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Reaction Engines SABRE engine (Skylon Spaceplane)

TomcatViP

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There is no burning of ammonia. It's Hydrogen and nitrogen that are used as fuel. See ammonia as a carrying fluid (more practical than heavy high pressure tanks).
Then the delta T you are referring is for the inlet fluid. The T from the entering fluid (mainly air) and the T at wich it is elevated before being expanded.
Here the air is still acting as the medium.
Then there is Nox (the nasty guy in all burning process). If they can claim burning a majority of H2 then the byproduct would have a very low fraction of Nox*. It's all in the purity of the injected fuel and the efficiency of the burning reaction (the main problem as you underline it with nasty Diesel engines).

*Sulfur being the main intermediate component acting in the production of Nox
 
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Archibald

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In 1963 the US Army had their nuclear energy depot. Portable reactors to turn (air nitrogen ) and water's hydrogen into ammonia methanol or hydrogen fuels. They studied DH Caribou transports and UH-1 choppers turbines with NH3. I have the pdf somewhere. Not very encouraging. Methanol and ammonia have half the energy of kerosene. Hydrogen is doomed by storage issues.
 

Zoo Tycoon

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Ammonia is pretty toxic in its own right, while gasoline is only moderately so. Although it is less flammable than gasoline, it is far more caustic; you really do not want it in your lungs for example. Because of this, localised ammonia storage has a lot more safety red tape than gasoline, you can't just fill up a plastic can and stick it in the back of your car. A cloud of gasoline fumes rolling over your town will cause more harm from the additives than from the gasoline fumes, but the same cannot be said for ammonia. The stuff was even used as a poison gas during WWI, though it was admittedly not very effective in the field.

Ah No ;-
- unleaded gasoline vapour is highly Carcinogenic due to its benzene content https://www.sciencedirect.com/science/article/abs/pii/S0013935105802439
- Gasoline is heavier than air so it will roll along the ground. NH3 under most environmental conditions is lighter, so it will go up at point of release.
- I can find no reference to ammonia ever be used as a WW1 chemical warfare agent, please supply a source & reference. Under most circumstances it’s lighter than air, so it’s a bit like trying to gas someone in a trench with hydrogen/helium;- makes no sense to even try.

Despite your surprised opinion on NOX, it’s correct that NH3 can both be used to suppress NOX in conventional gas turbine combustion and if burnt directly produce lower NOX than fossil fuels. I can provide sources.

NH3 is the second most produced and transported chemical in the world today (approx 200 million tons a year) from brown carbon sources. However there are now a number of multi million ton/year fully funded, billion dollar schemes to produce Ammonia from sunlight/air/water;- the latest being In Saudi. It dissolves in water, where it naturally decomposes, so no more oil slicks in the event of a tanker leaks/sinkings.

The principal advantage is storage costs and it’s well to tank energy conversion;- there’s more hydrogen in a cubic meter of anhydrous ammonia than there is in liquid hydrogen.... yes really, google is your friend. NH3 storage cost about 5% compared to liquid hydrogen, has close to zero storage loss and requires 10-20% less energy to produce compared to energy available at point of use.

There’s no missing heat exchanger in the diagram, after it’s converted to gas it just burnt, as was proven by Prof Kobayashi gas turbine demonstrator,;- https://www.ammoniaenergy.org/articles/ammonia-fueled-gas-turbine-power-generation/

I really can’t work out your thermodynamic logic at all.

The “least vile option rocket fuel”;- Rocketdyne Project Leader for the X15 XLR99 - Robert W Seaman actually said “I have worked with a quite a few propellant systems and found NH3/LOX to be among the easier ones to work with. We did encounter a few challenges along the way, but none were related to the fuel itself” ;-
I believe his assessment far more than yours.
 
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Zoo Tycoon

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In 1963 the US Army had their nuclear energy depot. Portable reactors to turn (air nitrogen ) and water's hydrogen into ammonia methanol or hydrogen fuels. They studied DH Caribou transports and UH-1 choppers turbines with NH3. I have the pdf somewhere. Not very encouraging. Methanol and ammonia have half the energy of kerosene. Hydrogen is doomed by storage issues.
I too have these;- as you say the objective was producing jet fuel at point of use, so therefore being independent of a critical supply chain. I think there was also an agenda to channel money into a theatre deploy-able tactical nuclear plant......Yeah, just behind a battlefield. Scary for Warsaw Pact, but maybe not so for Nam.

Yes, NH3 doesn’t have the energy density of a fossil, but it’s volumetric energy is the best of all the zero carbon’s. That’s pretty important in delivering zero carbon emission mass air travel.
 

