Why is hydrogen not generally used or seen in jet engines?

[aquaticharpy]

It's cleaner, cooler burning, and dissipates faster than propane or gasoline, so it doesnt linger too long while your turbine is off, yet most projects here use propane or some kind of fossil fuel ie: Gasoline/Diesel.

What are the drawbacks of using hydrogen gas in a homebuilt turbine/ what reasons not to?

Thanks
John

[racket]

Hi John

Hydrogen would be a great fuel , but its availability is limited , much easier to use hydrogen atoms combined with some carbon atoms .

Cheers
John

[monty]

I used to work with liquid and gaseous hydrogen as a fuel. (rockets)

It is possibly the WORST fuel to deal with there is. I have never bought into the hype-rogen economy nonsense.

H2 has terrible energy density. It has to be a cryogenic liquid to have ANY use. It is only good as a rocket fuel because the combustion products are relatively light, the temperatures are high and therefore the ISP is really good...on paper. In practice, the fact that it has such a low energy density, and other drawbacks make it less desirable to fuels like methane.

It likes to explode....a lot. It has an enormous flammability limit compared to almost everything. It burns at very lean and very rich mixtures. See: Hindenburg...

Early jet engine designer Von Ohain used this wide flammability range and high flame speed to help develop the hardware until they got the combustor worked out.

It is impossible to contain. Being a very small molecule and requiring high pressure for storage as a gas it leaks past all manner of seals.

It even leaks into the metal that contains it- embrittling the metal and making for limited tank/piping life.

It burns with a clear flame that you can't see. Before IR cameras, the fire crews waved a straw broom in front of them as they advanced to a fire. If the broom caught on fire, they knew to stop....otherwise it was them getting torched.

It's a terrible aviation fuel because of the energy density issue. The whole plane would need to be a gas tank.

Compare this to a hydrocarbon that is a nice dense stable liquid at room temp and can be stored in a plastic can, while being safe for grandma to pump into her car.....

Mother Nature prefers hydrocarbons to store energy....for very good reasons.

[miuge]

Watched a clip about the topic on Youtube some time ago:
www.youtube.com/watch?v=imhla4eovcg

[CMDR_Boom]

Jan 6, 2020 18:42:32 GMT -5 monty said:

I used to work with liquid and gaseous hydrogen as a fuel. (rockets)

In the interest of opinions, 80% of what you said is only YOUR opinion or heavily influenced by bias, so put on your flame suit. 

It is possibly the WORST fuel to deal with there is. I have never bought into the hype-rogen economy nonsense.

Is it the worst fuel? Nature doesn't seem to think so. I rather enjoy the constant byproduct of THE SUN for one example, which does not run on hydrocarbons. If we're talking about base supply, I direct your attention to the Periodic Table. But in practical human terms, at present, hydrogen hasn't had the resources dumped into R&D that many of the traditional hydrocarbons have. Let's throw a few hundred billion at the problem and have this conversation again. 

It has to be a cryogenic liquid to have ANY use. It is only good as a rocket fuel because the combustion products are relatively light, the temperatures are high and therefore the ISP is really good...on paper. In practice, the fact that it has such a low energy density, and other drawbacks make it less desirable to fuels like methane.

Sure, as a ROCKET fuel. Now put an on-demand hydrogen generator next to your ground-based gas turbine electric generator skid. It is not stored at subzero temperature, it's only combustion byproduct is water vapor in the form of steam which could be recaptured and reused for any number of things, it can be made in great quantity on site, etc etc, and all of your complaints go away completely. 


It likes to explode....a lot. It has an enormous flammability limit compared to almost everything. It burns at very lean and very rich mixtures. See: Hindenburg...

Really? Using the Hindenburg, that was also painted in a film containing ROCKET FUEL, was one of a very limited example of a bad idea in engineering. But if you want to go down that road, how many SRB's have decided to go tits up very inconveniently or have caused a launch to be scrubbed during the shuttle program's existence? More than one? Yeah. 
Let's put hydrogen in a proper container and any liquid fuel of a consumer level in it's container and involve them in a car accident. Which one would you prefer to have in your vehicle and be seated next to in the event of impact? 

