Re: Alternative jet fuel?


Steve & Leslie Swartz wrote:
> Eunometric:
>
> Sorry to rain on your parade- but what are you going to burn to make the
> hydrogen?

Nuclear, Wind, Solar thermal electric are the best candidates in order
of best price.


> Whatever you are going to burn to make the hydrogen, you are of
> course well aware that you will have to burn much more of it, due to the
> inefficiencies of H2.

Electrolysis followed by liquifaction can be achieved at 57%
efficiency. This is state of the art for current commercial technology.

In addition there is the thermochemical water spliting that uses the
heat of a reactor to directly split water into hydrogen and oxygen.
This it once required High Temperature Gas Cooled Reactors) HTGR
reactors to achieve 850C opperating temperatures but a copper iodine
cycle can now opperate at 500C.


>
> Replacing petroleum at use point of use with hydrogren would require the
> consumption of 140% (assuming perfect solution of all technical issues,
> assuming zero cost of infrastructure conversion, etc.) of the original
> petroleum that was consumed in the first place.


This argument is a red herring. Proponents of Hydrogen have always
focused upon Hydrogen obtained from renewable resources or nuclear.
Coal is also seen as a source because it can be converted to hydrogen
mauch easier than it can be converted to synthetic petroleum fuels (and
the CO2 produced during conversion could be sequestered geologically).
Natural gas is only seen as an interim source to help build up the
distribution infrastructure.


>
> And- oh by the way- while we have studied the effects of petroleum leakage,
> spillage, outgassing, etc. etc. quite extensively I'm not sure we want to
> pay the tremendous environmental cost of dumping tremendous quantities of
> yhdrogen into our atmosphere . . .

Hydrogen gas is not toxic in anyway and simply floats away rather than
pool or settle anywhere.

There are some fairly extensive studies of hydrogen leakage (or rather
boil off). The main concern is that the leakage can not be limited in
a large infrastructure in some worst case scenarios. There are fears
of effects on the ozone layer and also the eventual depletion of the
earths water as the hydrogen leaks into space. It is important to
realise that hydrogen is not lik the chlorine atom that catalyses ozone
destruction but would simply be converted to water once only.
Compared to some of the other problems we have seen with other
technologies they are fairly minor. Wikipedia has a discusion on this.

I am not advocating a 'total' hydrogen economy. I see it as a niche
for certain types of jet transport and as a replacement for natural gas
in the chemicals industry.

It is possible to extract CO2 from the atmosphere and combine it with
hydrogen using a number of reactions (sabatier, lurgi, fisher-tropsch)
to make alcaholes and hydrocarbons. Efficiencies of 44% have been
achieved and 60% is conceivable when integrated with thermochemical
water spliting.


