Merlin vs. DB601

[thedab]

How long does a late 43 DB605A goes for on 1.42 ata boost? (i.e.what the time limit at maximum boost)

and what are time limits for the DB605AM?

 

[drgondog]

Amen to Milosh - particularly Solex carbs

 

[fastmongrel]

Amen to Milosh - particularly Solex carbs

Milosh was talking about British Carbs. Solex were French now part of Magnetti Marelli.

 

[Reluctant Poster]

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

A comment to:



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.

That's exactly why I said: "at least until recently". In fact I've owned a car with direct fuel injection since 2006. The point is that it took 50 years after WWII for it to become a truly viable system. In addition modern systems do not meter fuel in the same way as the WWII systems. Today's systems use a common rail with fuel metering via electronically controlled fuel injectors. Such a system is only possible due to the enormous processing power of modern microprocessors.

I have found a truly "apples to apples" comparison test of carburetors, indirect fuel injection and direct fuel injection that was conducted by NACA in 1939. A single cylinder engine with a Wright R-1820-G air cooled cylinder was used. The results are quite specific "The values of minimum specific fuel consumption with each method of mixing fuel and air were the same." The paper does indicate that fuel injection has advantages in the distribution of fuel to individual cylinders, which was the main impetus for its adoption on the Wright R-3350.

I've attached the NACA Paper

 

[GregP]

People tend to think fuel injection is the be-all, end-all. A good carb is just fine if coupled with a good intake. It is easier to get fuel injection right these days because of microprocessors. Before that, using cams for injection adjustment, it was about as good as a carb with the added benefit of not cutting out under negative g.

The engines of today have a host of improvements that allow them to go 100,000 miles between tuneups ... not just digital fuel injection. I wouldn't trade a digital new engine for an old carbureted engine ... but, if the carbs had the development DFI has had, they might be VERY comparable in fact.

We know they haven't but, then again, nobody has made the effort to do it. Since DFI is so well understood, nobody may EVER make the effort. Had they done so, carbs might still be in the mainstream. Maybe not. I can say I had a Suzuki 100 with 4 carbs that ran absolutely great for years. I had a DFI GPZ 100 Kawasaki that also ran great for years. To this day I'm not sure which one ran better. The only thing I know for sure is the Suzuki had a choke and, if you left it ON, the bike was very slow after it warmed up ... I did that only once.

 

[Koopernic]

The big advantage of direct injection from the DB601E onwards was that a large valve overlap between intake valve and exhaust valve allowed scavenging and tuned ports that flushed our the last 15% of exhaust in the system. This was not possible on a carburator system since the fuel was premixed and would tend to be flushed out during scavenging. With direct injection the fuel could be injected after scavenging. This kind of tunning caused a problem with rough idling at low RPM so the DB601E and DB605 had variable length induction ports to aid idling and engine starting by tunning the length.

Apart from flushing in more air for combustion it also disposed of residual endgases that could cause pre-ignition. This helped greatly with low octane fuels. The injection also helped engine starting in the cold.

This technique was also used in the BMW801 but not as aggressively as intake ports could not be made variable length(instead they experimented with variable exhaust valves on the BMW802).

When German fuel improved from about 94/115 octane to about 96/125 in 1943 the BMW801 boost could be increased from 1.42 ata to 1.65 ata, thus giving the aircraft 1900hp instead of 1700hp.

Those aircraft tasked for ground attack were given what was called "C3 einspritzing" or C3 injection whereby the fuel during special increased emergency power could be fed instead to the intake of the engine ahead of the supercharger thus precooling the air/fuel mix and allowing increased power to 2050hp. Effectively the BMW801 acted like it had a carburettor when in War Emergency Power.

The direct fuel injection thus provided very good high speed cruise and military power while C3 einspritzung added a little more power again at a cost in efficiency.

The DB601/605 was a better engine than the Merlin for the Germans.

