Published Accounts of the Fw 200 C-3 – A Critique on Water-Methanol Injection

[INM@RLM]

Thank you, Jukka.

I shall let the engine experts resolve this one, only slipping in this quote for Ed from Alec Harvey-Bailey: The Merlin in Perspective: The Combat Years (Roll Royce Heritage Trust, Historical Series No.2) - Appendix IV The Merlin and 100 Octane Fuel on p87.
"This set the pattern and without 100 octane fuel the further power development of the Merlin would not have been possible. As an example, the two-stage blown Merlin 66 was capable of over 1 600 hp at 16,000 ft using 3,000 rpm and 18 lb boost. The pioneering work of Esso to produce a suitable 100 octane fuel was the key to high power Merlins in all spheres of operation and it was not until 1944 when 150 grade fuel became available that further advances in boost pressure to 25 lb were made, allowing over 2 000 hp to be used in squadron service."
He does use 150 grade rather than 150 octane but whilst I'm not able to put my finger on any example just now, in accounts by squadron pilots (Clostermann?) I recall the upgraded fuel being referred to as 130 octane or 150 octane, whilst I have no recollection of a PN number being mentioned. So whilst this is the wrong usage technically could this have been a common usage in squadrons at the time?

[edwest2]

From another website, so unverified but with good references:




Almost any engine could use 150 octane, but not all could run at the
higher boost pressures to get any benefit.

A Bristol document, AVIA 8/434 and AVIA 15/2922, gives the following:

Centaurus 7.5 - 8.5 lbs boost, no change with 150 octane (the
Centaurus was later increased to 10 lbs boost with water injection, 12
lbs with 150 octane, and possibly 16 lbs with water and 150 octane
(don't know if this last one was approved, although I've seen the
power chart for it)

Hercules: no change with 150 octane

Sabre: no change at 11 lbs (although they later increased to 13lbs,
iirc)

Merlin 63, 64, 72, 73 18lbs with 100, 21 lbs with 150

Merlin 66, 70, 71, 76, 77, 266, V-1650-7, 100, 101, 130, 131, 113, 114
18lbs with 100, 25lbs with 150 (there is a note about changing
ignition timing with Merlin 66)

Griffon 61, 65, 66 18lbs with 100, 21lbs with 150.

Griffon 64, 67, 85 18lbs with 100, 25lbs with 150

There are minor increases with some Pratt & Whitneys, the Packards and
Wrights listed all remain the same. Note however that these may have
changed later, certainly some of the British engines did.

[Jukka Juutinen]

Ed, I referred to German piston engines that are extremely poorly covered esp. in English. Just compare what is available to e.g. Dan Whitney's V-1710 book and the gap becomes clear.

As for the above post, the Merlin 130 could use +20 boost on 100/130 fuel. 100/150 fuel does allow approximately 15.5 % greater IMEP.

[INM@RLM]

Thank you, Ed. And alongside that commonplace use extract we can also put this example of the more technically correct usage from http://www.wwiiaircraftperformance.o...rade-fuel.html


"Testing continued, with an Air Ministry Memorandum on Introduction into Service Use of 150 Grade Aviation Fuel of 25 January, 1944 summing up the position with respect to performance, production and requirements. The Memorandum concluded in part:

• On the basis of the figures used, it is apparent that the earliest a substantial quantity of fuel can be allocated, i.e. 40,000 or 60,000 tons for Home Based Fighters is May/June. This would still permit the allocation of one month’s consumption and one month’s reserves, i.e. 73,000 tons to A.E.A.F. Fighters in June."

There is also a link on this page to a full reproduction of the Jan-44 Air Min memo.

[INM@RLM]

Jukka has made an entirely fair point. I shall endeavour to now always use 'grade' instead of 'octane' for all values greater than 100.

[Jukka Juutinen]

An addendum: there is an equation which allows converting octane numbers to PN (and vice versa): PN=2800/(128-octane number). Examples. Octane number 100 gives 2800/(128-100)=100. Octane number 90 gives a PN=2800/(128-90)=2800/38=c. 74. And and ON=80 gives a PN of 58. As can be seen, the anti-detonation efficiency of the fuel rises greatly when the octane number approaches its maximum (100).