside the bell in a bright flame.
I was thinking about it, and a different possible inefficiency occurred to me.
It could be that the rotating detonation rocket works better because
more of the
Post by Quadibloc
heat goes into expanding the combustion products, thus providing
thrust... and
Post by Quadibloc
less into heating up the rocket engine itself instead.
Typically, liquid fueled rocket engines are regeneratively cooled.
Propellants are circulated through the combustion chamber and nozzle
walls before being burned, so heat lost through these surfaces pre-heats
the propellants and the energy is recovered during combustion. Once
the engine is up to full power its temperature stabilizes.
Among liquid hydrogen/ liquid oxygen rocket engines, the
Aerojet-Rocketdyne
RL10B-2 has the highest efficiency I've seen listed. It has a specific
impulse of 465 seconds, which works out to an exhaust velocity of 14,700
feet per second, or 4,490 meters per second.
Liquid hydrogen has an energy of combustion of about 120
megajoules per
kilogram when combined with oxygen and the resulting H2O remains in
vapor form, as it does in a rocket. Burning one kilogram of hydrogen produces
nine kilograms of water vapor. If all the energy of combustion of one
kilogram of hydrogen goes into kinetic energy of the resulting exhaust,
this works out to a theoretical maximum exhaust velocity of 5,160 meters
per second, or 17,000 feet per second. This is fifteen percent higher than
with the best conventional engines, so some improvement is possible,
but not a great deal.
Peter Wezeman
I dunno.  Any time you can get a double digit percent improvment, it's a
great deal.
"If it can be scaled up, this technology could significantly lighten
rocket payloads, and reduce the costs of rocket launches, but it has
other potential applications, too. In 2012, the US Navy predicted that
rotating detonation engines could result in a 25 percent reduction in
fuel use in its ships, and shave 300-400 million of its annual US$2
billion fuel bill."
You cannot read for comprehension.
The ARTICLE doesn't make that claim.
The article quotes the NAVY making that claim.
The US Navy doesn't use rocket engines,
I did wonder about that.
But they use rockets on 4th of July, right?
Hmmm.  I wonder what those missile guided cruisers are firing then ?
Hmmmm. I wonder if missiles are a part of the "US$2 billion fuel bill"
for "fuel use in its ships" you quoted.

Navy missiles were what the article was talking about. Something you'd
have known if you'd followed the link that was attached to "In 2012" to
read this:

"With its strong dependence on gas-turbine engines for propulsion, the
U.S. Navy is always looking for ways to improve the fuel consumption of
these engines."

<https://www.nrl.navy.mil/news/releases/navy-researchers-look-rotating-detonation-engines-power-future>

It was in the first paragraph, so there was a fighting chance you might
have read that far.
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