Why was Luftwaffe fuel Octane so low?

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Ah well, the German Direct injection engines do get the benefit of large overlap with potentially great end gas scavenging and exhaust valve cooling without loss of mixture. Mind you, they needed it with the poor materials.

Cheers

Eng
 
Shortround6: Fuel consumption data from the DB 605A manual:

Take-off/emergency 2800 rpm/1.42 ata (1475 PS) sea level 480 litres/hour

Maximum continuous 2300 rpm/1.15 ata (1075 PS) sea level 320 litres/hour

Fuel B4. Assuming 0.72 kg/litre, it results in 234 g/PS and 214 g/PS.
 
Here is the page from the manual (handwritten figures are older figures written by me based on 0.74 kg/litre).
 

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I have done a few quick conversions of P-38L engines.

At 1600hp they were using 180 gallons an hour and using 306g/hp/hour
At 1425hp they were using 167 gallons an hour and using 318g/hp/hour
At 1100hp they were using 113 gallons an hour and using 279g/hp/hour
At 795 hp they were using 63 gallons an hour and using 215g/hp/hour

This is from the engine chart and is not exact at they used the same consumption at all altitudes.
1600hp was War emergency
1425hp was Military power
1100hp was normal rated or max continuous.
795 hp max cruise ( lean mixture)

Anybody want to argue exact grams per gallon of fuel go ahead ( I just used pounds per gallon)
The Allisons had to be adjusted to get the worst cylinder of 12 to get a mixture that would not detonate so it is going to use more fuel than the Germans.
But that is an awful of fuel going into the Allison just for bad mixture?
 
Shortround6: Obviously the Allison used the excess for cooling. By the way, check a manual for an R-2800-equipped fighter with ADI and compare the sfc between maximum wet power and maximum dry power. The difference in sfc is massive!
 
Love when people post this tiny bits of engineering pr0n! I've some material on the Italian version of the DB601, which was built by Alfa Romeo, stashed somewhere including the service manual and the field maintenance manual for the aircraft; I'm going to check (if I can find them in the mess I've at home!) if the timings are similar. (Should be about the same).
 
Hi msxyz,
The DB601A is similar but, was at a much less adventurous stage of development. The timing details are different with a cam that is much more like a normally aspirated engine profile.
601A cam overlap is just 34 degrees and the timing is Exhaust opening at 53 (+/-1.5) degrees BBDC on power stroke. Max ignition advance is 40 degrees.
BTW, I have done some work on an Alfa Romeo 601. It was a very nicely finished motor.
Cheers

Eng
 
Thanks for the info. Your data is indeed the same stated in various manuals I've seen.

I found the service manual of the 'Iniex' fuel pump (a close copy of the Bosch DE54, with which it was interchangeable) but, oddly, no detailed timing is reported. The only hint is that injection start 30° after top dead centre; as for the rest it seems mechanics just had to align the various marks on the gears when mating the pump to the engine (as it's done on many engines after changing the distribution belt/chain).

My grandfather worked on them in the years preceding and during the war but never discussed with me in depth his time at Alfa (he was over 80yrs old when I was adult enough to become seriously interested in engineering). Most of what I know about that are stories relayed by my father.
 
German engineers realised quite a bit earlier than anyone else that fuels needed to be characterised across the entire air/fuel range.
 
Conslaw said:
Greg's Airplanes and Automobiles made a very good youtube video addressing this subject that is linked here.
Click to expand...

Greg has plugged my book in the video, so I should not complain - but Greg really should NOT have used "effective compression ratio" to look at this,
its not a useful comparator when the differences are not huge, and with the German engines having dramatically higher valve overlap, it
makes comparison of ECR a waste of time (because a huge amount of the supercharger boost goes right out the exhaust pipe in a DB601E onwards),
and so I`m afraid this section of the video is a spirited and laudable (but scientifically useless) analysis.

