Luftwaffe with just B4 fuel

[mack8]

I was reading about the more difficult and resource intensive processes needed to obtain C3 fuel, of which they never had enough except for a part of Jagdwaffe. I recall seeing somewhere that they could only make 70% C3 fuel for any B4 quantity given, not sure how accurate that is.

Now even before the war the germans recognized their severe lack of most resources, hence among others the metal substitution program that wrecked their engines by 1942. But let's say they extend this to fuel, what if they recognize they can't afford the C3 fuel (they already gave up on C2 before the war) and just focus on B4 production.

On one hand they have more fuel, maybe 1/3 more than whatever C3 quantity they produced during the war, so more fuel for operation and crucial things like training. It also eases the logistical burden, and iirc easier to store as well?

On the other hand some engines will be affected, such as the DB-601N and BMW-801D plus several late war DB and BMW models which will have to de tailored for B4 fuel, so less power. On the DB-601N though they might avoid the oil dilution problem perhaps, and also rubber fuel tank corrosion. Presumably they have to reduce the CR on the 601N but they can still have the higher rated supercharger(s) and increased rpm? And about the redesigned cylinder head, was that specifically to cope with C2/C3 fuel or was it adapted from the 601E? What kind of power can they get from a B4 powered 601N? Rough guess about 1100 PS at rated altitude (datasheet says iirc 1175 PS at 4900 metres with C3)?

As to the BMW-801D, could they get it to run eventually on B4 (at reduced power, probably not much more than the 801C at around 1600 PS)? The next step would be to try to adapt it for MW-50 boost for more power, which i understand posed serious issues with cylinder head cracking. They would have to get it to work somehow if they want more power though, they could probably get 1800-1900 PS out of a hypothetical DM, while from TS (TSM?) maybe not more than 2000 PS with MW-50, am i in the ballpark?

On the other hand, if they can't get the 801D and later models to give more power with barely acceptable reliability with B4 and MW-50, then perhaps they would relegate the BMW-801 as a bomber engine and put the DB-603 and Jumo-213 in the FW-190 a soon as the absolute bare minimum of reliability is reached, so FW-190C and FW-190D but earlier.

So more fuel for operations and training, but on the other hand the E/N and F1/2 models and the FW-190A models from A-3 onward have a bit less power and hence performance compared to OTL. Also late war DB-605AS/D engines would only run with B4 and MW-50, so probably can't get much past 1800 PS,

What gives then, better or worse for Luftwaffe to just run on B4 only?

 

[z42]

I was reading about the more difficult and resource intensive processes needed to obtain C3 fuel, of which they never had enough except for a part of Jagdwaffe. I recall seeing somewhere that they could only make 70% C3 fuel for any B4 quantity given, not sure how accurate that is.

Maybe. Depends on how, and what, you measure though? They had a practically unlimited amount of the raw material (coal), the bottleneck was getting it out of the ground, and the industrial infrastructure required to turn that into usable aviation fuel. But yes, C3 required even more industrial infrastructure to produce than B4. It was a massive investment.

Now even before the war the germans recognized their severe lack of most resources, hence among others the metal substitution program that wrecked their engines by 1942. But let's say they extend this to fuel, what if they recognize they can't afford the C3 fuel (they already gave up on C2 before the war) and just focus on B4 production.

On one hand they have more fuel, maybe 1/3 more than whatever C3 quantity they produced during the war, so more fuel for operation and crucial things like training. It also eases the logistical burden, and iirc easier to store as well?

On the other hand some engines will be affected, such as the DB-601N and BMW-801D plus several late war DB and BMW models which will have to de tailored for B4 fuel, so less power. On the DB-601N though they might avoid the oil dilution problem perhaps, and also rubber fuel tank corrosion. Presumably they have to reduce the CR on the 601N but they can still have the higher rated supercharger(s) and increased rpm? And about the redesigned cylinder head, was that specifically to cope with C2/C3 fuel or was it adapted from the 601E? What kind of power can they get from a B4 powered 601N? Rough guess about 1100 PS at rated altitude (datasheet says iirc 1175 PS at 4900 metres with C3)?

In the OTL, 601N was relatively soon replaced in service by the 601E and then the 605, so I wouldn't expect any big changes here in the ATL.

