Merlin vs. DB601

[tomo pauk]

The V-1710 did have problems with engine's intake (ie. between supercharger and pistons), where the fuel would cease to be 'atomized', and started to revert into fluid as it was before exiting carburetor nozzles. Low temperatures worsened the situation, ie. when aircraft was flying high, and proper intercooler was used (as in P-38J/L, and the P-38J was seriously plagued with the problem, especially if low boost was used). The solution was to insert a venturi pipe in the intake duct, so the air stream was sucking any of the fuel from the bottom of the duct and re-atomize it. That way V-1710 also got rid with backfire screens (wire mesh, located just before the pistons), thus gaining 1000 ft in full throttle altitude (single stage engines, eg. installed in late P-39Qs) or 1500 ft (in P-38L).
On the opposite side, the earlier P-38s have had low-capacity intercoolers, and fuel in the duct didn't plagued them? The fuel injected there might've helped to cool the compressed air slightly better? They still have had the backfire screens, though, and these do lower the engine output.

So, after this lengthly intro - IMO, the direct injection would've improved the V-1710. We can take a look at the two stage V-1710 for the P-82 - those were without the screens, but backfired violently when pushed to the limits. The NAA installed backfire screens on their own, but GM (owner of Allison) was against that and managed to cancel the NAA's effort, employing political pressure. At the end of the day, the Allison engined P-38 have had slightly less performance vs. Merlin-engined ones. Edgar Shmued was very bitter on that GM's move.

 

[thedab]

well it looks close to me (DB605AS+MW-50 v merlin 63+ 21lb Boost (1ps=0.9863hp)

how much do the DB605ASM with it MW-50 system weigh compare to the merlin 63 with all it's bit's

 

[tomo pauk]

The quirk with the Merlin chart is that it includes the effects of ramming the air, ie. aircraft speed 'helps' the supercharger to do it's job. Note the remark at the bottom of the chart. Another thing with the chart is that it lumps together the distinctively different 2-stage Merlins together.
Without, or with small ramming, ie. the engine is on the test stand, or plane is at low speed, the altitude power is lower. You can check out the power of different Merlins here, including the Mk.70 (=1475 HP at 23250 ft, or 1500 PS at ~7090 m). Or, almost 200 PS more than DB-605ASM, and a tad better than DB-605D.
The Merlin 66 (for LF Spitfires) have had more power down low (~1620 PS at 4890 m), but less at higher altitudes, both vs. Merlin 70 and late was DB-605s. The mid-alt Merlin 63 have had ~1525 PS at 6400m, ie. it's power at altitude was between the AS/ASM and D. The main shortcoming of the DB-605AS and later was not so much the power they developed (the small and light Bf-109 was the major user anyway), but that they emerged too late to influence the income of the war.
Weight of the late war DB-605s with MW system and 2-stage Merlins (+ intercooler) was in the ball park?

 

[gjs238]

Wonder how the DB's would have performed with Allied fuel.

 

[fastmongrel]

Wonder how the DB's would have performed with Allied fuel.

Which Allied fuel there were plenty of different blends, late war 100 octane was different to early war 100 octane and early US and UK blends of 87 and 100 were vastly different. Once the DB engineers tuned the engines for the different fuel probably much the same at altitude. The late war 130 and 150 octane Allied fuels might have made a difference at lower levels.

 

[tomo pauk]

Wonder how the DB's would have performed with Allied fuel.

By 'Allied fuel' I reckon you mean 100 oct and better? German C3 fuel was roughly comparable with Allied hi-oct fuel, at least it seems so by GregP's post here. This chart, belonged to DB-605G, the engine later named DB-605AM.
With B4 fuel, the manifold pressure was 1.42 ata up to 5.7 km. With C3 fuel, the manifold pressure was 1.7 ata, but only up to 4 km. Greater manifold pressure means more power - up to ~230 HP more with better fuel, but under 5.7 km. We can draw paralels with Merlin here - better fuel increased power since it enabled greater manifold pressure before detonation occurred. Above those altitudes, the supercharger was limiting engine power, and it did not mattered whether C3 or B4 were used above 5.7 km. For greater power high up, new supercharger was needed, and the DB-605A 1st received the supercharger from DB-603, thus becoming DB-605AS.
In the graph we can see that internal mixture cooling (accomplished via MW-50 system) was still providing 1.7 ata under 4 km, but was packing more mixture in cylinders, since it was colder, thus the engine was capable for even more power. The benefits were falling sharply above 4 km.

