The Reaction Engines Skylon/SABRE Master Thread (7)

[JCRM]

It's an interesting idea but ammonia is not without it's challenges - not the least of which is the amount of energy used to manufacture it in the first place.  Also, according to Wikipedia, one of the main industrial byproducts of ammonia production is CO2 (that's their "low emissions" gone).

While current production methods (SMR of methane) have a large carbon footprint, they have the advantage, that the emissions are "easy" to capture - resulting in processes capable of 0.1 unit of CO2 emitted to the atmosphere for every unit of ammonia produced.  So that's their "low emissions" in place.

By switching to sourcing the hydrogen from water then the only carbon production is from the energy source, which can be zero if renewables are used. This is, of course, more expensive. and the use of "green" hydrogen was one of the factors which caused the S-ELSO projected Skylon launch costs to be higher than they needed to be.

but ammonia is a caustic and flammable chemical that is toxic by inhalation, resulting in permanent lung damage and even death at high exposure levels - and the "chilled, pressurised liquid" is sure to be venting on a continuous basis.  A spill in an airport environment would be deadly.

and yet they managed to run buses on the stuff over three quarters of a century ago.

I was almost expecting you to tell us taht global warming isn't a problem
As interesting as it is, I'm not at all sure we'll see this leave the drawing board.

I would guess it'll leave the drawing board, but I wouldn't want to bet it'll leave the ground.

[Soundbite]

I would guess it'll leave the drawing board, but I wouldn't want to bet it'll leave the ground.

I am not so sure.  It may not be able to compete with items that require power on the ground, but when you are looking at zero emission aircraft carrying more than 100 passengers there are very few options that will give you a similar range to jet fuel without costly whole infrastructure changes. Hydrogen is the closest competitor but it comes with even greater challenges.

1. Ammonia is globally one of the top 10 most commonly produced chemicals and well trodden handling and transportation procedures already exist for it. The main risk is ammonia release in enclosed environments.

2. Compared to hydrogen as a fuel, ammonia is much more energy efficient, and could be produced, stored, and delivered at a much lower cost than hydrogen which must be kept compressed as a cryogenic liquid. Although not as powerful as other hydrocarbon fuels, the raw energy density of liquid ammonia is 11.5 MJ/L,[71] which is about a third that of diesel.

3. At standard temperature and pressure, ammonia is less dense than the atmosphere and has approximately 45-48% of the lifting power of hydrogen or helium, so in an open environment like an airfield/airport it will quickly disperse upwards and will not be deadly.

4. Liquid ammonia has a very high standard enthalpy change of vaporization (23.35 kJ/mol, cf. water 40.65 kJ/mol, methane 8.19 kJ/mol, phosphine 14.6 kJ/mol) and can therefore be used in laboratories in uninsulated vessels without additional refrigeration.  So liquid ammonia can be used in aircraft fuel tanks with little venting.

5. Ammonia does not burn readily or sustain combustion so it is less flammable than jet fuel or hydrogen.  Its auto ignition temperature is 651 deg C so it will burn in a combustion chamber.  That is partly why ammonia has to be partially decomposed first, so that the hydrogen can be ignited in a combustion chamber at room temperature to start the combustion process.

Any comments?

[libra]

Brilliant !

Can't remember if I mentionned this before but... in 1963 the US Army had an intriguing idea: the mobile, nuclear "energy depot".

The idea:
1 - portable nuclear reactors (small, compact and reliable things carried close enough from the front line on medium-size trucks - how about TRIGA, for example ?)
2 -  to split a) air's nitrogen and b) water's hydrogen
3-  recombine that into methanol, ammonia, or even liquid hydrogen
4 - use that as fuel for tanks, jeeps, helicopters, transport aircraft !

Basically: ran the US Army land and air vehicles I.C engines  on nuclear-nitrogen-carbon-hydrogen fuels !

The Army is free of the oil (supply) tyranny. Their vehicles are running on air and water !

I've attached a bunch of documents found on the web (NTIC and elsewhare).

The concept eventually failed at the cost and practicality levels.

Yet imagine, if it had been made to work AND ready to be passed to the civilian world exactly ten years later, I mean: 1973, the year of the first oil shock.

Can't help thinking if the idea was related to the 1944 situation. When from D-Day, French Normandy in June to the seizing of Antwerp harbor in November, Wallies armies oil had come through PLUTO pipeline, from Great Britain, off the beaches ! This brought wallies armies to a halt late august, after Paris.

[The Ex-Engineer]

4. Liquid ammonia has a very high standard enthalpy change of vaporization (23.35 kJ/mol, cf. water 40.65 kJ/mol, methane 8.19 kJ/mol, phosphine 14.6 kJ/mol)
Any comments?

