1. Rns

    Rns Member

    And to make things even more complicated there are plans in the works to use bio fuel jet fuel which naturally carries more water for various reasons.

    I am surprised that no one has gone off the deep end about JP-7 which was used for very specific aircraft and pretty much all of them in a spy/secret category.

    The fuel alone had some additives but they also needed to carry ignition inducer for use of afterburners because the JP-7 would not ignite in the afterburner stream without help.
     
  2. MikeC

    MikeC Closed Account

    I hadn't heard that - water in jet systems is a contaminant, because it freezes and blocks fuel lines, so I can't imagine that bio-fuel standards will allow any more water than current ones.

    It as developed for the SR71 & is used by some modern hyper-sonic research craft too for the same reason.

    And so what....????

    ALL fuels have "some additives" - the petrol in your car has "additives" - the oil in it's crankcase is a complicated mix of chemicals, and look at the ingredients next time you buy something packaged & see what additives there are for your body's fuel!

    Do you have a specific claim, or is this just a vague "additives bad, mkay?" accusation?
     
  3. Rns

    Rns Member

    I am not suggesting they are used for intentional spraying.

    Do you know the items used in the fuel and as ignition sources?
     
  4. MikeC

    MikeC Closed Account

    I am unaware of what additives are in JP-7 - AFAIK its characteristics are determined more or less "simply" by choosing a different mix of "normal" hydrcarbons from that used in Jet A1.

    the specification for JP-7 can be seen here
    - there are additives such as lubricity enhancers, anti-oxidants and metal inhibitors that look much the same as those used in Jet A1

    Ignition of the JP-7 in the SR71 is accomplished by injecting a particularly volatile substance -

    - from here
     
  5. Rns

    Rns Member

    And they also mixed the TEB with another pyrophoric liquid.

    That was the @#$% about the 71 if you had to use the afterburners you could be plainly seen and your only defense at that point was sheer speed.

    That was one of the reasons that for a very long time the U2 had no afterburner.

    I guess none of the CT crowd has ever done any deep study of things that actually are and were used in aircraft other than to parrot "top secret leaked" rumors of science fiction.
     
    Last edited: Feb 20, 2014
  6. Rns

    Rns Member

    It isn't "free" water but rather water held in the residual alcohols from the bio fuel process.

    That is what many even quite knowledgeable people miss about current ethanol blended gasoline.

    It isn't only the lower caloric value of the ethanol that lower MPG it is the water that the ethanol carries with it through the engine which keeps all of the alcohol from burning and adds to the production of additional acids and aldehydes out the tail pipe.
     
  7. MikeC

    MikeC Closed Account

  8. Rns

    Rns Member

    We shall see eh?

    I only know first hand from making my own bio fuels and going to ridiculous lengths to attempt to clean and remove ALL contaminants and to recover the alcohols for use in further batching.

    Water doesn't burn in jets any more than it burns in ground based diesels or gasoline engines.
     
  9. MikeC

    MikeC Closed Account

    And were you using the same industrial processes being proposed for this stuff??

    For example one of the major routes being proposed is from Algae - which AFAIK pretty much produces/involves no ethanol at all.

    Indeed - which is why I said it is a contaminant!

    Water in fuel has been a problem ever since aircraft started using hydrocarbons - it is a bit naïve to think that all the work going into changing to biofuels is going to ignore it.
     
    Last edited: Feb 20, 2014
  10. Rns

    Rns Member


    Just a slight correction

    FREE water in fuel has been a problem.

    It may indeed end up being a wash and the net result may be the same as alcohol dried petroleum fuels.

    They may well be "drop in" but the two fuels are not identical and can't be made to be so.

    You can get close but they will never be 100% identical.

    It may very well be as well that there will be government grants to use yet more food stock or at the very least land area converted from food to make "cleaner" jet fuel.

    From my understanding the reason for heavy contrail science study at present is due to the accepted issues that water vapor IS indeed a "greenhouse gas" so I sit and watch the show and competing agendas and more often than not just shake my head.

    Jet engines were "cleaned up" along with their jet fuels so that "only" water vapor or a huge percentage of the exhaust is water vapor and now we are looking at possibly going back and purposely spreading sulfur compounds that we just recently did our best to completely remove from jet fuels.
     
