WWII aviation gasoline

[Grittis]

What do the numbers mean in the aviation fuel grade designation 100/130?
Were the different fuel grades dyed different colors in the USAAF?
What grade was referred to by the British term "purple passion?"
While most of the American octane boosters involved tetra-ethyl lead, what were the main octane boosters added to British aviation fuels? Were the aviation fuels blended in England or at the refineries over seas? I see the names of the Dutch refineries in Curacao and Aruba as important.

 

[Tom Fey]

Octane ratings can not exceed "100" (100 = detonation resistance equivalent to100% iso-octane), so values over 100 are termed "Performance Numbers" (PN). The "100" number in PN 100/130 is the octane rating at lean mixtures and the "130" number is the Performance Number at rich mixture. Tetra-ethyl lead was the predominant agent used by the American and the Brits to boost the octane ratings of their fuels. Fuels were dyed various colors to denote the octane/PN ratings and I'll leave it to others to define the Allied and Axis fuel color assignments.

 

[Grittis]

Octane ratings can not exceed "100" (100 = detonation resistance equivalent to100% iso-octane), so values over 100 are termed "Performance Numbers" (PN). The "100" number in PN 100/130 is the octane rating at lean mixtures and the "130" number is the Performance Number at rich mixture. Tetra-ethyl lead was the predominant agent used by the American and the Brits to boost the octane ratings of their fuels. Fuels were dyed various colors to denote the octane/PN ratings and I'll leave it to others to define the Allied and Axis fuel color assignments.

Thanks, Tom. I am also interested in the distribution of 100 octane fuel in East Anglia among the U.S. bomber bases. Pipelines did exist in a network that served the 8th AAF and RAF, although I have not seen their top secret wartime locations. To which ports did the ocean tankers deliver the fuel from the US and Carribean? The amounts of fuel used by a Bomb Group was significant, and I have seen that the bases received fuel by truck delivery and not pipeline spurs. Is that true? If so, would that mean high traffic levels of tankers on UK minor roads? My particular interest is in the 389th BG at Hethel and how close it was to the pipeline network.

 

[Luft.4]

A bit of a backgrounder (from a publication I am working on):

"American fuel chemist Dr. Graham Edgar was the first to make iso-octane, discover its anti-knock value, and develop a method by which iso-octane could be produced in 1926.[1] The following year he came up with the octane rating system as a measurement of the 'anti-knock' tendencies of a fuel,[2] knock being the audible sound from a fuel's auto-ignition in the cylinder outside of the normal ignition phase. This auto-ignition, usually caused by pressure, damages engine components leading to increased maintenance, decreased performance and ultimately catastrophic failure. For the creation of the octane rating scale, two reference fuels were compared: isooctane (2,2,4 trimethylpentane) and n-heptane. These were used as the scale's 100 and 0 points respectively. At the time, isooctane was the most anti-knock fuel available while n-heptane easily ignited.[3] Levels of 'knocking' were recorded at different ratios of isooctane and n-heptane to get points of reference for the scale, then the test fuel's anti-knock tendencies were compared against these ratios to find a 'match'. Here it should be noted that the knocking resistance of fuel is strongly dependent on variables such as combustion chamber size, temperature and the air-to-fuel ratio. Changing these variables will also change the octane rating despite using the same fuel."

As correctly stated above, there is no 100+ octane fuel moleculary, rather a fuel which performs X% better than pure iso-octance under certain conditions (usually rich mixture).

 

[EwenS]

This is a short article on the workings of petroleum storage & distribution in the UK in WW2. There is a series of references at the end for you to follow up. It includes a map of the pipeline network in 1944.

https://journals.sagepub.com/doi/full/10.1177/0020294013499112

As for import sites the main ones were on the Mersey near Liverpool and at Avonmouth near Bristol.

Oil was also delivered to an oil terminal at Bowling on the Clyde, west of Glasgow, where there were a number of different storage facilities nearby. Distribution was then by rail. Not sure if it included aviation grade fuels or not. Some of the storage tanks around there were destroyed during the Clydebank blitz in March 1941.