Archibald

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There are not many substitutes for gasoline in IC cars... and aircraft turbines.
Hydrazine is extremely toxic and corrosive. Hydrogen is pure energy, sure but it is horrible in temperature, storage, density...
Methanol and ethanol are pretty good but still have carbon.
Ammonia is kind of similar to them except with carbon replaced by nitrogen. Better for fighting global warming but nitrous oxides are harmful too so not sure.
While Musk managed to make electric cars significant through lithium batteries, such trick won't work on aircraft.
So I was intrigued by the article posted in this thread... ammonia aircraft seems to make some sense indeed.
So I ask the question: what changes would it take to run a CFM-56 on NH3 ?
 

steelpillow

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<snippy remarks>

Well, so much for unbiased assessment of the facts and civil discourse. Here are a few more facts for you to disagree rudely with.

Here are the UK Health Protection Agency's Petrol: Toxicological Overview and the US NCBI Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 6. 2 Ammonia Acute Exposure Guideline Levels. According to these reports, petrol vapour causes irritation from 140 ppm (parts per million), ammonia from only 30 ppm. Petrol causes serious symptoms from 900 ppm, ammonia from only 220 ppm. In other words, ammonia is about four times as toxic as petrol. Both can cause long-term harm, which I leave others to worry about; I note here only that benzene content of US gasoline is under 1% and of British petrol a little more, it is just the tip of the iceberg.

Trying to recall the poison gas anecdote, I have a hazy memory coming back that ammonia was only trialled away from the battle by the British, and found to be ineffective for the reasons you mention, but it was several years ago and I did not note the source. At the time I was researching J W Dunne's WWI excursion into poison gas, revealed by his unpublished document collection in the Science Museum Archive. I may have found it there or in related Army documents.

The thermodynamic logic is simple. cooling the intake air, whether it be a two-stage supercharged Merlin or a supersonic jet, increases the thermodynamic efficiency of combustion. See any decent source on the subject. One hardly needs Sherlock Holmes to inform one that heating the intake air achieves the reverse. Note that the intake conversion process, required for the Reaction Engines ammonia cycle described, requires just such pre-heating. An intermediate cooler would be necessary to restore thermodynamic efficiency of the engine to modern levels. Is there any part of that you still struggle with?

Finally, I thought my assessment of ammonia as a rocket fuel summed up Seaman's rather nicely; his ammonia bottle is half-full, mine is half-empty.
 

Zoo Tycoon

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<snippy remarks>

The thermodynamic logic is simple. cooling the intake air, whether it be a two-stage supercharged Merlin or a supersonic jet, increases the thermodynamic efficiency of combustion. See any decent source on the subject. One hardly needs Sherlock Holmes to inform one that heating the intake air achieves the reverse. Note that the intake conversion process, required for the Reaction Engines ammonia cycle described, requires just such pre-heating. An intermediate cooler would be necessary to restore thermodynamic efficiency of the engine to modern levels. Is there any part of that you still struggle with?
Steelpillow
While the charge cooling principle is not disputed, the claim the intake air is heated ? The ammonia is at -33 Deg C and turns to gas when heated so the heat transfer will cool the air charge thus increasing the cycle efficiency ? and then you assert the Reaction Engine cycle requires an extra inter cooler to restore efficiency to modern standards? Where has that come from ?

The relative toxicity data is unbalanced as the ammonia will go upwards at the point of release while gasoline will spread outwards at ground level. The NH3 normal safe storage device is a water mist surrounding the tanks, its already stored In hundred thousand ton quantities without issue or even people noticing. The whole chemical weapon claim is at best unvalidated, and in my opinion nonsense.


With this and previous post you seems to have an agenda with Reaction Engines and call anybody rude who challenges it..
 
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Zoo Tycoon

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global warming but nitrous oxides are harmful too so not sure.

ammonia aircraft seems to make some sense indeed.

So I ask the question: what changes would it take to run a CFM-56 on NH3 ?
I feel from the data I’ve seen the nitrogen oxide problem is manageable within combustion design.

How much of a CFM 56 could be used with NH3? Well the compressor, the gearbox .........and not much else.
 

Archibald

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Ok so one can't substitute ammonia for kerosene in jet engines.
Unlike cars IC engines where ammonia could replace gasoline with minor changes.
 

steelpillow

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While the charge cooling principle is not disputed, the claim the intake air is heated ? The ammonia is at -33 Deg C and turns to gas when heated so the heat transfer will cool the air charge thus increasing the cycle efficiency ? and then you assert the Reaction Engine cycle requires an extra inter cooler to restore efficiency to modern standards? Where has that come from ?

