Test results skewed by fuel octane

[Akuma]

During WWI many allied pilots reports of the apparently superior performance of German aircraft were written off by their superiors as 'Jitters'. As proof, the superiors would bring out their flight test results of captured machines. These would always include the fact that since the Allied fuels were higher octane than that of the Germans, the test results should have shown increased performance in the captured aircraft but consistently did not. The Superiors argued that their tests proved the inferiority of enemy planes.
After the war the discovery was made that although the German fuels were lower in octane than that of the allies, the Germans were blending additives with the fuels to give a higher octane than that of the allies. At that point the Superiors did not have to worry about the egg on their faces.

 

[Shortround6]

The allies were constantly testing samples of captured fuels. Sometimes recovered from downed aircraft.

Since the standard way of testing fuel was to run it in a test engine and adjust the compression until the test engine "knocked" and then repeat the test with "reference fuels", that is to say refence fuel of 92 octane knocked before the fuel being tested and reference fuel of 96 octane knocked later one could say the fuel under test was somewhere between 92 and 96 octane.
Since this was a "performance" test it didn't matter what additives were used, the fuel either knocked or it didn't.

two things complicate this,
1. Not all engines respond to changes in octane the same way. This means everybody in the gasoline production/purchasing chain has to use the same test engines.
2. There is a difference in the octane rating (which only goes to 100, anything higher is a performance number) when running lean and running rich. This can be a slight variation or it can be a big variation depending on the fuel blend (additives come in here) but since this was known and being tested for by 1941 at the latest it would seem that any captured fuel would have been tested both lean and rich.

fuel was also chemically analyzed when captured. This was to look for any new additives the Allies might not be aware of and to help identify potential shortages of components/additives. As in fuel captured after such and such a date uses a lot more of additive A and a lot less of additive B than the same grade fuel did a year earlier
it may mean that Germany was experiencing a shortage of Additive B.

Both the allies and Germany color coded their fuels, not the same color code, but as an aid to identifying fuels in the field for ground crew and air crew.

German fuel improved during the war years in the rich rating but the Germans didn't specify it or list it. Late war 96 octane fuel (C3) would allow more boost (higher performance)
than early war C3 fuel. However the fuel injected German engines usually were not set up to run as rich as the Allied planes/engines were.

A DB605DC used a lot less fuel per hp hour at full power than an R-2800 did for instance. This also tends to skew test results. Even if the German fuel in a test engine was equivalent to Allied 100/140 (or 100/150) the Germans weren't running the aircraft engine rich enough to reach the 140/150 rating.

 

[pbehn]

I dont know what they called it in WW1 but octane ratings came later, Henry Tizard of the Tizard committee played a part in it.
from wiki
After the end of the war, he was made Reader in Chemical Thermodynamics at Oxford University, where he experimented in the composition of fuel trying to find compounds which were resistant to freezing and less volatile, devising the concept of "toluene numbers", now referred to as octane ratings.

 

[Shortround6]

Sorry guys, I didn't see that it was WW I.

Allies (or the Americans?) had trouble with fuel as there was no real way to measure it, as pbehn has stated.
The allies certainly didn't fuel rated by octane numbers in WW I.
For the US (and British/French planes that got US fuel) there was no way of knowing if you getting 38-40 octane fuel (measured in the mid 20s) from Pennsylvania or nearly 70 octane fuel from California.

Since the octane rating scale didn't exist until the mid to late 20s this tale seems to be a bit off.

 

[pbehn]

Sorry guys, I didn't see that it was WW I.

Allies (or the Americans?) had trouble with fuel as there was no real way to measure it, as pbehn has stated.
The allies certainly didn't fuel rated by octane numbers in WW I.
For the US (and British/French planes that got US fuel) there was no way of knowing if you getting 38-40 octane fuel (measured in the mid 20s) from Pennsylvania or nearly 70 octane fuel from California.

Since the octane rating scale didn't exist until the mid to late 20s this tale seems to be a bit off.

Tizard was working on it just after WW1 (according to previous quote) and harmonisation of 100 octane wasnt achieved between USA and UK until around 1939/40.

 

[Akuma]

The allies were constantly testing samples of captured fuels. Sometimes recovered from downed aircraft.

Since the standard way of testing fuel was to run it in a test engine and adjust the compression until the test engine "knocked" and then repeat the test with "reference fuels", that is to say refence fuel of 92 octane knocked before the fuel being tested and reference fuel of 96 octane knocked later one could say the fuel under test was somewhere between 92 and 96 octane.
Since this was a "performance" test it didn't matter what additives were used, the fuel either knocked or it didn't.

two things complicate this,
1. Not all engines respond to changes in octane the same way. This means everybody in the gasoline production/purchasing chain has to use the same test engines.
2. There is a difference in the octane rating (which only goes to 100, anything higher is a performance number) when running lean and running rich. This can be a slight variation or it can be a big variation depending on the fuel blend (additives come in here) but since this was known and being tested for by 1941 at the latest it would seem that any captured fuel would have been tested both lean and rich.

fuel was also chemically analyzed when captured. This was to look for any new additives the Allies might not be aware of and to help identify potential shortages of components/additives. As in fuel captured after such and such a date uses a lot more of additive A and a lot less of additive B than the same grade fuel did a year earlier
it may mean that Germany was experiencing a shortage of Additive B.