As to the BMW-801D, could they get it to run eventually on B4 (at reduced power, probably not much more than the 801C at around 1600 PS)? The next step would be to try to adapt it for MW-50 boost for more power, which i understand posed serious issues with cylinder head cracking. They would have to get it to work somehow if they want more power though, they could probably get 1800-1900 PS out of a hypothetical DM, while from TS (TSM?) maybe not more than 2000 PS with MW-50, am i in the ballpark?

On the other hand, if they can't get the 801D and later models to give more power with barely acceptable reliability with B4 and MW-50, then perhaps they would relegate the BMW-801 as a bomber engine and put the DB-603 and Jumo-213 in the FW-190 a soon as the absolute bare minimum of reliability is reached, so FW-190C and FW-190D but earlier.

So more fuel for operations and training, but on the other hand the E/N and F1/2 models and the FW-190A models from A-3 onward have a bit less power and hence performance compared to OTL.

Wasn't the 801D basically a 801C modified to take advantage of the extra octane in C3 fuel? So tweaking it to run on B4 you're basically back to the 801C again?

But anyway, this would be the big impact from a lack of C3 mid-war(-ish). I agree the result would have been to hurry up the development of the DB603/Jumo213 engined versions of the FW190/Ta152, with the BMW801 relegated to a bomber and ground attack (FW190F and A's converted to F's).

Also late war DB-605AS/D engines would only run with B4 and MW-50, so probably can't get much past 1800 PS,

What gives then, better or worse for Luftwaffe to just run on B4 only?

I think, overall, it would have been a slight improvement, subject to a few (modest?) assumptions:

• Assuming they would have been able to bring in the long-nosed FW190 faster, to compensate for lack of performance in the 801C.
• Also earlier and more wide spread usage of MW50?
• They had huge problems in taking advantage of the extra octane in C3 anyway, largely due to strategic material shortages. Not only valves, but also spark plugs and bearings were also a problem.
• C3 production was a massive industrial investment, resources that could have been spent elsewhere, like more trucks and tanks for the Wehrmacht, or just more investment into increasing B4 production?
• Late in the war they might be at a slight disadvantage compared to the OTL, but of course by then the LW was largely a spent force and what little they did had little effect on the overall outcome.

 

[Luft.4]

The USN July 1945 report states that they guesstimated that 66.66% (2/3) of the fuel supply was C3 by the end of the war. In reality, it was closer to 50% (1/2) when one reads various fuel stock reports. The Luftwaffe also went to desperate meansures to approximate C3 fuel with B4. Engine manufactures were opting to create engines running on B4 as that was the safest bet considering the war.

 

[Denniss]

Was C3 direct-produced in the Bergius plants or was it a spiced-up B4 with aromatics produced in Fischer-Tropsch plants?

 

[z42]

Was C3 direct-produced in the Bergius plants or was it a spiced-up B4 with aromatics produced in Fischer-Tropsch plants?

You can find a diagram on page 159 of the Secret Horsepower Race, and a more detailed explanation, but tl;dr: C3 was, in a way, "spiced up" B4. Put B4 through a dehydrogenation reactor to increase the aromatics fraction, and then add 10-15% high octane alkylate (largely iso-octane). IIUIC the C3 production was largely colocated with the B4 (Bergius plants) production.

 

[mack8]

FWIW, some options with the BMW 801, that can avoid the need for C3 fuel and still be very worthy of service. Will probably require BMW cancelling any other engine that is not the 801, though.
- install the better, debugged parts from the 801D (like the chrome-coated valves and spark plugs, etc) on the 801C, so the reliability is where it should be
- 2700 rpm operation for 2nd gear as standard for the 801C, as it was supposed to be from late 1941 on (keeps the 190 competitive at high altitudes until mid/late 1943)
- retrofit the supercharger system from the 801E on the power section of the 801C, for the better power all-around (hopefully in ballpark of normally rated 801D)
- later, cut the CR even further so that engine (801C with E's S/C) can play well with the turbo while still on B4 fuel
- MW 50 system for the 801s all-around, also for the turbo version
- external air intake, where high altitude performance is needed; these are also conductive for the installation of dust filters
- devise the better external air intakes, that are more streamlined for lower drag and better speed
- not a part of the engine, but ditch the cowl MGs ASAP

The above post from another topic in large part answers to the question of BMW-801 evolution if only B4 was available.