Well, I am going by the Daily Mail article you linked to:
- "Ammonia fuel is stored in the wings, just like kerosene-based fuel is today." I am not aware that today's fuels are maintained at -33 deg. If ammonia has to be, with all that area of wing tankage insulated accordinly, everbody forgot to say so.
- "In order to be burned in a combustion chamber, ammonia needs to be mixed with hydrogen — which can be released from ammonia itself using heat and a catalyst. The researchers are proposing, therefore, to use a heat exchanger to warm up the fuel en route to the engine". In the diagram the heat exchanger is nowhere near the intake airflow, so the claim that it cools the air is untenable.

The relative toxicity data is unbalanced...
The data is correct. You are claiming that the relative risks posed by the given toxicity data are unbalanced. We have been discussing the toxicity, not the risk it poses. Those risks depend greatly on particular scenarios, which we have not discussed - and I have no intention of doing so in a Reaction Engines topic.
 

TomcatViP

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Fuel and air is there unrelated. The fuel is only there to increase the delta P of main air prior to the expension process. As hinted to you, the catalysis reaction is endothermic, meaning that it will even (marginally) cool the flow of air.
You've also to understand that some points of the article might be wrong (nobody needs anything to burn H2 in the presence of O2).
 
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steelpillow

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When do you think Rolls Royce will takeover Reaction Engines?

Was wondering that myself.
The way the markets are going, I wouldn't rule out RE going public and making a reverse buyout! ;)
But they'd have to get their flight demonstrator into the air first.
 

steelpillow

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Interesting presentation. I am glad to see that TSTO is now favoured over the absurdly ambitious SSTO concept.

But, and, call me an old cynic if you will, I still see two elephants conspicuous by their absence.

First, the report highlights engine failure as one of the more significant risks. Yet we are offered twin engines mounted right out on the wing tips. A single engine failure at hypersonic speeds would create massive yaw for which there is no compensation. The Lockheed Blackbird had large twin fins primarily for this purpose, but they are absent from this design. The only way to survive would be to immediately cut the other engine, making the design less reliable even than a single-engine type. Adding fins would of course severely compromise the performance and weight estimates.

Second, for the Skylon predecessor NASA highlighted impact of the hot exhaust plumes on the rear fuselage as a major problem. This design is remarkably similar to Skylon, yet the analysis does not address the issue.

And perhaps a small sea-cow (closest living relative to the elephant) in the location of the payload; since the SABRE-powered stage is sub-orbital, why not mount the main payload externally, like every other two-stage horizontal-launch system to date? Front-mounting hits structural weight penalties (just ask Pegasus), while internal mounting creates a severe balance problem with fore-and-aft fuel storage, leading to the Skylon problem.

Indeed, a SABRE-powered M-21 Blackbird with rocket-powered D-21 payload should be capable of reaching space before separation, thus avoiding the aerodynamic issues which caused a collision and terminated the Tagboard program. Shame there is no airworthy M-21 airframe around any more, but I'd quite like to see that worked out as a reference design from which to judge any concrete proposal.
 

sublight is back

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At Mach 5 the heat exchanger needs to cool air from 1,000°C to minus 150°C, in 1/100th of a second, displacing 400 Mega-Watts of heat energy (equivalent to the power output of a typical gas-powered power station) yet weighs less than 1¼ tonnes.

Are we still in the "believable" mode ? If you even have the capability to generate the equivalent to 400 megawatts of energy 100 times a second (aka 40 billion watts aka 40 gigawatts a second) then surely you would be better off just using that resource for thrust instead of cooling?
 
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Trident

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Are we still in the "believable" mode ? If you even have the capability to generate the equivalent to 400 megawatts of energy 100 times a second (aka 40 billion watts aka 40 gigawatts a second) then surely you would be better off just using that resource for thrust instead of cooling?

Watt is a unit of power, not energy (that would be Joule - one Joule per second is one Watt). Gigawatts a second makes no earthly sense in this context. In any case, these 400 Megajoules per second are not generated on board, they are *extracted* from the hot inlet air via a helium cooling circuit which ultimately uses the cryogenic hydrogen fuel as a heat sink. On the way, it drives the turbines powering the propellant pumps and intake air compressor, so nothing goes to waste.
 
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sublight is back

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Are we still in the "believable" mode ? If you even have the capability to generate the equivalent to 400 megawatts of energy 100 times a second (aka 40 billion watts aka 40 gigawatts a second) then surely you would be better off just using that resource for thrust instead of cooling?