It even leaks into the metal that contains it- embrittling the metal and making for limited tank/piping life.

To my knowledge, any gas in storage is under exceptional pressure--some more than others--which tends to have that effect on metal tanks, such as for example, oxygen, propane, or acetylene, which is so unstable that it requires it's own storage medium INSIDE the tank.  

Mother Nature prefers hydrocarbons to store energy....for very good reasons.

Mother Nature prefers to store energy in whatever medium is most efficient for it's given process.

Hydrocarbons by way of petroleum, or coal for that matter, is very convenient for humans that have discovered how to harness it in many forms from vehicle fuel to plastic, but it is far from the best fuel derived from anything found in nature. It does jack all for plants. It takes millions of year to form naturally. In the global or universal scale, it's quite scarce. It's hardly clean or efficient to produce. If Rockefeller had put a less or equal amount of resources into producing hydrogen on a commercial or global consumption scale 100 years ago, imagine what we could have now. 

I'm of the opinion that hydrogen is very useful for jet engines, but there's a lot to be optimized in the process that we have available now to getting there. The most limiting factor of which is the global economic concern which is fighting tooth and nail to maintain another generation of oil, or what will happen to the economy as we know it when the rug gets pulled out from under the oil empire. It's a touchy subject for a lot of people, like most of the globe a lot. Let's not throw science and history out the window, however, when we have this conversation. 

[monty]

OK CMDR you got me...The worst fuels are actually the hypergolics....RFNA or maybe Hydrazine, but at least they have high energy density.... and you might conceivably use hydrogen for stationary applications where gas storage is possible.

Under no circumstances do I want pressurized hydrogen in my car....ever. Maybe a metallic storage lattice....but they are not dense enough.

Hydrogen is no fun to work with, and it's not something you can dig out of the ground. If I have to make a fuel from scratch, as an energy carrier... why not add a few carbon atoms through catalytic processes and have a nice stable alcohol or hydrocarbon liquid? That is useful as a NON-stationary fuel. Even for stationary applications, storage costs money. And hydrogen embrittlement is not the same as what happens with other gases..look it up. Just by adding one carbon- ONE! you get CH4 which is much nicer to deal with and can be made into all manner of liquid fuels (see: Sabatier, Fischer-Troppish processes). 1 CO2 molecule for every 2 water when burned..... Pump it into a greenhouse and make the plants grow faster!

Why use hydrogen over a nice dense liquid? I want a good scientific answer from somebody.

Water being the only product of combustion does not count. This only happens if you burn it in pure oxygen. In air is another thing entirely. Because of the high flame temp, hydrogen makes a horrible fuel for combustion engines in air. You get a lot NOX formation. So that argument in its favor doesn't wash.

If only water as a product is the goal use hydrogen peroxide....not too nice either.

Tell me one instance where a natural process stores energy as pure hydrogen as a living thing, I'm not talking about thermonuclear fusion! All living things store energy primarily as FAT, carbohydrate, or alcohol ie hydrocarbon, or oxygenated hydrocarbon.

We are of differing opinions about un-carbonated hydrogen's usefulness as a transportation fuel. Mine won't be changed until someone builds it, and sells it at a non-subsidized profit while paying taxes like everyone else. And if they do, it will be stored in a metal or metal-carbon lattice and consumed in a fuel cell....not a combustion engine.

When that happens I will happily purchase you the beverage of your choice and publicly admit I am wrong.

I'm done.

[monty]

I forgot:

one thing I do like about hydrogen: a small hydrogen torch is excellent for welding thermocouples....just so you don't think I totally hate it.

[finiteparts]

Well I thought that I might weigh in on this since I did spend several years of my career designing ultra low emission combustors for power generation turbines and a big part of that time was spent designing for high hydrogen fuels.

First point...for ground based engines, it was a good fuel, especially when you are trying to eliminate carbon emissions. The Department of Energy spent some big money on trying to launch the first carbon sequestration power plant that would gasify coal and pump the carbon bearing gases back into the ground, leaving a blend of nitrogen and hydrogen fuels called syngas. There were a lot of big dreams for this technology that never came to be.

