Is it possible a super fuel may be discovered or made in the lab that be more fuel efficient?
Most modern space rockets 90% of the rocket is fuel to get that 10% of payload into space!!! Do you think a super fuel may be discovered or made in lab that would be more fuel efficient? Where may be only 5% of the rocket is fuel to get 90% or 95% of payload into space!!
I was reading some thing about chemistry limiting factor may make this impossible some thing to do with chemistry factor unless some sort of exotic matter is discovered.
What would be these chemistry limiting factor or thermodynamically limiting factor.
The same answers that were given there apply here, for the most part. Cost, safety, and the limits of physics. Are you looking for something specific about theoretical energy density of fuels?
I’m talking about rockets and super fuel and super fuel for rockets and not they should make it or why they are not making it!!! But is it even possible chemistry and thermodynamically limiting factor.
Some people say it is chemistry not possible for space rockets to get much more fuel efficient than they are. With out exotic matter being discovered some kind of chemistry limiting factor or thermodynamically limiting factor.
Well, if you’re looking for a theoretical upper limit, that would be a total conversion of matter into energy, completely wiping out the matter, following the famous E = mc² formula. That would give you an energy density of 90,000 terajoules, or 90 billion megajoules, per kilogram of fuel. Kerosene has, according to Wikipedia, 42.8 megajoules per kilogram, so the theoretical upper limit would be more by a factor of about two billion. How in Earth you would find a technology that can actually convert the fuel into energy completely is a very different question.
Let’s first exclude nuclear fuels. Nuclear rockets are possible and have been designed, but they come with all the downsides that you might imagine. As space-only engines they may yet work out, but as launchers they’re just not happening.
There are more energetic fuels than hydrogen and oxygen, but they are… evil. For instance, fluorine is a more powerful oxidizer than oxygen. But fluorine is toxic and corrosive and no one who values human life wants to come anywhere near the stuff.
Another possibility is the boranes. They have somewhat worse mass density than hydrogen, but are better than kerosene. And they have excellent volumetric density, so they should make great rocket fuels. Unfortunately, burning them leaves nasty deposits on the inside of your engine and no one figured out how to fix the issue.
One huge problem with all high-energy fuels is that they tend to be explosive. That’s really just the nature of it; you pack a lot of energy into the fuels and it wants to come out one way or another. Many fuels have a habit of rapidly decomposing all on their own.
You may want to read Ignition by John Clark if you’re really interested in this stuff, and want to hear some amusing stories.
To get thrust out of a rocket engine, you need two things:
-mass to toss out the back
-energy with which to impart some exit velocity on that mass
The fuel (and oxidizer, if any) gives you both the mass and the energy. In fact, setting a fuel flow rate sets also sets the energy flow rate, since you only get so much energy by oxidizing a kilogram of fuel.
Your rocket gives more thrust if you toss that propellant mass out the back with a lot of velocity. Since propellant mass flow rate also dictates energy flow rate, that means you want a propellant that releases a lot of energy per unit mass when you oxidize it.
The winner for efficiency/specific-impulse so far is hydrogen, as you can see from this graph of specific impulse. Each H2 bond has a lot of energy bound up in it, and very little mass. In fact, it has the least possible mass of any chemical bond. Every other element out there has an atomic mass considerably greater than hydrogen, but the bonds they make aren’t proportionately more energetic, so pretty much every other fuel you can think of is going to give you a lower theoretical maximum specific impulse.
One problem with hydrogen is its density, or lack thereof. Stored as a cryogenic liquid, its density is only about 71 grams per liter. The Saturn V rockets were massive, but the first stage was fueled with kerosene, which has a density of around 800 grams per liter; had they used liquid hydrogen instead, the first stage would have been much more voluminous. Similarly, the space shuttle used hydrogen for its main engines, but these were primarily useful for the later phase of the flight, after the solid booster motors (fueled with very dense ammonium perchlorate, 1950 grams per liter) had done most of the heavy lifting. If the space shuttle had been designed to launch its payload from earth’s surface on just hydrogen rockets, it would have been absolutely gigantic.
In looking at that specific impulse chart, my question for the real rocket scientists here is this: Why does the space shuttle main engine fall so far short of the theoretical maximum indicated for hydrogen?
Some people say chemical rockets really cannot get any more fuel efficient for some reason. There is some kind of chemistry limit.
That some how a super fuel may be discovered or made in the lab is not possible a chemistry limit make it not possible for chemical rockets to get much more fuel efficient.
Some chemistry limiting factor or thermodynamically limiting factor.
That is somewhat limited to the combination of stable states of the elements and exhaust products that need to be really small.
Because it doesn’t include the oxygen. Their chart assumes the oxidizer is “free”.
The highest specific impulse fuel tested is a lithium-fluorine-hydrogen tripropellant, which achieved 542 seconds (compare to 452 for the SSME). However, to keep lithium liquid it has to be 453 K, whereas the hydrogen has to be 21 K. It’s in no way practical and yet is still only ~20% better than plain hydrogen-oxygen (admittedly, the rocket equation means that the 20% translates into much more than a 20% payload increase).
so the fuel numbers are without oxygen on board, but the SSME performance spec incorporates the mass of oxygen? If so, that’s a poorly made chart.
