Pre-Cooled Jet Engine: way of the future.

It anyone has not noticed airplane technology leveled off since the 1960's in achieving speed and altitude records. The man reasons I would say is that no successor to the jet engine was created, the technology peaked out at ram-jet assisted jet engine gobbling down highly specialize petroleum fuel (SR-71). Some attempts over the decades have been made to introduce scram jets but their performance has been less then desirable, have very poor thrust to weight ratios. A better alternative to the scramjet would be the pre-cooled air-breathing rocket engine! The idea is simple: use cryogenic fuel to pre-cool the incoming air, thus allowing a normal turbocompressor to work up to mach 5.5+ without melting, achieve fuel and air densities that blurs jet engine with rocket engine (and thus the thrust to weight far greater then a jet engine). This would allow an aircraft to take off from a speed of 0 to mach 5.5 or greater, then the engine could switch over to internal liquid oxygen and travel faster and higher (even into orbit) as pure rocket engines. Excess fuel (for cooling) is burned in assisting ram/scramjets. Anyways I think its a sweet idea, fat chance it going to get a funding it deserves but still very sweet:

http://www.reactionengines.co.uk/sabre.html

 

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Fuel economy would make for much better spacecraft and even high-performance aircraft, certainly...

But take a good look at some of the diagrams. I mean, holy crap. You have a helium loop in amongst liquid hydrogen and oxygen lines, making for what I count as two internal heat exchangers, a precooler that's exposed to high-subsonic, maybe supersonic flow, and three cryogenic pumps plus a helium-driven turbo-compressor. This is a very sophisticated and, thus, will be a very expensive system not to just develop, test, and produce, but to maintain as well. Also, a system similar to this is the RB545 by Roles Royce, which at one point the Brits wanted to develop and put into their HOTOL vehicle, wiki links this as a pic...

http://www.flightglobal.com/airspac...mscutaways/images/10296/bae-hotol-cutaway.jpg

The engine is similar in that it pre-cools fuel but does so in a more simple fashion: they seem to get rid of the helium loop and just pre-cool with the onboard liquid hydrogen. The details seem to still be British secret, but the fact that the SABRE engine, a newer concept, incorporates a helium loops leads me to think there was a problem with the use of hydrogen for pre-cooling.

This is a downside with reusable engine systems, even the ones as elegant-seeming as this system. For the fuel they might be able to save and, particularly, the fact that they can be reused, one might think they save alot of money, as people once thought the Space Shuttle would do. Unfortunately, even the shuttle's relatively simple LH-LOX rockets and even simpler external solid fuel boosters cost bundles to keep running not just safely, but absolutely perfectly. Every time. Space vehicles are not cars, if they break down, they can't just pull over. And they're not traditional planes, if the engines fail, they don't just glide down. They either loose control in launch, or blow up, or get stuck in orbit, or spin erratically in space because some leaking gas is applying moment to the craft. Engines for this kind of application have to be PERFECT, and the more complicated they are, the more pumps and fluid lines and heat exchangers there are, the more redundancy systems are put in, the more monitoring systems get developed and wired up the wazzo, the more inspectors get hired, the more down-time of the craft as said inspectors go over it with a fine-tooth come and flip out at the slightest microscopic imperfection in a piece of sheet metal near the engine, and will completely ground a space program if one of their engines develops a slightly unexpected vibration, the equivalent of a sniffle.

I wish stuff wasn't this beaurocratic, but let's face it, simple systems are cheap systems. We need to find a reusable, stupid-simple system that either can't go wrong, or can easily recover from failure. I just get nervous when I think of NASA looking at this kind of engine system and counting the hozes!

 

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The main reason is that there was no actual need for higher speeds.
It's not just a question of getting the engines right, the entire aircraft needs to be capable of handling far higher temperatures, look here for examples.
Concorde has been claimed to have accumulated more time at Mach 2 than all other aircraft in the world put together - even the so-called M+2.5 fighters rarely go that fast.

Check out XF-103, XF-108, X-15 and whole slew of British (!) hypersonic projects.
Faster isn't necessarily better unless there's a genuine need for it.