Rail distribution also played a major part. While today there is about 10,000 miles of track in the UK, in 1914 there was some 20,000 miles which pre the Beeching cuts of the 1960s still extended to 17,500 miles. This is a map ofvthe network in 1957, which wouldn't be that different from WW2

Note the extensive branch network (the thin red lines) especially through East Anglia where the US airbases were.

That map doesn't show all the stations that existed. Many of the local lines had stops in nearly every town and village where goods and passengers would be picked up & dropped off to service local needs.

When you look at the RAF Expansion Scheme airfields built in the 1930s it is noticeable how many were built close to the main railway lines, often with their own railway spur lines. An Expansion Scheme airfield typically had 6x12,000 gal spread across 3 separate sites with each tank separated from its partner by 100 ft, and buried under concrete protection. An underground pump room was placed between them. Piping then ran to tanker filling points.

 

[Geoffrey Sinclair]

Mighty Eighth War manual by Roger Freeman notes road transport, the British grey pool, shuttled fuel from rail depots to airfields, though at times the US needed to use its own road tankers. The strain become such that the Thames was reopened to fuel imports in October 1943 and a pipeline was laid from the Thames to the first Air Division Area, by April 1944 Bassingbourn reported as the first station to receive fuel direct. It looks like Hethel is almost exactly on the pipeline to near Norwich, second Bombardment Division Area.

 

[Grittis]

A bit of a backgrounder (from a publication I am working on):

"American fuel chemist Dr. Graham Edgar was the first to make iso-octane, discover its anti-knock value, and develop a method by which iso-octane could be produced in 1926.[1] The following year he came up with the octane rating system as a measurement of the 'anti-knock' tendencies of a fuel,[2] knock being the audible sound from a fuel's auto-ignition in the cylinder outside of the normal ignition phase. This auto-ignition, usually caused by pressure, damages engine components leading to increased maintenance, decreased performance and ultimately catastrophic failure. For the creation of the octane rating scale, two reference fuels were compared: isooctane (2,2,4 trimethylpentane) and n-heptane. These were used as the scale's 100 and 0 points respectively. At the time, isooctane was the most anti-knock fuel available while n-heptane easily ignited.[3] Levels of 'knocking' were recorded at different ratios of isooctane and n-heptane to get points of reference for the scale, then the test fuel's anti-knock tendencies were compared against these ratios to find a 'match'. Here it should be noted that the knocking resistance of fuel is strongly dependent on variables such as combustion chamber size, temperature and the air-to-fuel ratio. Changing these variables will also change the octane rating despite using the same fuel."

As correctly stated above, there is no 100+ octane fuel moleculary, rather a fuel which performs X% better than pure iso-octance under certain conditions (usually rich mixture).

Thanks for the info on octane quantification. It's complicated, relying on standard equipment and testing protocol. Many different hydrocarbons have been tested for their effect on engine 'knock' or pre-ignition. Most, even if they slow the pre-ignition, can't meet the requirements of simplicity and economy.

 

[Grittis]

Mighty Eighth War manual by Roger Freeman notes road transport, the British grey pool, shuttled fuel from rail depots to airfields, though at times the US needed to use its own road tankers. The strain become such that the Thames was reopened to fuel imports in October 1943 and a pipeline was laid from the Thames to the first Air Division Area, by April 1944 Bassingbourn reported as the first station to receive fuel direct. It looks like Hethel is almost exactly on the pipeline to near Norwich, second Bombardment Division Area.

Thanks for the memory jog from Freeman's book. I used to have a copy about...
EwenS's reference showed the 60 km pipeline from Saffron Walden NE to Hethersett (Norwich). So by the end of '43, the pipeline system was in place to supply the 8th AAF bases.
Q: what was the 'British grey pool'? A civilian or military transport service? The US also supplied road tankers for fuel delivery. I can only imagine a 19 yr. old airman with a 45 ft tanker negotiating the country roads at night in E. Anglia...
I see Thetford and the terminus at Hethersett as depots. The trucks could only pick up fuel from the depot locations, I presume? BGs shown that are close to the line are Bury St. Edmunds, Hethel, Old Buckingham and a few more.

