German 2-stage engines

[tomo pauk]

Something that Germans maybe missed? Anyway, this is an invitation for a discussion about the 2-stage (mechanically) supercharged engines Made In Germany, ww2 time frame.

Oh, yes, the politics sub-forum is at 5th floor, 4th doors to the left from the elevator, thanks

 

[Denniss]

At first RLM saw no need for high alt engines, otherwise they may have developed both turbocharged or multi-stage superchargerged engines. At second it may also have been a problem of rare materials as you need highly stress-resistant materials for a very high rpm high alt stage (or use less quality materials at the cost of service life as in Jumo 004B).
Junkers had a hell lot of problems with the high alt stage in the Jumo 213E/F and the DB engines were too late to get these kinds of reports.
DB preferred a single-stage supercharger with more rpm or, of increased volume or both to get better high alt performance although at the cost of some low alt performance but switched to a two stage system with prototype/preproduction 603/605 L-series engines at the end of ww2.

 

[Jenisch]

Hans Lerch, Luftwaffe test pilot, page 37:

"Occasionally I would receive via Switzerland foreign reports on German aircraft, and it was interesting to read that they quiet often not only praised the construction of the machines but the engines as well, more often than not concluding that the Germans just did not have the necessary heat-resistant materials for even better performance"

 

[Shortround6]

The Germans had something of a fuel problem. High altitude engines need a lot of compression in the superchargers. The Merlin 61 was compressing the air at over 5 to 1 at 23,000ft or so. The German engines didn't need quite as much but if you want 1.42 AtA at 30,000ft you need a pressure ratio in the supercharger of about 4.8 to 1. This requires a good inter/after cooler or high performance number fuel or both.

we get into the chicken or the egg dance here. Did the Germans not develop high pressure superchargers because their fuel was n't good enough to support them or did they lag behind in the development of fuel because their engines/superchargers didn't need it as much?

It doesn't really matter that the German fuel eventually reached a performance number of around 140. what was needed was PN number fuel of 120-130 in 1940-42 AND the assurance it would be available in large quantities to make developing an engine/supercharger to use it worthwhile.

 

[tomo pauk]

Hi, Dennis,
RLM was widely experimenting with the GM-1, so they were looking for good performers at 30000 ft and above? Could you please post something about Junkers' developments?

Hi, Jenisch,
Was Lerch stating what were the particular parts of engine needing the better materials?

Hi, SR6,
Thanks for analysis.
The German inlines were of much greater displacement than Merlin or V-1710, so, for a given engine weight, they should be using less boost and/or RPM to achieve the same output. The boost without resorting to C3 and MW-50 should be at least 1,42 (for Notleisung) - as achieved historically? At what point we need intercooler, or C3, or both? Anyway, here is a table from Allied post-was analysis of German engines - 1150 PS at 31400 ft on 1,43 ata and 2600 RPM. Some performance!

 

[wuzak]

Hi, Dennis,
RLM was widely experimenting with the GM-1, so they were looking for good performers at 30000 ft and above? Could you please post something about Junkers' developments?

Hi, Jenisch,
Was Lerch stating what were the particular parts of engine needing the better materials?

Hi, SR6,
Thanks for analysis.
The German inlines were of much greater displacement than Merlin or V-1710, so, for a given engine weight, they should be using less boost and/or RPM to achieve the same output. The boost without resorting to C3 and MW-50 should be at least 1,42 (for Notleisung) - as achieved historically? At what point we need intercooler, or C3, or both? Anyway, here is a table from Allied post-was analysis of German engines - 1150 PS at 31400 ft on 1,43 ata and 2600 RPM. Some performance!

That is max climb you are showing there.

For comparison, Griffon 65 (same capacity, give or take) using 100/130 fuel 1345hp @ 2600rpm, +9ps @ 26,100ft. Max power 2005hp @ 6000ft (MS gear, 1810 @ 20,500ft (FS gear), both 2750rpm, +18psi (data from Lumsden).

 

[tomo pauk]

A slight misunderstanding there - I was talking about the power achievable by using 87 oct (B4) fuel. The 1,43 ata manifold pressure seem well within the scope of B4 fuel, unlike the 1,75 (for Notleistung, ie. without MW-50, or C3 injection, or intercooler)?
I did not envisioned this as a competition vs. Allied 2-stagers; the Notleistung of 1350 HP at 31400, on C3, does look great when we compare what Germans had in production. Wonder what an intercooled DB-628 would be able to do? Too bad the table does not state a difference in power with or without MW-50 engaged.

