Is Port Energy validation just around the corner?????

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Re: Is Port Energy validation just around the corner?????

Post by David Vizard » Sun Sep 24, 2017 11:40 am

Correct me if I am mis-enterpreting the situation but I seem to remember that if the air is accelerated a little downstream of the point where the pressure wave was created the amplitude drops as the velocity increaces and the frequency becomes longer. This would mean a port big and lazy for 4000 rpm would sustain whatever pressure waves were generated. The key here would be generating them in the first place. Secondly as the velocity, for about the same amount of airflow, increases so the port energy increases as the square of the velocity.

As far as upping the ramming pressure at the end of the induction stroke a high energy port concept delivers an increase AT ANY RPM.

A word here on the pressure going up as the air slams into the back of the valve. Yes it does do this but that pressure energy is hardly utilized and then only possibly minimally in some part of the next induction cycle. WE have to look at the gap between the seats as a flow restriction and that we are going to utilize the change of kinetic energy into pressure energy during the closing phase to increase the port side pressure pushing the charge through an ever decreasing gap.

For those still doubtful imagine the closing gap is ballistic gel. The higher the energy of the bullet striking it the deeper the penetration (for a given calibre)
DV
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Re: Is Port Energy validation just around the corner?????

Post by David Vizard » Sun Sep 24, 2017 11:45 am

SchmidtMotorWorks wrote:Chrysler has a system that effectively changes both duct cross-section and length with a valve that opens about 25%.

Image

The concept and quantities involved are only a mystery to anyone that doesn't bother to learn from a 1D simulation.
Jon,
To what extent are the lengths and cross sections varied? Is there any cutaway drawings of this??
Thanks
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Re: Is Port Energy validation just around the corner?????

Post by hoffman900 » Sun Sep 24, 2017 2:15 pm

David Vizard wrote: A word here on the pressure going up as the air slams into the back of the valve. Yes it does do this but that pressure energy is hardly utilized and then only possibly minimally in some part of the next induction cycle. WE have to look at the gap between the seats as a flow restriction and that we are going to utilize the change of kinetic energy into pressure energy during the closing phase to increase the port side pressure pushing the charge through an ever decreasing gap.

For those still doubtful imagine the closing gap is ballistic gel. The higher the energy of the bullet striking it the deeper the penetration (for a given calibre)
DV
Except that's not what is happening, David.

There is reverse flow, not because the air is hitting the back of the intake valve, but because the valve is still slightly open when the cylinder pressure reaches a point that is higher than the port pressure. To cram the most amount of mass into a cylinder, you'll always have a small amount of this. This is just the life we live with camshaft operated poppet valves.

The rapidly accelerating piston down the bore (with the valve open) is what causes this big reflection. Forget RPM in a traditional sense, it's all about piston speed. The big 'push' is the positive reflection of the big negative pulse caused by the piston as it reaches maximum piston speed (MPS).

Pressure in the intake valve actually drops before it closes (as the more positive pressure in the cylinder tries pushing back out). Fortunately the orfice between the valve and the seat is closing rapidly at this point and is relatively small.

vannik wrote:John,

Some graphs to help you visualize things better. In your visualization exercise just remember that the pressure wave that leaves the inlet valve is a low pressure wave (suction wave).

The first graph shows the pressure traces at the inlet and exhaust valves and the pressure inside the cylinder. This graph is just so we are all on the same page of what we are talking about. It was created by simulation but can also be measured by instrumentation such as Nitro's. (The red line labelled MPS is the position of maximum piston speed)

Image

The next graph decomposes the wave at the inlet valve into its two components, the leftward and rightward moving waves (the pressure trace we measure is the superposed of these two waves) where the leftward moving is from the cylinder to the open end and the rightward is moving from the open end to the cylinder. As can be seen they are the same when the valve is closed as a closed end reflects the wave without sign changes.

