Volumetric Efficiency

[digger]

Dynamic pressure

[David Redszus]

Seems the issue still needs clarification. Here goes.

Momentum is the product of mass times velocity: M = m * V.
Since the mass is moving at constant velocity, momentum must be constant as well.
But at any different steady state velocity, the mass momentum will be different.

Now for Inertia, which is completely different and defined as I = M * A.
The Laws of Motion state that a body at rest, tends to stay at rest;
a body in motion tends to stay in motion.

A body at rest has an acceleration value of zero, as does a body at any steady state velocity.
It must then have an inertia value of zero.

But it takes energy to move a body from a resting state, or to change the velocity of a moving body,
or to change direction, which is reflected by its required inertia force. Since the mass is constant,
inertia is determined by the rate of change or its acceleration.

Momentum is stored energy. Inertia is required energy to cause a change of position, velocity or direction.

Easy to say on paper or backlit screen. In the real world it becomes a bit more complex.
Air particles are compressible and therefore their mass (density) will change.

Pulsed air flow causes local variations in air velocity (and acceleration) which then results in changes
to V and A. And to Momentum and Inertia numbers.

Steady state air mass measurements never match pulsed air mass measurements. Nor should they.

[Roundybout]

"Momentum is stored energy. Inertia is required energy to cause a change of position, velocity or direction" Is it correct to say something that has mass has inertia and to have inertia you have to have mass?


Are inertial effects more significant that acoustical resonance effects in a racing engine? I'm trying to get it in my head how this applies to VE.

[vwchuck]

VE is most definitely not massflow.

[MadBill]

How about: "The momentum of the in-flowing mixture contributes to cylinder filling at the end of the induction cycle, increasing in effect as the RPM and hence gas velocity and momentum rises, whereas the finite amplitude pressure waves in a 'tuned' intake runner, while increasing in intensity with RPM, will over a band of ~800 RPM add, subtract or have no effect, depending on how they are synched with the RPM and valve timing."

[digger]

Seems the issue still needs clarification. Here goes.

Momentum is the product of mass times velocity: M = m * V.
Since the mass is moving at constant velocity, momentum must be constant as well.
But at any different steady state velocity, the mass momentum will be different.

Now for Inertia, which is completely different and defined as I = M * A.
The Laws of Motion state that a body at rest, tends to stay at rest;
a body in motion tends to stay in motion.

A body at rest has an acceleration value of zero, as does a body at any steady state velocity.
It must then have an inertia value of zero.

But it takes energy to move a body from a resting state, or to change the velocity of a moving body,
or to change direction, which is reflected by its required inertia force. Since the mass is constant,
inertia is determined by the rate of change or its acceleration.

Momentum is stored energy. Inertia is required energy to cause a change of position, velocity or direction.

Easy to say on paper or backlit screen. In the real world it becomes a bit more complex.
Air particles are compressible and therefore their mass (density) will change.

Pulsed air flow causes local variations in air velocity (and acceleration) which then results in changes
to V and A. And to Momentum and Inertia numbers.

Steady state air mass measurements never match pulsed air mass measurements. Nor should they.

For fluid momentum in a tube it is
Momentum.= Density x Area x velocity squared


Inertia is not M x A

"Mass" is the inertia for translation motion
"Mass moment of inertia" is the inertia for the rotational motion

[Roundybout]

How about: "The momentum of the in-flowing mixture contributes to cylinder filling at the end of the induction cycle, increasing in effect as the RPM and hence gas velocity and momentum rises, whereas the finite amplitude pressure waves in a 'tuned' intake runner, while increasing in intensity with RPM, will over a band of ~800 RPM add, subtract or have no effect, depending on how they are synched with the RPM and valve timing."

The bold part is the negative, positive and equal pressure differential waves that arrive at the valve, correct?

The column of air traveling down an intake of an engine at 100MPH or 500MPH can't have much momentum. It doesn't have much mass. It therefore doesn't have much inertia. So in that respect it doesn't contribute much to the VE of an engine compared to the many other factors that do in my head.

[Warp Speed]

How about: "The momentum of the in-flowing mixture contributes to cylinder filling at the end of the induction cycle, increasing in effect as the RPM and hence gas velocity and momentum rises, whereas the finite amplitude pressure waves in a 'tuned' intake runner, while increasing in intensity with RPM, will over a band of ~800 RPM add, subtract or have no effect, depending on how they are synched with the RPM and valve timing."

The bold part is the negative, positive and equal pressure differential waves that arrive at the valve, correct?

The column of air traveling down an intake of an engine at 100MPH or 500MPH can't have much momentum. It doesn't have much mass. It therefore doesn't have much inertia. So in that respect it doesn't contribute much to the VE of an engine compared to the many other factors that do in my head.

Pretty much!
It's all about pressure differentials and catching the waves!