  11. Rns

    Rns Member

    Last thoughts on this.

    ALL oxygen carrying fuels without exception carry additional bound water.

    All biofuels carry oxygen.

    biofuels burn a little cooler which will in many instances increase apparent water vapor at the exhaust and in current jets would seem very likely to increase the likelihood of visible contrails.
     
    Last edited by a moderator: Feb 20, 2014
  12. MikeC

    MikeC Closed Account

    Not sure what your point is any more - Jet A1 is based on hydrocarbons, as is the biofuel version - they are synthetic kerosene, either bio- or Fisher-Tropsch derived - and AFAIK in neither case are they "oxygen carrying".

    they do not burn any differently from regular Jet A1 - that is the whole point of them!

    alcohol-to-jet fuel is a different pathway that is much less advanced - but which involves removal of the oxygen from alcohol molecules.
     
  13. pseacraft

    pseacraft Active Member

    Not quite but it was an effect defense...

    The U2, in any of its configurations, to the best of my knowledge has never had an afterburning engine.
     
  14. Rns

    Rns Member

    I didn't think it did either but I had heard that the last ones in use currently may have for the intended use in the particular area and purpose.
     
  15. Rns

    Rns Member

    The processes used still have a first step involved to make the crude stock.

    I understand the confusion but when you see "burns cleaner" and yet it isn't an oxygen carrier and is identical to petroleum it is talking out of both sides of the mouth.

    There are always trade offs and there isn't any magic when it comes to internal combustion engines and fuel.

    For the record the on road bio diesel available locally is a poor joke compared to simple home esterfied and properly washed biodiesel.
     
  16. MikeC

    MikeC Closed Account

    Biodiesel is quite different from aviation bio-fuel tho and you cannot compare the 2 in any way - diesel itself is quite a crude fuel, and yes there are oxygen atoms in the molecule. Not so with kerosene.

    Again I am unsure what you are referring to as the "crude stock" or why it is important - only the stuff that actually gets burned is important for what comes out the exhaust.
     
  17. Rns

    Rns Member

    Have you compared the btu numbers?

    I may be wrong but it would help if you had some comparisons.

    I will go and look for the stuff I had done a couple of years ago now.
     
  18. MikeC

    MikeC Closed Account

    Did you not read the link I provided above to the IATA factsheet on biofuel?? the fuels have to be DROP IN - that means they have ti be effectively IDENTICAL - down to the BTU value so the fuel control units will meter the right amount and the turbines will not melt!!

    this page provides some value comparison between various standard and jatropha derived fuels - jatropha oil in its raw state is almost identical in calorific value to aviation jet fuel.
     
  19. Pete Tar

    Pete Tar Moderator Staff Member

    Nerds! :p
     
    • Funny Funny x 2
    • Like Like x 1
  20. pseacraft

    pseacraft Active Member

    Ya heard wrong...same plant (F118-GE-101) as the B2 (F118-GE-100) with a few mods.

    http://www.airforce-technology.com/projects/u2/
     
  21. Rns

    Rns Member

    Now look at the BTU comparison in that same chart.
     
  22. Rns

    Rns Member

    I did find some newer systems from several manufacturers but I still do not see any 100% biofuel that is approved for use.

    looks like it is all at this point up to 50 % in a "drop in" replacement.
     
  23. Joe

    Joe Senior Member

    Interesting .
     
  24. MikeC

    MikeC Closed Account

    It does not have a btu figure for jatropha oil - which is why I noted the calorific value.
     
  25. Rns

    Rns Member

  26. Rns

    Rns Member

    A rough comparison can be made with the diesel dervied from it as diesel is very close to the jet fuel but with more of the longer chains.

    I do find it interesting that they left it out and also leave out the values for the jet fuel but then it is not in their best interest to do so as it is not one of the highest energy content base plant oils.
     
  27. MikeC

    MikeC Closed Account

    There is a value for jet fuel - it is given as 19,800 btu/lb or 120,200 per US gallon.

    You seem hung up on comparisons with diesel - perhaps because you use it yourself - but jet fuel has little in common with it as far as hydrocarbons go - saying it is similar but for het length of the chains is about as useful as saying gasoline is the same as diesel except for the length of the chains!
     