Both the allies and Germany color coded their fuels, not the same color code, but as an aid to identifying fuels in the field for ground crew and air crew.

German fuel improved during the war years in the rich rating but the Germans didn't specify it or list it. Late war 96 octane fuel (C3) would allow more boost (higher performance)
than early war C3 fuel. However the fuel injected German engines usually were not set up to run as rich as the Allied planes/engines were.

A DB605DC used a lot less fuel per hp hour at full power than an R-2800 did for instance. This also tends to skew test results. Even if the German fuel in a test engine was equivalent to Allied 100/140 (or 100/150) the Germans weren't running the aircraft engine rich enough to reach the 140/150 rating.

I'm sorry. Are you speaking of WWII?

 

[Shortround6]

I'm sorry. Are you speaking of WWII?

Yes I was, my apologies for the confusion.

However as noted by pbehn work on the octane scale wasn't started until around 1921, it's adoption as an international "standard" took quite a few more years.

Nobody was measuring fuel in WW I using the octane scale.

 

[pbehn]

Yes I was, my apologies for the confusion.

However as noted by pbehn work on the octane scale wasn't started until around 1921, it's adoption as an international "standard" took quite a few more years.

Nobody was measuring fuel in WW I using the octane scale.

Harmonising, agreeing and mass producing 100 octane fuel was done more quickly than the introduction of computers, from university idea to being available pretty much everywhere.

 

[Akuma]

Yes I was, my apologies for the confusion.

However as noted by pbehn work on the octane scale wasn't started until around 1921, it's adoption as an international "standard" took quite a few more years.

Nobody was measuring fuel in WW I using the octane scale.

Okay good. I used the word octane since I do not know what standard was used by the allies during WWI. Whatever it was, the allies determined that their fuel was superior to that used by Germany and that when their superior fuel was used in German aircraft the results were always less than the performance observed and reported by allied pilots. After the war they found out that yes, their fuel was superior but that the Germans had been using the benefits of their outstanding chemical industry to not only make up the deficit but to actually exceed the performance of the allied fuels.

 

[pbehn]

Okay good. I used the word octane since I do not know what standard was used by the allies during WWI. Whatever it was, the allies determined that their fuel was superior to that used by Germany and that when their superior fuel was used in German aircraft the results were always less than the performance observed and reported by allied pilots. After the war they found out that yes, their fuel was superior but that the Germans had been using the benefits of their outstanding chemical industry to not only make up the deficit but to actually exceed the performance of the allied fuels.

High octane fuel doesnt give more power of itself, as far as I know, it just allows higher compression ratios and boost pressures which gives the higher power.

 

[Akuma]

High octane fuel doesnt give more power of itself, as far as I know, it just allows higher compression ratios and boost pressures which gives the higher power.

I do remember that the article I read said the allied fuels were causing considerable knock and other forms of rough running on the aircraft tested. I believe they must have readjusted the engine settings to diminish or clear up the knock. But then the aircraft did not perform according to allied pilots observations.

 

[Shortround6]

The Americans had plenty of trouble with their engines knocking and running rough depending on which oil field supplied the base stocks in WW I.

There was no quick and easy test.

They knew about adding some compounds or blending fuels but most of the additives and mixtures had problems of their own.
Benzene for example could raise the knock point rather well but since Benzene freezes at 42 degrees F (6 degrees C) there is only so much you can add to gasoline in the winter for aircraft.

 

[MikeMeech]

I do remember that the article I read said the allied fuels were causing considerable knock and other forms of rough running on the aircraft tested. I believe they must have readjusted the engine settings to diminish or clear up the knock. But then the aircraft did not perform according to allied pilots observations.

Hi

Reference fuel during WW1, here are extracts from 'The Aviation Pocket-Book 1918' by R. Borlase Matthews:

The book 'British Piston Aero-Engines and their Aircraft' by Alec Lumsden has some information on the period in Appendix 1 ''Aviation Fuel' pp. 312-313:

I hope that aids discussion.

Mike

 

[Akuma]

Hi

Reference fuel during WW1, here are extracts from 'The Aviation Pocket-Book 1918' by R. Borlase Matthews:
View attachment 629328
View attachment 629329
View attachment 629330

The book 'British Piston Aero-Engines and their Aircraft' by Alec Lumsden has some information on the period in Appendix 1 ''Aviation Fuel' pp. 312-313:
View attachment 629331
View attachment 629332

I hope that aids discussion.

Mike

Thanks for posting this. The part about blended Alcohol fuels of that era gives an idea of the progress that had been made up to then.

 

[pbehn]

I love the appliance of non scientific science. What on earth is a fuel that smells badly before or after combustion? Some like the smell of petrol, diesel or paraffin others dont. If you are surrounded by it you lose your sense of smell and smelling exhaust fumes on a regular basis is unwise to say the least.

 

[Akuma]

I love the appliance of non scientific science. What on earth is a fuel that smells badly before or after combustion? Some like the smell of petrol, diesel or paraffin others dont. If you are surrounded by it you lose your sense of smell and smelling exhaust fumes on a regular basis is unwise to say the least.

'Does it pass the smell test?'