Had Britain been forced to operate all of its bomber force and over half of its fighter force on 87 octane they probably would have lost the war. It would have been hard to get much above 1030hp.

I imagine the best way forward, without 100/130 or even 100 was to introduce Water injection as soon as possible and move onto the Griffon XII spitfire in 1943 with water injection.

 

[GregP]

About 3/4 of the way down you posted: "The direct fuel injection thus provided very good high speed cruise and military power while C3 einspritzung added a little more power again at a cost in efficiency."

Perhaps you meant valve overlap thus provided same. All fuel injection did was to change the method of fuel metering, unless I miss my logic here. Could be.

I've certainly seen carbureted engines outperform fuel injected engines. All you have to do is go to an NHRA drag race to see it. Since that is true in 2015, it was probably true in 1940. The NHRA top fuel racer today, on a carburetor, is making 10,000 HP from 500 cubic inches and going 1,000 feet in less than 4 seconds. No fuel injected piston engines are going any quicker, anywhere in the world. So they probably didn't either in 1940. What they DID do is not lose power under negative g-force. That was a major advantage for the Bf 109 in 1940.

 

[wuzak]

Top fuel cars do not use carburettors - they use direct fuel injection.

 

[GregP]

If you say so ...

Here's a nice top fuel pump demo ...
View: https://www.youtube.com/watch?v=xGTbQuhhluY

The sound is the fuel pump. NO reason why it couldn't be injected. It's just a fuel delivery system. Neither one is superior to the other unless one can be controlled better. At this point, digital fuel injection SHOULD be better by a wide margin simply due to the ability to be controlled instantaneously. But the main need is 1.3 - 1.5 gallons per second.

 

[fastmongrel]

I dont think there are any Top Fuelers or Funnys still using carbs but in the lower classes carbs are still regulary used. The top Pro Stock cars in Europe were using carbs last time I looked. Dont know if NHRA rules are the same.

 

[Milosh]

Again I can't load an image.

Twin fuel pump schematic
http://images109.fotki.com/v782/photos/4/41615/228570/TwinFuelPumpSchematic-vi.jpg

 

[tomo pauk]

How long does a late 43 DB605A goes for on 1.42 ata boost? (i.e.what the time limit at maximum boost)

and what are time limits for the DB605AM?

The time limit for the DB 605A for 1.42 ata was 5 minutes. Not sure for the 605AM, though.

That's exactly why I said: "at least until recently". In fact I've owned a car with direct fuel injection since 2006. The point is that it took 50 years after WWII for it to become a truly viable system. In addition modern systems do not meter fuel in the same way as the WWII systems. Today's systems use a common rail with fuel metering via electronically controlled fuel injectors. Such a system is only possible due to the enormous processing power of modern microprocessors.

Was driving the 4 carb Alfa 33 1.5 TI, consumption was horrible. The injected, though not directly injected, 1.7 was giving more, while being more frugal with fuel.

I have found a truly "apples to apples" comparison test of carburetors, indirect fuel injection and direct fuel injection that was conducted by NACA in 1939. A single cylinder engine with a Wright R-1820-G air cooled cylinder was used. The results are quite specific "The values of minimum specific fuel consumption with each method of mixing fuel and air were the same." The paper does indicate that fuel injection has advantages in the distribution of fuel to individual cylinders, which was the main impetus for its adoption on the Wright R-3350.

Both Bristol and NACA were testing fuel injection on a 'wrong' engine type - a single row radial engine. The V-12 engine does not feature the inlet manifolds that are of same length and layout, as it was the case with the single row radial. A eupercharged V-12 with one carb will hence run some of the cylinders on a little more rich the mixture, in oder that other cylinders get just the mixture they need.
However, the gain in fuel consumption via injection on the ww2 era German aero engines was probably in single digits, the other part of a bit better consumption was due to the greater compression ration; both of these were not without trade-offs, though.

