TU-155

With biofuel being the new thing the airlines are looking itno, I found a blog entry on Flight that I found rather interesting.

In 1988, the Soviet Union flew a TU-155. It was a modified TU-154B, that had number three engine replaced with a Kuznetsov NK-88 running on liquid hydrogen. The aft portion of the cabin was filled with cryogenic tanks holding the hydrogen at -253C, along with 30 other systems related to the fuel.

After the first few flights, it was switched over to liquid natural gas. The first flight with LNG was made January 15, 1989. Shortly after, the TU-156 was proposed. It would be propelled by three cryo-fueled Kuznetsov NK-89 engines. It would have had 70 seats, with the aft cabin holding the cryo-tanks.

Further proposals included the TU-204K, TU-334K, and the twin turboprop TU-136.

Twenty years ago, long before ‘biofuel’ became a marketing hook, the Soviet Union quietly flew for the first time a modified version of the Tupolev Tu-154B to demonstrate how aircraft could be powered with an alternative energy source.

Designated the Tu-155 the aircraft took to the air on 15 April 1988, its thrust partly generated using liquid hydrogen.

Source

Is there any reason to believe this type of fuel is more dangerous? Also the article states that it is an alternative, not necessarily better for the environment. It really depends on the goals of the builders, alternative fuel, enivronment, or something else entirely.

I personally think it was a major acheivement for the day and era of the testing. With global warming and other delimmas with crude and refined oil prices today, seems as if they were a head of the technology curve.
Good find Zap!!

reply to post by Zaphod58

Doesn't it actually take more energy to "make" hydrogen from sea water than the hydrogen the process produces can generate?
Cost efficiency is still not where it need to be to have wide usuage of hydrogen fuel cells.

That said, good for the Russians - as Allred said, I would think that was a major acheivement for that day and age.



[edit on 4-27-2008 by intelgurl]

Isn't Sir Richard Branson, Founder and CEO (billionaire extraordinaire) of Virgin Atlantic Airways experimenting already with a bio-fuel, or synthetic fuel?

Sheesh, oil at $120 is outrageous....airline travel as we knew it is about to die....

reply to post by intelgurl



Most hydrogen is extracted from natural gas or other fossil fuels because fo that very issue cost. Untill a truly cheap source for hydrogen production can be found it would not really be a true bio fuel.

The precourcer to the A-12/SR-71 was Project Suntan. The CL-400 would have been a giant thermos bottle to house the liquid hydrogen. Too many difficulties were encountered esp dealing with the hydrogen pluys range issues and the project was scrapped.

There is an amusing tale by Ben Rich in his auto bio when Kelly Johnson had him doing research and building the largest civilian controlled hydrogen plant in the world

Originally posted by intelgurl
Doesn't it actually take more energy to "make" hydrogen from sea water than the hydrogen the process produces can generate?
Cost efficiency is still not where it need to be to have wide usuage of hydrogen fuel cells.

That said, good for the Russians - as Allred said, I would think that was a major acheivement for that day and age.
[edit on 4-27-2008 by intelgurl]

That was one reason why they switched to LNG instead of hydrogen. Their ultimate goal was to have a Liquid Natural Gas propulsion system. It fit better into their resource plans.

Originally posted by Vipassana
Is there any reason to believe this type of fuel is more dangerous?

Hydrogen is much safer than standard avgas.

When a hydrogren tank would rupture and burn, evaporation would quickly mean the fuel burns ABOVE the plane - most of it wouldn't actually burn in the airframe at all.

Whereas conventional fuel is a liquid, restrained by gravity, and will burn in the airframe.



People only think hydrogen is dangerous because of Hindenburg, and then very few actually died of burns - most of the fatalities were from jumpers. There have been studies comparing hydrogen and avgas, with hydrogen the clear winner - but public perception is different.



Oh, and your right... there are still big questions over its environmental impact - particularly the dumping of water vapour at high altitudes. It could have a larger effect than all of the traditional pollutants combined.

[edit on 28/4/08 by kilcoo316]

Originally posted by intelgurl
Doesn't it actually take more energy to "make" hydrogen from sea water than the hydrogen the process produces can generate?
Cost efficiency is still not where it need to be to have wide usuage of hydrogen fuel cells.

Yeap, conventional electrolysis is very inefficient.


However, newer approaches using bacteria have yielded promising results:

See here

Originally posted by kilcoo316
most of the fatalities were from jumpers.

It's a vicous world out there in teenage fashion...

