Simple Tunnel ram Question

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Re: Simple Tunnel ram Question

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SchmidtMotorWorks wrote: Mon May 20, 2019 9:39 pm I am not certain that the buoyancy argument applies given the cylinder is not open at the other end.

Let's consider the model below:

If gravity did play a factor in this it seems that air would flow into the upper duct and out the lower duct (i think we can agree it doesn't)

If the system had a 3rd duct pulling a small depression from the inside of the box so that air could flow into the box from either duct...

If gravity mattered there would be a difference in flow in the upper and lower duct.


If the above is true, it seems that there would be a low level of vacuum where the upper duct has flow and the lower duct does not. (I doubt that is true)

tunnel_ram.jpg

This would be interesting to try in a sealed environment at atmospheric pressure so now outside 'wind/breeze' could affect the test. And at very slight depression pulled see wether there were any difference in flow.
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Re: Simple Tunnel ram Question

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n2omike wrote: Mon May 20, 2019 10:03 pm
SchmidtMotorWorks wrote: Mon May 20, 2019 9:39 pm If gravity did play a factor in this it seems that air would flow into the upper duct and out the lower duct (i think we can agree it doesn't)
The ONLY role gravity plays, is its part in providing the pressure differential.
It doesn't matter if the carbs are updraft, downdraft or sidedraft. Makes ZERO difference. The pressure differential is the same.
The buoyancy example was to show that gravity alone is not providing a NET force on the air column in any given direction.
Gravity's sole role is it's part in providing the pressure differential.
Im no physics expert so imagination is at work here! I understand gravity's role in providing the pressure differential, so yeah no matter which way up the tunnel ram is, if you have a depression at one end , air will flow in the other end in an attempt to equalize the depression with the outside pressure(atmosphere).
Of course in an intake the air flow is not in one continuous direction or at a steady speed so gravity must play 'some' role on any incompletely vaporized fuel (liquid droplet) because if the depression were only slight and the tunnel ram was upside down(as in an updraft) and the airflow was not fast enough moving for it to carry the fuel droplet with the air , the fuel droplet would be subject to gravity and drop out of the air flowing upward. At some point in airspeed the fuel droplet will then equalize with gravity and (of course until it vaporizes) would 'hover' due to gravity pulling the droplet down and air speed pulling/holding the droplet up. Then increase the airspeed again and the droplet will begin to move in the direction of airflow.
Whereas the same scenario but with the tunnel ram in a down draft position, that droplet is going to fall with gravity down the runner no matter the air speed but will fall if course faster as the air speed increases.
This is probably a little off the actual subject but I would love to see Jon Kaase's clear intake test done in an up draft position, some of the fuel that is washing around and not really going anywhere 'looks' as though more than just air flow is affecting it.
https://youtu.be/7Iq1B-2paCs

Probably way off track again but and putting other forces at play, in a downdraft manifold/pipe scenario, keeping in mind that air has mass and is compressable, what would happen to the moving air column that is flowing toward a depression if we could suddenly accelerate the entire manifold, toward/inline with gravity and up to the same speed as the moving air colum?
Then same scenario BUT away from gravity,,, then in an updraft situation same again , , with and away from gravity?
From all that waffle I still dont know the answer but am having fun thinking about it!
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Re: Simple Tunnel ram Question

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Fuel falls out of suspension when the air turns because of inertia, not gravity.
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Re: Simple Tunnel ram Question

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Well I really enjoyed that Kaase video. Witness how empirical testing makes science a reality. You can see the airflow inertia is several magnitudes greater than either the pressure or gravitational effects. I think the mistaken concept here was that the pressure differential is not increasing but the mixture flow velocity is. So the mixture does have mass and gravity is pulling on it but the inertia of that mass due to high velocity is of a much greater magnitude. The pressure differential remains mostly the same but the flow rate is what is increasing with the greater RPM as you observe the demonstrator in the video retains his finger. I guess you could say the dynamic pressure is increasing as it has to with higher velocity but the pressure differential between the cylinder and atmosphere is not. We can also see his finger oscillate with greater RPM and that is enhanced by the shock wave from the intake valve closing and reflecting up and down the runner - called the Helmholtz effect.