...
The direct fuel injection thus provided very good high speed cruise and military power while C3 einspritzung added a little more power again at a cost in efficiency.

The very good hi-speed cruise and military power from BMW 801 was due to the engine being of 'decent' displacement and RPM

The DB601/605 was a better engine than the Merlin for the Germans.

Maybe. The capacity for engine gun/cannon on the DB probably kept the Bf-109 competitive until the end of ww2 without a major airframe modification being necesarry.

Had Britain been forced to operate all of its bomber force and over half of its fighter force on 87 octane they probably would have lost the war. It would have been hard to get much above 1030hp.

I'm afraid that youre wrong on both accounts. Once the USSR and USA were in the fight vs. Germany, there was no way that UK will loose the war.
The RR have had in production, prior the war, the Merlin X, that was giving 1130 HP in low gear on 87 oct fuel. That is before Hooker improved the supercharger sytem (gaining in both rated height and brake horsepower), and before tests with intercooled both Merlin XX and 45 that showed further gain in power and rated height on those engines.

I imagine the best way forward, without 100/130 or even 100 was to introduce Water injection as soon as possible and move onto the Griffon XII spitfire in 1943 with water injection.

Yep, water injection is a way to circumvent the lack of hi-oct fuel. The Merlin 46/47 with WI would've been an really interesting engine, let alone the 2-stage Merlin and Griffon.

 

[bobbysocks]

I dont think there are any Top Fuelers or Funnys still using carbs but in the lower classes carbs are still regulary used. The top Pro Stock cars in Europe were using carbs last time I looked. Dont know if NHRA rules are the same.

are they using jetted carbs or throttlebody....which is the first type of fuel injection....a carb body with an injector instead of jets.

 

[fastmongrel]

are they using jetted carbs or throttlebody....which is the first type of fuel injection....a carb body with an injector instead of jets.

In Pro Stock it is Jetted Carbs iirc. The engines are stock apart from you can build them with forged cranks, rods, pistons and heads. Though everything must be dimensionally similar to stock and only have 2 valve heads. Thats the extent of my knowledge without googling it comes from a programme I kept from the last drag race I went to.

 

[EKB]

I can say I had a Suzuki 100 with 4 carbs that ran absolutely great for years. I had a DFI GPZ 100 Kawasaki that also ran great for years. To this day I'm not sure which one ran better. The only thing I know for sure is the Suzuki had a choke and, if you left it ON, the bike was very slow after it warmed up ... I did that only once.

When I was a teenager I rode a 4-cyl Yamaha Seca 550. With 50 hp, I thought it was pretty fast in stock trim.

That is until I rode a Kawasaki 750 triple that was built in the 1970s. Factory specs on the H2 Mach IV motor was 75 hp but the owner did some minor upgrades (tuned to about 100 hp). Even though the bike was ten years old, he was running 11 second ETs at the local 1/4 mile strip. I did not ride the bike to its limits and I recall having problems keeping the front wheel on the ground. The two-stroke triples were the budget superbikes of their day. Just insanely quick off the line and often wrecked by inexperienced riders.

 

[Koopernic]

The very good hi-speed cruise and military power from BMW 801 was due to the engine being of 'decent' displacement and RPM

Maybe. The capacity for engine gun/cannon on the DB probably kept the Bf-109 competitive until the end of ww2 without a major airframe modification being necesarry.

I'm afraid that youre wrong on both accounts. Once the USSR and USA were in the fight vs. Germany, there was no way that UK will loose the war.
The RR have had in production, prior the war, the Merlin X, that was giving 1130 HP in low gear on 87 oct fuel. That is before Hooker improved the supercharger sytem (gaining in both rated height and brake horsepower), and before tests with intercooled both Merlin XX and 45 that showed further gain in power and rated height on those engines.

Yep, water injection is a way to circumvent the lack of hi-oct fuel. The Merlin 46/47 with WI would've been an really interesting engine, let alone the 2-stage Merlin and Griffon.

