The lean and rich ratings for the C3 fuel

Discussion in 'Aviation' started by tomo pauk, May 5, 2014.

  1. tomo pauk

    tomo pauk Creator of Interesting Threads

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    People, Id like to invite the knowledgeable to share their information about the ratings of the German C3 fuel here.
     
  2. Denniss

    Denniss Active Member

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    Per german definition it had 100 Oktan but this value may have been obtained using methods different from the allied side.
     
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  3. Mike Williams

    Mike Williams Active Member

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    This might be of interest:

    [​IMG]
     
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  4. Milosh

    Milosh Well-Known Member

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    #4 Milosh, May 5, 2014
    Last edited: May 5, 2014
    Does anyone have a data sheet as Mike posted for Allied 100 octane fuel for comparison?
     
  5. Aozora

    Aozora Well-Known Member

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    Not quite the same, but A.C Lovesy of Rolls-Royce describes how 150 grade was developed on pages 222 223 (5 6) of this article:

    Development of the Rolls-Royce Merlin (1946 article)
     
  6. tomo pauk

    tomo pauk Creator of Interesting Threads

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  7. Piper106

    Piper106 Member

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    For those who don't want to go through several hundred pages, the short version is;

    - early C3 fuel (late 1940 to early 1941) was 95 octane number for lean mixture with 110 performance number for rich mixture i.e. 95/110
    - late 1943 vintage C3 was 97 octane number lean and 125 to 130 rich i.e 97/130

    I recall seeing reports that 1944 to 1945 C3 was rated 140 to 145 performance number for rich mixture i.e 97/140
    Not quite as good as American / British '100 octane' fuel under lean mixture conditions, but it appears that it stayed pretty well neck and neck with with the best allied fuel in terms of rich mixture rating.
     
  8. Koopernic

    Koopernic Active Member

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    #8 Koopernic, May 5, 2014
    Last edited: May 5, 2014
    German B4 fuel was 87 octane. It was produced by hydrogen being compressed at 450 atmospheres into a coal toluene slurry in the presence of iron catalyst. It took very special alloys to resist the pressures, temperatures and hydrogen embitterment that occurred with conventional alloys. Fuel with a RON of about 80 could be distilled of this and then increased to 87 through the addition of TEL (tetra ethyl lead).

    To produce C3 fuel iso-octane 22% was added to the B4. Iso-octane was produced first by gasifying coal with steam and oxygen in a Lurgi gasifier. The coal was scrubbed of sulfuric and other acids with ammonia. The resulting gas was adjusted via pressure swing absorption and then passed over a chromium catalyst to produce butanol. The butanol was dehydrated to n-butene in a multi-step process and this was then polymerized into iso-octane. The butene was also needed for production of buna-n and buna-s synthetic rubber and this prevented the adoption and expansion of C3 production early in the war.

    It's worth considering the huge investment required for coal handling, oxygen and ammonia production as well as the reactor vessels and piping etc which has been compared to producing 1/3rd of the US navy.

    It's worth noting this early C3 (green dyed) was about RON 93/115, at least according to early allied analysis of downed German aircraft and drop tanks.

    Only small amounts were used in the DB601N engine for the Bf 109E4/N and Bf 109E7/N towards the end of the Battle of Britain. It retained some use in the Me 109F1/F2 but the Me 109F4's DB601E reverted to B4 as did the Me 109G's DB605A. The Fw 190A initially used B4 for its BMW801C but then switched to C3 with the introduction of the BMW801D.

    British 100/130 fuel added 30% to the power of the Merlin (that's what the 130 term is about) and increased Merlin power from about 1030hp to 1310hp. (thereabouts depending on supercharger settings etc)

    It's difficult to see the Spitfire being superior in any substantive way without this 20% extra power over the Me 109 despite a tighter turning circle. Even if an aircraft can turn inside another but has superior power it can use it to just get on the tail of its opponent using superior speed or to sustain the turn longer without loosing height.

    As the hydrogenation plants were developed the source of n-butane was switched to exploitation of byproduct gas rather than gasification of coal.