If that’s the case, then the specific impulse of the hydrogen/oxygen combo should be about 5400 * 2/18 = 600 s, is that right? So the SSME achieved 452/600 = 75% of its theoretical maximum possible specific impulse? That seems a little better.
That 25% shortfall still bears discussion. Starting with an SSME, what would need to be done to make a hydrogen/oxygen rocket achieve its maximum theoretically possible specific impulse?
I agree, but I think the point is that air-breathing devices (turbofans, ramjets, scramjets, etc.) are all much better than even the best rockets.
If every bit of chemical input energy went into exhaust velocity, that sounds about right. Of course you can’t hope to achieve this, even on a theoretical basis–Carnot is a problem, if nothing else.
For starters, an infinitely large nozzle. In a vacuum, ignoring practical considerations, you want as long a nozzle as you can get. The more you expand the gas, the cooler it gets. In principle, you can expand all the way down to the CMB temperature of 2.7 K. The Carnot losses would be minimal at this point since the combustion temperature is ~3500 K.
The pumps use quite a lot of energy. Some rockets use tank pressure instead of turbopumps, but these are generally impractical for large rockets (though Truax’s gigantic Sea Dragon possibly demonstrated otherwise). There is the expander cycle which essentially converts waste heat from the exhaust into pump energy, but this also has scaling limits, and you don’t get any waste heat with a theoretically perfect nozzle.
I’m sure SoaT can provide a longer list of inefficiencies but I think these are the big ones.
One thing is that all hydrogen engines run significantly fuel-rich–i.e., there’s lots of unburned H2 in the exhaust. This is wasteful in a theoretical sense but beneficial practically, since the lighter exhaust carries away less thermal energy in internal vibrational modes, and keeps combustion temperatures cooler.
A different method may be required to really achieve a new standard of propulsion. Currently electrically powered Xenon in a ion drive is much better then the theoretical best rocket fuel, however the power output is very small. It does point to other methods may be better, much better, then what we do now.
So if I understand it for rocket to work using newton’s third law For every action, there is an equal and opposite reaction. For rocket to go up, mass has to be toss out the back. The more mass being toss out and really fast the more thrust.
Where does energy come into play here?
So for rocket to have high thrust you have two option for high thrust.
1 toss that propellant mass out the back with a lot of velocity
Or
2 toss a propellant mass that is more dense.
Where does energy come into play here.
And how does any of this correlate to some fuels are more fuel efficient than other fuels.
In fact the only really important thing for high performance rockets is specific impulse. And the winner at present is Mercury Ion motors using electrostatic acceleration.
Probably the ultimate would be Tungsten or Uranium(?) Ion motors. All that’s required is generating the electrostatic fields - which is presently done in Mercury Ion spacecraft using solar panels.
Energy is conserved, so you can’t get any more energy into the mass you throw out theback than there was in your energy source. You have a fixed amount of energy, and you know that mass - that absolutely defines the maximum velocity of the mass you eject.
The complication for conventional rocket motors is that the mass is created by the burning of the fuel. So the mass is doing two things here. The fuel is the source of the mass, and is also the reaction mass. Because of this things get messy. The energy is limited by the chemical energy of the fuel components, and the nature of the reaction mass is dictated by the combustion products. So you don’t have an easy answer, you have to balance the compromises between energy available, combustion components, safety and logistics of the fuel you choose, and cost.
After all of this, for any sort of conventional rocket motor we know we are pretty much at the limit of what is feasible. There are no vastly more energetic chemical reactions around that we don’t know about, and of the very energetic ones we do have there is a clear sub-set of those that are viable as a fuel. Further, we already know what is available as potential combustion products, and what is the best. So, within a very small set of constraints, we can be as close to sure as it gets that there is no super fuel for a conventional rocket motor yet to be discovered. New super rockets will need something much more exotic than simply new chemicals. This is where you get into the realm of ideas like laser propulsion. Where you keep the energy source on the ground and only lift the reaction mass. So you can optimise the reaction mass, and not pay the cost of lifting the energy.
Right after my previous post I remembered that practical rockets in a vacuum are always underexpanded - but to what degree, I have no idea. If the bell of the SSME were extended to infinite size, how much would the performance improve? IOW, to what extent is the finite nozzle length causing the SSME to fall short of its theoretical maximum specific-impulse performance?
Well it’s not the only thing, timing is important to efficiency in orbital travels. If you can’t get the power at specific moments you need more fuel to do the same thing and these ion engines produce very little thrust. Still it’s much higher efficiency more then makes up for that loss.
A friend of mind was saying super fuels are impossible because of chemistry and thermodynamically law.
In short of extremely exotic states of matter no way of it getting any more fuel efficient.
That thermodynamically speaking chemical energy is somewhat limited to the combination of stable states of the elements and as exhaust products need to be quite small symmetric molecules so that their thermal energy isn’t lost as wasteful vibration/rotation. reactions of the elements or small molecules that produce such products are required.
So there is chemistry and thermodynamically law. And chemical energy is at that limit. now.
so the fuel numbers are without oxygen on board, but the SSME performance spec incorporates the mass of oxygen? If so, that’s a poorly made chart.
now.