 

[Grittis]

Thanks for the memory jog from Freeman's book. I used to have a copy about...
EwenS's reference showed the 60 km pipeline from Saffron Walden NE to Hethersett (Norwich). So by the end of '43, the pipeline system was in place to supply the 8th AAF bases.
Q: what was the 'British grey pool'? A civilian or military transport service? The US also supplied road tankers for fuel delivery. I can only imagine a 19 yr. old airman with a 45 ft tanker negotiating the country roads at night in E. Anglia...
I see Thetford and the terminus at Hethersett as depots. The trucks could only pick up fuel from the depot locations, I presume? BGs shown that are close to the line are Bury St. Edmunds, Hethel, Old Buckingham and a few more.

Geoffrey, I think it was Freeman's Mighty Eighth War Manual that had a spot on "purple passion" as the common British name for the experimental 130/150 grade fuel that was introduced in early 1944 to a few fighter groups for evaluation. It was dyed purple and basically was the highest octane fuel used during WWII, though not wide spread. It shows up in my father's writings from Stalag Luft III as the name of an innovative POW treat made from Welch's Concord grape jelly and cottage cheeze. Bright purple, sweet; what's not to like? A snack or dessert? He said it was, as many Kriegie inventions, an acquired taste. Dad was there from June '44, so that would be the right time for the term to start circulating.

 

[Geoffrey Sinclair]

Freeman does not specify where the term grey pool came from, the assumption is civil vehicles painted grey. They were the standard supply method but at times US tankers were needed as well, later came direct pipelines. When it comes to the UK pipelines they were for fuel, not just aviation fuel. The 100/150 fuel was dyed purple, I think 100/130 dyed green as aids to identification.

Early British 100 grade fuel was around 100/125, US less, then came the joint specification of fuels, the US was looking at lowering the rich mixture performance in the interests of more production, the British resisted and the compromise was to raise rich mixture performance which created 100/130 grade.

It would be worth checking out "Aviation Gasoline Production and Control", Army Air Forces Historical Study 65

In 1944 some RAF fighters in Europe and the 8th Air force fighter units started using 100/150 fuel. The 8th Air Force received its fuel supply from the British, so records consumption in imperial gallons starting in May 1944 100/150 grade consumption totalled 53,321,258 gallons by end April 1945. Peak consumption 7,036,248 gallons in July 1944.

The US had produced test quantities of 115/145 performance number by the end of 1944 (75,000 barrels in December 1944). They wanted the new fuel but they could not produce enough 100/130 even as late as March 1945, when 100/130 production was 525,000 barrels a day and more 115 fuel meant even less 100 fuel. It is clear some 115 performance number fuel made it to the Pacific in 1945, in what was essentially a series of tests by both the USAAF and USN.

As for other contenders that might have made it, in May 1945 the British were experimenting with a 130/170 fuel. I am sure the US was also trying various other high performance number blends.

 

[Luft.4]

The 115/145 fuel would have been killer in the Pacific, boosting the lean-mixture cruise performance of aircraft. In early 1944, 120/150 fuel was being tested and this was the fuel ultimately desired (woe to those opposing the USAF should this have been introduced!) but 115/145 was produced instead.

 

[Art Medcalf]

By the end of WWII, the USA was developing Triptane. Shell actually produced Triptane fuel for the 1948 Cleveland Air Races. The performance number was 200/300. That information and a list of no less than 45 anti-knock (detonation reducing) fuels come from an AAHS Journal article on Racing Merlins in the Summer 1990 issue. The next best fuels were: benzine, tolulene, and xylene.
Artie Bob

 

[Daggerr]

A bit of a backgrounder (from a publication I am working on):

"................... This auto-ignition, usually caused by pressure, damages engine components .......

Not caused by pressure, but by temperature.

At the time, isooctane was the most anti-knock fuel available .....

