Optimize the FW190 for the Eastern Front

[wiking85]

One huge problem the Germans faced was their lower octane fuels.

87 octane fuel has a PN performance number of only 62.5%, so for the same swept volume the Germans in theory could get only 62.5% the power of an Allied engine running on 100 octane.

What they did was use an unusual form of construction on the DB601 such that the DB601 had slightly less weight and frontal area as the single stage Merlins. The Merlin had a swept volume of 27L while the DB601 had a swept volume of 33.93L which is 26% greater. They lost a lot of this advantage with lower RPM but not all of it and their RPM increased from 2500 to 2800 between DB601A to DB601E (compared to 3000 for Merlin)

They then added multi point fuel injection. This meant the last component of end gas during the exhaust stroke could be scavenged by using either blower pressure and inlet/outlet tunning (known as extractors by hot roders) perhaps 10% more fresh air inducted without fear of loosing air/fuel out of the exhaust.

This perhaps also allowed a higher compression ratio (more like 7:1 versus the Merlin 6:1) which allowed more power and efficiency since residual end gases can cause preignition.

Even with this effort a 87 octane Merlin could produce 1030hp wheras the DB601A little more and the more advanced DB601AA maybe, just maybe 100hp more (1175 ps say 1150hp) The reality is that the Merlin was on 100 octane by the time war broke out and producing 1310hp, then soon enough by 1942 1500 and then 1620. The DB605 never reached these power levels till 1944 and the DB601E never did.

The DB601E introduced a sharp valve overlap that allowed even more scavenging and did so by having variable length inlet ducts to 'tune' the manifolds at high RPM.

A crical year was 1942. The Merlin added power mainly by improved fuels getting to 1620hp on the Merlin 25 single stage. However the Merlin 61 added an two stage supercharger to increase critical altitude and an intercooler to allow slightly higher supercharger compression ratios at high altitude (but also slightly a low altitudes).

The DB601 increased piston swept volume while retaining DB601 key dimensions but increasing weight from 580kg to 720kg (about same as Merlin 61 two stage) but the result is that in 1942 Me 109G1 with 1300 hp DB605A are facing 1560hp Spitfire IX with Merlin 61 (and likely a lot more jet thrust).

The single stage DB engines did quite well on a single stage because by their design they did not use the supercharger to 'overboost' the engine to gain power but mainly to altitude compensate. Hence the DB605AS which increased the volume of air that could be compressed by being bigger rather than focusing on pressure ratios.

However it is possible to imagine that Daimler Benz instead stayed with the DB601 but added an intercooler and maybe a two stage supercharger to gain power as the Merlin did. Afterall Junkers added a intercooler on the Jumo 211J. Perhaps the Me 109 couldn't have coped with a longer engine and intercooler might require. Without an intercooler a two stage DB601 would surely need water injection or C3 fuel. (Note 1942 C3 fuel was much lower grade than allied 100/130)

A two stage DB605L did not appear on production till 1945, it used C3 and MW50 to achieve critical altitudes of nearly 9.7km but did not have an intercooler.

Earlier attempts were the DB627, a DB601 with two stages. I think the concept was sound but it probably couldn't fit into the Me 109 since the first stage supercharger was coaxial with the gearbox.

So what was the potential of the DB605 with lots of C3 fuel available? Or the Jumo 211?

 

[tomo pauk]

Seems it was 1700+ HP at low alt, 1640 PS at 4 km, for DB 605 with 'normal' S/C; that is at 1.7 ata. The 605D was making 1.8 ata under FTH, at low level it was 1800+ PS. For the C3 with MW 50, add another 100-200 PS.

BTW:

Earlier attempts were the DB627, a DB601 with two stages. I think the concept was sound but it probably couldn't fit into the Me 109 since the first stage supercharger was coaxial with the gearbox.

The attempts on DB 601 with 2-stage S/C were named DB 601C and 601D, and I'd appreciate any good data on those, other than it's written by Von Ghersdorf et al.
The DB 627 was the DB 603 with 2 superchargers - one supercharger at each side. S/C installed on the left side fed the S/C installed on the right side, after that the compressed air went through the after-cooler and entered intake manifold.

edit: very worth reading (pics tables): link

 

[Shortround6]

It is not just one thing.