You can see that during the initial phase of inlet valve opening (mostly the overlap period) the rightward wave still has a positive value and helps with the cylinder filling and/or prevents reverse flow. Once the piston motion has created a big suction pulse which gets reflected as a big pressure pulse this overrides the residual wave action from the previous cycle.

Image

The next graph shows these same waves but in the middle of the inlet pipe (it is 315mm from valve face to open end). Now the left and right moving waves are not the same even during the closed period.

Image

Hope this helps. What engine builders do is to measure the initial traces using equipment like Nitro's, then they create a sim to match the measured traces and use the simulation further to decompose the waves into left and right moving components, study the mass flows, mach numbers etc and use that to understand what is happening. They then make changes in the sim to study its effect and when they have a solution they build it, test it, measure the performance and the pressure traces to fine tune the sim and repeat the process.
Vannik
http://www.vannik.co.za/
Note: the pressure trace image disappeared, but it should look like this:
Image

Additionally, seeing how most MCSA is well upstream of the valve, the potential energy through this section will be turned into kinetic energy in the form of pressure behind the intake valve. Unless the MCSA is at the valve seat, which it rarely is not, the port is really two seperate nozzles. The divergent section leading up to the MCSA and the convergent section leading away from it. Then the convergent section to the valve seat and the divergent section (chamber into the cylinder). The latter's divergent section is in constant flux as the valve moves about its lift curve.

Again, the name of the game is pressure, pressure, pressure and turning as much of the potential energy of the system into something useable.

Going back to the original topic, since the shape of the convergent and divergent section drive the entire discharge coefficient's success (or failure), it's not as simple to create a real time manipulable port area and still realize the same peak efficiency as one that is fixed.
-Bob

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Re: Is Port Energy validation just around the corner?????

Post by RevTheory » Sun Sep 24, 2017 3:00 pm

What piston speed are you guys looking for to make use of the intake tract?

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Re: Is Port Energy validation just around the corner?????

Post by hoffman900 » Sun Sep 24, 2017 3:06 pm

RevTheory wrote:What piston speed are you guys looking for to make use of the intake tract?
Rev,

Nothing set in stone, but it's what drives the 'strength' of the pulse. This goes back to what Darin was talking about. It's always present, and he wasn't really clear in that first quoted post, but the second one I found, he acknowledges it. The strength just keeps going up with speed. The timing of it arriving when you need it to is contingent on the length and shape from valve seat to either atmosphere or a plenum.

Remember,

The last generation NA Formula One engines at 20,000rpm still had piston speeds that were on par with a NASCAR engine at say 9,000rpm. RPM alone is misleading. A drag racer can realize more wave tuning, due to the fact that service intervals are narrower than a circuit engine and consequently, can run more piston speed.

I'm not going to pretend I figured this one out, but as was pointed out to be by someone who has done a lot of simulation work and jointly (in the same conversation) a top engine builder of the venerable BMC A-Series engines (I4, 1&2 share a common port and 3&4 share a common port), the expansion in area in the shared port section causes degradation of the pulses that we are talking about here, as it just gets 'eaten' up in the void, thus it can never realize the same power potential as an engine with an individual port per cylinder, even if you can get some decent airflow out of it.
-Bob

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Re: Is Port Energy validation just around the corner?????

Post by RevTheory » Sun Sep 24, 2017 3:24 pm

Thanks, Bob. Yeah, I followed that thread a couple of years ago when Darrin was talking about simply not having the piston speed to do anything with the intake tract. That isn't something I'd considered back then so it was a real eye-opener for me.

It would be nice to have at least some frame of reference, though. Like "3,600 avg. fps isn't going to cut it. 4,500 avg fps will give you something you can work with..." or whatever the numbers end up being.

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Re: Is Port Energy validation just around the corner?????

Post by DaveMcLain » Sun Sep 24, 2017 3:57 pm

RevTheory wrote:Thanks, Bob. Yeah, I followed that thread a couple of years ago when Darrin was talking about simply not having the piston speed to do anything with the intake tract. That isn't something I'd considered back then so it was a real eye-opener for me.