That leaves the DB-601N, i'm still trying to figure out the power levels on B4. I note that the CR ratio in OTL was 8.2, while of the DB-601E was 7.2. Also the later DB-605 versions when on C3 had a CR of 8.3/8.5 instead of 7.3/7.5 on B4. So does that mean that a DB-601N running on B4 would have a CR of 7.2 ie just like DB-601E, and does this further means that the cylinders heads of DB-601N and E were more or less identical? The DB-601N cylinder heads were redesigned compared to the DB-601A and were domed as i understand.

So what would roughly be the power ratings of the DB-601N on B4 fuel, 2600 rpm, probably CR of 7.2 and probably 1.4 ata?

 

[tomo pauk]

So what would roughly be the power ratings of the DB-601N on B4 fuel, 2600 rpm, probably CR of 7.2 and probably 1.4 ata?

We can take a look at the graph here (the base I can show on the topic of low CR vs. high CR, same engines). It shows that the high CR version of the Jumo 213E has some 10% more power, CR in question of 6.5: vs. 8.5:1 (a rather high jump?). So we'd probably be getting 5% less for the 7.2:1 CR version of the 601N? That is a deficit of about 50-60 HP at max rpm and boost. It would've been getting a bit worse mileage, too.

 

[Denniss]

a 601N on B4 would be just an 601A

 

[mack8]

We can take a look at the graph here (the base I can show on the topic of low CR vs. high CR, same engines). It shows that the high CR version of the Jumo 213E has some 10% more power, CR in question of 6.5: vs. 8.5:1 (a rather high jump?). So we'd probably be getting 5% less for the 7.2:1 CR version of the 601N? That is a deficit of about 50-60 HP at max rpm and boost. It would've been getting a bit worse mileage, too.

Thanks for your insightful comments as always Tomo. I just realized something though, the oft quoted figures and table seen for DB-601N of 1175 PS for TO and at altitude are they not for the DERATED 1.35 ata version? Probably derated because of the oil dilution issue (among others?), which shouldn't really happen with B4? Elsewhere you calculated about 1250-1260 PS for a fully rated 1.42 ata DB-601N.

So my logic is that our hypothetical DB-601N on B4 at 1.4 ata (because DB-601A models were already able to do so?), maybe even 1.42 ata like the DB-601E, should actually run at the more or less the same power as the DERATED OTL DB-601N? Am i close or there's a flaw in my thinking that i haven't thought about? I do recall that there were frequent supercharger changes both on the A and N models, not sure how this affects my theory.

 

[mack8]

a 601N on B4 would be just an 601A

Well the 601N was running at higher rpm ie 2600 rather than 2400-2500 of the 601A, and ITTL probably at a CR of 7.2 which is a bit more than the 6.9 of the DB-601A?

 

[Deleted member 68059]

a 601N on B4 would be just an 601A

Has flat top pistons with no bowl at all, so its not just a 601A with better fuel.

 

[Deleted member 68059]

The USN July 1945 report states that they guesstimated that 66.66% (2/3) of the fuel supply was C3 by the end of the war. In reality, it was closer to 50% (1/2) when one reads various fuel stock reports. The Luftwaffe also went to desperate meansures to approximate C3 fuel with B4. Engine manufactures were opting to create engines running on B4 as that was the safest bet considering the war.

NB that is STOCKS.

Production is very elusive, but I do have data for 1941 showing that about 20% of AVGAS made was C3.

 

[tomo pauk]

Thanks for your insightful comments as always Tomo. I just realized something though, the oft quoted figures and table seen for DB-601N of 1175 PS for TO and at altitude are they not for the DERATED 1.35 ata version? Probably derated because of the oil dilution issue (among others), which shouldn't really happen with B4? Elsewhere you calculated about 1250-1260 PS for a fully rated 1.42 ata DB-601N.

No calculations there, I've just read the chart



OTOH, I was certain that the 601N was with the 1.40-1.42 ata boost, however it was just at 1.35 ata.
(the manual for the 109F1/F2 hoped to get to 1.42 ata, but 1.35 was the real max there listed; the loss of power was 6% vs. 1.42 ata operation - see also the small print; they also note the over-revving to 2800 is possible, for a gain of 10-15 km/h at the rated altitude)



See also this, where duration of the Start & Notleistung was limited to just 1 min very early, ie. some time before it entered regular service.

