87 octane fuel vs. 100 octane !

[Topspeed]

If there is a person who knows about oil industry I 'd like to ask how much more difficult is it to produce 100 octane fuel than it is to do 87 octane what was used in Me 109:s for instance ?
100 octane fuel in Mustang for instance possibly burned better.

Any comments or views on this ?

rgds,

Juke

[Kurfürst]

I think it only differed in added aromatics and antiknock additives. The advantage of higher grade fuel is that you can maintain higher boost/power wihtout fear of detonation.

100 octane fuel was an W.allied priviliage. Germany was using it from 1939 - in fact German 100 octane C-3 synthetic fuel had better knocking qualities than British 100/130 grade due to its high aromatic content.

The Bf 109 also used 100 octane in some of it`s subtypes, though 87 octane was more typical early in the war. 100octane useres included the DB 601N powered versions (E-x/N, F-1/-2,) in `40-41, DB 605D, AM, ASM powered versions (late G-14, G-14/AS, G-10, K-4) in `44-45 .

There`s a bit of confusion with octane ratings, there are many standards for it...

[Topspeed]

OK !


Thanks Kurfürst.


rgds,

Juke

[Bronsky]

If there is a person who knows about oil industry I 'd like to ask how much more difficult is it to produce 100 octane fuel than it is to do 87 octane what was used in Me 109:s for instance ?

It was found after WWI that "normal" gasoline predetonated when used in sparked internal combustion engines ("knocking" as car users say, which has somwhat more serious consequences in aircraft engines ) before the completion of the piston compression stroke. This made engines less efficient in practice than in theory. Methods were developed for measuring the difference between theoretical and actual performance, which resulted in the Octane Number. Straight run gasolines were around 56 octane.

At the same time, petroleum makers introduced "cracking" technology. This maximised the gasoline production from a given crude oil stock at the expense of using up a small quantity of rare-earth catalysts. A further benefit was that cracked gasoline stocks were found to have octane ratings in the 70--76 range. It was also discovered that tetraethyl lead (TEL), as an additive, significantly increased octane ratings.

In practice, you can consider the octane rating as an indicator of performance per pound of fuel burned. If you have more advanced fuel, you have a more powerful engine for a given weight which increases takeoff weight - and therefore range - and gives you better combat performance (depends on the altitude and the power setting, but let's not go into that now).

Now the Germans were perfectly aware of the basics of the technology involved - although Allied research continued on the matter, so the Germans couldn't have developped the 150 ON fuel in use in Allied airforces by 1945 without a major additional research effort - but they never produced fuel of higher than 96 octane for regular service. The reason is that by adding a ton of TEL from normal oil stocks (including those produced in the synthetic plants) you could get as high as 96 ON but to go to 100+ octane fuels required reprocessing the 87-96 ON avgas by reforming, which would cost up to a third of the initial stock in the process. The Allies could afford to do that, but the Germans couldn't.

That is one of the reasons why they decided that the future for German air power rested on the turbojet, which would be able to operate on a much less heavily refined fuel that could be produced from crude oil and coal in much larger quantities.

So in terms of avgas, the Allies only really had an edge by 1943 when their 100/130 ON fuels were developped (100 at lean mixture, 130 at "rich", i.e. in combat) which gave their engines a 30% better power to weight ratio. This was up to 50% by the end of the war.

[Uncle Joe]

Bronsky, you are quite wrong. As Kurfürst pointed out, C3 fuel had very good rich mixture response (=anti-knock value) and was almost equal to British 100/150 fuel. And that high rich PN of the C3 was obtained without resorting to very high TEL content.

As a general note, I wish folks realize that octane scale ends at 100 and all ratings above and PN, Performance Numbers. There is not such thing as e.g. 150 octane fuel.

[Bronsky]

Bronsky, you are quite wrong.

Why, how helpful of you to make a blanket statement like that instead of quoting the parts that you believe to be wrong.

As Kurfürst pointed out, C3 fuel had very good rich mixture response (=anti-knock value) and was almost equal to British 100/150 fuel. And that high rich PN of the C3 was obtained without resorting to very high TEL content.

As a general note, I wish folks realize that octane scale ends at 100 and all ratings above and PN, Performance Numbers. There is not such thing as e.g. 150 octane fuel.

Right you are. I wanted to keep things simple, and there you go.

So there was a 100/130 PN fuel available by 1943, and a 115/145 PN one available more or less by D-Day - the latter was mostly US more than British, by the way. The British did develop a 150 PN fuel which wasn't reliably available until very late in the war.

However, I stand by my claim that no German fuel stocks of ON number higher than 96 were produced for regular service. German 96 octane was produced by the addition of large quantities of TEL to standard avgas produced from cracked crude stocks and synthetically from coal. In order to produce 100 octane gas as well as base stocks for higher-than-100 octane fuels to follow, this avgas would have had to be reprocessed by reforming, with the consequent loss of up to 1/3 of available gasoline.

If this is wrong, then I'd be interested in the details, you can keep the blanket statement.

In a nutshell, what I'm saying is that the Germans managed to match Allied fuel until fairly late in the war, but they couldn't afford to develop really high-PN fuels because that was too expensive in terms of raw fuel supply. So they were increasingly being outpaced, not because of intellectual shortsightedness but because of a lack of resources, and this is one of the reasons why they looked to jet engines as a way out of their predicament (which was true but not a realistic solution within WWII technological parameters, but that's another topic).

[JamesL]

If I remember my chemistry courses, octane rating is a measure of performance compared to a standard of 2,2,4-trimethyl pentane which is also known as iso-octane. The local airport, which has 3 pumps, rates its avgas as 87, 100, and 130 octane. I believe they use 100 octane on their hi-horsepower (>200 HP) engines.

[brodeur]

If there is a person who knows about oil industry I 'd like to ask how much more difficult is it to produce 100 octane fuel than it is to do 87 octane what was used in Me 109:s for instance ?
100 octane fuel in Mustang for instance possibly burned better.

Any comments or views on this ?

rgds,

Juke

It is not a matter if it is dificult or not, The germans did not know how to refine fosil oil in to high octane fuel.

The me 109 had an injection engine and you can mix in a small part of waster to increase the compression ratio which they did.

[Bronsky]

It is not a matter if it is dificult or not, The germans did not know how to refine fosil oil in to high octane fuel.

Actually, my understanding is that they did - though they didn't push the technological research as far as the Allies in the mid-40's - know how to do, but couldn't afford to so they didn't try.