It would be nice to have at least some frame of reference, though. Like "3,600 avg. fps isn't going to cut it. 4,500 avg fps will give you something you can work with..." or whatever the numbers end up being.
I say that looking at piston speed in absolutes is nonsense, it makes no difference. Two cylinders of the same displacement, one with a large bore, short stroke and the other the opposite, with the same rod/stroke ratio pull on the port EXACTLY the same. They both sweep the cylinder and change the volume at EXACTLY the same rate. Any changes you see are all secondary effects but not caused by the speed of the piston itself.

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Re: Is Port Energy validation just around the corner?????

Post by David Vizard » Sun Sep 24, 2017 4:01 pm

hoffman900 wrote: DV wrote:-
A word here on the pressure going up as the air slams into the back of the valve. Yes it does do this but that pressure energy is hardly utilized and then only possibly minimally in some part of the next induction cycle. WE have to look at the gap between the seats as a flow restriction and that we are going to utilize the change of kinetic energy into pressure energy during the closing phase to increase the port side pressure pushing the charge through an ever decreasing gap.

For those still doubtful imagine the closing gap is ballistic gel. The higher the energy of the bullet striking it the deeper the penetration (for a given calibre)
DV
Bob, I am going to have to sort this out not because you were wrong(well you were with just one statement)but because I was not as explicit as I should have been. That was a comunication failure on my part I am afraid. Here then is my response to your comments.

Except that's not what is happening, David. This is the only statement you got wrong. If I had been more explicit you would not have needed to make this post.

There is reverse flow, I should have mentioned this. The reason that we should hold the valve open until a small amount of reversion comes about is that the consequences of closing it earlier means it has less lift all the way down the backside of the closing event and what is lost here is way more than is gained by eliminating the revsersion.

not because the air is hitting the back of the intake valve,
A high speed air stream running into a solid flow resistance will cause a substantial increase in pressure. As I pointed out this, in an intake port, is next to useless as it could only have any effect, and a very minor one at that, on some part of the next cycle.

but because the valve is still slightly open when the cylinder pressure reaches a point that is higher than the port pressure. To cram the most amount of mass into a cylinder, you'll always have a small amount of this. If I had of made my post longer I would have said this instead of having to do it as above. I go into a lot of detail in my seminars on this by showing that there is a link between the rate of change of a closing intake valves CFM and the torque developed.

This is just the life we live with camshaft operated poppet valves. Undeniable!

The rapidly accelerating piston down the bore (with the valve open) is what causes this big reflection. I would have described this as the generation of a pressure wave not the reflection. The reflection comes about when this positive pressure wave hits the end of the intake runner as in the plenum or open air.

Forget RPM in a traditional sense, it's all about piston speed.Actually it is more about the rate of change of volume above the piston with respect to valve and port sizes.


The big 'push' is the positive reflection of the big negative pulse caused by the piston as it reaches maximum piston speed (MPS). Which is substantially augmented by kinetic energy transitioning to pressure energy as velocity decays.

Pressure at the intake valve actually drops before it closes (as the more positive pressure in the cylinder tries pushing back out). As can be seen in the many intake pressure traces I have posted.

Fortunately the orifice between the valve and the seat is closing rapidly at this point and is relatively small. And the subsequent reversion is the small price paid for having the valve further open throughout the rest of the opening event.

So what am I taking home with me from this post? An obvious one is that if any doubt as to how explicite my wordage is I need to ask 'How would Bob interpret this' and fix it as required.

Thanks Bob for pulling me up on this one.

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Re: Is Port Energy validation just around the corner?????

Post by hoffman900 » Sun Sep 24, 2017 4:18 pm

DaveMcLain wrote:
RevTheory wrote:Thanks, Bob. Yeah, I followed that thread a couple of years ago when Darrin was talking about simply not having the piston speed to do anything with the intake tract. That isn't something I'd considered back then so it was a real eye-opener for me.