So my logic is that our hypothetical DB-601N on B4 at 1.4 ata (because DB-601A models wre already able to do so?), maybe even 1.42 ata like the DB-601E, should actually run at the more or less the same power as the DERATED OTL DB-601N? Am i close or there's a flaw in my thinking that i haven't though about? I do recall that there were frequent supercharger changes both on the A and N models, not sure how this affects my theory.

I'll correct myself here.
At 1.42 ata and 2600 rpm, we'd probably see a tad better power values, say a 60-70 HP gain between S/L and rated altitude (judging by the 601A, that gained 100 HP down low when boost was upped from 1.30 ata to 1.40, on same 2400 rpm, as well as judging the stated 6% loss when 1.35 ata is used instead of 1.42).

Of course, there is a question now of how to force the 601N to make the bigger boost despite using the lower-octane fuel, while remaining on the relatively big CR.

 

[mack8]

Well i've just looked at a chart of a DB-601Aa showing 1.45 ata and 2500 rpm, unless there is a typo somewhere (looks like 1175 PS TO and 1225 PS at 1000m, but seems this setting can't be used above 2000 metres)? Since the CR is only 7.2 ITTL compared to 6.9 for an A, probably about 1.4-1.42 ata should still be achievable? I'm just guessing hence why i appreciate input from people who really know their engine stuff.

 

[tomo pauk]

Well i've just looked at a chart of a DB-601Aa showing 1.45 ata and 2500 rpm, unless there is a typo somewhere (looks like 1175 PS TO and 1250 PS at 1000m, but seems this setting can't be used above 2000 metres)?

The Aa was with the slower-turning supercharger IIRC, so it was okay for it to be run at a bit higher setings down low. The 2500 rpm/1.45 ata was for take off only, same as with the 601A running at 2400/1.40.
The 'mainstream' 601A engines, those with a better S/C than the earlier 601A, have had a bit better altitude power than either these early 601A, as well as than the 601Aa.

Since the CR is only 7.2 ITTL compared to 6.9 for an A, probably about 1.4-1.42 ata should still be achievable? I'm just guessing hence why i appreciate input from people who really know their engine stuff.

You are stuck with me until the people who know their engine stuff are around
In my mind, the 601N looks as a ... temperamental and not-sturdy engine, that had the bad luck of being made for service when Germany was having ever less of some materials the engines needed (cobalt, nickel), that was, at least on the early 109F, with a bad material used for the fuel tanks that messed up with hi-oct fuel, CR was upped, RPM was upped - not the good forecast to demand even more from it.

 

[mack8]

Well, glad i'm stuck with you Tomo.

Ok so going the conservative route, if we say this B4 DB-601N remains at 1.35 ata, then we shave 75 PS and we say 1100 PS TO, 1100 PS at rated altitude with around 1175 PS at 2000 metres or so, does this sound realistic enough? And possibly, like the DB-601A the 1.40-1.42 ata boost might be allowed for TO only with again roughly 1175 PS? These ratings still bringing some extra PS at altitude compared to the A models, and if reliability is good enough (and better than the OTL N) many more N engines would be built for new or retrofitted Bf-109s and Me-110s, and even bombers (aiui a number of He-111Ps and maybe a few Do-215s had N engines?), since it's not limited by C3 stocks.

On the issue of CR ratio, the two-stage DB-601C/D was also 7.2 like the E, so it seems DB adopted this CR for the newer DB-601 versions which almost certainly would also apply for our B4 DB-601N.

Finally, materials wise was the N worse than the A and E built around that time more or less in parallel? Again my understanding is that the 2 biggest issues of the OTL 601N were oil dilution due to C3 fuel vaporization point being too high, thining the oil hence wrecking the bearings, rods and so on, and secondly same C3 fuel dizolving the self sealing fuel tank coatings thus clogging the engine. So the two above issues shoudn't happen with B4. It is true that the E was derated for at least six months, and i can't recall now reading what were the reasons? We have pretty good idea of the DB-605 faults with valves, sparkplugs, oil system etc. and how they were fixed, how about the 601E?

