Author Topic: Rocket Engine Q&A  (Read 382927 times)

Offline nimbostratus

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Re: Rocket Engine Q&A
« Reply #540 on: 10/13/2014 03:56 am »
@nimbostratus

You are not supposed to read the attached file but load it into the software I provided link for :)

Chamber temperature is connected to chamber pressure. RD-170 Pc is very high, therefore the Tc is high too. IIRC only RD-180 has higher Pc among kerolox engines, the RPA tool calculates Tc nearly 3900K for it.

I run several cases on this software, it is really good for selecting the proper area ratio.

After runnig the software,I found that flow seperation stops 1st stage Hydrolox engines from adopting too big an area ratio, so both rs-25 and rd-0120 adopt the highest area ratio possible in which case flow seperation doesn't occur.

And thank you for sharing the software
« Last Edit: 10/13/2014 05:59 am by nimbostratus »
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Offline MarsMethanogen

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Re: Rocket Engine Q&A
« Reply #541 on: 10/30/2014 12:47 pm »
While is may have already been addressed somewhere in this thread, I was hoping that someone could educate me on how hypergols are used in the Antares rocket engine of launch vehicle.  My question originates from the recent launch failure and the post-event warning for civilians not to enter the area given the remnanats of hypergols, which I presume was something like a hydrazine derivative and/or N2O4.  I am aware that the first stage propellants are RP-1 and LOX, and I am aware that the second stage uses solid propellants.  So then I thought that maybe the first stage turbopumps are powered by these hypergols.  But then I found out that the first stage engines are staged combustion engines.  So hypergols wouldn't be involved here, as the gas driving the turbines are generated by using the kerolox propellants in the pre-burner.  So where are these hypergols used in this launch vehicle?  Is there an APU, conceivably used to provide hydraulic power to what I preseme might by TVC?  Please educate me here.  Thank you.

Offline kch

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Re: Rocket Engine Q&A
« Reply #542 on: 10/30/2014 12:53 pm »
While is may have already been addressed somewhere in this thread, I was hoping that someone could educate me on how hypergols are used in the Antares rocket engine of launch vehicle.  My question originates from the recent launch failure and the post-event warning for civilians not to enter the area given the remnanats of hypergols, which I presume was something like a hydrazine derivative and/or N2O4.  I am aware that the first stage propellants are RP-1 and LOX, and I am aware that the second stage uses solid propellants.  So then I thought that maybe the first stage turbopumps are powered by these hypergols.  But then I found out that the first stage engines are staged combustion engines.  So hypergols wouldn't be involved here, as the gas driving the turbines are generated by using the kerolox propellants in the pre-burner.  So where are these hypergols used in this launch vehicle?  Is there an APU, conceivably used to provide hydraulic power to what I preseme might by TVC?  Please educate me here.  Thank you.

As far as I know, they're used in the Cygnus cargo ship.

Offline MarsMethanogen

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Re: Rocket Engine Q&A
« Reply #543 on: 10/30/2014 01:00 pm »
Of course!  You're right!  I went out and read about the cargo craft and it uses hypergols in the "propellant system".  I feel so silly for limiting my thinking to the launch vehicle and not the cargo vehicle.  The use of hypergols as the propellant for the engines and the RCS is an industry standard that goes way back. 

Offline kevin-rf

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Re: Rocket Engine Q&A
« Reply #544 on: 10/30/2014 02:38 pm »
While I don't know the answer for Antares.

I do know that other launch vehicles have in the past used Hypergols in the first stage. The typical use would be roll control. Atlas IIAS, and many solids have used them for that reason.

It is also not uncommon to use them on the second stage for not only roll control, but also keeping the second stage at the correct attitude. The Antares second stage has a coast period before the solid fires. It is possible they might be used on the second stage to keep it properly oriented during the coast period.

So while Cygnus is a no brainier, they may be used in other parts on the Antares.

Also, nasty chemicals like TEA/TEB are often used to "light" the engine. While it is usually provided by the ground  support equipment, there may be some sort of tank and contaminated plumbing in what remains of the engines.