    British development of 100/130 fuel initially relied upon distillation of exotics but essentially was industrialized to come out of a process called acid alkylation which produced the alklyte that tended to produce the rich mixture response. The US 100 Octane fuel (which was probably somewhere between 100/120 to 100/125) relied upon catalytic cracking using a regenerated catalyst.

    Various forms of cracking were not so applicable to the German hydrogenation produced fuel, but they did start construction of alkylation plants in 1940 of which only one got into production by wars end (1943). Production of iso-octane by polymerization remained the primary method. The expansion of C3 production continually increased as did its quality but was effected by the bombing campaign just as a new generation of engines relying on C3 was coming out. This lead to cancellation of many engine types, serious delays and the introduction of types that could run better on B4. The intended Jumo 213E and DB603EM of the Ta 152C and H was effected as was the Me 109's DB605DCM engine.

    German C3 fuel certainly reached 97/130 but it has to be noted that allied 100/130 was really 103/130+ and that 100/150 was really 110/150. Having a lower lean rating does effect engine design and impacts the performance in rich.

    Whereas the allies were able to run their entire bomber, trainer, transport,fighter fleet on 100/130 the Germans were able to do so only for a portion of their fighter fleet. Many BMW801D2 installed in bombers were reset to run on B4.

    There is no evidence of the production of anything like 100/140. I've seen kurfurst posts but never a single document and even he has it as an R+D fuel intended to boost the DB605 engine from 1.98ata to somewhere between 2.2 to 2.4 ata.

    Either way, non of the German engines we discuss here ever benefited from an operational fuel better than 97/130.

    I would argue then that the Germans had about a 4% disadvantage when C3 is compared to allied 100/130. The disadvantage was even greater when the B4 used in Jumo 211 and DB605 engines is concerned. That these engines were able to stay reasonably competitive is a testament to their advanced engineering, particularly that of their fuel injection systems. Nevertheless this made a big difference.

    Jet fuel, despite the quantities required, was much easier to produce synthetically giving more yield for the same amount of coal with far less plant. There were even a series of 3 gas turbines developed to power panther and tiger tanks. (described in Anthony Kay's book. ) One of the reasons the He 162 was developed was the fact that a fleet of Me 262 would consume to much fuel for the petrochemicals industry to produce to maintain the sortie rate required.
     
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  9. vikingBerserker

    vikingBerserker Well-Known Member

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    I've learned more about fuel in 8 posts than I ever knew, well done gents and great info!
     
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  10. Aozora

    Aozora Well-Known Member

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    #10 Aozora, May 5, 2014
    Last edited: May 5, 2014
    ??? the 100 refers to the fuel's rating at lean settings, while the 130 refers to the rating at rich, it has nothing to do with the 30% extra power generated by the Merlin. The fuel used by all of Fighter Command's frontline aircraft - not just Spitfires - from late 1939/early 1940 was always referred to as 100 Octane. The 100/130 rating was introduced in 1943 with the introduction of a new fuel developed to a joint British/American specification:

    [​IMG]
    [​IMG]

    View attachment Fuel Development 1945.pdf
     
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  11. Koopernic

    Koopernic Active Member

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    #11 Koopernic, May 6, 2014
    Last edited: May 6, 2014
    The first number in the 100/130 figure is the RON or Research Octane Number. The second number is the performance number or PN. The octane number is established by varying the compression ratio of a special test engine with a fuel running stoichiometric (about 14.2 lbs air to 1 lb fuel) to the point that knock develops equivalent to an equivalent octane/heptane ratio. Since octane can't exceed 100% the neither can RON so the second number is the PN number. It is established by running the mixture 'rich' and increasing the compression ratio till the maximum power is established. The ratio of rich power to lean power is the PN or Performance Number. The lean power base used is that of pure iso-octane. It doesn't seem to matter much whether the increase in power was by increasing compression ratio of the engine or pressure increase by the supercharger. Hence a 100/130 fuel can potentially produce 30% more power in the appropriate engine when running rich. Rather than increase manifold boost the German DB engines used a mechanically different engine with higher compression ratio when that engine was optimized for C3. This likely didn't increase the power as much but it did increase power without reducing fuel efficiency.