87 octane had a PN of 68.29 not 62.5 PN.

It depends on the year. Early C-3 fuel was not the same as late C3 fuel.

The DB 605 had problems with the pistons which limited boost for a while from 1.42 to 1.4 Ata ( Not sure if better fuel would that problem or not)

The DB 605 could go to 1800hp with the better fuel, but like the Allison and Merlin the supercharger limited the altitudes at which that power level was available.

As in:
DB 605A was good for 1355PS at 5700 meters.
DB 605AM was good for 1700PS at 4000 meters.
DB 605AS was good for 1200PS at 8000 meters.
DB 605ASM was good for 1500PS at 6400 meters.
DB 605DB was good for 1600PS at 6000 meters.
DB 605DC was good for 1800PS at 4900 meters..

The Big supercharger from the 603 simply wasn't going to deliver enough air to make 1800hp at above 4900 meters no matter what fuel you put in it. Better fuel and/or MW50 allowed higher powers below the critical altitudes.

There are a slew of different Jumo 211s and even on the later ones (with higher rpm and stronger crankshafts,etc) you are going to be limited by the supercharger and engine strength. A single stage Griffon, 36.7 liters went about 812 KG. Which is about 90kg more than the 211F, a 33 liter engine.

 

[tomo pauk]

The DB 605 had problems with the pistons which limited boost for a while from 1.42 to 1.4 Ata ( Not sure if better fuel would that problem or not)

Only 1.30 ata was allowed for more than a year, also max RPM was down to 2600 instead of 2800.

I was also thinking the Ha109 and some models of Kasei were on a similar (or slightly better) level of altitude performance than the 801. (or at least relative to size, weight, and/or displacement)

The Ha-109 has several stong points. It was light compact, the nominal power was rather good on 92 oct fuel: 1220 CV at 5200 m, at +200 mm Hg boost and 2600 rpm (how much power at more aggressive settings?), take off power was also decent (1500 CV on 2650 rpm and +300 mm Hg);probably a better layout of air intake. Shortcomings vs. the fully rated BMW 801D would be overall power at short term aggressive settings, less refined exhaust system. Actually, the DB 605A should provide more power overall than the Ha-109, or at least in the ballpark, with less drag and better exhaust thrust.
Kasei was of wider diameter, that spurred Mitsubishi for extension shaft in the Raiden to get some streamlining. The power at altitude for late war engines was excellent, a bit over what BMW 801D was making, but greater diameter would've eat that power, and maybe then some.

<about possible improvements for the BMW 801>Or a larger (or faster) single stage unit with aftercooler, or single speed integral stage + 2 speed+neutral aux stage like American engines adopted. (and in any case, better ducting arrangement, minimizing intake losses and allowing ram)

The low-alt power was good/great, so maybe going for an increased speed of the S/C would be the most expedient job? Loose 150-200 PS down low, gain 100-150 PS high up?
I cant be bothered to calculate the tip speed of historic S/C of the 801D, however, it was a long day

 

[Koopernic]

So what was the potential of the DB605 with lots of C3 fuel available? Or the Jumo 211?

As Shortround said, it depends on the C3 fuel.

My estimate is as follows
The BMW801 went from 1560hp to 1700hp when early C3 was allowed using a combination of slightly higher compression ratio and boost. Boost went from 1.3 ata to 1.42 ata. (there was a short period of 1.38 ata boost in between)

So you could say B4 to early C3 = 10%
The Jumo 213A was a 1750hp bomber engine, however C3 powered version, the Jumo 213b was also offered, it was nominally 2000hp. It also offered a motor canon.

The DB605 was a 1750hp bomber engine, the G version used C3 and produced 1900hp, it featured an improved supercharger.

So you could say B4 to Early C3 about 10% (as shown on the DB603G) to 14% (as shown on the Jumo 213A->213B

As C3 improved the BMW801 was allowed to increase boost from 1.42 to 1.68 and reach over 1900hp. This is about 20%.
B4->Late C3 about 20%.

