Which country designed the best engines for WWII?

[Sid327]

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.

Hi Dan,
Yes, I understand this and how it applies to N/A engines. Thank you.

......But I'm still trying to find out about an application like the Allison and Merlin V12's.
I want to know why when the intakes have been pressurised with boost from the supercharger why would runner length, diameter, and to a certain extent shape for good flow matter.

 

[Dan Fahey]

Hi Dan,
Yes, I understand this and how it applies to N/A engines. Thank you.

......But I'm still trying to find out about an application like the Allison and Merlin V12's.
I want to know why when the intakes have been pressurized with boost from the supercharger why would runner length, diameter, and to a certain extent shape for good flow matter.

Same issue when charging except that you can have the Manifold Backfire because the heat ignites the pressurized fuel.

 

[pbehn]

Hi Dan,
Yes, I understand this and how it applies to N/A engines. Thank you.

......But I'm still trying to find out about an application like the Allison and Merlin V12's.
I want to know why when the intakes have been pressurised with boost from the supercharger why would runner length, diameter, and to a certain extent shape for good flow matter.

Because it is a dynamic not a static system, the fuel air mixture is being pumped in continuously and leaving continuously with a pressure measured at a point in the manifold. Various twists and turns in the system could result in cylinders having different mixtures.

 

[Deleted member 68059]

Thanks,
Any links or source information? .....I need to understand this better.
.

I posted a complete mathematical solution about one mouse-wheel-scroll above your post.... ?

Why do I post this stuff when nobody even reads it - its not like it was 25 pages back..... its all about
resonance which in pipes is explained below.

When the valve is closed its a pipe with one end closed....see if you can figure it out.... *HINT* when the wave motion is zero... pressure is high.....

Organ Pipe Resonance

A nice video... when the flames are higher its because the pressure in the tube is high, when engine speed matches the resonance..... one
can make the pressure behind the valve higher. Note that in this case its a "closed-closed" tube so the resonance nodes are not in the
same location as they would be in an engine, but the principle is clear.

NB - Its possible to confuse this with what is always talked about as a variety of badly named effects like "ram tuning", "inertia tuning"
and so on - which often include discussion about the pressure wave moving up and down the pipe.

However both things are happening at once, it is the little zones of high pressure moving up and down the pipe at resonance which
creates the "standing waves" (waves which dont change) in the first place. The standing waves are the measurable manifestation
of the pressure pulses moving up and down the tube - so its simply two different ways of looking at exactly the same thing.



Source for below:
Tubes

 

[Sid327]

I posted a complete mathematical solution about one mouse-wheel-scroll above your post.... ?

Why do I post this stuff when nobody even reads it - its not like it was 25 pages back..... its all about
resonance which in pipes is explained below.

When the valve is closed its a pipe with one end closed....see if you can figure it out.... *HINT* when the wave motion is zero... pressure is high.....

Organ Pipe Resonance

A nice video... when the flames are higher its because the pressure in the tube is high, when engine speed matches the resonance..... one
can make the pressure behind the valve higher. Note that in this case its a "closed-closed" tube so the resonance nodes are not in the
same location as they would be in an engine, but the principle is clear.

NB - Its possible to confuse this with what is always talked about as a variety of badly named effects like "ram tuning", "inertia tuning"
and so on - which often include discussion about the pressure wave moving up and down the pipe.

However both things are happening at once, it is the little zones of high pressure moving up and down the pipe at resonance which
creates the "standing waves" (waves which dont change) in the first place. The standing waves are the measurable manifestation
of the pressure pulses moving up and down the tube - so its simply two different ways of looking at exactly the same thing.



Source for below:
Tubes

View attachment 555851

You are talking about naturally aspirated engines, where the ''tuned length'' and resonance helps draw or suck in the next charge of air.
(You are not obliged to read my previous posts).

How does this apply to an intake manifold on an engine such as the Merlin/Allison specifically, where the whole intake after the supercharger is pressurised and as I understand it does not need this?
And why would a convoluted manifold matter when every part of it contains air charge under pressure?

 

[pbehn]

And why would a convoluted manifold matter when every part of it contains air charge under pressure?

Can you explain weather? Why doesn't the air pressure equalise? What is this "sucking" how does it work? Does a normally aspirated engine at 20.000 ft become a supercharged one at sea level?

 

[Sid327]

Can you explain weather? Why doesn't the air pressure equalise? What is this "sucking" how does it work? Does a normally aspirated engine at 20.000 ft become a supercharged one at sea level?

Can we keep it amiable?
All I have done is ask a question to which I am hopefully waiting for someone to explain (nicely) how this works.
I finished with the military twenty years ago and since than, maybe naively expect people to have some patience and understanding.
Is that asking too much?

 

[pbehn]

Can we keep it amiable?
All I have done is ask a question to which I am hopefully waiting for someone to explain (nicely) how this works.
I finished with the military twenty years ago and since than, maybe naively expect people to have some patience and understanding.
Is that asking too much?