PS: Found this regarding the OTL distribution of 601N engines, very interesting

Question about octane fuel requirements for DB601A and DB601N engines for the Bf109E [Archive] - Luftwaffe and Allied Air Forces Discussion Forum

[Archive] Question about octane fuel requirements for DB601A and DB601N engines for the Bf109E Luftwaffe and Axis Air Forces

forum.12oclockhigh.net

 

[tomo pauk]

Ok so going the conservative route, if we say this B4 DB-601N remains at 1.35 ata, then we shave 75 PS and we say 1100 PS TO, 1100 PS at rated altitude with around 1175 PS at 2000 metres or so, does this sound realistic enough?

If the DB 601N stays as-is, runs the same RPM, pushes the same boost (without pre-detonation happening - this might be the kicker) etc, the resulting power should be as it was - no decrease.

And possibly, like the DB-601A the 1.40-1.42 ata boost might be allowed for TO only with again roughly 1175 PS?

Upping the boost further, to ~1.40 ata, will see the increase of another 5%? That is more than 1200 HP for TO.
Again - on a same engine type, the lower octane fuel and greater boost are usually mutually exclusive things. I'd strongly suggest reduction of compression ratio, preferably to 6.5:1, if not to the Merlin's value (6:1). Yes, some power will be lost for same boost and RPM, but there should be peace of mind for B4 operation.

These ratings still bringing some extra PS at altitude compared to the A models, and if reliability is good enough (and better than the OTL N) many more N engines would be built for new or retrofitted Bf-109s and Me-110s, and even bombers (aiui a number of He-111Ps and maybe a few Do-215s had N engines?), since it's not limited by C3 stocks.

601N was running at extra 200 rpm at rated altitude vs. the 601A, so we indeed should be getting better power at altitude.

On the issue of CR ratio, the two-stage DB-601C/D was also 7.2 like the E, so it seems DB adopted this CR for the newer DB-601 versions which almost certainly would also apply for our B4 DB-601N.

Going with increased CR is fine and dandy if engine can take it. Otherwise, staying conservative with CR is probably less troublesome approach.

Finally, materials wise was the N worse than the A and E built around that time more or less in parallel? Again my understanding is that the 2 biggest issues of the OTL 601N were oil dilution due to C3 fuel vaporization point being too high, thining the oil hence wrecking the bearings, rods and so on, and secondly same C3 fuel dizolving the self sealing fuel tank coatings thus clogging the engine. So the two above issues shoudn't happen with B4. It is true that the E was derated for at least six months, and i can't recall now reading what were the reasons? We have pretty good idea of the DB-605 faults with valves, sparkplugs, oil system etc. and how they were fixed, how about the 601E?

Time for the experts to chime in

 

[z42]

It is true that the E was derated for at least six months, and i can't recall now reading what were the reasons? We have pretty good idea of the DB-605 faults with valves, sparkplugs, oil system etc. and how they were fixed, how about the 601E?

I used the (very good!) index of "The Secret Horsepower Race" [1] to reread all mentions of the DB 601E, and it seems the E suffered from the issues with the sparmetall valves, but also in particular, it had an issue with poor fuel atomization causing knock or detonation with rich mixtures (the opposite of what you'd expect in any "normal" engine). Eventually this was solved by increasing the fuel pump pressure, but that was too late for the 601E and was done to help the same issue on the 605 when they wanted to crank up the boost of that engine. For the 601E, the more immediate solution to the problem was to bore out the cylinders, thus creating the 605. Or IOW, the 601E was withdrawn from service without the derating restriction ever being lifted.

[1] If you have a weird nerdy fascination with WWII aero engines, you owe it to yourself to get the book.

 

[Snautzer01]

you have a weird nerdy fascination with WWII aero engines, you owe it to yourself to get the book.

Yes. One would have too.
Not only for the power race but it makes decisions made to be seen far more clearly and not as random as one could have thought.
It is a a good chunck of the puzzle that explains why.

 

[tomo pauk]

Or IOW, the 601E was withdrawn from service without the derating restriction ever being lifted.

I'd beg to disagree.
2500 rpm and 1.30 was the max allowable rating before late 1941 (or maybe before January 1942?) - ie. Start & Notleistung setting (= 2700 rpm, 1.40 ata) was banned. The ban was lifted very early in 1942.