I also really dont understand why Greg has rubbished my argument about valve alloys being the primary cause of the lowered boost, the book
literally quotes high level RLM conference meeting records with Erhard Milch saying "we have to reduce the boost because of the low Nickel
valves" - there is NO wiggle room there for argument.

Berlin, 16th May 1942, RLM Conference, Milch presiding> (my book page 271)



<REF: MILCH 35mm Microfilm, 32 Reels — "Foreign
Documents: Milch Collection". {see Volume 45, Frame #8042}>

Three days later, Berlin, 19th May>



He also says I`m wrong because the lowering happened after operation Torch, again this suggests that Greg has either willfully ignored the books
findings (100% referenced to German air minstry meeting records) - or just has never done more than flick through the book.

Torch was about cobalt, for stellite, the original problem was the Nickel shortage reducing the valve alloy from ~13/14% to ~8% Nickel.

Greg, please READ the book if you`re going to plug it to people.

This is exactly why I plead with people not to skim or dip into my book, because its in chronological order, if you miss even a page, you`ll
find youself in a real mess later on.
 
Last edited:
Yes nickel shortage plagued the German war machine in many ways. Late war tank armour was very rich in Chrome and Molybdenum in an attempt to overcome Nickel shortages (in plates below 100mm it was often kept below 1%!). Unfortunately, not even Krupp best forging treatments could make this steel plastic enough to absorb the kinetic energy of a round without spalling and shattering.
 
Conslaw said:
D Deleted member 68059 could you give the info for your book in case anybody is inclined to purchase it? Thank you. (If that violates a rule, please ignore.)
Click to expand...

Umm I suppose if I was spamming all the threads with "Buy my book!!" all day the mods would get upset, but I`m pretty sure telling someone who wants to know how to buy one, how to buy one ought to be ok !

The advice depends a bit on where you live, because for reasons that escape me apparently a virus delays freight.

Anywayyyyy without opening THAT can of worms the point is that international post is absolutely appauling right now.

The books are stored in the UK, and we post out consignments of a few hundred at a time to Amazon warehouses worldwide, which have to go via surface
freight. So I do NOT recommend ever ordering it from Amazon unless it says "IN STOCK" as you might be waiting anything up to 3months otherwise!

The publisher also sells both e-book (NOT KINDLE!!!!) versions, and printed direct. Which I encourage as (I kid you not) from Amazon I get
a total profit of under one pound, for a £35 RRP book.... because (*reasons*). So I make wayyyy more if you buy direct from Mortons.

E-books:

Mortons Books - The Secret Horsepower Race

Buy subscriptions and issues of Mortons Books - The Secret Horsepower Race. Available on Desktop PC or Mac and iOS or Android mobile devices.
pocketmags.com

Printed:

THE SECRET HORSEPOWER RACE - WESTERN FRONT FIGHTER ENGINE DEVELOPMENT | Mortons Books

They will ship pretty much anywhere, but based on current experience a few typical "real" transit times are:

Mainland Europe, 3 weeks
Austraila, 5 weeks
USA, 4 weeks

Note, that the tracking system they provide ONLY works if you register with Mortons before buying, I very strongly urge doing so, because if the
***** ********* **** **********`s who work for people like Hermes lose it, you`ll have no come-back if you dont.
 
spicmart said:
Was the German water-methanol injection technology better than the Allieds's?
Click to expand...
Curious question. Water Methanol mix is usually injected in the manifold and is independent from the main fuel system. Its main purpose its to raise the boost pressure without causing detonation by lowering the air temperature fed to the engine. So, in a sense, it works on the same principle of heat exchangers (intercooler) for turbo cars.

To my knowledge, the Germans were the first to use Nitrous Oxide which has another advantage compared to Methanol. NOX is a monopropellants by itself (meaning that it will decompose energetically under certain conditions) and it will not only produce a net energy output, but it will also release oxygen which becomes available to burn a secondary fuel.
Nox boost is best used at altitude to combat the decrease of atmosphere pressure (and thus of air available for combustion).
 
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