I was asking a simple question because you seem to be working under a misconception. An engine doesn't "suck" gas into the cylinders just as humans don't suck air into their lungs, it just seems that way. The system in a supercharged or turbocharged engine may be pressurised but it isn't static. On a 36litre engine one bank of a V12 operating at 3,000 rpm is drawing 9 litres of air every revolution, it is revolving at 50 revs per second so 450 litres/sec. If there is a sharp turn in the system the gas on the inside covers less distance than the outside of the bend causing turbulence and drag. The rail supplying the engine has 450L/s at the first valve and progressively less until the last cylinder has only the flow for one valve. If you take all the inlet valves out of a Merlin and replace them with a single valve from a car you will still have the same manifold pressure but much less power because the gas just cant get past the valve quickly enough.

 

[Deleted member 68059]

You are talking about naturally aspirated engines,

I would respectfully suggest you dont tell me what I`m trying to tell you, it will make it much easier for us to both communicate.

I did read all your previous posts, and am perfectly aware that you are interested in boosted engines.

(very) Briefly:

1) Most people with boosted engines dont bother with resonance effects because they are lazy, and would rather turn the boost up
than have a good intake system. It is certainly much more critical to get it right on an n.aspirated engine - but if you are after performance -
nearly all very high end highly boosted engines will have resonace tuning on the inlets. Packaging frequently prevents it however.

2) It is very rarely used on aero engines because at low engine speeds (3000rpm) to get a decent resonance you will need an intake
runner of over 1meter in length, which is usually prohibative for packaging, although the V-1710 makes an attempt at it.

3) Pressure does indeed NOT care about pipe bends and convolution, but MOVING air under pressure does. Every bend removes
energy from a moving fluid or gas, and reduces its pressure. To rectify a terrible intake system means running higher boost
pressures which has all sorts of very important knock-on consiquences which engine designers wish to avoid.

Modern turbocompound F1 engines are running about 4bar manifold pressure, and all have resonance tuned inlet systems,
being hidden under carbon fibre inlets you wont find that out unless you work for a company who designs them - so this
fact is not know to all casual observers.

I hope that helps explain.

 

[Dan Fahey]

Then there is the Density Altitude characteristics that changes as a plane climbs and dives.
I do a lot of Drag Racing and the DA can change dramatically changing the performance of my car.
Sometimes in as little as 5 minutes if a front moves by.

My engine output will vary as much as 100 hp from hot miserable high DA day to a below sea level as much as a 1000 ft.
I suspect that the P-40 did better in cold air Russia than it did in steamy hot SW Pacific weather.
One of the major issues in the Pacific was canopies fogging up as the planes dived from higher altitudes with cooler dryer weather to the warm tropical sea ai

 

[Ivan1GFP]

You are talking about naturally aspirated engines, where the ''tuned length'' and resonance helps draw or suck in the next charge of air.
(You are not obliged to read my previous posts).

How does this apply to an intake manifold on an engine such as the Merlin/Allison specifically, where the whole intake after the supercharger is pressurised and as I understand it does not need this?
And why would a convoluted manifold matter when every part of it contains air charge under pressure?

Hello Sid327,

Hopefully I didn't just walk into the middle of an argument. If so, then I shall bow out shortly.
Here is how I see things:

Whether or not the Mixture at the Throttle Body is above or below ambient pressure is really irrelevant.
The air coming into through the throttle body is a column of gas that has a speed and mass and thus momentum.
For best flow, you want that column of air moving at a steady state and not stopping and then accelerating back to speed again.

The column of air splits into each intake runner to individual cylinders but for each of these runners, the flow is NOT constant.
The flow in each runner starts when the intake valve opens and only flows during the intake stroke.
It stops during the other three strokes of a typical four stroke engine.

If this were a one cylinder engine, then the impulse of the changing airflow during the four stroke cycle would propagate back up to the throttle body even further back into the intake.

If it is a multi cylinder engine, the volume of each intake runner, engine volumetric efficiency, and engine speed can be calculated so that when the flow in one intake runner stops, the flow in another intake runner begins and thus the flow at the throttle body remains constant.

The are of course going to be issues with harmonics and shockwaves and such and this kind of thing is going to probably be easier to figure out with a Normally Aspirated engine than with a Supercharged version where the boost can change, but the principles are still going to be the same.

Sometimes, because of space limitations, or because of a wide operating range of engine speeds or some other reason, there may not be a precise match up in volumes. In those cases, there is often an "air box" or plenum put into the intake system to dampen the shocks of the changing air velocity before they get back to the throttle body.

Hope that makes sense.

This is why one some of the older street rods, one could often see a Roots blower sitting on top of a tunnel ram intake manifold. That tunnel ram manifold wasn't there just for looks, but was there to give correctly sized intake runners.

- Ivan.

 

[Shortround6]

When comparing WW II aircraft engines to Formula I engines (of any era/date, baring pre WW I) ) you had vastly different intake lengths and vastly different ideas (or realities) of what low end and top end power consisted of.

