CFD.. Info & catch all - Ferrari Life
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post #1 of 25 Old 03-29-2013, 12:53 PM Thread Starter
 
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CFD.. Info & catch all

Just a thread to dump the CFD modeling info and insights.

First up, particle study on fuel flow in stock 2v port.
pics are worth a thousand words so take a look. this one is a velocity flow, blue to red color scheme typ inverse function, i.e. red=fast, blue=slow. a techinical note, blue is hot and red is cooler but since we humans evolved to associate red with heat and blue with cold i.e. water,ice, it's flipped. back on topic.

the funny hourglass shape to the stock port makes some sense when looking at the fuel flow from the injector, the boundary layer and velocity of the air pulls the fuel to top side and into the chamber past the plug vs dropping down, now what is really interesting to note is that the shape is present on the carb'd heads as well. was the head designed for fuel injection before it went into production? also further interesting is that it only works with the fuel pressure and spray pattern of the CIS injector, a modern injector has a different velocity and droplet dia which is affected by the air velocity differently.
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post #2 of 25 Old 03-30-2013, 05:17 AM
 
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the funny hourglass shape to the stock port makes some sense when looking at the fuel flow from the injector, the boundary layer and velocity of the air pulls the fuel to top side and into the chamber past the plug vs dropping down, now what is really interesting to note is that the shape is present on the carb'd heads as well. was the head designed for fuel injection before it went into production? also further interesting is that it only works with the fuel pressure and spray pattern of the CIS injector, a modern injector has a different velocity and droplet dia which is affected by the air velocity differently.
Ports for a carb'd car have to be designed for wet flow. The mixture coming from the carb is going to be full of fuel droplets also, so the port has to keep those droplets entrained in the air stream in order to get the mixture right in the chamber.

The CIS is lower pressure and velocity than modern EFI, right? So the droplet size and speed distribution might be similar to that of a carb...
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post #3 of 25 Old 03-30-2013, 05:24 AM
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The CIS is lower pressure and velocity than modern EFI, right? So the droplet size and speed distribution might be similar to that of a carb...
The CIS pressure is up to 5 bar I thought? so higher than most EFI, but some of the new stuff is up there.
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post #4 of 25 Old 03-30-2013, 06:09 AM
 
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I don't know... I had @$$umed it was more like TBI
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post #5 of 25 Old 03-30-2013, 07:00 AM
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The CIS pressure is up to 5 bar I thought? so higher than most EFI, but some of the new stuff is up there.
Yep... I had to go check my Bosch Fuel Injection & Engine Management book because you made me curious what exact pressure it's running... 5.4-5.8 bar for the K-Jet (depending on application).
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post #6 of 25 Old 03-30-2013, 07:58 AM
 
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also further interesting is that it only works with the fuel pressure and spray pattern of the CIS injector, a modern injector has a different velocity and droplet dia which is affected by the air velocity differently.
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Yep... I had to go check my Bosch Fuel Injection & Engine Management book because you made me curious what exact pressure it's running... 5.4-5.8 bar for the K-Jet (depending on application).
Interesting... so how does the CFD say that the EFI fuel stream will be affected differently than the CIS fuel stream?
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post #7 of 25 Old 03-30-2013, 09:50 AM Thread Starter
 
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Interesting... so how does the CFD say that the EFI fuel stream will be affected differently than the CIS fuel stream?
Ahh, now that is the question, with the higher velocity of the CIS spray the fuel droplet has the ability to move thru the incoming air stream velocity. lower pressure EF injection does not and will wash down the port wall, now in reality this is only going to be for 7krpm and up, not really an issue for idle or mid range, but something to consider when modifying the ports.
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post #8 of 25 Old 03-30-2013, 09:54 AM Thread Starter
 
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The CIS pressure is up to 5 bar I thought? so higher than most EFI, but some of the new stuff is up there.
true, but the injector opening pressure is much lower. 2.5~3.5bar and then you have the pintle orifice that determines droplet size. the new injectors are down to around 50uM that mist is much smaller then the CIS flow and will be further influenced by the air velocity.

read an article on carbon electrostatic tubes for fuel atomization, now that sounds like the ideal injector.
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post #9 of 25 Old 03-30-2013, 09:57 AM
 
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Would the EFI injector pattern work better with a larger angle relative to the centerline of the port?

Just getting an understanding...