It would be nice to have at least some frame of reference, though. Like "3,600 avg. fps isn't going to cut it. 4,500 avg fps will give you something you can work with..." or whatever the numbers end up being.
I say that looking at piston speed in absolutes is nonsense, it makes no difference. Two cylinders of the same displacement, one with a large bore, short stroke and the other the opposite, with the same rod/stroke ratio pull on the port EXACTLY the same. They both sweep the cylinder and change the volume at EXACTLY the same rate. Any changes you see are all secondary effects but not caused by the speed of the piston itself.
Yes they will, but I've given up looking at rpm as it doesn't tell the full story.

With varying rod/stroke ratios, an engine with 6000rpm, 10,000rpm, or 20,000rpm could have the same average piston velocity.

It's hard to quantify what is 'a lot', rpm because in some cases, it really might not be 'a lot' of average piston speed.
Last edited by hoffman900 on Sun Sep 24, 2017 4:35 pm, edited 1 time in total.
-Bob

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Re: Is Port Energy validation just around the corner?????

Post by RevTheory » Sun Sep 24, 2017 4:24 pm

Lot's of truth in that, Bob.

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Re: Is Port Energy validation just around the corner?????

Post by hoffman900 » Sun Sep 24, 2017 4:35 pm

David Vizard wrote:
hoffman900 wrote: DV wrote:-
A word here on the pressure going up as the air slams into the back of the valve. Yes it does do this but that pressure energy is hardly utilized and then only possibly minimally in some part of the next induction cycle. WE have to look at the gap between the seats as a flow restriction and that we are going to utilize the change of kinetic energy into pressure energy during the closing phase to increase the port side pressure pushing the charge through an ever decreasing gap.

For those still doubtful imagine the closing gap is ballistic gel. The higher the energy of the bullet striking it the deeper the penetration (for a given calibre)
DV
Bob, I am going to have to sort this out not because you were wrong(well you were with just one statement)but because I was not as explicit as I should have been. That was a comunication failure on my part I am afraid. Here then is my response to your comments.

Except that's not what is happening, David. This is the only statement you got wrong. If I had been more explicit you would not have needed to make this post.

There is reverse flow, I should have mentioned this. The reason that we should hold the valve open until a small amount of reversion comes about is that the consequences of closing it earlier means it has less lift all the way down the backside of the closing event and what is lost here is way more than is gained by eliminating the revsersion.

not because the air is hitting the back of the intake valve,
A high speed air stream running into a solid flow resistance will cause a substantial increase in pressure. As I pointed out this, in an intake port, is next to useless as it could only have any effect, and a very minor one at that, on some part of the next cycle.

but because the valve is still slightly open when the cylinder pressure reaches a point that is higher than the port pressure. To cram the most amount of mass into a cylinder, you'll always have a small amount of this. If I had of made my post longer I would have said this instead of having to do it as above. I go into a lot of detail in my seminars on this by showing that there is a link between the rate of change of a closing intake valves CFM and the torque developed.

This is just the life we live with camshaft operated poppet valves. Undeniable!

The rapidly accelerating piston down the bore (with the valve open) is what causes this big reflection. I would have described this as the generation of a pressure wave not the reflection. The reflection comes about when this positive pressure wave hits the end of the intake runner as in the plenum or open air.

Forget RPM in a traditional sense, it's all about piston speed.Actually it is more about the rate of change of volume above the piston with respect to valve and port sizes.


The big 'push' is the positive reflection of the big negative pulse caused by the piston as it reaches maximum piston speed (MPS). Which is substantially augmented by kinetic energy transitioning to pressure energy as velocity decays.

Pressure at the intake valve actually drops before it closes (as the more positive pressure in the cylinder tries pushing back out). As can be seen in the many intake pressure traces I have posted.

Fortunately the orifice between the valve and the seat is closing rapidly at this point and is relatively small. And the subsequent reversion is the small price paid for having the valve further open throughout the rest of the opening event.

So what am I taking home with me from this post? An obvious one is that if any doubt as to how explicite my wordage is I need to ask 'How would Bob interpret this' and fix it as required.