Originally posted by HowlrunnerIV

Originally posted by kilcoo316
most of the fatalities were from jumpers.

It's a vicous world out there in teenage fashion...

I think it was granny's knitted wool jumpers that caused the problem...


static build up leading to discharge

Originally posted by kilcoo316

Hydrogen is much safer than standard avgas.

When a hydrogren tank would rupture and burn, evaporation would quickly mean the fuel burns ABOVE the plane - most of it wouldn't actually burn in the airframe at all.

Whereas conventional fuel is a liquid, restrained by gravity, and will burn in the airframe.

You point would be valid if we were talking about hydrogen in its gaseous form - but we are not. Liquid hydrogen actually has a boil off rate of around 1%, meaning even if you pour some into a bucket, it would remain in a liquid state for quite a while. That means its going to remain around your crashed aircraft for some time.

Secondly, theres a lot more liquid hydrogen than aviation fuel in the equation - while LH has a better energy density per unit of weight than JetA, it has a poorer energy density per unit of volume - its about 3 to 4 times less dense when talking about energy in volume, meaning you have to have 3 to 4 times as much onboard the aircraft for the same mission.

Lastly, you are assuming all the fuel tanks are equally and instantly breached, to allow the fuel to escape. This does not happen.

Originally posted by RichardPrice
You point would be valid if we were talking about hydrogen in its gaseous form - but we are not. Liquid hydrogen actually has a boil off rate of around 1%, meaning even if you pour some into a bucket, it would remain in a liquid state for quite a while. That means its going to remain around your crashed aircraft for some time.

Secondly, theres a lot more liquid hydrogen than aviation fuel in the equation - while LH has a better energy density per unit of weight than JetA, it has a poorer energy density per unit of volume - its about 3 to 4 times less dense when talking about energy in volume, meaning you have to have 3 to 4 times as much onboard the aircraft for the same mission.

Lastly, you are assuming all the fuel tanks are equally and instantly breached, to allow the fuel to escape. This does not happen.

Your last point answers the first

Liquid hydrogen will not burn in concentrations above 75%. (3 parts hydrogen to one "part" air). Thus, it pretty much has to be a gas to burn.


The middle paragraph is somewhat irrelevant. You carry less weight in hydrogen but more volume for the same energy. With the added aircraft weight, you will need more energy, so would carry additional energy in comparison to a conventional design. But that is like comparing a 737 to a 777 in a crash.




This isn't the paper I read previously - I dunno where it is, if I find it, I'll post, but is useful anyway (you can get it on sciencedirect).


Hydrogen aircraft and airport safety

Schmidtchen, U., Behrend, E., Pohl, H-W. & Rostek, N.
Renewable and sustainable energy reviews, Vol. 1, No. 4, pp 239-269, 1997



A quote:

"While most experts agree that the risks associated with hydrogen are even smaller than in the case of conventional fuels [1] (not even considering the ecological balance), the public have a quite different opinion."


[1] Is hydrogen safe?

Hord, J
NBS Technical Note 690, 1976

Originally posted by kilcoo316

Your last point answers the first

No it doesn't - liquids and gasses have different reactions in the situation.

Liquid hydrogen will not burn in concentrations above 75%. (3 parts hydrogen to one "part" air). Thus, it pretty much has to be a gas to burn.



However, assuming the fuel tanks are ruptured, the liquid hydrogen will be all over the place and it will be boiling off while on the ground. This means there will be a fairly decent gas mixture near the crash site with an ongoing replenishment. It won't simply evaporate as you suggested in your original post.

The middle paragraph is somewhat irrelevant. You carry less weight in hydrogen but more volume for the same energy. With the added aircraft weight, you will need more energy, so would carry additional energy in comparison to a conventional design. But that is like comparing a 737 to a 777 in a crash.

A higher volume means the aircraft either has to be bigger or carry less because of physical space limitations - convert a 777 to liquid hydrogen (LH) and you either have to cut the range by 75% if you rely on the normal fuel tanks capacity, or you cut the payload capacity by 75% because you are carrying a significantly greater volume of fuel which has to be stored somewhere - like the cargo hold.

The weight difference is pointless because you also carry more weight due to the extra weight of the increased strength fuel tanks, increased thermal protection and higher capacity fuel pumps (due to lower energy density, you need to pump fuel at a faster rate) you would also have to carry due to the nature of LH - you can't just throw it in the same holding tanks and expect everything to be hunky dory, its a cryogenic substance with all the problems of handling that come with that.