Wikipedia specifically states the Merlin X producing that power in 100 octane fuel (not 100/130 but just 100) not 87 octane.

See:
"At the start of the war the Merlin I, II and III ran on the then standard 87 octane aviation spirit and could generate just over 1,000 horsepower (750 kW) from its 27-litre (1,650-cu in) displacement: the maximum boost pressure at which the engine could be run using 87 octane fuel was +6 pounds per square inch (141 kPa; 1.44 atm).[nb 8] However, as early as 1938, at the 16th Paris Air Show, Rolls-Royce displayed two versions of the Merlin rated to use 100 octane fuel. The Merlin R.M.2M was capable of 1,265 horsepower (943 kW) at 7,870 feet (2,400 m), 1,285 horsepower (958 kW) at 9,180 feet (2,800 m) and 1,320 horsepower (984 kW) on take-off; while a Merlin X with a two-speed supercharger in high gear generated 1,150 horsepower (857 kW) at 15,400 feet (4,700 m) and 1,160 horsepower (865 kW) at 16,730 feet (5,100 m).[48]"

It further states this was at 9 psig which is beyond the 6 psig possible on 87 octane at the time. I think the head design had to be strnghtend and 70/30 glycol were needed to get to 12psig but either way greater than 6psig was not possible with 87.

A gain of 100 hp is a great deal merely for a gear speed change. Seems possible only with extreme optimisation for low altitude WEP.

Another section of Wiki gives
1,130 hp (843 kW) at 3,000 rpm at 5,250 ft (1,600 m) with maximum boost pressure +10 psi (69 kPa); this was the first production Merlin to use a two-speed supercharger; Used in Halifax Mk.I, Wellington Mk.II, and Whitley Mk.V bombers. First production Merlin X delivered 5 December 1938.[6] It also gives 1,280 hp (954 kW) at 3,000 rpm, +10 psi (69 kPa) boost, sea level

there is a useful chart here:
https://en.wikipedia.org/wiki/List_of_Rolls-Royce_Merlin_variants
This is where I'm lifted the quote from.
https://en.wikipedia.org/wiki/Rolls-Royce_Merlin

 

[GregP]

The Kawasaki 750 triple and the original KZ900 had mild steel frames, and you'd get into frame flex if you hit the poower hard ina turn. The 750 triple had head shake when the front end came down, but the KZ900 did not ... or at least MINE didn't, but DID have a bit of head shake if you got into washboard while turning. I had ample opportunity to sample that behavior. I added a steering damper and it was better at high speed. The only real cure for frame flex was an aftermarket chromolly frame and swing arm.

 

[tomo pauk]

Koopernic - I don't know why going to the Wikipedia, when on this site there is far more accurate data on the Merlin X.
Eg. in the post #10 of this very thread, Aozora kindly posted data for different early Merlins, and it is stated that in the 1st gear max power was 1130 HP on the Merlin X on 87 oct fuel, while for anything above that the 100 oct fuel is needed. The power settings requiring 100 oct fuel are marked with asterisk (*).
As for the boost level that is feasible on 87 oct fuel - the Jumo 213 was god for 1.6 to 1.8 ata without MW 50, or +8 to +11 psig. The Merlin featured an even lower CR than Jumo 213, so we can still expect it t do at least that boost, if not greater.

A gain of 100 hp is a great deal merely for a gear speed change. Seems possible only with extreme optimisation for low altitude WEP.

Bingo for the 1st sentence, totally wrong on the second.

 

[Denniss]

One has to be careful with power comparisons as one may refer to power available for take-off at sea level and another may refer to maximum available power at altitude.

 

[tomo pauk]

Of course.
This chart (http://ww2aircraft.net/forum/aviation/merlin-vs-db601-39722-7.html#post1092184) shows that Merlin X will give some 1075 HP at sea level, 1130 HP at 5000 ft, all on +5.75 psi.