Thanks Bob for pulling me up on this one.

DV
Thanks, David. It all makes the discussion better. Hopefully others are learning as I've learned a lot from discussions like this.
-Bob

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Re: Is Port Energy validation just around the corner?????

Post by MadBill » Sun Sep 24, 2017 5:45 pm

David Vizard wrote:...The rapidly accelerating piston down the bore (with the valve open) is what causes this big reflection. I would have described this as the generation of a PRESSURE wave not the reflection. The reflection comes about when this positive pressure wave hits the end of the intake runner as in the plenum or open air...

...The big 'push' is the positive reflection of the big NEGATIVE pulse caused by the piston as it reaches maximum piston speed (MPS). ...DV
Isn't this an oxymoron? :?
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Re: Is Port Energy validation just around the corner?????

Post by digger » Sun Sep 24, 2017 5:54 pm

Perhaps negative void

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Re: Is Port Energy validation just around the corner?????

Post by hoffman900 » Sun Sep 24, 2017 6:13 pm

MadBill wrote:
David Vizard wrote:...The rapidly accelerating piston down the bore (with the valve open) is what causes this big reflection. I would have described this as the generation of a PRESSURE wave not the reflection. The reflection comes about when this positive pressure wave hits the end of the intake runner as in the plenum or open air...

...The big 'push' is the positive reflection of the big NEGATIVE pulse caused by the piston as it reaches maximum piston speed (MPS). ...DV
Isn't this an oxymoron? :?
Some posts...

MadBill, here is a post from yours from 2005 (when you were a "newbie" :lol: ):
<Newbie Alert!>
Hi All.
I've been following this thread with great interest and am now prepared to stick at least one toe into the meat grinder of conflicting explanations!

I find the discussion about water hammer effects to be irrelevant for one big reason: In a properly specced race engine at its designed optimum RPM, there will be no inertia-induced 'pile up' of air against the closed valve because the valve should not be closed until all forward flow has ceased. (in fact, optimum IVC timing is often such that a small amount of reversion occurs)

There are plenty of long-disproven theories on this subject, but the explanation that has gained traction in recent years (borne out by CFD, Computational Fluid Dynamics, analysis) is that the wave is induced by the piston's downward motion, and an optimum tuned length (which BTW, is significantly affected by any taper of the intake runner) for a given RPM is that which puts the returning negative pulse right on top of the next induction cycle's minimum pressure point (usually the point of maximum piston velocity, ~78 -82 degrees ATDC) In this way, a resonance builds up which reinforces the flow through the TDC to BDC portion of the induction cycle. The high flow rate also creates greater momentum at the IVC point, allowing a later closing without excessive reversion. Examination of the pressure graphs from Dynomation or other high end engine simulation packages clearly illustrate this phenomenon.
From a later thread:
SchmidtMotorWorks wrote:I think many of us got this idea of inertia ramming in our heads from reading Peterson Publishing magazines that made this explanation many times. And it does seem intuitive. Once your mind "learns" something and repeats it enough, it gets stuck in there and almost becomes instinctive (especially if you learn it when you are young) even after you have good reason to know it is incorrect.

The damage Peterson Publishing has done to engineering is massive.
SchmidtMotorWorks wrote:
In all seriousness, it would help your case dramatically if you posted your qualifications.
If it mattered I would.
I'm trying to teach you a bigger point, hero worship does not lead to a better understanding of anything.
I will just discuss the science and facts, saying that "I know X because I worked at Y" should not convince anyone of anything. We all lean on that way of arguing sometimes myself included and I strive to avoid it.
You seem to have the opinion that being an engine builder adds weight to their opinion on a matter of physics, this seems odd to me.
If I want to get a better understanding of a matter of physics, I would ask someone learned in the subject of physics.
I think it is fair to say that most engine builders have never seen the inside of a physics book.

So lets concentrate on the facts and see what we can learn.