So what attainable speed would that translate into if used in a SABRE 3 or 4 pre-cooled engine cycle?

My thermodynamics is a bit rusty so I'm sure someone else will be able to do the back of the envelope calculations far better than me....

[Asteroza]

4. Liquid ammonia has a very high standard enthalpy change of vaporization (23.35 kJ/mol, cf. water 40.65 kJ/mol, methane 8.19 kJ/mol, phosphine 14.6 kJ/mol)
Any comments?

So what attainable speed would that translate into if used in a SABRE 3 or 4 pre-cooled engine cycle?

My thermodynamics is a bit rusty so I'm sure someone else will be able to do the back of the envelope calculations far better than me....

For a SABRE rocket cycle intended for a SSTO/TSTO rocket, ammonia sucks as a fuel/coolant. Using SABRE inspired precoolers on a sub mach 3 vehicle turbine powerplant with some precooling, it might have applications, if the ammonia can be sourced cheaply.

[JCRM]

Not entirely sure why the study talks about partially decomposing the ammonia prior to combustion? Anyone have any thoughts?

my previous suggestions were wrong.
From REL's press release:
"to provide a zero-carbon fuel blend of ammonia and hydrogen that burns stably just like jet fuel"
and
"we successfully produced the combination of ammonia and hydrogen that mimics jet fuel"
and
"Our study showed that an ammonia-fuelled jet engine could be adapted from currently available engines"
and
"ammonia as a fuel doesn’t require a complete re-think of the design of civil aircraft"

I would guess it'll leave the drawing board, but I wouldn't want to bet it'll leave the ground.

I am not so sure.  It may not be able to compete with items that require power on the ground, but when you are looking at zero emission aircraft carrying more than 100 passengers there are very few options that will give you a similar range to jet fuel

Oh, I'm not saying it wont happen, just that I'm not prepared to place a wager on it (either way, actually)
Without a compelling reason for zero-carbon-emission aircraft, there's no compelling reason for the switch -- and by compelling reason I mean money. With a compelling reason, this is an attractive (although not ideal) route.

Using SABRE inspired precoolers on a sub mach 3 vehicle turbine powerplant with some precooling, it might have applications, if the ammonia can be sourced cheaply.

The study seems to be about retrofitting existing jets for short-haul flights,  for the new designs you seem to be proposing I would hope a complete decomposition would be used.

I suspect ammonia's bulky nature would make it unattractive for the usual buyers of supersonic jets, especially as they tend not to be restrained by emissions regulations, or overly concerned by minor price differences. The hoped for supersonic business jet market, on the other hand....

[oddbodd]

https://www.bbc.co.uk/news/business-53598874

Mentions RE. Still reading...

[Edit] Meh. A bit of a non-article.

[JCRM]

https://www.bbc.co.uk/news/business-53598874

Mentions RE. Still reading...

[Edit] Meh. A bit of a non-article.

It quotes Dissel as saying they're looking at cooled iconel, instead of using ablatives like the space shuttle tiles - so make of that what you will

[t43562]

I think there's nothing new here really but perhaps very slightly more clarity way down in the last couple of paragraphs about some of the spin offs:

https://www.ingenia.org.uk/Ingenia/Articles/97f62cea-8e68-41a2-9d36-e16c97131d51

The test programme for the demonstrator core aims to begin in 2021.

Even if all goes to plan and funding is maintained, a SABRE vehicle in production is still probably at least a decade away, and meanwhile the company is exploring (with partners) other applications of its engine technology, particularly the precooler. This includes combining the precooler with a conventional jet engine – gas turbine, turbojet or turbofan – to improve performance. This could help produce faster jets, or more sustainable aviation. There is also potential for hybrid-electric propulsion.

The precooler could also be used for improving power station efficiency and, in particular, for converting waste energy into renewable electricity. Reaction Engines is also looking at developing miniature versions of the precooler for Formula 1 and the high end of the automotive market is being investigated.

For some applications, taking the precooling down below ambient to cryogenic temperatures (-150°C) can potentially improve engine performance. But there are drawbacks, particularly the tendency for frozen water vapour to block the precooler. An ingenious methanol frost-control system was devised to prevent this and has already been successfully tested.

But perhaps the most exciting of the spin-off developments is the potential for hypersonic flight within the Earth’s atmosphere. This opens up the possibility of commercial airliners capable of Mach 5 – a stated aim of one of the company’s investors, Boeing – which could, for example, fly from London to New York in less than an hour. There is also clear potential for a new breed of hypersonic military aircraft, which has engaged both the UK’s Ministry of Defence and DARPA in the US.