Does anyone know how toxic the battery chemistry  in launch vehicles is? The remains could easily be another source of nasty chemicals that could harm the careless.
« Last Edit: 10/30/2014 02:40 pm by kevin-rf »
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Offline mmeijeri

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Re: Rocket Engine Q&A
« Reply #545 on: 11/02/2014 03:00 pm »
Would a compressed air / helium powered turbopump be a reasonable alternative to a Flometrics-style pistonless pump?
« Last Edit: 11/02/2014 03:00 pm by mmeijeri »
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Offline Damon Hill

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Re: Rocket Engine Q&A
« Reply #546 on: 11/05/2014 01:22 am »
Silver-zinc batteries used to be popular for rocket systems; the technology may be leaning towards lithium-ion.  Eagle-Pischer has been a provider for decades.  As a rule, I don't think batteries are too much of a concern, compared to hydrazines and nitrogen tetroxide, which are the most commonly used hypergols.  There are other possible chemistries, but they are far less common.
« Last Edit: 11/05/2014 01:23 am by Damon Hill »

Offline mmeijeri

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Re: Rocket Engine Q&A
« Reply #547 on: 11/06/2014 02:07 pm »
The other day I found a partial answer to my question about compressed air turbopumps. It turns out that as early as 1941 the Russians were experimenting with compressed air turbopumps. It was only a temporary solution, and heavy, but it did work.

Rocketing Into the Future: The History and Technology of Rocket Planes

In that case, I wonder why you would ever prefer a valve-based Flometrics style pistonless pump to a compressed air turbopump, which doesn't need very reliable valves that are cycled many times. The energy density of compressed gas is similar to that of lead acid batteries, which suggests that lithium-ion or silver-zinc powered electric pumps might be even better. For high gravimetric density you could use dielectric immersion cooling, which is a mature technology and might already be in use in the automotive sector.
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Offline baldusi

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Re: Rocket Engine Q&A
« Reply #548 on: 11/06/2014 03:45 pm »
I fail to understand the conceptual difference between piston-less compressed air valve and normal pressure fed rockets.

Offline mmeijeri

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Re: Rocket Engine Q&A
« Reply #549 on: 11/06/2014 04:28 pm »
Only a small pressure vessel needs to be at high pressure, the propellant tanks themselves can be kept at low pressure. A small tank is filled with propellant from the main propellant tanks at low pressure, then the feed valve is closed, the pressurisation valve is opened, once the pressure has equalised it is closed again and then the discharge valve is opened and just before it's empty, it is closed again, and then the cycle repeats. It's a bit more complicated than that, but that's the general idea.

How the pistonless pump operates
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Offline kevin-rf

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Re: Rocket Engine Q&A
« Reply #550 on: 11/06/2014 05:39 pm »
One thing you could do to keep the weight of a pistonless system down is to generate the gas from an LN or LOX or LHe by running it through the cooling jacket of the engine. Storing it as a liquid and converting it into a gas would save a fair bit of weight on the container... Being warmed, it will also save on the amount of gas that needs to be dragged up hill.
« Last Edit: 11/06/2014 05:40 pm by kevin-rf »
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Offline MP99

Re: Rocket Engine Q&A
« Reply #551 on: 11/07/2014 07:38 am »
Only a small pressure vessel needs to be at high pressure, the propellant tanks themselves can be kept at low pressure. A small tank is filled with propellant from the main propellant tanks at low pressure, then the feed valve is closed, the pressurisation valve is opened, once the pressure has equalised it is closed again and then the discharge valve is opened and just before it's empty, it is closed again, and then the cycle repeats. It's a bit more complicated than that, but that's the general idea.

How the pistonless pump operates
Why is the pump gas vented overboard instead of being used to pressurise the main tank?

High pressure gas should be able to be vented into the main tank until it reaches a safe max pressure, then the rest vented overboard.

Cheers, Martin

Offline Proponent

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Re: Rocket Engine Q&A
« Reply #552 on: 11/07/2014 09:12 am »
The diagram shows the two pumping cylinders being the same size, but I've seen Flowmetrics diagrams in which one cylinder is about a quarter of the size of the other.  I see only disadvantages of differently-sized cylinders:

1. The need to manufacture more types of components, and
2. With the two cylinders having different cycle durations, the system generates a wider spectrum of mechanical forcings and has a higher probability of suffering a problematic resonance.

What advantage(s) of differently-sized cylinders am I missing?