Let's check to see if the following is true or false, OK?
Pulsation Effects in the Intake System
-The characteristic curve of volumetric efficiency is largely controlled by timing of the induction pressure pulsations (initially caused by inlet valve closure),,,
Let's begin by establishing what the optimum time to close the intake valve is.
The goal is to trap the largest volume in the cylinder possible, that's obvious right?

Question 1: So how do you know when the intake closes too early?
Answer 1: You are closing the valve too early if you are preventing air from moving into the cylinder (key word is moving)

Question 2: So how do you know when the intake closes too late?
Answer 2: You are closing the valve too late if you are allowing air to move out of the cylinder (key word is moving)

Question 3: So what is happening at the optimum time to close the intake valve?
Answer 3: The air has just stopped moving into the cylinder and about to reverse. (key word is stopped)

Question 4: So if the air has already stopped, what would closing the valve do to create a wave?
Answer 4: It doesn't do anthing, the claim is incorrect.

Question 5: Then where does the wave come from?
Answer 5: There is more than one, so I will post a video to explain it, it will take about 6 hours to process so I will let it run over night and post it in the morning if it doens't run into any errors. But to give a short partially correct answer to the question I think you are asking; a positive wave begins at the top of the piston about 2/3rds of the way down the intake stroke, just after the piston starts slowing down on the way to BDC. It of course picks up much more after BDC. This one is not what you are looking for though.
This explanation overlooks the negative wave that came earlier at the beginning of a previous intake stroke that has traveled up the runner and reflected back down as a pressure wave. That is a pressure wave and is what people mistake for inertia because it can occur at a time that one would expect inertia to be there.

I know it is much easier to imagine the inertia explanation of a moving fluid, I think this is partly because we see water flowing in everyday life and imagine that air moves in the same way; it doesn't.
Just looking for qualifications to back up the rather bold claims that entire OEMs are "wrong
By the way, no OEM including Honda believes what I said was wrong in that paper today.

nitro2 wrote:Inertia = 0% Waves = 100%

Lets say we ignore the pulsing effects in the intake at IVO, for simplicity lets say they aren't there. Then at IVO, the inertia when the intake valve starts to open is 0. The inertia in the intake is going to stay at 0 indefinitely, unless acted upon. The action, piston motion (and also residual intake waves but we got rid of them above, and exhaust suction or reversion), causes wave action which in turn causes the intake motion and of course intake inertia increases. Same idea when its all slowing down, wave action happens then the intake motion decreases. Absolutely nothing happens in the intake without wave action, it just sits there stopped. The A/F mixture half way up the runner (or anywhere else) knows absolutely nothing about speeding up from dead stopped until a wave from the cylinder travels up the runner to tell it to get going, and it doesn't know to stop either until a wave tells it to stop. Actually its a series of waves not a simple sinusoidal wave (see further below).

It's important to understand that "wave tuning" as most people think of it is a very specific thing that is primarily related to what happens during overlap rather than during the rest of the cylinder filling period. Only during IVC to IVO do the events in the intake behave like a sinusoidal (or similar) wave and what this wave is doing just before overlap determines to a large degree what happens during overlap. The exhaust wave at overlap plays the other part. So how much effect so called "wave tuning" will have on power really depends largely on how much gain can be made by having a good overlap flush event vs. a not so good overlap flush event.

Wave tuning during the rest of the intake process (i.e. the main cylinder filling process) is a whole different story. The waves are simply an infinite series of tiny wave events all summed up. How they sum up determines what you get for cylinder filling. This is not a sinusoidal event at all. It is also the part of wave tuning that most people don't know too much about.
nitro2 wrote:Just to add to my previous post a little. Pipe organ tuning only applies from IVC to IVO, no further.