 

[GregP]

I'm pretty sure the DB's would do fine with Allied fuel, so long as they were jetted and tuned for the differences between the blends.

Conversely, the Allied engines would do fine with the German fuels provided THEY were jetted and tuned for it. They might make slightly less power on German fuels depending on which one was used, but would run just fine if set up for it.

The trick is to get your engine running well on the fuel it must use. It's no good to have a thoroughbred Spitfire turned for 150 fuel if your local supply is 100 grade.

 

[tomo pauk]

An interesting experiment was tried in KIngdom of Yugoslavia just prior ww2. They have had license for Hurricanes, the engines should be purchased. Since they received a bit more DB-601 engines that needed for their Bf-109E3s, they mated the DB with Hurricane airframe (that particular airframe was purchased in UK, though). Resulting fighter (LVT-1, or, roughly "Fighter, by aero-techic section") was notably better than their stock Hurricane, especially during climb - Yugoslavia was operating the Hurricanes with 2-blade prop and likely on 87 oct fuel. The Yugoslavs were intending to produce 24 such fighters, but ww2 canceled the operation. link

 

[GregP]

Here is a drawing of the LVT-1:

 

[Gixxerman]

Great illustration GregP, interesting how the Hurricane (like the Spit similarly modded) still looks 'right' even with the inverted DB motor....something which I don't think quite works the same way with the RR equipped Spanish Me (Bf) 109's?

But that's just my opinion.... we all know what they say about them

 

[tomo pauk]

The story about single stage Merlin has another chapter, namely the engines that came after Merlin 45.
The Merlin 46 and 47 received bigger supercharger, with diameter of 10.85 in - compared with 10.25 in most of the single stage Merlins. Bigger supercharger gave better high altitude performance, at +9 psi boost it was capable for 1100 bhp at 22000 ft, or almost as good as the 2-stage V-1710 that was installed in P-63A! Emergency power was, on +16 psi, 1440 HP at 14500 ft. Here the Merlin turned the tables vs. the contemporary DB-601E, offering more power above ~13000 ft, but less under that altitude.
The altitude performance of the Mk.46 47 came at cost - low altitude performance was, without using the short term emergency power, barely above 1000 HP at 15000 ft. Unfortunately, the supercharger drive was still a single speed unit, and that, coupled with big supercharger, meant that supercharger itself was using too much power and heated the charge too much at lower altitudes; more power there was available with engine doing 2850 rpm, than 3000 rpm.
We can drive parallels here with Mikulin's AM-35/35A engine - fine at 5 km and above, but not that good at 2-3 km of altitude. The Spitfire V and VI received the Merlin 46s and 47s, not many of those engines were produced. The next Merlin installment, Mk.50, reverted to standard sized supercharger, and was, for all intents and purposes, similar in power as Merlin 45.
People will notice that I do not make much mention of Merlins with either smaller ("cropped", mostly 9.50 in diameter) supercharger, or the ones with decreased supercharger's drive ratio - those were used mostly for FAA needs, and for low-level Spitfires, and do not have a DB-601 variant that is directly comparable (apart from DB-601Aa?).

 

[Shortround6]

I think you can see the same effect with the DB 605 engines, the later ones with big supercharger had slightly less power for take-off and low altitude at the same pressures than the earlier small supercharger engines even with the variable drive although that helped considerably.

 

[tomo pauk]

Yep - the DB-605AS (= big supercharger) have had 1435 PS for take off, vs. 1475 PS for the DB-605A.
OTOH, one might wonder what would've do the Merlin 46/47 with water-alcohol injection...

