Merlin power with Modern Tech but Unleaded Petrol

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gruad

Airman 1st Class
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87
Jun 13, 2009
London
The Merlin was 27L and produced end of war 1800hp reliably. However this was on 150 Octane fuel which would be banned today based on the high lead content.

Clearly no one would build a piston engine like this today as we have jets. But let's say some billionaire with a love of WW2 engines did this with modern materials and CAD.

Now clearly the output of a modern car compared with 40s car is superior, but the Merlin relied on the high octane fuel to allow the high compression of the two stage supercharger.

So given the advantages of modern tech, but the constraint of unleaded fuel, could a 27L engine be built that delivers a reliable 1800hp?
 
Talk to Cosworth or Riccardo, I think the biggest advantage today is we have the machines and technology as well as the materials to make what they knew back then a reality, 1800hp out of 27L today I feel would be quite easy to achieve.
 
Of couse they could. You can achieve the equivalent octane rating without using lead. But apart from that 1800BHP from 27 litres is 66.7 BHP per litre, my car is a 3litre V6 diesel and produces 245 BHP which is 82BHP/L. Engine performance doesnt exactly scale but in the heyday of turbo F1 cars they were producing around 1,400 BHP from 1.5 litre engines (for a very short time). 30 years ago conventionally aspirated 3.5L engines in F1 were producing circa 700 BHP which is 200 BHP/L.
 
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You would not want F1-type power under any circumstances. An F1 engine has a very short lifespan. There used to be one for qualifying, and one for the race, to be rebuilt after every qual/race. Today, they qualify on the same engine and it has to last 2 races. Still, not something you'd want in ANY airplane. Expensive and no lifespan to speak of.

In an airplane, you want something that can make good power for many hours at a time, and be reusable for 1,500 - 3,000 hours of operation. So, you do NOT want to push the HP/liter or cubic inch up anywhere near the limit; you want RELIABLE power.

I think it can be done and you could, indeed, make 1,800 hp from a modern 27L engine and also have reliability. We know a LOT more about superchargers, turbochargers, intercoolers, and engines in general than they did in 1940. The main questions I have are: "What is the market and, given that market, what is the likelihood of ever breaking ever, much less making a profit from the engine? Also, you'd need to market both a 3 and 4 and maybe 5-blade propeller, with different lengths available, matched to this new engine, and a motor mount; sort of a "firewall forward" package for warbirds. You might want to make line of Spinners, too. If I were designing one, I'd design it for either upright or inverted Vee use (inverted fuel and oil system) so you could supply both Allied and Axis inline warbirds with powerplants. I'd use electronic ignition, fuel injection, and would have variable reduction gears so you could accommodate most diameter propellers.
 
I agree in part but an F1 race lasts 90 to 120 minutes and the time a WW2 engine could spend on full power was less than that. You certainly want reliable power but most ww2 fighter engines were considered tired and rebuilt or just replaced after 250 hours. F1 engines with or without turbos were subject to all sorts of restrictions that wouldnt apply to a military engine.
 
Two things.

The little engines use high rpm, 2-3 times that of the Merlin.


The Merlin was rated to last well over 300 hours before overhaul. It was also tested at that 1800hp level on a test stand for a number of hours even if the in service use was for 5-15 minutes. In fact post war commercial engines were rated at 1810hp at 3750ft at 20 1/4lbs boost.
Very few race car engines run at max power for more than a few seconds at a time (less than full throttle around corners) so even a several hour race might not put the same strain on an engine. Wonder what he power levels would have been if the Formula 1 engines had to last the season


Now forget the displacement. That Commercial two stage Merlin weighed 1740lbs dry weight. Or less than one pound per HP.

We do have better materials now and better lubrication.
However for context the Germans (Mercedes) got 480hp out a a 3 liter V-12 Grand Prix engine in 1939 for 162.1 hp per liter. Engine weighed 603 lbs so power to weight was 1.26lb per HP. Granted it wasn't running on gasoline. Inlet pressure was 2.31Atm (that is not "boost pressure" but absolute pressure).
Germans didn't come close in aircraft engines (except for power to weight)
 
pbehn said:
I agree in part but an F1 race lasts 90 to 120 minutes and the time a WW2 engine could spend on full power was less than that.
Click to expand...

I don't know about RR but Allison engines (in fact all US aircraft engines, including Packard Merlins) had to have a test engine survive 7 1/2 hours at the WER rating on a test stand 5 minutes at a time before the WER rating was approved. In Service the production engines were supposed to be limited to 5 minutes at a time.

How many times does a F1 engine run at 5 minutes at full throttle???
Mighty long straight away.
 
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I was just introducing comparison figures. WW2 engines were the F1 engines of their time. F1 introduced reliability requirements by limiting the number of engines that could be used and so reliability went up at the expense of peak power. Motor race engines have to deliver a spread of power and cope with being crunched up and down gears all the time. Like I said I was just giving figures, a 1.5L engine giving 1,400BHP for a short time or 700BHP for a longer time shows how much things had changed. In motorcycle racing the top guys are only on peak power for about 5% of a lap on most circuits, all the development is in power delivery and useable power while accelerating.
 