 

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Indeed, Concorde is the perfect example. Watching those first flights, we could be forgiven for thinking that by now, all aircraft would be supersonic, but no, market forces wanted cheaper flights, not faster ones.

Although I did meet Alan Bond once, and he's a total fucking genius, so I hope REL do have success with their project in some capacity. He got fucked over royally on HOTOL, and this project could be two fingers back at HMG.

 

Plus, of course, the whole "environmental" thing with supersonic aircraft.
Look at the US anti-Concorde lobbying that went on.
(Largely, I suspect, due to the NIH factor.)
I wonder how it would have gone if Boeing had managed to get their project working.

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Interesting, from that article;

"A major change in the design came when Boeing added canards behind the nose"

Of course, the Concordeski, or Tu144 had Canards, because they had trouble perfecting a wing design that worked well in both sub and super sonic speeds, so added canards. A popular rumour is that the Paris airshow crash was caused by a French Mirage causing the Tu-144 to bunt as it was trying to get pictures of the canards, and of course, Mirage jets ended up using them themselves.

Apparently the Russians stole some plans via some guy in Paris who knew the French side of the Concorde team, but the wing design wasn't perfected, so that's why they went with canards. Seems Boeing had the same problem, and ripped off the Russians, ....

I'd love to know how much of the above was true, and not just a good story!

 

Flying skateboards- way of the future.

I imagine that once we are able to extract thermal energy from the atmosphere such devices of locomotion will not be too far off. If you cool a cubic meter of air 10 degrees kelvin you get 13,000 joules. An air-scoop with a surface area of 1 square meter moving at 10 m/s will suck 10 cubic meters/second , if air flow is perfect.

The problem is providing surface area for air molecules to deposit their thermal energy without creating drag. If you try to extract heat [kinetic energy] using a fast moving surface you are actually going to create most of the kinetic energy by slamming the object against air particles, meaning that most of the energy is created through drag- completely pointless if you want to accelerate something.

This is why radiator fins have to be positioned to have surface area parallel to the motion of the vehicle- this way the only component of the air's thermal kinetic energy that interacts with the radiator is the component perpendicular to motion; IE surface area does not contribute to drag as much.

And thats how you design an aircraft based on ambient heat conversion.

 

If everything is parallel to the air flow (to reduce drag) how do you direct the flow in the required direction?
What stops the "exhaust" coming out the front?

 

No no no, this isn't the thruster, its the power source. A propeller or some other form of thrust has to be attached to it.

Since these fins get cooler, there will likely be condensation on them. Perhaps this water can be used as the propellant- collect it in a separate chamber, heat it up to form a gas and direct it out one end using a nozzle.

 

1) You're going to need a power source anyway, to get the air in.
2) Why would the air cool down? It'll stay at ambient temperature, surely? Another power source to force cooling?
3) You can't eliminate drag anyway, there'll be a boundary layer (which causes horrendous problems, including a stagnation barrier) if there's any air flow.

 

Here is another concern- what would happen to the colder air leaving the rear of the radiator? This colder air is more dense and has a smaller volume than air entering the front. This would mean that there is less pressure towards the rear of the radiator, encouraging air to enter through the rear. Of course, this will impede air flow.

 

1. There is a scoop, so that as the aircraft is in motion air enters the radiator. Kind of like a ramjet.
2. The air cools down because the fins are colder than air. You will have to trust me that the fins get colder when hooked up to my ambient heat conversion machine. These fins cool down when producing work, so extra heat has to be supplied from the atmosphere to keep the aircraft running; that is the point of the radiator.
3. Of course, drag cant be eliminated, but it should certainly be reduced as it is done when engineering airplanes.

 

So you need a power source to move the aircraft.

And the air temperature versus fin temperature differential is...?
So it will produce electrical(?) power?
Enough to power a turbine sufficiently for propulsion?

If only.
Drag is the bane of aircraft design: it's one reason why such powerful engines are developed. It occurs even within the engines themselves. Drag reduction goes only so far (especially in the real world).

 

Of course, the source is rather unconventional, but the aircraft certainly doesn't float on its own.