    100/130 was available by the BoB which means early 1940, The UK had stockpiled large amounts. During this time US supplied fuel ordered by Britain was for some 4 months worth only 100/125 at the time due to differences in plant making UK versus US fuel. This is because the US had developed its own 100 octane specification based more around economical sustained power. The more aromatic British fuel caused problems in the P-38 since Europe is colder than Long-beach California because it fractionated in the inlet manifold leading to some cylinders knocking. The Germans with their direct cylinder injection saved themselves a great many problems in regards to fuel fractionating, fuel formulation and fuel distribution. Fuel distribution issues was one of the more serious problems the R-3350 initially suffered from when the B-29 entered service.

    There is a lot more to fuels than RON and PN eg the vaporization issues which is probably why it took the allies till 1943 to fully harmonize fuel standards. Once this was done the aero engine manufacturers and air forces could make recommendations about increasing boost limits with less safety margin with the fear that fuel variations would nullify them or that issues like fuel fractionation, as happened to the P-38, could arise. During the 1970's German auto manufacturers developed the MON (motor octane number) to take into account the problems that were occurring under high speed autobahn running which thereby takes into account such properties. P-47's went through a period of engine problems which caused engine cut outs. This was caused by vapor lock when the aircraft pulled out of dives.
     
  12. Milosh

    Milosh Well-Known Member

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    You can provide documentation to support that statement?
     
  13. Koopernic

    Koopernic Active Member

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    #13 Koopernic, May 6, 2014
    Last edited: May 6, 2014
    It's not hard to find corroboration on the internet. Unfortunately lost my PC a few weeks ago and still have recovered the hard drive to my new one.

    Basically RAF was using US supplied 100 octane in 3 squadrons by 1937. James Doolittle having encouraged the development of 100 octane fuel. The British formulated their own version with a superior rich mixture response and stockpiled about 500,000 tons by the time of the Battle of Britain. The decision to completely convert over taken in March 1940. Presumably there were some pressure sensing aneroid capsules that need to be replaced or adjusted to control the manifold pressure delivered by the supercharger and something to increase the fuel/air ratio in the carburetor when WEP was engaged.

    A few links nonetheless
    http://grandprixengines.co.uk/Note_58-2.pdf
    The Narrow Margin of Criticality: The Question of the Supply of 100-Octane Fuel in the Battle of Britain
    http://mycommittees.api.org/rasa/jf...ry of Aviation Fuel Development in the US.pdf
    A Short History of Aviation Gasoline Development, 1903-1980
    A little on the German situation.
    http://www.airpower.maxwell.af.mil/airchronicles/aureview/1981/jul-aug/becker.htm

    The two processes used were catalytic cracking (as opposed to thermal cracking) developed in US and latter alkylation, I think developed at BP).

    The Germans synthesized iso-octane which was apparently more cumbersome but improved as they changed feedstock from syngas to byproduct gas from their hydrogenation plants.
     
  14. Aozora

    Aozora Well-Known Member

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    The modifications to the Merlin II II to use 100 Octane:

    [​IMG]
    [​IMG]

    Pilot's Notes:
    [​IMG]
    [​IMG]
    [​IMG]

    Boost control cut-out on Hurricane:
    [​IMG]
     
  15. Milosh

    Milosh Well-Known Member

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    I can find lots of info on 100 for the BoB but when it comes to 100/130, it is much later than the BoB.
     
  16. Glider

    Glider Well-Known Member

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    Going from the book quotes posted above, 100/130 octane was an improvement on the (can I call it regular) 100 Octane as used in the BOB.
     
  17. Shortround6

    Shortround6 Well-Known Member

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    The fuel used in the BoB was about 100/115-120. Not all batches were identical as the test procedure for measuring 'performance number' had NOT been worked out yet. Some batches of "american fuel" were actually 100/98 or so at the time.
    As has been stated many times, the difference between American 100 octane and British 100 octane was the amount of allowable aromatic compounds in the fuel.