 

[wuzak]

You did put the chart up for C3 + MW50.

I understood that B4 fuel was better than pre-war allied 87 octane fuel?

 

[Shortround6]

Whose pre war 87 octane Fuel

There was no "Allied" pre war fuel. Different counties had different specifications of which octane was only one requirement.

 

[tomo pauk]

You did put the chart up for C3 + MW50.

I understood that B4 fuel was better than pre-war allied 87 octane fuel?

We could really use a table for octane/PN rating for B4 and C3 fuel, per year of ww2

The table is indeed for C3 + MW 50, yet the table is not specific what manifold pressure is achievable with C3 only: was it those 1,75 ata, or lower, at Notleistung (Emergency rating, or take off as stated in table). My take is that some 1,90-1,95 ata would be achievable via use of MW-50, in line what the late war DB-605s were making.
On the other hand, we know that B4 fuel and 1,42 ata go well for standard DB-605, so I was quoting a MAP of 1,43 (here used in Climb combat rating - Steig kampfleistung) as a pretty good cue what we could expect from DB-628 when operating on B4. It's unclear to me how well could the DB-628 operate with 1,43 ata and 2800 rpm (it was 2600 rpm for Climb combat rating).

 

[Siegfried]

If your spend some time sifting through the allied intelligence files over at fischer-tropsch.org you will find that blued dyed B4 fuel (nominally 87 octane) that was receovered from jettisoned drop tanks or captured aircraft tested out at 90.5 octane. C3 or Green dyed fuel tested out at 94/115 in the early war and then from about early 1943 about 96/125 or 96/130 there was a big increase (probably late 1942 in reality) with a few tune ups. Allied intelligence notes this likely represents a the impending deplyment of a powerfull new engine.

It should be noted that allied 100/130 was more like 104/130 and 100/150 more like 110/150.

The Germans had a C3 or C2 formulation quite early. They defineltly had a supply problem for high octane fuels.

The first engine to use C3 in opperational use was the DB601N which saw service on Me 109E4/N and Me 109E7/N at the close of the Battle of Britain. The same engine with an improved supercharger impellor powered the Me 109F1 and F2. However, when the Me 109F4 came out it used the DB601E engine which reverted to B4 fuel but had considerably greater power. It did this via a radical valve overlap that resonance scavenged the end gases. Low speed idling was handled by changing inlet port lenght. Quite fancy for the day.

For some reason Daimler Benz was able to raise the boost level of the DB601N to the same level as the DB601E which meant that both the Me 109F4 and the older Me 109F2 ended up with the same power and performance.

The Daimler Benz series progressively increase compression ratio to 8.5:1 whereas the Merlin and almost all other engines stayed at 6.2:1. The higher compression ration produces both more power and better fuel efficiency but clearly would also limit maximum manifold boost. The DB series used an usual head attachement system; using the cylinder sleave as a giant bolt which had a giant nut applied, this allowed a larger volume with no increase in size and weight.

Hence while the DB produced about the same amount of power as the Merlin and needed to process about the same amount of air this air was required at lower pressure which meant that a single stage supercharger could do.

The Jumo 211j also added innovations such as intercooling to its single stage supercharger that helped keep power increasing.

All the important German engines were already two speed engines prior to WW2 as opposed to the Allison and the Merlins on Hurricanes and Spitifres.

They made C3 by upgrading B4 fuel with the addition of synthetic iso-octane. This iso-octane was made by passing syngas over a chromium catalyst which produced butanol, this was dehydrated over a zinc choloride salt to butane/iso-butylene which was then polymerised to iso-octane.

The butylene was however required for production of Buna N and Buna S synthetic rubber and this had priority over C3 fuel.

As it turned out the lions share of C3 fuel went to the BMW 801D2 engine when used on the FW 190 fighter.

The increase in quality of C3 fuel in 1943 seems to represent the comming on line of plant started in 1940, in particular alkylation plants. These would proably take 3 years to build and get running. Alylation was the way the allies made their 100/130 fuel.