  28. Rns

    Rns Member

    Well turbines can run on a wide range of fuels.

    And I have yet to see any as in not one comparison showing that the 100% plant oil derived jet fuel is as close to petroleum based as you seem to be stating.

    Why is the fuel only allowed up to 50 %?

    The last link that now is missing the following pages explained why but alas it is gone.

    I had researched this I guess around three years ago and found test results that do not agree with all the gee wiz press that is out currently.

    And I no longer use diesel as my raw stock supplies have been hijacked by companies grabbing the oil and also grabbing the government grants to make "green fuels"
     
  29. Rns

    Rns Member

    That is for commercially available petroleum based fuel.

    It would be very helpful to find the purely vegetable derived synthetic figures.

    And my memory could be wrong but I recall all fuels having a range of thermal values allowable in their specification.
     
  30. Rns

    Rns Member

    Mike you are insisting that there is magic going on with synthetic jet fuel and I am sorry but I am not one to partake of magical thinking.

    I am doing further re research to find the figures that I already did several years ago.

    Perhaps you could enlighten me on just how the plant oil based fuels and or blends can get lower consumption rates while also reducing emissions while also giving the same thermal output.

    Of course the sulfur will be eliminated but that is not the only newest emission reduction claims that I am seeing in the whiz bang "green" jet fuel world.
     
  31. Mick West

    Mick West Administrator Staff Member

    Perhaps you should quote exactly what you have an issue with?

    "Green" jet fuel will have about the same emissions when burned as ordinary jet fuel. It's basically the same thing. It's not more efficient, it's not less polluting.

    The "green" claims are from lifecycle analysis - i.e. the CO2 emission in creating the fuel.

    EDIT: Actually I see it's claimed "Has shown higher energy density in flight", but not clear how much. I think as Mike says, that as it is "drop in", then the energy density will just be in the same range.
     
    Last edited: Feb 20, 2014
  32. Rns

    Rns Member

    I am afraid it is being sold as a bill of goods very much like the ethanol gasoline mandate was.

    It makes no sense in the larger picture to me and I will go back through my bookmarks to retrieve all the latest claims regarding cleaner and greener advantages of plant based jet fuels.

    The original point I brought forward is that the plant based fuels have the ability to hold more bound water than petroleum based and will likely increase the density of contrails and may contribute to them forming in slightly different atmospheric conditions.

    CTers are not the only group to promote magical miracle solutions to real world problems real or imagined.
     
  33. Rns

    Rns Member

  34. Rns

    Rns Member

  35. Mick West

    Mick West Administrator Staff Member

    From there.
    "lifecycle analyses" being the lifecycle of the production of the fuel.

    http://www.aviationpros.com/press_r...missions-reduction-compared-to-petroleum-fuel
    84% is reduced to 42% when in a 50/50 blend.

    A lifecycle:
    [​IMG]
    Note the cycle includes carbon temporarily sequestered by the plants during feedstock growth.
     
    Last edited: Feb 20, 2014
    • Informative Informative x 1
  36. Rns

    Rns Member

    That does not state the formula used.

    I like to check these things everywhere.

    It looks like they very likely just took the estimate of the total emission from that flight with "non renewable" petroleum fuel but did not include the supply back end for the crop from seed to delivery plus the emissions from transport and processing.

    I should add that the amount of fuel gallons saved was more than used up just in planting and harvesting and then pressing the oil seed.
     
  37. Rns

    Rns Member

    It is not cost competitive

    Nowhere do I see where the cost per pound/gallon of finished fuel is stated.

    It is more government money paid out which we all pay for in taxes.
     
  38. Mick West

    Mick West Administrator Staff Member

    http://www.enviro.aero/blog/2009/04/lifecycle-emissions-reduction.html
    [​IMG]
     
  39. Mick West

    Mick West Administrator Staff Member

    That seems like an entirely separate topic.
     
    • Agree Agree x 1
  40. MikeC

    MikeC Closed Account

    Yes - as I said

    the standard for Jet A1 is Def Std 91-91 - AFAIK rev 7 is the latest and is available on the web if you search
     
    • Agree Agree x 1