I've read some topics on Speed Talk: Interviews - Racing Books - Racing Forum by people who've done development work on EFI race engines... In some cases, the engine runs best in the racing RPM range by spraying the fuel upstream, against the flow of air.
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post #10 of 25 Old 03-30-2013, 12:06 PM Thread Starter
 
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Would the EFI injector pattern work better with a larger angle relative to the centerline of the port?

Just getting an understanding...

I've read some topics on Speed Talk: Interviews - Racing Books - Racing Forum by people who've done development work on EFI race engines... In some cases, the engine runs best in the racing RPM range by spraying the fuel upstream, against the flow of air.

Depends, there are a number of factors to consider, port velocity, boundary layer turbulence, fuel droplet size and velocity. then we get into wave pressure dynamics and temperature effects. There are some very fascinating things with wall texture and boundary layer effects, that alone is worth more in HP then pure CFM flow.

unfortunately there just isn't the ROI on doing a real in depth look at the older heads, a compromise is made and that's about it. or as Mark puts it, shoot the engineer and get to it.

if one really wants to get into efficient burn and swirl, then we should also look at the ring land to deck volume and start cutting the top land to expose the area and get the fuel out of there, the 2V engine really suffers from the air flow going straight to the ring land.
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post #11 of 25 Old 03-30-2013, 12:53 PM
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There are some very fascinating things with wall texture and boundary layer effects, that alone is worth more in HP then pure CFM flow.
Bullshit.

Years ago ago now, I was talking to Jerry Branch who used to be the THE head guy and his answer to whatever it was I was on about was "I don't care if you're Jesus Christ himself, without air you aren't going to make HP"....and that's stuck with me over the years.

To your point there are lot of ways to screw stuff up and make low HP even when you have enough air but my rule is get the air first because that's the hard one.

Efficiency and fuel consumption are other questions and effected by lots and lots of things......but you still need air
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post #12 of 25 Old 03-30-2013, 01:02 PM
 
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Well... in a flow-limited application like... pretty much anything using production castings, there *may* be a situation in which the port geometry does not give ideal mixture motion, fuel mixing on chamber entry, etc.
In those cases, giving up CSA that would give 1% more airflow may yield 2-3% more power by correcting the features that affect mixture quality.

However, for larger effects, I agree that airflow comes first. Sacrificing 10% airflow for mixture quality is probably not a good idea.

On non-port-limited applications like pro-stock, it is possible to go too big through the port, and that's a case where giving up flow bench numbers for mixture quality would be a good idea also. HOWEVER 20+ year old production Ferrari heads do not fall into that category.

And even in that case, the port has to be right-sized to see the benefits of mixture quality.
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post #13 of 25 Old 03-30-2013, 02:38 PM Thread Starter
 
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Bullshit.

Years ago ago now, I was talking to Jerry Branch who used to be the THE head guy and his answer to whatever it was I was on about was "I don't care if you're Jesus Christ himself, without air you aren't going to make HP"....and that's stuck with me over the years.

To your point there are lot of ways to screw stuff up and make low HP even when you have enough air but my rule is get the air first because that's the hard one.

Efficiency and fuel consumption are other questions and effected by lots and lots of things......but you still need air
OK, didn't mean to touch a nerve there. however air is only one part of the equation, the engine needs fuel and the fuel should ideally be mixed properly, if the port velocity is too high then the fuel will be wetting the walls, if the walls are polished then the air velocity will slow down as frictional forces take over, basic physics at play there. they all work together in concert, to just look at air flow as THE discerning factor is a ham fisted way at trying to make more power. I prefer to look as mass air flow over pure volume velocity, for that of course temperature plays the role and velocity and pressure effect the mass flow.

lets get real technical here, where is the direct correlation of static CFM to HP? engines do not run in a static mode, you know that, it's highly dynamic with the pressure pulse and wave dynamics playing the critical role on cylinder filling. Given those parameters the engineer is going to look for ways to manipulate and use that to an advantage, boundary layers in air flow are critical, air moving at those velocities and pressures will exhibit conservation of momentum forces esp in turns, frictional forces from polished walls will slow the velocity and you will loose CFM, reduce the drag and it will increase the CFM, and that is with simply changing the wall texture. now toss in fuel with varying viscosity and temperature zones, accounting for that and designing the port so that the fuel stays in suspension is key to efficient burn and transfer of energy. the port needs to be designed for the fuel delivery system.