>
> --
> *********************************
> Steve & Leslie Swartz
> Abolish the Police State
> and
> the Welfare State
> VOTE LIBERTARIAN!
> ********************************
> "Eunometic" <eunometic@xxxxxxxxxxxx> wrote in message
> news:1127116962.090625.15590@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > Orval Fairbairn wrote:
> >> In article <1127090476.831895.225560@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> >> "Eunometic" <eunometic@xxxxxxxxxxxx> wrote:
> >>
> >> > Christopher wrote:
> >> > > Could a jet engine run on hydrogen, even a military jet engine, i.e.
> >> > > like a...F 16 engine, so instead of the F 16 having it's fuel in
> >> > > rubberised bladder fuel tanks you have a single tank [to save weight
> >> > > made of composite wound fibers] with liquid hydrogen?
> >> > >
> >> > >
> >> > > --
> >> > >
> >> > > Christopher
> >> >
> >> >
> >> > Most of the problems of storing, refueling LH (Liquid Hydrogen) safely
> >> > on aircraft and cars have already been solved.
> >> >
> >> > Hydrogen is an excellent fuel for jet engines: its rapid mixing and
> >> > stable flame actually significantly reduce combustion chamber length.
> >> > The worlds first jet engine, von Ohain's HeS 1 ran of hydrogen.
> >> >
> >> > You do need 4 times the volume to store LH but it is 1/3rd the weight
> >> > and overall there are energy savings (depending on aircraft mission
> >> > range)
> >> >
> >> > Here are some links of experimental LH aircraft:
> >> >
> >> > http://www.haw-hamburg.de/pers/Scholz/dglr/hh/text_2001_12_06_Cryoplane.pdf
> >> >
> >> > http://www.flug-revue.rotor.com/FRheft/FRH9809/FR9809k.htm
> >> >
> >> > http://www.hq.nasa.gov/office/pao/History/SP-4404/ch8-12.htm
> >> >
> >> > (This is the same people that developed SR-71)
> >> > "The Suntan team, particularly Seaberg, was not convinced that
> >> > Johnson's pessimism over range was justified. Contracts for additional
> >> > design studies were let not only with Lockheed but also with North
> >> > American Aviation, Boeing, and ConvairFort Worth. The additional study
> >> > at Lockheed did nothing to change Johnson's view. In all, 14 designs
> >> > were considered, ranging from bombers to Mach 4 reconnaissance aircraft
> >> > with comparisons between using petroleum fuels and liquid hydrogen.
> >> >
> >> > For the same range, Lockheed found that aircraft using liquid hydrogen
> >> > were larger but weighed less at takeoff than those using petroleum
> >> > fuels. At a given speed, hydrogenfueled aircraft exceeded the altitude
> >> > limits of petroleum-fueled aircraft by 3000 to 6000 meters.45 By March
> >> > 1958, a Boeing design appeared to be the most promising of the new
> >> > studies. Powered by four engines, it would fly at Mach 2.5, 30 500
> >> > meters altitude, [165] and have a radius of 4100 kilometers-almost
> >> > twice that of the CL-400. The Boeing airplane was also considerably
> >> > larger than the CL-400, with a length of 61 meters, a delta wing span
> >> > of 61 meters, and a takeoff weight of 75 750 kilograms.46"
> >>
> >> Certainly, you CAN run a jet engine on hydrogen, just as you can run any
> >> internal combustion engine on it. The engine will be very happy, with
> >> fewer pollutants in either the air or in lubricating oil or on
> >> combustion surfaces.
> >>
> >> HOWEVER:
> >>
> >> Remember, you can't just pull up to the fuel pump and start pumping LH2
> >> into the tanks.
> >>
> >> You first have to purge all air with dry nitrogen, to get rid of any
> >> stray water vapor and stray oxygen. (LH2 will freeze O2 into a very
> >> unstable FROX, which will detonate).
> >>
> >> Then you have to purge the N2 with He, so you don't freeze the N2 in
> >> critical parts (valves, pumps, etc.) when you add the LH2.
> >
> > This has to be done probably only once in the life of the tank. There
> > are also solutions. BMW have developed a system that "rains" a mixture
> > of gaseous and liquid hydrogen out of the same filling hose (actually a
> > robot arm) and needs only one hose to both fill and vent the gases.
> >
> >>
> >> You also have to vent the tanks to an approved burn pond, situates far
> >> from the fuel pit.
> >
> > Indeed there are virtually nill gases that need to be vented from the
> > BMW (auto) system and they are easily either burned of or reliquified.
> >
> >
> >>
> >> Also, you can't use wet wings anymore, because the tanks require a lot
> >> of insulation, which obviates the use of wet cells. Special tanks are
> >> necessary, thus adding a lot of extra weight.
> >
> > The tanks must be bigger but the weight they have to hold is less,
> > however there in insulation and cryogenic materials. Overall the
> > cryoplane is not far behined the classic hydrocarbon aircraft.
> >
> >>
> >> Maintenance becomes non-trivial, as special precautions have to be
> >> taken. With room-temperature liquid fuels, you can just drain or cap off
> >> fuel lines. Not so with LH2.
> >
> > No doubt. But there may be solutions.
> >
> > If hydrogen takes of it will have a niche market I think but it will
> > takeover up to 50% of the fuel market.
> >
> > Something looks like killing of mineral pertroleum whether its either
> > going to just run out or whether climate change concerns will do it.
> >
> > Given the choice of a LH Jet trasport between airport hubs or clipper
> > ships I suspect we'll solve those problems to favour the jet.
> >

.

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