[digger]

I always think of the strength of the wave (diameter and taper) and harnessing the wave at the right Crank angles by tuning the length of runner

[David Redszus]

How about: "The momentum of the in-flowing mixture contributes to cylinder filling at the end of the induction cycle, increasing in effect as the RPM and hence gas velocity and momentum rises, whereas the finite amplitude pressure waves in a 'tuned' intake runner, while increasing in intensity with RPM, will over a band of ~800 RPM add, subtract or have no effect, depending on how they are synched with the RPM and valve timing."

I agree.

[David Redszus]

Seems the issue still needs clarification. Here goes.

Momentum is the product of mass times velocity: M = m * V.
Since the mass is moving at constant velocity, momentum must be constant as well.
But at any different steady state velocity, the mass momentum will be different.

Now for Inertia, which is completely different and defined as I = M * A.
The Laws of Motion state that a body at rest, tends to stay at rest;
a body in motion tends to stay in motion.

A body at rest has an acceleration value of zero, as does a body at any steady state velocity.
It must then have an inertia value of zero.

But it takes energy to move a body from a resting state, or to change the velocity of a moving body,
or to change direction, which is reflected by its required inertia force. Since the mass is constant,
inertia is determined by the rate of change or its acceleration.

Momentum is stored energy. Inertia is required energy to cause a change of position, velocity or direction.

Easy to say on paper or backlit screen. In the real world it becomes a bit more complex.
Air particles are compressible and therefore their mass (density) will change.

Pulsed air flow causes local variations in air velocity (and acceleration) which then results in changes
to V and A. And to Momentum and Inertia numbers.

Steady state air mass measurements never match pulsed air mass measurements. Nor should they.

For fluid momentum in a tube it is
Momentum.= Density x Area x velocity squared


Inertia is not M x A

"Mass" is the inertia for translation motion
"Mass moment of inertia" is the inertia for the rotational motion

Quite wrong. please check your sources.

[digger]

Seems the issue still needs clarification. Here goes.

Momentum is the product of mass times velocity: M = m * V.
Since the mass is moving at constant velocity, momentum must be constant as well.
But at any different steady state velocity, the mass momentum will be different.

Now for Inertia, which is completely different and defined as I = M * A.
The Laws of Motion state that a body at rest, tends to stay at rest;
a body in motion tends to stay in motion.

A body at rest has an acceleration value of zero, as does a body at any steady state velocity.
It must then have an inertia value of zero.

But it takes energy to move a body from a resting state, or to change the velocity of a moving body,
or to change direction, which is reflected by its required inertia force. Since the mass is constant,
inertia is determined by the rate of change or its acceleration.

Momentum is stored energy. Inertia is required energy to cause a change of position, velocity or direction.

Easy to say on paper or backlit screen. In the real world it becomes a bit more complex.
Air particles are compressible and therefore their mass (density) will change.

Pulsed air flow causes local variations in air velocity (and acceleration) which then results in changes
to V and A. And to Momentum and Inertia numbers.

Steady state air mass measurements never match pulsed air mass measurements. Nor should they.

For fluid momentum in a tube it is
Momentum.= Density x Area x velocity squared


Inertia is not M x A

"Mass" is the inertia for translation motion
"Mass moment of inertia" is the inertia for the rotational motion

Quite wrong. please check your sources.

Be more specific please, it's actually correct

[MadBill]

..The bold part is the negative, positive and equal pressure differential waves that arrive at the valve, correct?

To be exact the +, - and 0 psig portions of each wave.

The column of air traveling down an intake of an engine at 100MPH or 500MPH can't have much momentum. It doesn't have much mass. It therefore doesn't have much inertia. So in that respect it doesn't contribute much to the VE of an engine compared to the many other factors that do in my head.

Not much compared to say a speeding bullet, but still enough to produce pressure spikes of several psi, as predicted by Dynomation and other software programs, and shown by in-cylinder sensors systems such as offered by TFX.

[swampbuggy]

Holy crap, i did not expect for my O.P.to end up starting a class/discussion/arguing/session on physics LOL. Volumetric Efficiency is------HOW efficiently the combined parts of the engine that fill the cylinder volume with air and fuel do their job, correct ?? And the objective is to obtain/produce/reach a pressure inside the cylinder after the intake valve has closed that is GREATER than the atmospheric pressure outside the engine, correct ?? Assuming the two above statements/questions are true/correct, can we give answers to what choices when building an engine help make a higher V.E. Mark H. "ONLY" a N.A. engine deal here.

[SchmidtMotorWorks]

The column of air traveling down an intake of an engine at 100MPH or 500MPH can't have much momentum. It doesn't have much mass. It therefore doesn't have much inertia. So in that respect it doesn't contribute much to the VE of an engine compared to the many other factors that do in my head.

An engine must effectively capitalize on momentum of intake charge to be competitive.
Everything beyond the sophistication of a lawn mower benefits from it.

Speaking of lawn mower, the Briggs & Stratton themed Jr dragster engines could not make the anywhere near the 10-20 times the power with short ducts.