I enjoy complex systems and the cascade effect, bit of a masochist I think or I wouldn't also spend my time in QED research. there is no simple answer, for every choice that's made there is compromise elsewhere in the system. DI is more or less an attempt and getting around a lot of port design issues with fuel air mixtures.
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post #14 of 25 Old 03-30-2013, 02:53 PM
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On non-port-limited applications like pro-stock, it is possible to go too big through the port, and that's a case where giving up flow bench numbers for mixture quality would be a good idea also. HOWEVER 20+ year old production Ferrari heads do not fall into that category..
The ports and valves need to be sized properly for the application and its really easy, even on 20+ year old ferraris to oversize stuff. If the ports and valves are oversized all kinds of bad stuff can happen....like piss poor fuel mixing for example
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post #15 of 25 Old 03-30-2013, 03:49 PM
 
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I would have expected that with "oversize" ports in a Ferrari, you just add a little more cam and raise the rev limit

On a pro-stock engine, that doesn't work because the engine's already turning as fast as the valvetrain can go.

But you've done a lot more along those lines than I have...
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post #16 of 25 Old 03-30-2013, 03:54 PM
 
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lets get real technical here, where is the direct correlation of static CFM to HP? engines do not run in a static mode, you know that, it's highly dynamic with the pressure pulse and wave dynamics playing the critical role on cylinder filling. Given those parameters the engineer is going to look for ways to manipulate and use that to an advantage, boundary layers in air flow are critical, air moving at those velocities and pressures will exhibit conservation of momentum forces esp in turns, frictional forces from polished walls will slow the velocity and you will loose CFM, reduce the drag and it will increase the CFM, and that is with simply changing the wall texture. now toss in fuel with varying viscosity and temperature zones, accounting for that and designing the port so that the fuel stays in suspension is key to efficient burn and transfer of energy. the port needs to be designed for the fuel delivery system.
Thicker boundary layer DOES keep fuel entrained better, but also reduces the effective cross-section of the port. As you allude, it can conform in turns and aid the flow, but still reduces the available cross section for high velocity flow.

Remember that exhaust ports are frequently polished, but they don't have to deal with wet flow

A dimpled golf ball flies further than a smooth one. The boundary layer makes the aero cross section LARGER, but the trail of the boundary layer behind the ball effectively makes the shape more efficient, lowering the coefficient of drag more than the frontal area is increased.

At least that's the way I understand it.
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post #17 of 25 Old 03-30-2013, 04:01 PM
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OK, didn't mean to touch a nerve there. however air is only one part of the equation.....
.......

lets get real technical here, where is the direct correlation of static CFM to HP? \
AIr is the only part that matter. The fuel is pumped in as a liquid so you can have as much as you want.....air not so much.

A CFM number by itself is of no value at all really.

as for the rest of the post....we'll have to agree to disagree
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post #18 of 25 Old 03-30-2013, 04:06 PM
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Thicker boundary layer DOES keep fuel entrained better, but also reduces the effective cross-section of the port. As you allude, it can conform in turns and aid the flow, but still reduces the available cross section for high velocity flow.

Remember that exhaust ports are frequently polished, but they don't have to deal with wet flow

A dimpled golf ball flies further than a smooth one. The boundary layer makes the aero cross section LARGER, but the trail of the boundary layer behind the ball effectively makes the shape more efficient, lowering the coefficient of drag more than the frontal area is increased.

At least that's the way I understand it.
That all sound right to me.

The only small point is that while an exhaust port doesn't need to deal with wet flow, it does need to be concerned with flow separation which can be reduce with some surface roughness just like on the golf ball. Also the ports are often over-size from the factory and cleaning/polishing just makes it worse so sometimes leaving it as cast is the best answer, short of welding it up anyway.
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post #19 of 25 Old 03-30-2013, 04:14 PM
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I would have expected that with "oversize" ports in a Ferrari, you just add a little more cam and raise the rev limit

On a pro-stock engine, that doesn't work because the engine's already turning as fast as the valvetrain can go.

But you've done a lot more along those lines than I have...
Well......it's about what you're trying to build right? Everything needs to match the application.

The 308 2v intake ports are quite a bit smaller than I would want then but the intake valve seats and bowls are sized for about 50% more flow then the head delivers. Everything about the exhaust ports is too big. It's just a mess really. You can get decent hp out of it by bumping the rev limit or the displacement but you never get what you would get is everything was properly matched.
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post #20 of 25 Old 03-30-2013, 05:02 PM
 
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"Properly matched" and "Too big" are different things.

If the exhaust port is shaped well, but sized for a larger engine, I'd say it's "too big".

If parts of the intake port are right and parts are too small, parts are too big, then it's "poorly matched" or "improperly shaped", meaning that it doesn't have the right cross-section profile along its length for the displacement and RPM of its intended use.
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