1. Hell if I know. The engine will continue drawing heat so it will get cold until an equilibrium is established or until it is caked with ice. This is another problem- this aircraft cannot get too cold or it will freeze, but the colder it is the faster it will draw energy from the atmo.
2. Hopefully it will produce work; I suppose it could be electrical but at the same time it could be heat to boil the propellant.
3. The limiting factor is probably the viscosity of air-
to increase heat conduction from the atmosphere you need larger and larger surface areas that would certainly impede air flows and especially if these surfaces were arranged in a dense grid.

 

No, even ramjets need taking up to 400 mph or so before they start to work.
What is going to get the aircraft moving to make the air enter the intakes?

So you'll need a method of keeping the fins cold and avoiding kinetic heating bringing the temperature up to anywhere near intake ambient.

Heat?
How, if you're keeping the fins cold?
Where is the heat coming from?
Where is the heat flowing to?

 

Hmm. I'm hoping that it will work at low speeds but will produce more and more energy as it is going faster as a way to keep up with increasing friction.

The fins will remain cold because heat is being drained from them using my ambient heat conversion machine; the heat flows into the machine and energy comes out.

I'm trying to combine the random movement of particles to produce macroscopic work. Something that most people would call perpetual motion out of ignorance.

 

DRZion, notwithstanding the fact that your effort could benefit by browsing a thermo textbook, you kinda hijacked the hell out of this thread! Why didn't you just kick off your own?

Don't mean offense, I'm just curious.

 

Fact is that my future tech ties into this kind of engine quite well. Instead of lugging around fuel to cool the air one cools it using an ambient heat conversion machine. The power gained this way could be used to power the lights and lcd s inside the aircraft.

Ambient heat conversion isn't that great of a contender for high altitude flights and is out of the question for space flight because of a thin atmosphere and zero heat, respectively.

 

But it doesn't work that way, and it certainly doesn't share much in common with this engine system! The precooled engine in question is on that precools air to increase it's density, allowing it to flow thorough the engine at a lower speed, and hence makes it more manageable to the turbo-machinery within. No net energy gain is achieved by cooling the incoming air, because the act of cooling the incoming air heats up the cryogenic on-board fuel. If the best rocket fuel didn't happen to need to be cryogenically cooled to be stored conveniently, this kind of engine wouldn't make sense.

Energy doesn't spontaneously come out of cooling air, work needs to be forced into moving that heat away from the air. The real energy comes when you have a hot and cold reservoir, and heat flows from the hot to cool the cold.

I think I get what you're getting at, that if molecules are in constant motion, one oughta be able to "leash" them and get some energy from them. The truth is that the motion of molecules in air stores energy only in the same sense that, say, a spring stores energy when compressed. But if the motion of the molecules in the air are moving the same as the rest of the ambient air molecules (the temperature is the same as ambient), it's like a spring stacked end-to-end with a bunch of other springs, the middle one isn't going to spontaneously release it's energy and expand for no reason unless the springs adjacent to it are allowed to expand too. This is the idea behind the hot and cold reservoir being used to make energy, it's like a compressed spring stacked end-to-end with a not-so compressed spring, and they of course would redistribute their energy such as to be equally compressed. The resulting redistribution of energy within the springs releases additional energy which, in the spring analogy, goes to rapid motion of the springs. Put a load on the springs and they move slower, but you tap some energy from the system! Same deal with air, when the energy (and temperature) redistributes, additional energy goes into convection, physical expansion, and all this can be tapped for useful energy.

 

i am thinking about doing a science project on a next generation aircraft. and since as ElectricFetus pointed out aircraft propulsion tech has plateaued redesigning the engines seemed like a good way to start. give an aircraft precooled jet engines, the engines are cooled by cryogenic hydrogen that is also the fuel for the plane. the hydrogen flows through the inlet before going into the combustion chamber. 2 for the price of one and you are getting some use back out of all the energy you spent cooling down the hydrogen in the first place.

ordinarily a plane with hydrogen fuel would have to have a proportionality larger fuselage, this would ordinarily increase drag all but cancelling out the usefulness of using hydrogen as fuel in the first place. that wouldent be a problem if you used a flying wing aircraft.

this will probably be the basis for a science fair project

if you guys could give me a hand by playing devils advocate that would be great.

thanks

DM