Author Topic: The Reaction Engines Skylon Master Thread (6)  (Read 79461 times)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #520 on: 03/13/2017 09:09 AM »
So listening to the bit about electric power production made me wonder about the potential for hybrid electric propulsion. If a distributed electric propulsion element could be integrated  with the SABRE hypersonic platform it might improve takeoff noise and thrust and allow improved subsonic efficiency.
SABRE is an engine for an LV. For this to be a net win you have to factor in what the extra weight will buy you over the whole trajectory. 
Quote from: lkm 
It occurred to me that the SABRE cycle would integrate well with a a solid oxide fuel cell given that it produces high temperature hydrogen in the right temperature range and that it has excess hydrogen at points in the cycle and that the cryogenic hydrogen would be available to cool superconducting motors.
And these motors are doing what exactly?
Quote from: lkm 
A hypersonic platform that could loiter efficiently at subsonic speeds might be useful, or indeed one that could takeoff quietly and fly efficiently over land.
Then you be looking at the Scimitar work REL did for LAPCAT.
Quote from: lkm 
The question I guess is could distributed motors be integrated in such a way that they can be protected at hypersonic speeds.
Such motors would have to be integrated into the wing of the vehicle, not SABRE. Skylon's wing is sized for  high speed takeoff because that's what REL trade studies indicate is the best way to save overall weight on the whole trajectory.

The major issue with fuel cells is that they are tough if you don't have a supply of H2. Once you've a supply there are about half a dozen approaches to choose from and Skylon is H2 powered to begin with. REL expect Skylon to use fuel cells for on orbit power anyway for reasons I don't quite understand why, given that water (useful for a human crew) is just a waste product for an uncrewed vehicle that has to be either stored or vented overboard.
« Last Edit: 03/13/2017 09:14 AM by john smith 19 »
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Offline lkm

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #521 on: 03/13/2017 12:03 PM »
So listening to the bit about electric power production made me wonder about the potential for hybrid electric propulsion. If a distributed electric propulsion element could be integrated  with the SABRE hypersonic platform it might improve takeoff noise and thrust and allow improved subsonic efficiency.
SABRE is an engine for an LV. For this to be a net win you have to factor in what the extra weight will buy you over the whole trajectory.
According to REL " SABRE - Synergetic Air Breathing Rocket Engine - is a new class of engine for propelling both high speed aircraft and spacecraft." and " is well suited for a variety of potential high-speed mission areas. SABRE enables more capable high-speed vehicles able to operate within and between expansive and unique flight envelopes, which improves many critical mission characteristics. "  so from their point of view SABRE is no longer exclusively an LV engine and I was talking explicitly about their " Hypersonic Mission Applications", I highly doubt that the extra mass would pay for itself over a launch trajectory, although you never know until you caculate this stuff.
It would be an interesting question to ask REL how they see the relation between SABRE, SABRE class and Scimitar in light of where they are now with the technology and their current business model?
Do they see Scimitar as just a SABRE class engine or is it still a second generation engine?
 Given they're trying to sell SABRE as an aircraft solution do they now have higher reliability goals?

 
It occurred to me that the SABRE cycle would integrate well with a a solid oxide fuel cell given that it produces high temperature hydrogen in the right temperature range and that it has excess hydrogen at points in the cycle and that the cryogenic hydrogen would be available to cool superconducting motors.
And these motors are doing what exactly?
As I understand it current designs for next generation transport aircraft revolve around improving fuel efficiency and noise profile by increasing the effective bypass ratio through moving to hybrid electric distributed propulsion where rather than having a jet engine powering a single large bypass fan it powers a generator which feeds a large number of electric motors which collectively have a much larger bypass area than a single fan could practically have and thus have a greater efficiency at subsonic speeds. As part of this design space SOFC's are sometimes integrated into the jet engine for power generation and superconducting motors are often used for the powerful bypass fans, but without a cryogenic heat sink they aren't yet very practical.
A hypersonic platform that could loiter efficiently at subsonic speeds might be useful, or indeed one that could takeoff quietly and fly efficiently over land.
Then you be looking at the Scimitar work REL did for LAPCAT.
Again, not if you listen to what REL is saying today and if you consider Scimitar as just a SABRE class engine. The question with Scimitar was wether you could just safely leave the bypass fan to open rotor in a hypersonic airstream, perhaps with distributed propulsion you can have your subsonic fan bypass without having to leave it open to the air stream.
The question I guess is could distributed motors be integrated in such a way that they can be protected at hypersonic speeds.
Such motors would have to be integrated into the wing of the vehicle, not SABRE. Skylon's wing is sized for  high speed takeoff because that's what REL trade studies indicate is the best way to save overall weight on the whole trajectory.

The major issue with fuel cells is that they are tough if you don't have a supply of H2. Once you've a supply there are about half a dozen approaches to choose from and Skylon is H2 powered to begin with. REL expect Skylon to use fuel cells for on orbit power anyway for reasons I don't quite understand why, given that water (useful for a human crew) is just a waste product for an uncrewed vehicle that has to be either stored or vented overboard.