[john smith 19]

4. Liquid ammonia has a very high standard enthalpy change of vaporization (23.35 kJ/mol, cf. water 40.65 kJ/mol, methane 8.19 kJ/mol, phosphine 14.6 kJ/mol) and can therefore be used in laboratories in uninsulated vessels without additional refrigeration.  So liquid ammonia can be used in aircraft fuel tanks with little venting.
.
.
Any comments?

Just to put that in perspective LH2 enthalpy of vaporization is about 4x that of water.

[john smith 19]

For a SABRE rocket cycle intended for a SSTO/TSTO rocket, ammonia sucks as a fuel/coolant. Using SABRE inspired precoolers on a sub mach 3 vehicle turbine powerplant with some precooling, it might have applications, if the ammonia can be sourced cheaply.

True.

But in this case it's REL's expertise in building small, high efficiency heat exchangers, that's being used. This is (possibly) being combined with internal catalytic coatings to bring about the partial decomposition to get enough free H2 in the mix to burn it easily.

[JCRM]

They've tickled their publicity concept - updated the logo to the precooler swirl and changed the "cargo bay doors"

Did anyone explain why the ramjet exhaust was yellow?

Oh, and I've only just noticed "We have stopped using the acronym REL and we prefer to
be called Reaction Engines, or even Reaction if a shorter version is needed."

[Asteroza]

That's putting the engines pretty far back, almost as bad as HOTOL. Wasn't one of the big merits of Skylon was putting the engines near the CoG to reduce aerosurface size? Or did all the simulation work on plume impingment make that no longer viable?

[john smith 19]

Wasn't one of the big merits of Skylon was putting the engines near the CoG to reduce aerosurface size?

Partly. More so to reduce the massive CoG/CoP shift as the vehicle moves through 23 Mach numbers and loses seventy five percent of its weight.

Or did all the simulation work on plume impingment make that no longer viable?

Doubtful.

This looks like something that's been done by an artist, not an engineer.   

[JCRM]

That's putting the engines pretty far back, almost as bad as HOTOL.

This is only a TSTO, so the weight penalties aren't anywhere near the problem they are for a SSTO.

[john smith 19]

That's putting the engines pretty far back, almost as bad as HOTOL.

This is only a TSTO, so the weight penalties aren't anywhere near the problem they are for a SSTO.

Fair point.

[t43562]

https://prod-physicsworld-iop.content.pugpig.com/blog/2020/09/25/eliminating-the-boundary-between-sky-and-space/pugpig_index.html

[JCRM]

https://prod-physicsworld-iop.content.pugpig.com/blog/2020/09/25/eliminating-the-boundary-between-sky-and-space/pugpig_index.html

I'm sure people will be pleased to know the concept vehicle in this article has mid-body wing-tip nacelles

I'm also sure it comes as no surprise, but...

While the precise timings of this latest phase of the test campaign have been hit by the COVID-19 restrictions imposed in the UK, an extensive design process has already been conducted in conjunction with the UK and European space agencies, which will enable the programme to swiftly progress once the restrictions are reduced

[john smith 19]

https://prod-physicsworld-iop.content.pugpig.com/blog/2020/09/25/eliminating-the-boundary-between-sky-and-space/pugpig_index.html

I'm sure people will be pleased to know the concept vehicle in this article has mid-body wing-tip nacelles

I'm also sure it comes as no surprise, but...

While the precise timings of this latest phase of the test campaign have been hit by the COVID-19 restrictions imposed in the UK, an extensive design process has already been conducted in conjunction with the UK and European space agencies, which will enable the programme to swiftly progress once the restrictions are reduced

Indeed. Somewhat light on new information.

Now if they had gotten some cash under the ESA Future Launchers Preparatory Programme to pursue the E/D nozzle to allow higher expansion ratios at sea level without flow separation..... 

[JCRM]

Philip Dunne MP joins Board of Reaction Engines Wed, 2020-09-23 16:12

[...]
Philip Dunne said:

“I am pleased to join the board of one of the UK’s most innovative and exciting aerospace companies. Reaction Engines is at a crucial point in its journey to revolutionise ultra-low cost lower emissions space access and high-speed flight, with many new and sustainable spin-out applications for SABRE engine technology. I look forward to playing my part in helping the UK journey towards net zero sustainable aviation.”

Philip Dunne has been MP for Ludlow since 2005. He served as Minister for Defence Procurement from 2012-2016 [. He is ] Deputy Chairman of the Defence Growth Partnership

Right Hon. Philip Dunne on Wikipedia