The DB601E and C3/96 octane fuel?

[JAG88]

That is a question that has been running around my head for a while, how much would the DB601E have improved with C3/96 octane fuel had it, and not the BMW 801 got it in 1942 once cleared for 1350PS?

I see the C3 as the crutch that allowed the 801 to live, what if it is used to help the 601E and prevent the premature introduction of the 605?

 

[Shortround6]

I am not sure how much it helps without doing some trade-offs that get us into "what if land" real quick.

The higher octane (PN) fuel makes more power in two basic ways.

It allows higher compression in the cylinders.
It allows higher boost to be used (cramming more fuel/air into the cylinder).

The DB 601N used 8.2 compression instead of the 69 compression of the 601A series engines and needed the C-2/3 fuel.
Boost was limited to the same 1.3 ata I believe. One source claims they were trying for 1400hp but got a bit less than 1200hp.
There were a few other changes in the engine.

The DB601E was an attempt to match or exceed this while still using 87 octane fuel. Please see: http://www.enginehistory.org/German/daimler-benz.shtml

The DB 605 was pretty much a DB601E with a 4mm bore job and different bearings. If the 154mm pistons were a problem in the 605 I am not sure how well the 150mm pistons in the 601E would have stood up to higher pressure/temperatures in the cylinder.

These engines trying to use 1.42 Ata dropped the cylinder compression down to 7.3/7.5 for about the same total cylinder pressure as the 601E although with the wide duration camshaft/valve timing actual compression may be a bit less than the nominal compression.

If the new supercharger with 16 vanes topped out at 5000 meters for FTH then that doesn't change by changing the fuel.

I would also note that even the DB 605 could NOT do some of the jobs the BMW801 did, like power the Do 217 bomber. It doesn't matter what the 5 minute rating was, for bombers and large twins you need a high 30 minute or one hour rating for climb and/or high speed cruise in the target area.

 

[JAG88]

Thank you for your detailed explanation, I imagined that the more reliable 601E would be better able to deal with the loads imposed by the C3 than the 605, thus giving the F4 a much better speed coupled with better reliability and preventing the death spiral that the constant increase in weight meant for the 109s maneuverability.

Would the same apply to MW50 for the 601E?

 

[tomo pauk]

Excellent, we don't have many German-specific threads as we speak

That is a question that has been running around my head for a while, how much would the DB601E have improved with C3/96 octane fuel had it, and not the BMW 801 got it in 1942 once cleared for 1350PS?

I see the C3 as the crutch that allowed the 801 to live, what if it is used to help the 601E and prevent the premature introduction of the 605?

Not all BMW 801s were created equal. The 801C have had a 'slower' supercharger than the 801D, as well as lower max RPM in the second gear initially - meaning that altitude power will be much better for the 801D, even if it was running at a bit restricted settings initially. Not everything was great with 801D, either - perhaps increase of compreession ratio pushed thermal loads a bit too much (while adding a small bit of power), necessitating the introduction of new sperk plugs and other mods for the engine to operate as fully rated (2700 rpm, 1.42 ata). Net result was the 801C making 1380 PS at 4.6 km at 2550 rpm/1.30 ata, vs. 801D making 1440 PS at 5.7 km at 2700 rpm/1.42 ata. The fully rated DB 601E: 1320 PS at 4.8 km at 2700 rpm
Point I'm trying to make is that, as SR6 above noted, the DB 601E will not be able to beat the 801D in power, with both engines fully rated. It will consume far less fuel, though.
Engineers at DB were aware that 601E has it's limits, hence the 605A - as small modification of the 'power section' as possible, extra 100 rpm, while introducing a new supercharger, meaning the power of 1250 PS at 5.8 km at 2600 rpm (30 min rating), and 1350 PS at 5.7 km at 2800 rpm. The 601E will do ~1175 PS at 5.8 km at 2700 rpm (= fully rated engine, 5 min rating).
Any late war Allied fighter would've had far easier time with a Bf 109G that has DB 601E fueled with C3 than it had with the historic 109G.

One can wonder how much the reliability and allowed boost would've increased with decrease of the compression ratio on the DB and BMW engines, a path not taken.

 

[tomo pauk]

The DB 601N used 8.2 compression instead of the 69 compression of the 601A series engines and needed the C-2/3 fuel.
Boost was limited to the same 1.3 ata I believe. One source claims they were trying for 1400hp but got a bit less than 1200hp.
There were a few other changes in the engine.