Skylon is just REL's reference design for a SSTO launcher, for the hypersonic mission space we've already seen BAE's single engine design and according to the lecture LM are having fun with theirs so the question is could there be a viable design that could utilise this. Perhaps with a single engine design the fans could be wrapped around the mid section shrouding its rocket exhaust with a larger mass of slower moving air providing some muffling.

Offline Soundbite

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #522 on: 03/13/2017 06:58 PM »
I have found two University Research Opportunities Programs with Cambridge University; "Designing Efficient Multi-Stage Counter Rotating Turbines for Rocket Engines" and "Super Aggressive S-shaped Ducts for Rocket Engine Compressors", see http://to.eng.cam.ac.uk/teaching/urops/projects.html. Both of them reference Reaction Engines, but I think its funded internally by Cambridge University. It gives a very brief overview of the problems, which some of you might find interesting.

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #523 on: 03/14/2017 07:10 AM »
Quote
Designing Efficient Multi-Stage Counter Rotating Turbines for Rocket Engines
Contact: Lead Supervisor: Dr. Graham Pullan Department of Engineering
Project Available

Project Description:

The concept of a counter rotating turbine has existed for almost as long as the jet engine, however in practise they are very rarely used. The idea is that instead of alternating between stationary and rotating aerofoils the machine alternates between aerofoils rotating in opposite directions.

There are many claims of much higher work output and improved efficiency compared to conventional turbines. This is often put down to the removal of the stationary vanes which are not generating any work output. Initial studies show that to achieve the increased work output previously claimed, results in very high relative blade speeds and hence high (>1) mach numbers when matched to a conventional gas turbine cycle. The high speed flow increases the loss and in reality the claims of improved efficiency are not realised.

A recent proposal for an air breathing rocket engine by Reaction Engines LTD currently includes a multi-stage counter rotating turbine linked to a conventional compressor. The reason such a design is of interest is that the turbine is operating with Helium as the working fluid, for which the speed of sound is roughly 3 times higher than air. This enables a successful CRT to operate without the performance penalty associated with high Mach numbers. However the design of such a system has been attempted only a handful of times and there is clear room for improvement.

An additional feature of multi-stage CRTs is that in an idealised infinite machine only one blade need be designed, it being employed for both rotors. This project aims to utilise this feature and the assumption of a true multi-stage machine, to simplify the problem and produce a high efficiency design for this relatively poorly understood type of machine. If a good design can be produced it is likely that generic design rules can be developed for this type of machine.

Link to Reaction Engines LTD

    Requirements: Aerodynamics modules 3A1 and 3A3.
    It is expected that the UROP should lead into a 4th year project.
    The project is being co-supervised by Dr. C. Clark , Dr. S. Grimshaw and Dr. J. Taylor
    Please contact Dr. S Grimshaw for further details or to apply.


Insertion Date: 9 March 2017

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #524 on: 03/14/2017 07:11 AM »
Quote
Super Aggressive S-shaped Ducts for Rocket Engine Compressors
Contact: Lead Supervisor: Prof. Rob Miller Department of Engineering
Project Available

Project Description:

Within a gas turbine there are often multiple shafts, which can have significantly different rotational speeds. To provide suitable blade speeds for the compressor, the radius of the annulus is sometimes changed between the two shafts. This change is performed in an interstage duct, the design of which represents an interesting engineering challenge.

It is found in practise that shorter ducts incur higher aerodynamic losses due to the increased endwall diffusion. Thus there is a trade-off for the designer between duct length and weight and aerodynamic performance. In land based gas turbines for power, where weight is not an issue, the aerodynamic performance is favoured. In an aerospace engine the trade-off is much more competitive as both weight and performance are desirable.

A recent proposal for an air breathing rocket engine by Reaction Engines LTD includes such a duct between the two compressor shafts. This engine, SABRE, is proposed for use on the SKYLON space plane. As such, minimising engine weight to allow for larger payloads is even more important than in jet engine applications.

This project will study the more "aggressive" end of the S-shaped duct spectrum. It is hoped that a design philosophy for such aggressive ducts can be developed as well as an understanding of the trade-off between length and performance of these designs.

The project is likely to include simple axi-symmetric computational fluid dynamics calculations to aid in the design, study and production of such ducts. With sufficient progress, designs of interest could be manufactured and tested aerodynamically in a low speed facility within the Whittle Laboratory.

Link to Reaction Engines LTD

    Requirements: Aerodynamics modules 3A1 and 3A3.
    It is expected that the UROP should lead into a 4th year project.
    The project is being co-supervised by Dr. C. Clark , Dr. S. Grimshaw and Dr. J. Taylor
    Please contact Dr. S Grimshaw for further details or to apply.


Insertion Date: 9 March 2017

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #525 on: 03/17/2017 09:06 PM »
This is what I saw at the Derby lecture:

« Last Edit: 03/17/2017 09:07 PM by t43562 »

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #526 on: 03/17/2017 11:22 PM »
So definitely British then?


Offline t43562

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Re: The Reaction Engines Skylon Master Thread (6)
« Reply #527 on: 03/19/2017 06:20 AM »
So definitely British then?

Unfortunatley so, I think, because that would mean it's highly unlikely to happen. I'm just thinking that if the e-go, a tiny aeroplane, cannot make a go of it in the UK then what chance a hypersonic business jet?
« Last Edit: 03/19/2017 10:31 AM by t43562 »

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