Which country designed the best engines for WWII?

[Shortround6]

Thank you .

 

[michael rauls]

If the supercharger is included as part of the engine I would have to give ot to the Brits. Imho the Merlin and Griffin seemed like they were one step ahead of anything else throughout the war.

 

[Shortround6]

That darn Stanley Hooker has a lot anwer for, knocking the US engines into 2nd place

 

[wuzak]

If the supercharger is included as part of the engine I would have to give ot to the Brits. Imho the Merlin and Griffin seemed like they were one step ahead of anything else throughout the war.

I would hope so - they didn't have much performance without the supercharger!

All major engine types for combat aircraft in the war had an integral supercharger.

 

[michael rauls]

I would hope so - they didn't have much performance without the supercharger!

All major engine types for combat aircraft in the war had an integral supercharger.

Yes 10-4. I just meant as a package I felt the British engines were the best of the war as oposed to if were talking with equivalent superchargers a case could be made that some other engines were as good or perhaps even a bit better.

 

[pbehn]

That darn Stanley Hooker has a lot anwer for, knocking the US engines into 2nd place

I think it was the end of the era where individuals made a huge difference, the whole of the supercharger/turbo charger/jet engine world was driven by just a few people world wide.

 

[Deleted member 68059]

Yes thanks I know how the DFV chamber works, I was trained by Duckworths protoge Geoff Goddard for six years - and you will find my interview with him on my website.

You are quite correct that the Allison inlet manifolds are appauling, they are. However the chamber shape is also absolutely fundamental to good perfomance as the narrow angle pent roof shape has the lowest surface area possible for practicable 4 valve layouts, and hence achieves better thermal efficiency, and despite the bad manifolds it will certainly still be exhibiting a fair measure of tumble. It also has some vestiges of an attempt at some squish, which almost nobody else got anywhere near. Although the V1710 doesnt have enough squish to really make a measurable leap.

However the V1710 chamber is a generational leap ahead of the Merlin, although as you correctly point out it was not really developed to the point where it made use of that step ahead in layout. In fact some Russian designs have surprisingly good chamber layouts too.

As for "ramming manifolds", nobody designed aeroplane engines with sucessful "ram manifolds" because at the speeds an aero engine runs at you cannot get a resonance without having an overall length of well over 1 meter. Try packaging that ! (it was tried...). If you do NOT have equal length for each runner your cylinders will all be running at totally different mixture strengths because the resonance effects will give you very different volumentric effiencies, however - again, I do not disagree at all with your view that the V1710 manifolds are very poor from a flow coefficient standpoint.

 

[Shortround6]

there is a relatively simply formula (that escapes me at the moment) for figuring out the needed intake length for a raming manifold but it has to do with the speed of sound and the rpm of the engine (divided by 2?) at any rate to get ramming effects for a low rpm engine you get things like the old Chrysler manifolds.

I believe there were two different lengths depending on the RPM band that was desired. The shorter one worked closer to 6000rpm?

But this is for a naturally aspirated engine. I don't know what happens in a supercharged engine.
BTW the length of the intake path is from the mouth of the carburetor (or velocity stack) to the intake valve.

 

[pbehn]

there is a relatively simply formula (that escapes me at the moment) for figuring out the needed intake length for a raming manifold but it has to do with the speed of sound and the rpm of the engine (divided by 2?) at any rate to get ramming effects for a low rpm engine you get things like the old Chrysler manifolds.
View attachment 514550
View attachment 514551
I believe there were two different lengths depending on the RPM band that was desired. The shorter one worked closer to 6000rpm?
View attachment 514552
But this is for a naturally aspirated engine. I don't know what happens in a supercharged engine.
BTW the length of the intake path is from the mouth of the carburetor (or velocity stack) to the intake valve.

Isnt that where the phrase "engine tuner" originated from, from when harmonics was involved, in some cases you can hear a tuned engine go "on cam".

 

[Deleted member 68059]

Isnt that where the phrase "engine tuner" originated from, from when harmonics was involved, in some cases you can hear a tuned engine go "on cam".

No idea about that particular anecdote, but the effect is caused by standing waves forming in the inlet runners. A simplified version is shown in Heinz Heizlers "Advanced Engine Technology" book (which is worth a read).

