BMW 803

[tomo pauk]

C3 fuel is often listed as being in the 96-100 octane range.

The 96-100 oct was lean response, as SR6 noted. Rich response was higher, easily above 120 PN ('performance number', or 'grade' sometimes), and improving in late war.

So what was the 130/150 octane fuel called?

There was no 130/150 fuel. Standard W. Allied fuel for mid/late war was 100/130 (= 100 PN for lean mixture, 130 PN for rich mixture), in 1944 the 100/150 was introduced. Post-war, US introduced 115/145, meaning 115 PN for lean mixture and 145 for rich mixture. Leaner mixtures were used for cruising, rich mixtures were used for combat and take off.

 

[camman]

Well, I guess I learned something new. I don't know why I never even thought of that.

 

[GregP]

I have not seen a report authored by anyone other than Kurfurst or a Kurfurst parrot that says early C-3 was above 120 PN rich. It did get better about mid-1942 or so, and the later C-3 was probably close to 96/126, depending on the batch. If you go look, there isn't a lot of data supporting the testing of WWII German fuels in English other than posts in forums by people who are self-appointed "experts." There are SOME reports, but you have to dig for them.

The only Allied tests I read showed some variation in German fuels from the spec, with a couple being a few points higher and most being a few points lower. Onlt 1 of about 6 test I read were right on spec, but they were all near the quoted lean numbers ± 3-4 points. I read these some 4 - 5 years back and have not found them again. These days, when I find a source, I keep track of it and save it.

One point hardly ever made about Allied vs. German fuels is that if you KNOW what you are using for fuel, you can design engine mixture things for it, whether fuel injection or carburetors. So even if German fuel WAS slightly lower in grade than typical Allied fuel, and I don't claim that to be true, they didn't seem to have any trouble making engines that burned it quite well at 35,000 feet in Bf 109s with hydrostatic superchargers. The P-38 was a wonderful example of being mis-jetted out-of-the-box when it went from Indiana, U.S.A. to England and experienced mixture issues with different fuel. When it got sorted out, the P-38 didn't have mxture problems going forward.

So comparing German fuels to Allied fuels is WAY less important than comparing the flight performance of the aircraft since German fuels were typically burned in German aircraft and Allied fuels were typically burned in Allied aircraft.

In more than one thread we have remarked how the Bf 109 and Spitifre traded advantages in performance as the war went on. If the German fuels were less good in relation to Allied fuels, how was that possible?

One obvious answer is that the Germans went to larger dispalcement engines, not necessarily heavier engines, to get torque and thus generated roughly equivalent and sometimes better performance, particularly at typical combat altitudes in the ETO/MTO.

 

[SpicyJuan11]

I have not seen a report authored by anyone other than Kurfurst or a Kurfurst parrot that says early C-3 was above 120 PN rich. It did get better about mid-1942 or so, and the later C-3 was probably close to 96/126, depending on the batch. If you go look, there isn't a lot of data supporting the testing of WWII German fuels in English other than posts in forums by people who are self-appointed "experts." There are SOME reports, but you have to dig for them.

The only Allied tests I read showed some variation in German fuels from the spec, with a couple being a few points higher and most being a few points lower. Onlt 1 of about 6 test I read were right on spec, but they were all near the quoted lean numbers ± 3-4 points. I read these some 4 - 5 years back and have not found them again. These days, when I find a source, I keep track of it and save it.

One point hardly ever made about Allied vs. German fuels is that if you KNOW what you are using for fuel, you can design engine mixture things for it, whether fuel injection or carburetors. So even if German fuel WAS slightly lower in grade than typical Allied fuel, and I don't claim that to be true, they didn't seem to have any trouble making engines that burned it quite well at 35,000 feet in Bf 109s with hydrostatic superchargers. The P-38 was a wonderful example of being mis-jetted out-of-the-box when it went from Indiana, U.S.A. to England and experienced mixture issues with different fuel. When it got sorted out, the P-38 didn't have mxture problems going forward.

So comparing German fuels to Allied fuels is WAY less important than comparing the flight performance of the aircraft since German fuels were typically burned in German aircraft and Allied fuels were typically burned in Allied aircraft.

In more than one thread we have remarked how the Bf 109 and Spitifre traded advantages in performance as the war went on. If the German fuels were less good in relation to Allied fuels, how was that possible?

One obvious answer is that the Germans went to larger dispalcement engines, not necessarily heavier engines, to get torque and thus generated roughly equivalent and sometimes better performance, particularly at typical combat altitudes in the ETO/MTO.

Thanks GregP

 

[johnbr]

 

[johnbr]

 

[Daggerr]

BMW 803 article from 'Flugzeug Classic' of March 2006 attached. It's in German, obviously.