Offline mmeijeri

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Re: Rocket Engine Q&A
« Reply #553 on: 11/07/2014 09:42 am »
I believe the main advantage is that the system will be lighter and more compact as a result.
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Offline R7

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Re: Rocket Engine Q&A
« Reply #554 on: 11/07/2014 10:26 am »
I believe the main advantage is that the system will be lighter and more compact as a result.

Yes.

http://www.rocketfuelpump.com/wp-content/uploads/2013/12/RocketPumpJPC2003.pdf

Quote
Instead of two similar pump chambers, it uses
one main chamber which supplies fuel for most
of the time and an auxiliary chamber which
supplies fuel for the rest of the time. The main
chamber is placed inside the tank, and it is filled
through a number of check valves so that it can
be filled quickly, thereby reducing the size of the
auxiliary chamber, which is typically one fourth
the size of the main chamber. The optimized
design offers a substantial weight savings over
the basic design, in that it uses one primary
pumping chamber and one auxiliary chamber
instead of two pumping chambers.

Wondering if the volume asymmetry also helps with avoiding bad resonances because the valving sort of "gallops" instead of steady cycling.
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Offline mmeijeri

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Re: Rocket Engine Q&A
« Reply #555 on: 11/07/2014 02:02 pm »
Here's a video of the pistonless pump in action. I don't know what to call the white things going up and down inside a cylinder, but apparently it's not 'piston'. :-)



And another one:



I love the steampunk sound of this thing!
« Last Edit: 11/08/2014 11:58 pm by mmeijeri »
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Offline kevin-rf

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Re: Rocket Engine Q&A
« Reply #556 on: 11/07/2014 03:51 pm »
The "disk" might be to prevent sloshing, ingestion of the gas, and loss of working fluid when the cylinder is vented. It may also not have a very tight fit and just float on the working fluid.

I wonder if the Flometrics definition of "piston" is it requires a rod to push it.
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Offline Proponent

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Re: Rocket Engine Q&A
« Reply #557 on: 11/07/2014 04:07 pm »
I believe the main advantage is that the system will be lighter and more compact as a result.

Yes.

http://www.rocketfuelpump.com/wp-content/uploads/2013/12/RocketPumpJPC2003.pdf

Quote
Instead of two similar pump chambers, it uses
one main chamber which supplies fuel for most
of the time and an auxiliary chamber which
supplies fuel for the rest of the time. The main
chamber is placed inside the tank, and it is filled
through a number of check valves so that it can
be filled quickly, thereby reducing the size of the
auxiliary chamber, which is typically one fourth
the size of the main chamber. The optimized
design offers a substantial weight savings over
the basic design, in that it uses one primary
pumping chamber and one auxiliary chamber
instead of two pumping chambers.

Wondering if the volume asymmetry also helps with avoiding bad resonances because the valving sort of "gallops" instead of steady cycling.

Why not have two equally-sized cylinders, each of which is filled by multiple check valves?

Offline mmeijeri

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Re: Rocket Engine Q&A
« Reply #558 on: 11/07/2014 04:22 pm »
I get the impression that the advantages over a pressure-fed system are much smaller if you don't use a gas generator / heat exchanger to supply the pressurant gas.

If I understand Wikipedia correctly the mass fraction of a pressure vessel does not improve with pressure, so I'm guessing the pressurant tank would be about as heavy as a high-pressure propellant tank, just smaller. Using a pistonless pump might reduce the mass of the propellant tank from 1M to 0.1M, but the pressurant tank would still be at 1M. So tankage in total would go from 2M to 1.1M, which is still significant of course, but only by a factor of about 2, rather than a factor of 10.

You can probably use composites for the pressurant tank however, even if the propellant isn't compatible with composites, so that might give additional efficiency.
« Last Edit: 11/07/2014 04:26 pm by mmeijeri »
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Offline Specifically-Impulsive

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Re: Rocket Engine Q&A
« Reply #559 on: 11/08/2014 10:59 pm »
Would a compressed air / helium powered turbopump be a reasonable alternative to a Flometrics-style pistonless pump?

One of the upgrades being studied for the STS was to replace the hydrazine APUs in the SRBs with a high pressure helium system that blew down through a turbine.  Don't know how far it got but it was being given serious consideration at one time (prior to STS-107).

 

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