Intake valve lift at BDC

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Re: Intake valve lift at BDC

Post by CGT »

Im assuming most here are likely not content with 100% VE or less. So why not look at things at and around the area where higher than 100% VE occurs.?
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Re: Intake valve lift at BDC

Post by zums »

CGT wrote: Tue Apr 28, 2020 9:04 am Im assuming most here are likely not content with 100% VE or less. So why not look at things at and around the area where higher than 100% VE occurs.?
Exactly
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Re: Intake valve lift at BDC

Post by Stan Weiss »

What I like to do is look at the intake port flow graphed as a function on the valve lift curve.

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Re: Intake valve lift at BDC

Post by hoffman900 »

CGT wrote: Tue Apr 28, 2020 9:04 am Im assuming most here are likely not content with 100% VE or less. So why not look at things at and around the area where higher than 100% VE occurs.?
This.

Focusing on the torque curve and horsepower will fall in line...

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Stan Weiss wrote: Tue Apr 28, 2020 1:55 pm What I like to do is look at the intake port flow graphed as a function on the valve lift curve.

Stan
Being able to graph mass flow in EngMod4T has been most revealing to me.
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Re: Intake valve lift at BDC

Post by swampbuggy »

Thanks folks for your input, Mark H.
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Re: Intake valve lift at BDC

Post by MadBill »

Here's a hypothetical premise for discussion:

"On a fluid dynamics basis, the ideal intake valve lifts approaching BDC and on to IVC would produce optimum mixture velocities through the curtain area in support of the inertial ram process to maximize V.E. From max lift onward, some of these 'ideals' might well be much less than the mechanically-constrained current practice." :-k
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Re: Intake valve lift at BDC

Post by swampbuggy »

Bill, i believe that i may have comprehended your Mechanical Engineer wording :lol: . Might you be thinking that the lift of the intake valve may well need to be a lesser amount at a given position in the cycle to maximize cylinder fill :?: Mark H.
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Re: Intake valve lift at BDC

Post by Walter R. Malik »

Stan Weiss wrote: Tue Apr 28, 2020 1:55 pm What I like to do is look at the intake port flow graphed as a function on the valve lift curve.

Stan
AND, then compare that to the piston position in the bore.
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Re: Intake valve lift at BDC

Post by MadBill »

swampbuggy wrote: Wed Apr 29, 2020 7:06 am Bill, i believe that i may have comprehended your Mechanical Engineer wording :lol: . Might you be thinking that the lift of the intake valve may well need to be a lesser amount at a given position in the cycle to maximize cylinder fill :?: Mark H.
Exactly! (It sounds so simple when you put it like that... :) )
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Re: Intake valve lift at BDC

Post by CGT »

Well, RPM would definitely be a factor. Lift at BDC is going to be directly tied to IVC, which is directly tied to RPM. You can only shut the valve so fast. Too much lift at BDC would mean too late of IVC..too late of IVC within a given rpm or application can definitely hurt power...
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Re: Intake valve lift at BDC

Post by hoffman900 »

My graph from an old thread. Simulated mass flow vs piston position vs valve lift profile.
3F6D2883-79F1-4815-A3C3-C728A991E951.jpeg
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Re: Intake valve lift at BDC

Post by Stan Weiss »

How does greater valve seat angles which reduces effective curtain area at lower lifts come into play?

I believe that this has been talked about before but can not find it.

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Re: Intake valve lift at BDC

Post by David Redszus »

hoffman900 wrote: Wed Apr 29, 2020 10:25 am My graph from an old thread. Simulated mass flow vs piston position vs valve lift profile.
3F6D2883-79F1-4815-A3C3-C728A991E951.jpeg
What if the piston position curve were replaced by a piston air demand curve?

The inlet air mass flow curve shows twin peaks at near maximum piston speed. But at BDC
the piston air demand is minimal so that any continuing air mass flow must be a function of
air column momentum (actually, column pressure). This value would change with rpm while the
position (not amplitude) of piston air demand would remain constant.

If the valve curtain area is inadequate (relative to piston air demand) then the port velocity
will never reach its maximum capability. As Darren Morgan often stated: inlet flow is a
function of valve seat geometry.
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Re: Intake valve lift at BDC

Post by hoffman900 »

David Redszus wrote: Wed Apr 29, 2020 12:16 pm
hoffman900 wrote: Wed Apr 29, 2020 10:25 am My graph from an old thread. Simulated mass flow vs piston position vs valve lift profile.
3F6D2883-79F1-4815-A3C3-C728A991E951.jpeg
What if the piston position curve were replaced by a piston air demand curve?

The inlet air mass flow curve shows twin peaks at near maximum piston speed. But at BDC
the piston air demand is minimal so that any continuing air mass flow must be a function of
air column momentum (actually, column pressure). This value would change with rpm while the
position (not amplitude) of piston air demand would remain constant.

If the valve curtain area is inadequate (relative to piston air demand) then the port velocity
will never reach its maximum capability. As Darren Morgan often stated: inlet flow is a
function of valve seat geometry.
I can work on that later. It should be noted that is mass flow a the valve seat. The port is more subdued of a curve and doesn't necessarily show as much negative mass flow at both ends of the lift curve.

The lower the rpm, the more the curve follows the motion of piston demand, as piston speed increases it does what you see there, where the column pressure (momentum) and wave dynamics take over the filling process.

I believe the twin peaks near maximum piston speed is the sim picking up what would be the wave reflection by the very fast moving piston.

I hope this also illustrates that air does not "slam in the back of the valve" as coined by Superflow (I believe this was an imagined phenomenon and has been put into print so many times, it's become a "rule"). As MadBill said here probably a decade ago, if the air is slamming into the back of the valve, then it's probably closing the valve too soon ;)
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Re: Intake valve lift at BDC

Post by Stan Weiss »

If my intake valve closes @ lets say 80 ABDC. Then the piston has been compressing the air / fuel mixture for 80 degrees. How much above outside BP is the pressure on the back side of the valve to continue to have flow into the cylinder?

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