    The American fuel could NOT contain more than 2% aromatic compounds.
    The British fuel could NOT contain less than 20% aromatic compounds.

    Aromatic compounds tend to eat or dissolve certain rubber compounds or items commonly used in fuel systems at the time including the linings of some early self sealing tanks. Obviously the fuels were NOT interchangeable.

    The Americans came up with a specification for 100/125 fuel and a number of engines were rated on it but before much use overseas was seen (if any, south pacific?) ) they had standardized on the British 100/130.

    However that is not the end of the story even for 100/130 fuel as the early specification called for no more than 3.0 ml of lead per gallon. In Nov of 1941 this was changed to 4.0 ml and the middle of 1943 it was changed again to 4.6 ml per gallon (post war Military 100/130 fuel could have 4.6ml while commercial 100/130 could have only 3.0 ml).
    While the actual performance change was minor, the change from 3.0ml to 4.0ml only changed the performance number by about 4% it allowed the use of different base stocks (more straight run gasoline) and increase production by 25%. The change to 4.6ml increase PN by 2% but increase production by 7%.
    Straight run base stock and cat-cracked stock do not behave the same when blended with aromatics or behave the same with similar amounts of lead added.

    There were quite a variety of blends that would meet the specifications and there was quite a bit of juggling going on to maximize production as refining capacity and techniques changed and as supplies of different aromatics changed (not all crude contains the same percentages of the different compounds). ALl of these compounds had different amounts of BTUs per gallon, different vaporization temperatures and so on. This created a few problems later as not all of the these blends actually performed the same in service use. Some of the compounds tended to separate out with time or temperature.

    BTW, the US most certainly did NOT run it's entire bomber, trainer, transport,fighter fleet on 100/130 fuel. The trainers ran on anything from 73 to 91 octane fuel depending on what the engines had been built for. Advanced fighter training, at least for the early part of the war, used 91 octane and the engines used retarded timing and limited throttle travel or restricted boost controls to prevent over boosting with 91 octane fuel. Most transport aircraft operating inside the US used 87 or 91 octane fuel.

    Engines responded differently to the high PN fuels and just because one engine saw a 30% gain in power does not mean another engine could or would.

    Adding to the confusion is the fact that several specifications for fuels between 100/130 and 100/150 were tried, that is small batches made and used in a few airplanes. In some cases the fuel did increase power in one engine but made no difference in allowable power in another and were judged not worth complicating the fuel supply situation.

    It is also worth noting that ALL of the US and British octane ratings and Performance numbers were obtained using one model of single cylinder test engine. Hundreds were made and issued to refineries, labs and government test agencies so there would be the least amount of confusion or interpreted results. Please note that the only way to measure octane or PN is in a test engine.
     
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  18. Aozora

    Aozora Well-Known Member

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    #18 Aozora, May 6, 2014
    Last edited: May 6, 2014
    View attachment Critique of fuel Tests in Single-Cylinder Engine.pdf
    A document on testing fuels NACA, July 1940:

    View attachment 19930081595_1993081595.pdf

    and a critique on testing fuels in single cylinder engines; this discusses German fuel tests

    View attachment Critique of fuel Tests in Single-Cylinder Engine.pdf

    I take it this is the type of test you're referring to S6?
     
  19. Shortround6

    Shortround6 Well-Known Member

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    #19 Shortround6, May 7, 2014
    Last edited: May 7, 2014
    The same link that was posted in the supercharger thread also goes on to a second book that was often bound with the first book.

    "Development of Aviation Fuels" by S.D. Heron.


    Development of Aircraft Engines: Two Studies of Relations Between Government ... - Robert Schlaifer - Google Books

    It is a very valuable book but it was written shortly after WW II and by a man who, while intimately involved with allied fuel development ( he was at least part responsible for the Performance Number scale and other things) had little access to war development in other countries.
     
  20. mhuxt

    mhuxt Active Member

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