Very few two stage supercharger engines came on line. The few I think of are
Jumo 213E1 of the Ta 152H
DB603LA of the Ta 152C3
Jumo 213F of the FW 190D-13

one reason for the introduction of the intercooled two stage supercharged engines was not their altitude performance but their abillity to opperate at high power levels on lower octane levels. The DB603EM was likely never built because its 2260hp needed C3+MW50 whereas the DB603LA could do the same job on B4.

 

[tomo pauk]

Would the single stage supercharger be sufficient? Germany was outnumbered almost through all of ww2. The situation was worsening on daily basis from 1942, further augmented with new pilots fuel issues. So, having fighter planes that perform only as good as enemy's just won't cut it*. Though, I'm not claiming that Germans would've won the ww2 with 2-stagers in their planes.
With advent of P-47, and then P-51B, even the performance parity was being lost. The introduction of the DB-605 AS/ASM engine was too little too late (but mere 6 months too late? by the time most of the Bf-109s were being produced with AS/ASC/D engines, fuel good pilots were hard to come by.). The two stage 605 was offering far better power high up, even with 1,43 ata boost and 2600 RPM. IIRC no intercooler was used?
Seems it just dawned too late for the people in charge.

*I'm not forgetting the Soviet lagging behind technologically; their way of (not only) air war Germans were ill capable to replicate

 

[Denniss]

DB 601E also introduced pressurized water cooling leading to higher performance even of B4 fuel.
I never heard of a DB 601N coming even close to the 1350PS Notleistung of the 601E.

The DB 603EM specifications changed a lot and I'm sure they made a ~2000 PS engine on B4+MW-50 and a higher-powered variant requiring C3+MW-50

 

[Shortround6]

The two stage supercharger is going to add around 100lbs minimum and perhaps 200lbs to the weight of the engine and that is without intercoolers. F4F two stage engines suffered from "surging" at times. The second impeller stalling and un stalling cause pressure fluctuations in the duct work that caused loud rumbling sounds.

As far as doing without the intercooler?
Remember that the interim P-38s were often limited in power at high altitude because their intercoolers were too small.
The goal was to reduce the air temp leaving the turbo to 100 degrees F at 25,000ft were the nominal temperature is -30 degrees F. This they failed to do. Taking out the intercooler completely would result in in an intake scores of degrees hotter with the corresponding loss in both power and the ability to withstand detonation.

Take a look at the two stage Alison in the P-63 as an indication of th Eli it's of a two stage engine with no intercoler..

 

[davebender]

WWII German weapons design put a lot of emphasis on low production cost. Me-109 fighter aircraft were dirt cheap compared to contemporary fighter aircraft. In fact low production cost is the primary reason the Luftwaffe selected the Me-109 over the He-112B for mass production.

I suspect using a single stage supercharger with hydraulic coupling rather then a two stage supercharger or turbocharger was part of the reason for Me-109 low cost.

 

[Shortround6]

Two stage superchargers did not exist for aircraft when the 109 was selected, it had nothing to do with cost or expense.

Adding them at a latter date to an existing design was difficult as not only is there a weight penalty but there is a considerable cost in volume and a drag penalty for the intercooler airflow. The P-39 was too small to house an effective intercooler and the 2 ft longer P-63 also might have had problems. The 109 may have been too small to house the needed intercooler without major redesign.

 

[davebender]

That was a design choice.

Auto Union race cars used two stage superchargers during 1936. Dr. Porsche could have applied the same technology to the new DB601 aircraft engine.

 

[Shortround6]

Using what for fuel?

Edit: There is also some doubt that the 1936 Auto union used a two stage supercharger. Or at least when in 1936 it showed up. The 1934 and 35 cars used a single stage supercharger and they started 1936 with a single stage. At some point in 1937 they had the two stage which was continued on in 1938.

Using the latest Formula I Grand Prix technology on a service aircraft may not be the brightest idea either. Considering that Formula I cars don't have to worry much about elevation changes makes things a lot easier for them too.

 

[tomo pauk]

The DB-628 was not an intercooled engine, the frontal compressor feeding the engine compressor via a simple tube. Image by jerryw.

 

[Shortround6]

Thank you Tomo,

I can just picture this on the front of a 109, and the prop spinner to go with it

Does the pipe connecting the two superchargers go inside or outside the cowl?

Put it on the outside with a bunch of fins and you have a 1930s Era race car intercooler