The current F1 regulations allow 3 engines per car per season, this season being 23 races long. The engines have to do 3 practice sessions, qualifying and a 300km race.

They make around 800hp, from 1.6L, without the electric motor, are restricted in the fuel they can use (110kg per race and 100kg/h maximum fuel flow rate). They could easily be detuned for a longer life.
 
At the end of WWII (or maybe just post-war?) the Merlin 100 series were putting out 2000 BHP in Military using 150 grade fuel. In Korea and Vietnam the US was running its higher power piston engines on 145 grade (US ~equivalent to UK 150 grade). Sometime after NATO really got going the US 145 and UK 150 grade had to meet the ~same performance standards.

Subsequently there was a NATO spec for 145LL (Low Lead) grade that lasted at least until the early 1980s (I do not remember the dates of service entry and have not run across any termination dates, nor do I know how common its use was - it might still be used or it might not.) IIRC the only problem was the significantly increased cost.

Shell began to market a 100 (100/130) grade NO LEAD aviation gasoline in 2015. I think this fuel was subsequently deemed to perform as well as the 100 and 100LL grades. Maybe someone more familiar with civil aviation knows more?
 
So- as stated above lead content has nothing to do with octane. Changing valves and such will eliminate the need for lead. Last I knew current av gas still has lead due to the large fleet of old engines out there.

It would be expensive to build a modern "Merlin equivalent" but not because the technology is hard to replicate. Just as you said, turboprops are much easier way to get that kind of performance today so you would only be making a few of them. Making a few of anything that complex is expensive.

I do not own a plane, but my understanding that the current push for diesels in general aviation is due to the fact they can burn Jet A fuel which is readily available globally.
 
Tetraethyllead was used as an octane booster, but it isnt the only way to achieve the same result. Tetraethyllead - Wikipedia
 

I did some rough numbers on it a couple of years ago, and in my estimation you can reduce the size of the required engine about three times, if you want to
retain the same sort of duty cycle. So I think you`d still want something pretty hefty in size, 8 or 9 litres. You can do it with one litre these days, but,
not with any sort of lifespan.

The fuel question depends on the application, its actually very easy to make fuels with as good knock resistance as 150 PN without lead, but, you need to use alchohol fuels, which are no good at all for serious aviation use for anything other than sprint-races because the fuel consumption is collossal, and hence fuel weight makes alchohol fuels worthless for any imagined pretend-wartime replacement specification discusssions. Nowadays, I think it would be possible to make a petroleum based fuel with 150 PN without lead or high alcohol content, it would probably have a lot of Toluene, Acetone and 2.5% Monomethylaniline.

However, I would think that those fuel components might also get banned if you tried to actually sell a commercial fuel containing them.

Modern engineering would get around it by making much less knock sensitive combustion systems which would allow very high boost with 100/130 PN equivalent instead.
Modern F1 standard engines can run 4bar boost with fuel you can buy from a commercial fuel station on the street (a select few in the UK at least sell 99 RON octane stuff (Shell V-Power).
 
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Triptane, or 2,2,3-trimethylbutane which I think in MON/RON about 112?

Didnt the BMW M12/13/1 produce 1400hp from 1.4L on standard street fuel? A result of very effective intercooling and high RPM presumably.
 
Thanks to a lot of research into combustion behavior in piston engines (most of which is due to environmental regulations), a V-12 of 1,650 cubic inch displacement could likely meet or exceed a Merlin's performance on currently available fuels. It just depends on how much money one is willing to spend.

That money is an important point: current large spark-ignition engines are almost all operating on natural gas (and have bores up to 50 cm), but large gasoline engines are pretty much dead technology; there are few beyond those in cars (and oversized pickups masquerading as family cars or station wagons) and they tend to be designed for a lower duty cycle.
 
Thanks for all your replies. Got this from PBehn's link (thanks)

Aviation spirits with TEL used in WWII reached 150 octane to enable supercharged engines such as the Rolls-Royce Merlin and Griffon to reach high horsepower ratings at altitude.[19] In military aviation, TEL manipulation allowed a range of different fuels to be tailored for particular flight conditions.

In 1935 the licence to produce TEL was given to IG Farben, enabling the newly formed German Luftwaffe to use high-octane gasoline. A company, Ethyl GmbH, was formed that produced TEL at two sites in Germany with a government contract from 10 June 1936.[20]

So if the Germans had TEL why were they running their planes on 87 Octane?
 

Lol I assume Monomethylaniline is the kind of stuff Walter White uses to make his 'product'.
 

Because the standard German aviation fuel (B4, of 87 octane) needed TEL in it just to get to 87. I would say the comments on that Wiki
page are a bit "basic" (a nice way of saying they`re slightly misleading when simplified to the level of saying things like high octane fuel
was available to the Germans because of TEL, fuel is a bit more complicated than that, as you can see from the chart below, showing that
the fighter grade German "C3" fuel had 97 octane without any TEL in it at all, which is because of the very high aromatic content).

 
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