At that time there were already aromatics available with better detonation resistance than iso-octane.
In fact there was already a Toluene Number in use before Graham Edgar came up with his Octane Number, that soon replaced the Toluene Number.

As correctly stated above, there is no 100+ octane fuel moleculary, rather a fuel which performs X% better than pure iso-octance under certain conditions (usually rich mixture).

One can assign an octane number higher than 100 to various molecules without that number being a performance number.
It is then called a "blending octane number".
For example: toluene has a blending MON of about 112. Other gasoline components can have a blending MON that is even higher.

 

[Luft.4]

Not caused by pressure, but by temperature.

At that time there were already aromatics available with better detonation resistance than iso-octane.
In fact there was already a Toluene Number in use before Graham Edgar came up with his Octane Number, that soon replaced the Toluene Number.

One can assign an octane number higher than 100 to various molecules without that number being a performance number.
It is then called a "blending octane number".
For example: toluene has a blending MON of about 112. Other gasoline components can have a blending MON that is even higher.

Both pressure and temperature (The Secret horsepower Race, p.25). While I did say "usually casued by pressure..." will update my notes to include temperature explicitly as well. Knock is caused by both. One cannot increase temperature in a closed off space without causing an increase in pressure, and vice-versa.
I worded the final portion a little strange, I should have explicitly states iso-octane. Iso-octane was the extreme high end of Edgar's scale, 100. If one uses this scale, anything above 100 is x% relatively more knock resistant compared to iso-octane. So no, one may not have a fuel that is over 100% iso-octane molecularly. An iso-octane molecule cannot be greater than 100% of itself. Fuel however can perform x% greater than the pure iso-octane molecule when measured on Edgar's octane scale, ie assigning an number to a fuel which outperforms the scale (0-100) relative to the scale. This was regularly done throughout the war, such as with the Allies 130 grade an 150 grade fuels.
To your point on the PN, absolutely! One can of course create a fuel when the lean mixture octane number is above 100, (the rich mixture number is the PN), thereby having an octane number above 100 that is not the PN. This was actually very desirable for air forces which had to fly long distances for missions such as the USAF. US 115/145 grade would be one example.

 

[z42]

I recall reading either/both(?) US/UK also used methyl anilines (like N-methyl aniline, NMA) as supplemental octane boosters in addition to TEL.

 

[Daggerr]

Both pressure and temperature (The Secret horsepower Race, p.25).

It's not clear to me exactly which line on page 25 you are referring to.

Pre-ignition and detonation are caused mainly by temperature, although pressure may also have some impact due to impact on the partial pressure of oxygen and fuel vapor.

Each hydrocarbon has an auto-ignition temperature (AIT), not an auto-ignition pressure.
A high pressure alone, without a high temperature, will not cause auto-ignition.
A high temperature alone, without a high pressure, will cause auto-ignition.

Autoignition temperature - Wikipedia

en.wikipedia.org

One might think that in a diesel engine ignition is caused by increased pressure but that is not correct: it is caused by the high temperature that results from the compression. Basic thermodynamics.

Also in a gasoline engine the air/fuel mixture temperature increases with increase in pressure. The higher the compression ratio the higher the resulting temperature. Same basic thermodynamics.
A too high combined compression ratio of supercharger plus piston engine can result in a too high temperature causing pre-ignition or detonation.
A very high combined compression ratio would require a fuel with a very high octane number. Or merely a high octane number plus an intercooler between supercharger and piston engine to reduce the inlet temperature of the piston engine enough to avoid that the temperature after compression in the piston engine would be too high for the available fuel octane number / performance number.