Amazon product ASIN 0340568224
View: https://www.amazon.co.uk/dp/0340568224/
The procedure to calculate the length from first principles

Choose rpm, lets say 19,000rpm
Choose air temperature, lets say 20 degrees C
Calculate speed of sound =331.4+(0.6*temp_air) = 331.4+(0.6*20) = 343m/s ("ssound")
Choose a length for the inlet tract, lets say 0.148meters ("r_length")
Time for wave to travel one lengthe =r_length/ssound = 0.00043seconds
Time for wave to travel back AND forth = 0.0004*2=0.00086seconds
Choose inlet valve opening points in crank degrees:
Inlet Valve Opening Point Crank Deg=360
Inlet Valve Closing PointCrank Deg=560
Inlet Valve opening duration = 560-360 = 200 crank degrees
Calculate time for one crank degree to rotate = 8.77x10^-6 seconds
Calculate time the inlet valve is open = 200 x 8.77x10^-6 = 0.002seconds
Calculate ideal length of inlet runner for first order reflection = Inlet Opening Time * Speed of Sound / 2 = 0.002 x 343 /2 = 0.301meters
Calculate actual tuned order length of chosen runner length = 0.301meters / 0.148meters = 2

Thats a pretty convoluted way of doing it, but at least you can see whats happening, which is why I have typed it all out. I suggest you make an EXCEL sheet
plug all that in, and then play with the rpm, you`ll see very soon why with low revving engines it gets VERY hard to have
resonance tuning ! The above numbers are about right for the last of the naturally aspirated F1 engines, hence the very high crank speed
and short runner length.

(as the orders get higher, the effect of the resonance drops, once it gets to about 6th order, you can consider that
its probably not doing much)

 

[MiTasol]

If you do NOT have equal length for each runner your cylinders will all be running at totally different mixture strengths because the resonance effects will give you very different volumetric efficiencies..

I thought that the theory behind the abomnimable Allison manifold? Right idea - wrong application

 

[fliger747]

R2800 "C" series engines, magnificent dependable "Piston Pounder", remains in commercial service, I have friends that still fly them daily!

 

[Reluctant Poster]

The attached report describes an early attempt to optimize intake length on a single cylinder Liberty converted to compression ignition.

 

[Sid327]

Why would intake manifold length,

.....or design shape matter in an engine that was force fed boost?

 

[pbehn]

Why would intake manifold length,

.....or design shape matter in an engine that was force fed boost?

It does, for all sorts of reasons, there is a whole science built around it.

 

[Sid327]

It does, for all sorts of reasons, there is a whole science built around it.

Thanks,

Any links or source information? .....I need to understand this better.
The Merlin had an aftercooler and flame traps that were surely restrictive to airflow, the Allison didn't, which make me think there wasn't as much boost pressure loss.
I don't see how this had anything to do with tuned length. Can somebody explain this to me in layman's terms?
(I fully understand the need on a naturally aspirated engine).

 

[GrauGeist]

In a nutshell: the longer the intake, the better the air/fuel mixture and distribution, which results in better peak horsepower under load.

The automotive industry is working on a technology called "Variable Length Intake Manifold" (VLIM) to take advantage of that.

 

[pbehn]

Thanks,

Any links or source information? .....I need to understand this better.
The Merlin had an aftercooler and flame traps that were surely restrictive to airflow, the Allison didn't, which make me think there wasn't as much boost pressure loss.
I don't see how this had anything to do with tuned length. Can somebody explain this to me in layman's terms?
(I fully understand the need on a naturally aspirated engine).

Just from reading various posts on here by very learned posters. There are all sorts of issues from the mixing and temperature/pressure of the charge to the actual flow. Don't forget that even with a two stage supercharger as you approach maximum altitude the engine trends towards working at atmospheric pressure anyway.

 

[Sid327]

In a nutshell: the longer the intake, the better the air/fuel mixture and distribution, which results in better peak horsepower under load.
The automotive industry is working on a technology called "Variable Length Intake Manifold" (VLIM) to take advantage of that.

Okay.
Yes this is for N/A engines, Ilmor brought this out on a Formula One engine many years ago. Increasing runner length moves the power band down, short runner length for top end power.
But where does this apply to the type of supercharged engines used in WW2 aircraft?

 

[Dan Fahey]

Why would intake manifold length,

.....or design shape matter in an engine that was force fed boost?

Flow and the Type of Flow...
Runner Length, Size, Configuration of the Runner restricts at various speeds.
Some work better than others.

Airflow behaves differently in a Carburation system than a Direct Fuel Injection system.
Carburated you have both Fuel and Air mixing, moving, twirling and tumbling which behaves different than just air alone.