We must remember that the beauty of a gas turbine is that it can function on any form of enthalpy increasing fuel...but some fuels are better than others.

I can tell from some of the comments that some people have never worked with hydrogen, while some people have. If you have, you are definitely in the camp of telling people to NOT use it...ESPECIALLY hobbyist.

As Monty has pointed out, hydrogen molecules are the smallest ones out there and they do diffuse into metals and wedge themselves between the metal's crystal lattice, causing interstitial stresses that embrittle the metal...thus the term "hydrogen embritttlement". Not all metals are equally susceptible to this kind of crystalline level attack, but without a good resource telling you what to use and getting the metal quality certifications, you are running a big risk.

Other gases do not do this. Go Google methane or propane embrittlement and tell me what you find...I'll give you a hint...nothing!

The only seals we were allowed to use were..."welds". A flange and gasket do not work for H2...it will leak through those like crazy. If we had a location that required a flange or a Swagelok fitting, we had to have a sniffer there to detect when the leakage was too close to the flammability limit. While I am on the topic of flammability limits, that is one of the biggest safety issues.

Methane in air has a flammability range of 5% to 15% by volume in air...gasoline is around 1.2% to 7.1% by volume in air.
Hydrogen is from 4% to 75% by volume in air!!!

Then, lets say we do get a flammable concentration built up, the next problem is that the minimum ignition energy require to get the H2 going is tiny! Like a spark from some static electricity buildup. H2 requires only 17 micro-joules, while the next fuel up the HC ladder is CH4 and it requires 300 micro-joules.

Are we seeing the bigger picture yet. As Monty pointed out, the H2 flame is a pale blue and almost invisible in daylight...so you won't even know your fuel lines are burning till it is too late. Also, they can't add mercaptan to give the gas an oder, because H2 is so light that the mercaptan molecules (being heavier), just can't follow the H2 gas as it diffuses away.

On top of everything cited above, H2 has a nasty habit of detonating. If the concentration sits somewhere between 18.3% to 59% H2 by volume in air then you are in range of where detonation can occur. Notice that the detonation limits are orders of magnitude wider than just the flammability limits of methane or other CH fuels. If you have a mixture in this range contained in a volume, you can easily achieve the transition from deflagration to detonation.

I hope that I have painted a sufficient image of just how unsafe the use of H2 can be. In the right situation and with the right tools, it can be used safely and effectively...but I don't see that as something that the hobbyist has at their disposal.

Unfortunately CMDR BOOM, we have to burn hydrogen, while nature gets to uses a fusion reaction to convert the hydrogen mass into energy. Not exactly equal comparison.

As for the comment on the lack of research and funding for H2 as a fuel, that is a very incorrect statement. Since the advent of the jet engine, the US government has spent billions on the development of higher energy, better fuels...and you know what we are using in 2020...basically kerosene. Even for ground based power generation, the cost of making H2 systems work (on low emissions systems) outweighed the benefit.

The use of H2 is very promising for high speed engines were you need all the flammability that you can get just to keep that little candle burning in the supersonic hurricane that is coming through the engine, but the ridiculously low volumetric energy density of the H2 means that the fuel tanks, which now have to be high pressure containment vessels (read that statement as meaning "heavy"), take up all the space in the airframe. Go look at Project Suntan (Lockheed) if you want to see how far that got. The complexity of just making the fuel lines aircraft level safe is a daunting task, let alone the rest of the fuel system. If aircraft or engine manufactures could make the carbon free by just switching to H2, they would be all about it, to get that competitive edge. But the logistics of implementing H2 safely is staggering.

The green nature of H2 should also be questioned as the bulk of it today is produced by reforming natural gas. I am not sure what happens to the carbon that is stripped off and thus the H2 in a bottle might be of little benefit to the global CO2 production. There maybe a small amount made by electrolysis of water, but that process is upside-down on the energy of production scale.

I hope that I may have made a small case for avoiding the use of H2, based solely on the safety aspects. With my experience on how rigorous we had to be to make sure safety was #1, I am just a tad bit concerned that the home hobbyist might not be so rigorous.

- Chris