IVO to IVC is a totally different process. IVO to IVC air is accelerated by wave action and it is decelerated by wave action. The waves come from various sources, piston motion, valve motion, reflections at the runner entrance, tapers, steps, exhaust (during overlap) and so forth. Obviously the air gets up some speed during the intake stroke due to wave action (waves generated by piston motion etc.) and it is going to stay at speed until wave action slows it down. If there was no wave action to slow the flow down it would just continue at speed (ignoring friction of course). Anything in front of that flow that changes with time will affect the flow. It affects the flow by creating a wave. Towards the end of the intake process the front of the flow sees the cylinder pressure rising, a closing valve, etc. all of which create pressure waves at the front of the flow that travel up the runner against the flow and tell the flow up in the runner to slow down (while at the same time causing a pressure increase). This is not a single wave but an infinite series of impulses that are trying to slow down the flow. Also there is, or should be, a pressure wave traveling down the runner heading toward the cylinder during this time which is trying to speed up the flow.

This pressure wave traveling down the runner towards the end of the intake process is critical, if it doesn't happen cylinder filling will be awful. Fortunately it happens in just about every engine at all engines speeds. At some speeds it is timed ideally, and some speeds it is not, but even if it is not timed ideally thats better than not happening at all.

If you wanted to prevent this return wave from happening during the intake process, so that you had an "inertia fill" at least in the sense that you generate high speed flow in the intake (via waves), but you don't have any wave reflections in the intake assisting the flow, how would you do it and what would be the result? You would make a constant diameter runner that was sufficiently long to make sure that any reflections of waves could not reach the engine until after IVC. Without these reflections the most pressure you are going to get in the cylinder is atmospheric pressure, you aren't going to get it at BDC and you aren't going to get it at normal IVC either. You would have to leave the valve open longer than the normal IVC. What you end up with is atmospheric pressure in the cylinder at some ludicrous IVC valve. Cylinder filling (VE) is on the order of 40-60% depending on rpm.

Cylinder filling with no waves - VE = 0%
Cylinder filling with waves, but no reflections before IVC - VE = 40% to 60% (higher at very low engine speeds)
Cylinder filling with normal wave action - VE = up to +120%
vannik wrote:The gasdynamic equations used by the simulators that simulates the gasdynamic effects are all based on the same conservation principles of:
1. Mass
2. Energy
3. Inertia.
The equations show clearly that the inertia of the gas is an integral part of the motion and is not seperate from the pulsation. That is why Blair, Winterbone, Benson, Shapiro, Mucklow, Rudinger, Ballentine etc., all the way back to Riemann, who is usually credited with the derivation of the equations, do not consider the pulsation effects seperate from the inertia effects as they are parts of the same.
vannik wrote:Kevin,

When you read the set of papers by Mucklow, Wilson, Bannister etc. from the late 40's to late 50's please keep in mind that they were not sure at that stage whether the flow in the pipes were conforming to acoustic theory or finite wave theory and a large number of the referees were also unsure. Towards the late 50's they felt confident that you have to use finite wave theory.

If you go through the derivation of acoustic vs finite waves you will see that at some stage you assume that the delta P is small enough to ignore a pressure term which for small delta P is second order but not for large delta P. The two theories are based on the same initial assumptions but diverge at the point where the small delta P assumtion is made. (Earshaw, somewhere in the late 1800's)

Blair does not debunk ramming, only saying you cannot have inertia all by itself but that it is part of compressible unsteady gasdynamic flow.

Vannik
-Bob

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Re: Is Port Energy validation just around the corner?????

Post by David Vizard » Sun Sep 24, 2017 8:18 pm

MadBill wrote:
David Vizard wrote:...The rapidly accelerating piston down the bore (with the valve open) is what causes this big reflection. I would have described this as the generation of a PRESSURE wave not the reflection. The reflection comes about when this positive pressure wave hits the end of the intake runner as in the plenum or open air...

...The big 'push' is the positive reflection of the big NEGATIVE pulse caused by the piston as it reaches maximum piston speed (MPS). ...DV
Isn't this an oxymoron? :?
Geez Bill I hate it when you are right!!!

when this positive pressure wave

I should have said when this negative wave hits the end of the runner!

DV
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