The DB601E was an attempt to match or exceed this while still using 87 octane fuel. Please see: http://www.enginehistory.org/German/daimler-benz.shtml

The DB 601E was with max RPM of 2700, vs. (in most cases) 601N of 2600, thus preventing any loss of power due to decrease of the CR vs. the 601N, and indded exceeding the power of the 601N by handsome amount.
The max boost supposedly expected for the 601N was initially 1.42 ata, at least by looking at the manual for the Bf 109F1 and F2, and the manual states that current actual limit is 1.35 ata, also stating the resulting 6% drop in power at max RMP and that boost. At 2.1 km, the 601N was making 1260 PS.

I would also note that even the DB 605 could NOT do some of the jobs the BMW801 did, like power the Do 217 bomber. It doesn't matter what the 5 minute rating was, for bombers and large twins you need a high 30 minute or one hour rating for climb and/or high speed cruise in the target area.

The 30 min power at rated height (or 2nd S/C speed):
- BMW 801C: 1310 @ 4.4 km
- DB 601E: 1200 @ 4.9
- DB 605A: 1250 @ 5.8 km
- BMW 801C (fully rated): 1320 @ 5.3

To me it looks like the Do 217 would've been well served by the DB 601E/605A engines, especially once we account for a much better consumption figures of the DB engines.

Thank you for your detailed explanation, I imagined that the more reliable 601E would be better able to deal with the loads imposed by the C3 than the 605, thus giving the F4 a much better speed coupled with better reliability and preventing the death spiral that the constant increase in weight meant for the 109s maneuverability.

Would the same apply to MW50 for the 601E?

MW 50 for the 601E would've been interesting for the East front. The weight creep of the 109 can't be effectively battled via lower powered engines.

 

[rinkol]

The DB601R, a related DB601 development using C3 fuel, was tested, but proved too unreliable for service use. The dry cylinder liners used by the DB engines, and possibly limitations on the availability of key raw materials, seem to have contributed to thermal issues. The DB601E and DB605 both had to be derated until improvements were made.

The DB engines (with the possible exception of the DB605DB) that did use C3 fuel employed higher compression ratios rather than increased boost pressures - the main effect was to improve the altitude performance.

 

[JAG88]

Thanks to all for the responses, I apologize for not responding, real life got seriously in the way...

 

[JAG88]

The DB601R, a related DB601 development using C3 fuel, was tested, but proved too unreliable for service use. The dry cylinder liners used by the DB engines, and possibly limitations on the availability of key raw materials, seem to have contributed to thermal issues. The DB601E and DB605 both had to be derated until improvements were made.

The DB engines (with the possible exception of the DB605DB) that did use C3 fuel employed higher compression ratios rather than increased boost pressures - the main effect was to improve the altitude performance.

Many thanks, I was looking at the possible improvements at mid to low altitudes expecting a similar boost as in the case of the 801...

 

[JAG88]

MW 50 for the 601E would've been interesting for the East front. The weight creep of the 109 can't be effectively battled via lower powered engines.

What I was specifically thinking about was what would and hypothetical F based-109T3 be like in 1942, over water an unreliable 605 simply wouldnt do, forcing the issue of the 601E...

Best

 

[Koopernic]

What I was specifically thinking about was what would and hypothetical F based-109T3 be like in 1942, over water an unreliable 605 simply wouldnt do, forcing the issue of the 601E...

Best

The DB601N ran on C3 fuel of around 92 octane. (The Germans improved it several times, majorly in 1942 latter 96). The DB601E reverted to the use of B4 87 octane but developed the same and latter more power. They did this by an extreme overlap of the inlet and exhaust port. This ensured the final 12% of exhaust was scavenged and by the tuning of the inlet port resonance with engine rpm a degree of pressurisation was achieved. This usually leads to poor result at low RPM because the pressure wave can reverse so the DB601E had variable length inlet ports that altered with RPM.

I don't see why it's power couldn't be improved with a higher octane fuel either by higher super charger pressure (which would increase power only at low altitude below Full Throttle height or by increasing of the engine co Pression ratio which would increase power without a requirement of more fuel or air, thereby increasing power at all altitudes.

For best effects the C3 would be injected into the supercharger. This kind of conflicts with the idea of direct injection which can inject the fuel after the exhaust valve is closed before it is blown out.

Below is compression ratio vs octane number vs efficiency

5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %

An increase of ON from 87 to 92 would have increased power from 28% to 30% which is a 7.1% increase. If ON goes from 87 to 96 then it's a 14.2%. Rich mixture injection into the SC would achieve potentially more.

Air cooled engines are more sensitive to knocking.

The 1935 USAAC decision to go from 87 octane to 100 was predicated on a 30% increase in power.

 

[MIflyer]

Here is some detail on the DB601 and its fluid-coupled supercharger.