Even an auto union 6 liter V-16 of 1936 was turning 5000rpm. later pre war V-12s were 7000rpm and above
Some of the flow benefits of "short" or "long" intakes depend on the speed of sound in the intake duct and pressure pulses bouncing back and forth between the intake and the valve or port.
Obviously you can't change the speed of sound to suit the size of the engine and a short intake runner on a 27-36 liter engine is a very long intake runner on a 6 liter (or smaller) engine.

The Airplanes (once they got constant speed propellers) didn't really have to worry about low end power. The prop would automatically adjust it's pitch to suit the power the engine made at a preset RPM. That is the engine could run at max RPM and the prop would adjust to the airspeed like having a car with a variable speed drive instead of one with only 3-5 speeds in the transmission and the engine might fall off the power peak when shifted to a higher gear.

As noted above by others this principle worked great when used on NA engines and the intake length was measured from the valve to the intake of the carb or velocity stack mouth

What happens when you stick a multi blade fan turning thousands of rpm in the middle of that gas flow?

 

[wuzak]

Modern turbocompound F1 engines are running about 4bar manifold pressure, and all have resonance tuned inlet systems,
being hidden under carbon fibre inlets you wont find that out unless you work for a company who designs them - so this
fact is not know to all casual observers.

They are also variable length intakes.

The exhausts are also resonance tuned, but they are not allowed to be variable length.

 

[Sid327]

I would respectfully suggest you dont tell me what I`m trying to tell you, it will make it much easier for us to both communicate.

I did read all your previous posts, and am perfectly aware that you are interested in boosted engines.

(very) Briefly:

1) Most people with boosted engines dont bother with resonance effects because they are lazy, and would rather turn the boost up
than have a good intake system. It is certainly much more critical to get it right on an n.aspirated engine - but if you are after performance -
nearly all very high end highly boosted engines will have resonace tuning on the inlets. Packaging frequently prevents it however.

2) It is very rarely used on aero engines because at low engine speeds (3000rpm) to get a decent resonance you will need an intake
runner of over 1meter in length, which is usually prohibative for packaging, although the V-1710 makes an attempt at it.

3) Pressure does indeed NOT care about pipe bends and convolution, but MOVING air under pressure does. Every bend removes
energy from a moving fluid or gas, and reduces its pressure. To rectify a terrible intake system means running higher boost
pressures which has all sorts of very important knock-on consiquences which engine designers wish to avoid.

Modern turbocompound F1 engines are running about 4bar manifold pressure, and all have resonance tuned inlet systems,
being hidden under carbon fibre inlets you wont find that out unless you work for a company who designs them - so this
fact is not know to all casual observers.

I hope that helps explain.

Yes, thank you.

This explains it at a level I can understand.

 

[Sid327]

Yep. All the major countries had good engines with the Germans and Americans having good rotaries and the British having a good inline. For me I voted for Britain because of the Merlin among others with the US and Germany very close behind.

Can someone change the England in the poll to Britain (or UK)...

Agree with this post.

Some of the U.K's best engineers and inventors came from Scotland.
I'm sure the Irish and Welsh won't be too quick offering you a beer either!

 

[mad_max]

Agree with this post.

Some of the U.K's best engineers and inventors came from Scotland.
I'm sure the Irish and Welsh won't be too quick offering you a beer either!

Opps I confused articles and typed crap. Sorry for the confusion.

 

[Sid327]

Stanley Hooker came to the states after the war and I believe everyone old enough knows Hooker Headers were the go to choice for performance back in the 50's-70's.

Is that a fact? !
Yes, I remember these, but I didn't realise the connection.

 

[pbehn]

Is that a fact? !
Yes, I remember these, but I didn't realise the connection.

Hooker was a mathematician who specialised in the science of fluid mechanics/ dynamics which is what I alluded to earlier.

 

[MiTasol]

Hi Dan,
Yes, I understand this and how it applies to N/A engines. Thank you.

......But I'm still trying to find out about an application like the Allison and Merlin V12's.
I want to know why when the intakes have been pressurised with boost from the supercharger why would runner length, diameter, and to a certain extent shape for good flow matter.

To break it down to the most basic level for those could not understand Calum's excellent summary.

In a normally aspirated engine the air in the manifold is below atmospheric so the atmosphere is a "high pressure source" that is forcing air into the carburetor.

In most supercharged engines the carburetor has just been moved to before the high pressure source instead of after the high pressure source. but the basic wave patterns caused by the valves opening and closing remain the same regardless of the manifold pressure. I say most because some of the Allison ASB engines had the first stage engine driven supercharger before the carb resulting in a configuration that is essentially the same as an engine with a turbosupercharger.

Turbosuperchargers add pressure before the carb and then the engine driven supercharger adds more pressure after the carb but the basic wave patterns caused by the valves opening and closing again remain the same regardless of the manifold pressure.

 

[mad_max]

Is that a fact? !
Yes, I remember these, but I didn't realise the connection. [\quote]

Opps confused articles that I've read. I posted crap. So Sorry; although it was a Hooker, but it was Gary.