 

[thedab]

A Merlin with water injection

I know it was bit late

 

[Reluctant Poster]

"The specific fuel consumption of DB-601 was lower than of 1-stage Merlin, by some 10%."
This is one of those internet numbers which is not based on a real apples to apples comparison. Flight magazine published an interesting comparison of a Merlin X vs a Jumo 211D. This article claims the Merlin's fuel consumption was actually lower. Admittedly this was written by a Rolls Royce engineer so there may be a bit of bias. It does point out that the Merlin is penalized by 3% due to its lower compression ratio. There are more differences between engines that can account for differences in fuel consumption than just fuel delivery. The only truly valid comparison would be based on engines that are identical save for the method of delivery. There is no reason to suppose that the Bosch direct injection system was better than the good old fashioned carb given the technology of the day. It took the invention of the microprocessor to make fuel injection truly effective. The direct injection system was an adaptation of the diesel system and proved to be an evolutionary dead end. Modern fuel injection system are not direct injection (at least until very recently) and do not meter the fuel using the mechanical jerk pump as used by Boschn The float type carb was actually a pretty precise instrument at the time and it took a very long time for fuel injection to replace it in gasoline engines, at least in cars.

 

[Reluctant Poster]

The Flight article on the Merlin X Jumo 211D comparison is attached along with one on the Bendix Stromberg Carb

 

[GregP]

The two hottest Merlins in the world are both running very low compression. That's how they can run 140 inches of boost at Reno.

If they were running 6.0 : 1, you couldn't get that level of boost without detonation and blowing out the tops of the pistons.

Wasn't particularly practical for war use, but makes for a FAST racer. Neither Strega nor Voodoo would ever make Berlin and back on the race engines ... even if they had the fuel capacity (which they don't anymore).

Thanks for the linked articles ReluctantPoster!

 

[tomo pauk]

"The specific fuel consumption of DB-601 was lower than of 1-stage Merlin, by some 10%."
This is one of those internet numbers which is not based on a real apples to apples comparison. Flight magazine published an interesting comparison of a Merlin X vs a Jumo 211D. This article claims the Merlin's fuel consumption was actually lower. Admittedly this was written by a Rolls Royce engineer so there may be a bit of bias. It does point out that the Merlin is penalized by 3% due to its lower compression ratio. There are more differences between engines that can account for differences in fuel consumption than just fuel delivery. The only truly valid comparison would be based on engines that are identical save for the method of delivery. There is no reason to suppose that the Bosch direct injection system was better than the good old fashioned carb given the technology of the day. It took the invention of the microprocessor to make fuel injection truly effective. The direct injection system was an adaptation of the diesel system and proved to be an evolutionary dead end. Modern fuel injection system are not direct injection (at least until very recently) and do not meter the fuel using the mechanical jerk pump as used by Boschn The float type carb was actually a pretty precise instrument at the time and it took a very long time for fuel injection to replace it in gasoline engines, at least in cars.

Hello, Reluctant Poster,

I do have some remarks re. this post.
You unfortunately did't bother to quote the relevant part of the original post, or at least the post number. Then, I've posted the consumption numbers here, for the Merlin XX and DB-601E, that you unfortunately either did not read, or, you did read, but didn't offer your data math. Further, DB sheet about DB-601A states that benefits of fuel injection, vs. carburated DB-600, are greater power and lower fuel consumption. The float type carb penalized Merlin's performance, and part of the British test that I've quoted here clearly states so. It's just under the sentence you quoted in the post #135

 

[DonL]

For the WWII aircraft engines tomo pauk has posted all relevant data's and arguments.

A comment to:

The direct injection system was an adaptation of the diesel system and proved to be an evolutionary dead end. Modern fuel injection system are not direct injection (at least until very recently) and do not meter the fuel using the mechanical jerk pump as used by Boschn The float type carb was actually a pretty precise instrument at the time and it took a very long time for fuel injection to replace it in gasoline engines, at least in cars.

This is a very wrong claim for modern gasoline engines.

Gasoline direct injection - Wikipedia, the free encyclopedia

Here in Europe nearly every very modern gasoline engine has direct fuel injection.

 

[Milosh]

I missed that comment DonL. All I can say is that any British carb whether it was on a car or motorcycle had to be continually fiddled with.