Put into context of the discussion, the human body doesn't care if hydrogen has a lower energy density, if its on fire its going to kill. After the crash, it doesn't take a lot to cause a fire, and if you are carrying three to four times the volume of fuel, theres a greater chance of that fuel catching light.

Hydrogen may not be as dangerous, but its certainly no silver bullet.

Originally posted by RichardPrice
No it doesn't - liquids and gasses have different reactions in the situation.

All current concepts use LH in the tanks, there are a number of benefits.

Originally posted by RichardPrice
However, assuming the fuel tanks are ruptured, the liquid hydrogen will be all over the place and it will be boiling off while on the ground.This means there will be a fairly decent gas mixture near the crash site with an ongoing replenishment. It won't simply evaporate as you suggested in your original post.

Within 60 seconds of being exposed to 300 deg K surface temps, you can expect between 2 and 4 inches of liquid hydrogen to regress (dependant on surface texture).

It will not take long to boil with the attendant heat from a fire.

I maintain, the majority of the LH will be H2 before ignition and will burn safely above the aircraft.

A higher volume means the aircraft either has to be bigger or carry less because of physical space limitations - convert a 777 to liquid hydrogen (LH) and you either have to cut the range by 75% if you rely on the normal fuel tanks capacity, or you cut the payload capacity by 75% because you are carrying a significantly greater volume of fuel which has to be stored somewhere - like the cargo hold.

The weight difference is pointless because you also carry more weight due to the extra weight of the increased strength fuel tanks, increased thermal protection and higher capacity fuel pumps (due to lower energy density, you need to pump fuel at a faster rate) you would also have to carry due to the nature of LH - you can't just throw it in the same holding tanks and expect everything to be hunky dory, its a cryogenic substance with all the problems of handling that come with that.

You reading my stuff? I said:

"With the added aircraft weight, you will need more energy"

Put into context of the discussion, the human body doesn't care if hydrogen has a lower energy density, if its on fire its going to kill. After the crash, it doesn't take a lot to cause a fire, and if you are carrying three to four times the volume of fuel, theres a greater chance of that fuel catching light.

If it is on fire above the plane, it is not going to burn, asphyxiation may be an issue.

Hydrogen may not be as dangerous, but its certainly no silver bullet.

Hence: "Hydrogen is much safer than standard avgas."

Originally posted by kilcoo316

All current concepts use LH in the tanks, there are a number of benefits.

There are also a huge number of problems with that, some of which I covered before.

Within 60 seconds of being exposed to 300 deg K surface temps, you can expect between 2 and 4 inches of liquid hydrogen to regress (dependant on surface texture).

It will not take long to boil with the attendant heat from a fire.

I maintain, the majority of the LH will be H2 before ignition and will burn safely above the aircraft.

And I totally disagree - whats it going to do, rise 30 ft and *then* decide to burn? I think not.

You reading my stuff? I said:

"With the added aircraft weight, you will need more energy"

I am reading your stuff, you obviously are not reading mine - replacing JetA with LH does not reduce the weight, while it does increase the volume. You have three to four times more LH to do the same job, which means three to four times more fuel tank capacity.

If it is on fire above the plane, it is not going to burn, asphyxiation may be an issue.

Again with the 'above the plane' rubbish - if its bioling off of spilt liquid hydrogen, the plane and ground is most likely going to be soaked in it. Its not going to be burning above the plane, its going to be burning around the plane.

Hence: "Hydrogen is much safer than standard avgas."

Safe is a matter of degree, theres nothing to suggest a plane flying using hydrogen is any *more* safe than a current JetA fueled aircraft.

As an example, the flash point of hydrogen is *vastly* lower than aviation fuel.

I think one important point to remember with THIS particular project was that the ultimate goal of this was to have an aircraft powered by Liquid Natural Gas, NOT hydrogen. The PROTOTYPE was originally flown with hydrogen, but it was only flown with a few flights before they switched over to LNG. LNG was a much better fit with the Soviet resources than hydrogen was.

This is why I love ATS, cause nowhere else will you see an engage, intelligent argument about liquid hydrogen.

Now, what's the final verdict?

Shattered OUT...

Hydrogen doesn't scare me all that much, any decent high school lab has the bits for a jacob's ladder...

but this does scare me

en.wikipedia.org...

I'm no expert, but can liquid hydrogen leaking from ruptured tanks create a BLEVE?

On which subject: LPG is a damn good source for BLEVEs, so how about LNG or CNG?