I worded the final portion a little strange, I should have explicitly states iso-octane. Iso-octane was the extreme high end of Edgar's scale, 100. If one uses this scale, anything above 100 is x% relatively more knock resistant compared to iso-octane. So no, one may not have a fuel that is over 100% iso-octane molecularly. An iso-octane molecule cannot be greater than 100% of itself. Fuel however can perform x% greater than the pure iso-octane molecule when measured on Edgar's octane scale, ie assigning an number to a fuel which outperforms the scale (0-100) relative to the scale. This was regularly done throughout the war, such as with the Allies 130 grade an 150 grade fuels.
To your point on the PN, absolutely! One can of course create a fuel when the lean mixture octane number is above 100, (the rich mixture number is the PN), thereby having an octane number above 100 that is not the PN. This was actually very desirable for air forces which had to fly long distances for missions such as the USAF. US 115/145 grade would be one example.

You seem to have missed my point.
The octane number MON and RON of a gasoline are determined by specific ASTM testing methods.
Even though the octane scale runs from 0 - 100 one can have a gasoline component (such as various aromatics) that has a (blending) MON well above 100. That has noting to do with rich or lean or performance number.

For example: suppose you have a gasoline with a MON of 90 and you blend it 80/20 with an aromatic component X, resulting in a blend with a MON of 95, what is then the MON of component X?
Answer: MON of X is 115 because 0.80 * 90 + 0.20 * 115 = 95
By this kind of simple blending tricks one can determine the MON even if it is above 100 and then it is called blending MON, not PN.

Blending MON (and blending RON) numbers are used daily in refineries all over the world to prepare the correct gasoline blends for sale.

 

[MikeMeech]

I recall reading either/both(?) US/UK also used methyl anilines (like N-methyl aniline, NMA) as supplemental octane boosters in addition to TEL.

Hi
There is some information on Aviation Fuel and octanes in 'British Piston Aero-Engines and their Aircraft' by Alec Lumsden:

Mike

 

[Luft.4]

You seem to have missed my point.

I must say likewise, I was talking about iso-octane (explicit once I expanded that thought). Pure toluene is a different chemical so naturally it will have a different rating than iso-octane on the octane scale. "one may not have a fuel that is over 100% iso-octane molecularly. An iso-octane molecule cannot be greater than 100% of itself." Totally agreed that Toluene has a different octane rating than pure iso-ocatane. It is a different chemical after all.
Blend a fuel with other fuels (ex add toluene), you are bound to create a new octane rating. That is why 130 grade fuel means the fuel is rated as 30% more knock resistant an pure iso-octane, rather than 130% iso-octane. Measuring that rating using various testing methods will produce different results.

Agreed that the quoted octane number does depend on which testing method you choose. The least accurate CFR RON will give you a higher octane number owing to its low RPM test setup, followed next by the slightly more accurate MON, then by the German OOZ method, then by probably most accurate ww2 era testing method employed by the DVL supercharging. RON and MON provide a singular number (such as the octane number of the gasoline you buy at the pump), OOZ will provide a 2-D graph of octane numbers between two mixture settings, while the DVL supercharging method will output a 3-D graph plotting mixture, temperature, and pressure. It is the final two methods of measuring fuel which are really applicable to accurately understanding how a fuel will perform in an aircraft. If understanding how the fuel reacts to variable is not important to the end consumer then a single number will suffice (hence MON and RON).

It's not clear to me exactly which line on page 25 you are referring to.

Left column, half way into the second last paragraph. "Experiments involving measurements...".
One may not have high temperatures without high pressures. That is why in an engine it is both and why Calumn put an emphasis on both.

high temperature that results from the compression. Basic thermodynamics.

Absolutely, I agree with you there. Compression in a cylinder leads to more pressure which increase the temperature, hence why it is both temperature and pressure. If there were no pressure present in an engine cylinder the burning fuel would never be as reactive if pressure was also present, no matter how high the octane rating is.
All the best,
Dan.

 

[don4331]

My 2¢ based on what I've learned here on the forum (what I'm here to do). We'll see how well I've learned.

The common fuel rating method is a scale based on n-Heptane at 0 and iso-Octane at 100.