Watt is a unit of power, not energy (that would be Joule - one Joule per second is one Watt). Gigawatts a second makes no earthly sense in this context. In any case, these 40 Gigajoules per second are not generated on board, they are *extracted* from the hot inlet air via a helium cooling circuit which ultimately uses the cryogenic hydrogen fuel as a heat sink. On the way, it drives the turbines powering the propellant pumps and intake air compressor, so nothing goes to waste.
These aren't my energy figures, I am quoting directly from the Skylon page. Color me extremely skeptical that the hypersonic-super-cooler, which has to have super thin fins in order to be super efficient can withstand the hypersonic blast, can somehow fit in the engine bay without being as large as Dodger stadium.
 
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steelpillow

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These aren't my energy figures, I am quoting directly from the Skylon page. Color me extremely skeptical that the hypersonic-super-cooler, which has to have super thin fins in order to be super efficient can withstand the hypersonic blast, can somehow fit in the engine bay without being as large as Dodger stadium.
Seeing you turn temperature, effectively energy, per second into Watts per second does not lend us confidence in your technical understanding. Are you sure you meant that? Nor does your failure to grasp the point that the heat is already present in the airflow and is not "generated" by SABRE. And what do you expect of a hypersonic airbreathing rocket big enough for a spaceplane, a slightly bigger firework than a £1 rocket?

Let's look at the history behind the numbers. Of course none of us has access to the raw test data, but do bear in mind that the thing has been bench-tested by directly feeding it supersonic engine exhaust, met its cooling spec, and did not require a test bench "the size of Hyperbole Stadium" or wherever you ranted about.
You might also need to get yourself up to speed on the mechanical design of pressure vessels; the narrower the diameter is, the thinner the walls need to be to withstand a given fluid pressure. The key breakthrough in the heat exchanger design has been the reliable manufacture and leakproof assembly of precision small-diameter tubing, which allows precisely the "super thin" walling you cannot believe exists.
In this context I recall a contemporary conversation with a good friend who was a metallurgist at R-R when the original Hotol was in the news. The reason R-R pulled out was exactly yours, they could not believe that the heat exchangers would be practical. Once Reaction Engines successfully demonstrated the thing actually working, R-R returned to form a strategic partnership with them. So too did BAe Systems.
The current design also deals with foreign object ingestion, such as a birdstrike; the air follows a curved path to the delicate bits, while any dense solid is carried straight past by its inertia and momentum, to be harmlessly diverted out the back.
Have R-R and BAe gone soft in the head over the years, or are you a few decades out of date in your engineering knowledge? I know which I believe.
 
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Zoo Tycoon

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I would recommend the following interpretation for the RE information:-

The 1/100 of a second is the occupation time for a molecule of air within the heat exchanger.

The heat exchanger is not subject to the hypersonic blast. The hypersonic air is slowed by the intake to a few hundred meters/sec before entering heat exchanger. The principle function of the intake is to convert the air’s kinetic energy, I.e it’s high velocity, into potential energy I.e heat and pressure at significantly lower velocity.

The heat exchanger is one element of a system so really needs comparing to one element of a power station rather than the plant land area. A 400Mw steam power turbine weighs maybe 7-8 tonnes so this heat exchanger is about one third of that. Also please remember that power station equipment has little or no weight sensitivity and is designed to provide 24/7 operation continuously for many years without significant down time. The RE heat exchanger is highly weight sensitive but operates for just 3-4 minutes per flight, with a design life of a few hundred cycles maybe, a thousand flights with inspections possible at intervals between flights. It’s total design life at equivalent power levels to the steam turbine would be one to two days.
 

steelpillow

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A propos of which, in supersonic flight a large proportion of the thrust is actually generated by the air intake duct. Unlike a subsonic duct, it expands in area, which means its walls slope outward not inward. The high pressure reacts against these walls to push the plane forwards. Especially in a ramjet, the fuel burn is little more than a way to create that pressure by expanding the exhaust volume, and the exhaust nozzle just a way to react against it without a rear wall, by allowing the exhaust to accelerate backwards; there is an element of truth in regarding a divergent nozzle as a secondary afterthought.

SABRE in airbreathing mode can be understood in engineering terms as a conventional supersonic turbojet, with its combustion chamber replaced by the pre-cooler and pre-burner, its hot-air turbine stage driven instead by hot helium, and a large bypass flow to the afterburner (rocket chamber). As such, one can expect to see the intake geometry of a practical engine to be revised from the concept diagrams, to improve the aerodynamics of the expansion zone immediately behind the intake lip.

In passing, the pre-burner and its exhaust heat exchanger play a crucial role in driving the subsonic thermodynamic cycle.

Here's that old concept diagram again, to illustrate all this:
sabre_cycle_1024.jpg
 

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