A modification, still at the 1.68ATA limit involved running a fuel pipe to the air inlet ahead of the supercharger and injecting the C3 fuel there, this increased power to 2050. It precooled the air and contracted it so more could be forced in, this I think is one of the effects of the aromatic content that produces a high PN rich mixture number.

So oddly while the late model BMW801 used multipoint injecting, metering fuel into each cylinder via multiple cam operated plunger pumps, when in WEP it used a throttle body injection carburettor like the Packard Merlin. This was introduced on the BMW801D2 but was standard on the BMW801TS of the Fw 190A9.

When the Me 109G was introduced in May 1942 it was restricted to 1.3 ata boost for the next 18 months till about October 1943 though there was some periods of 1.42 ata boost. As a result the speed of the Me 109G1 fell from 400.5mph to 387mph for the Me 109G6 as weight and drag went up. When 1.42 ata became available speed went up to 397mph (a gain of about 10mph) so the Me 109G1 probably would have had a speed of 412mph.

The DB605 engine had three issues AFAIKT

1 when the DB605 replaced the DB601 the crankshaft bearing went from roller bearing to journal bearings that used a high pressure lubrication system, at 42psi or so much higher than the Allison and Merlin. At high altitude the oil would froth and the oil would loose a lot of its cooling and lubricating properties. This was discovered only belatedly. It was solved with a deaerating device

2 piston could burn through (a sign of preignition)

3 The original spark plug on the DB605A was the Bosch DW250ET 7 and this
sometimes caused pre-ignition at 1.42ata MAP for the DB605A meaning
the Me 109G frequently had to be restricted to 1.3 ata
(atmospheres or Barr of pressure) as fuel quality was also a problem.

New spark-plugs were needed to the end of the war for each increase in
manifold pressure.
1.30ata - Bosch DW250ET 7
1.42ata - Bosch DW250ET 7/1.
1.80ata - Bosch DW250ET 7/1A and 10/1.
1.98ata - Beru F280 E43. (Driving the DB605DCM and ASCM to 2000hp)

My guess is that C3 fuel for the DB605A would have allowed an immediate start on 1.42ata, perhaps with time restrictions given the lubrication issue but no need to wait for better plugs or pistons.

Swedish DB605A ran at 1700hp no problems with allied 100/130. The DB605DC using C3 could run at 1.8ata (1800hp) compared to 1.42ata for the DB605A ie 22% more. DB605DC it could run at 1.45 ata with B4 only.

For some reason the DB605AM and ASM used C3+MW50 rather than just B4+MW50. It may have been required to prevent preignition, others have claim it was a precaution against fuel depletion as running out of MW50 while at 1.7 ata would cause immediate engine destruction. Obviously a pressure or flow switch is required.

C3 fuel was more expensive to produce apparently you got only 70% as much fuel for the same amount of coal and plant. However the German oil industry was introducing improvements such as alkylation to improve this and had made several others.

I estimate the allies had a 20% advantage in power due to 100/130 fuel.

Large scale production of 100/100 octane fuel was due to catalytic cracking. Houdry was the chemist, Doolittle the USAAC man that demanded it.

large scale production of 100/130 was possible due to alkylate being added.

The Germans synthesised iso-octane from syngas from gasifying coal and latter iso-butylene that they obtained in quantity from butane from their hydrogenation plants. The octane was used to improve B4 into C3. The iso-butylene was also required for the buna synthetic rubbers and this also restricted C3 production.

Thermal cracking wasn't applicable to hydrogenation based fuel but I don't know about catalystic cracking. The Germans seem to have been behind on alkylation a bit(possibly a BP patent), they started building plants in 1940 but only 1 got operation and had a few other advanced processes going as well. the Allied oil campaign had an effect on the quantity as well as quality of fuel production. Many aviation books refer to the Germans rejigging their engine production to allow multifuel engines that operate on both C3 and B4 well.

I can see only two solutions
1 early introduction of MW50 water injection, yet this only happened in April 1944 on the DB605AM and ASM. The P-47 introduced it in 1943.

2 have two fuel systems in German aircraft, one filled with C3 and the other with B4. The C3 is used when required.
some German transport aircraft used this eg the Ju 352.