As it is a scale, it is possible to have both values less the 0 and greater than 100.​

Heptane is C7​H16, ​Octane is C8​H18​ but that isn't accurate enough for the purposes of this discussion, because there are a number of isomers of each of the alkalines (?9? for Heptane and ?23? for Octane) and they have vastly different Octane ratings. We need to know which you are referring to:

Heptane family​

n-Heptane (H3​C–CH2​–CH2​–CH2​–CH2​–CH2​–CH3​) <Probably the one you wrote out in high school chemistry class> has Octane rating of 0​

2,2,3-Trimethylbutane, H3​C–C(CH3​)2​–CH(CH3​)–CH3​ (i.e. Triptane) has Octane rating of 125 (So, Heptane isomer with rating well over 100)​

Octane family​

n-Octane (H3​C–CH2​–CH2​–CH2​–CH2​–CH2​–CH2​–CH3​) has Octane rating of –15​

2,2,4-Trimethylpentane (CH3​)3​–C–CH2​–CH–(CH3​)2​ (i.e. iso-Octane) has Octane rating of 100.​

Aside: Was iso-octane selected as it is has best rating versus production cost?​

2,2,3-Trimethylpentane (CH3​)3​–C–CH–CH3​–CH2​–CH3​ has Octane rating of 110 (So, there would be an Octane isomers with rating over 100; I believe there are 3 Octane isomer over 100, )​

When you get crude oil from the ground, initial method of "refining" was distillation. As the various isomers above have different boiling points, you can separate out the compound you want (gasoline) by heating to the desired boiling point and extracting. But it would be horrendously inefficient (read prohibit-ably expensive) to extract the desired compound (iso-octane) at an industrial scale using this method.

Rather, the refineries most commonly produce iso-butene* and iso-butane and then using catalysts, produce iso-octane.

The creation of iso-butane is its own process (cracking the crude/isomerization of n-butane); iso-butene is dehydrogenation using catalysts of iso-butane.​

IMHO, performance number, PN was added to provide a rating that demonstrated the improvement of fuel when a rich mixture was used.

Continuing on the expensive theme, rather than make 100 octane fuel from "straight" iso-octane, the refineries took an output of a mix of organic compounds (and their isomers) of octane rating less than 100 and added tetraethyl lead. And it is the "mix" of other organic compounds which differentiated US from British 100 octane fuel.

Depending on the precise definition of "closed off space", while the statement:

One cannot increase temperature in a closed off space without causing an increase in pressure is always true; the corollary isn't.​

One can increase pressure in a closed off space without causing an increase in temperature if done slowly enough that the thermal energy is dissipated to the surrounding environment. e.g. My Cummins diesel doesn't get to auto ignition temperature when it is -40, despite increase of pressure in a "closed off space" as the energy goes into heating the piston/cylinder wall and head.​

​

Now, if your '"closed off space" definition includes preventing thermal energy transfer, the corollary would be...but that isn't possible in 'the real world'.​

The chemists putting all this together are some of the unsung heros; along with the metallurgists (I consider it separate as I'm including heat treating and manufacturing).

 

[z42]

Aside: Was iso-octane selected as it is has best rating versus production cost?

I'm not sure of the original logic behind it, but I'd suspect it has to be a compound that has

1. Reasonably high "octane" (or whatever you call your scale)
2. Can be produced from common feedstocks in reasonable quantities.
3. Can be produced in reasonably purity at reasonable expense, to make sure you're actually measuring what you think you are.

IMHO, performance number, PN was added to provide a rating that demonstrated the improvement of fuel when a rich mixture was used.

My understanding is that PN is just a way to extend the scale beyond 100. The actual test protocol that you're following (rich, lean, RON, MON being the most common ones) is orthogonal to the use of PN.

Continuing on the expensive theme, rather than make 100 octane fuel from "straight" iso-octane, the refineries took an output of a mix of organic compounds (and their isomers) of octane rating less than 100 and added tetraethyl lead. And it is the "mix" of other organic compounds which differentiated US from British 100 octane fuel.

There are other properties that a usable gasoline gasoline needs in addition to just octane. Like sufficient but not too much vapor pressure, distillation curves (how much of the gasoline evaporates as a function of temperature), etc. etc. 100% iso-octane would most likely not satisfy all the other requirements.