So to the OP if you want to know the advantage of a tunnel ram IMHO you should investigate the Helmholtz effect in different types of runners. Again my representation/explanation is the straight shot into the cylinder that adds cylinder filling.
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Re: Simple Tunnel ram Question

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cardo0 wrote: Tue May 21, 2019 2:27 am Well I really enjoyed that Kaase video. Witness how empirical testing makes science a reality. You can see the airflow inertia is several magnitudes greater than either the pressure or gravitational effects. I think the mistaken concept here was that the pressure differential is not increasing but the mixture flow velocity is. So the mixture does have mass and gravity is pulling on it but the inertia of that mass due to high velocity is of a much greater magnitude. The pressure differential remains mostly the same but the flow rate is what is increasing with the greater RPM as you observe the demonstrator in the video retains his finger. I guess you could say the dynamic pressure is increasing as it has to with higher velocity but the pressure differential between the cylinder and atmosphere is not. We can also see his finger oscillate with greater RPM and that is enhanced by the shock wave from the intake valve closing and reflecting up and down the runner - called the Helmholtz effect.

So to the OP if you want to know the advantage of a tunnel ram IMHO you should investigate the Helmholtz effect in different types of runners. Again my representation/explanation is the straight shot into the cylinder that adds cylinder filling.
I think that you’d have to have a dual plane “tunnel ram” to really take advantage of the Helmholtz plenum resonance. All right cylinders connecting to the same plenum will not really work to produce twin torque peaks because there’s too much cancellation of pulses, so one will instead just get a single torque peak.
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Re: Simple Tunnel ram Question

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SchmidtMotorWorks wrote: Tue May 21, 2019 2:15 am Fuel falls out of suspension when the air turns because of inertia, not gravity.
Inertia: a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.

Air is at rest before it enters the intake system where in the manifold runner it is accelerated to 300 FPS. Which direction, up or down, requires the most energy to accelerate to 300 fps?
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Re: Simple Tunnel ram Question

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Tuner wrote: Tue May 21, 2019 1:44 pm
Air is at rest before it enters the intake system where in the manifold runner it is accelerated to 300 FPS. Which direction, up or down, requires the most energy to accelerate to 300 fps?
Up, down, sideways... it's irrelevant. All the same.
Just like a water balloon under water, the air is at an equilibrium before being accelerated. There is NO net force acting on it outside of the pressure differential. Since the pressure differential is the ONLY net force acting on it, it is the only thing accelerating the air mass. Direction is irrelevant.
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Re: Simple Tunnel ram Question

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Gravity is a vector force and always acts in the same direction, "down". F = ma Acceleration is the sum of all vector forces acting on a mass. Depending on the direction of acceleration, gravity is either a positive or negative vector, either adds or subtracts from the total acceleration force.
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Re: Simple Tunnel ram Question

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Gravity acts down, but just like the ground providing a reaction force to your weight as you stand on it, the gravitational attraction of the 30+ mile high atmosphere applies a force of 14.7 psi at sea level which is balanced by an equal reaction force from the ground, thus no net force acting on still air.
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Re: Simple Tunnel ram Question

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"thus no net force acting on still air." In Acceleration from still to 300 fps gravity acts to add to or subtract from the vector sum.
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Re: Simple Tunnel ram Question

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MadBill wrote: Tue May 21, 2019 2:29 pm Gravity acts down, but just like the ground providing a reaction force to your weight as you stand on it, the gravitational attraction of the 30+ mile high atmosphere applies a force of 14.7 psi at sea level which is balanced by an equal reaction force from the ground, thus no net force acting on still air.
With a diving belt set to neutral, it's about as easy to swim up or down in water...
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Re: Simple Tunnel ram Question

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Let's put another part into play here. What about fuel entering the airstream in a carb application? While gravity has a fixed effect, acceleration and deceleration plays a bigger part. That is measured in G force, and if you think the has little to no effect think again...
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Re: Simple Tunnel ram Question

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jmarkaudio wrote: Wed May 22, 2019 5:28 pm Let's put another part into play here. What about fuel entering the airstream in a carb application? While gravity has a fixed effect, acceleration and deceleration plays a bigger part. That is measured in G force, and if you think the has little to no effect think again...
Yes , there is a lot more at play in this scenario. We're not working with a simple column of air and a pressure differential.
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Re: Simple Tunnel ram Question

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Gravity is not a factor with tunnel rams, downdraft, updraft or sidedraft carbs.
Even if forces did not cancel out, look at how it compares atmospheric pressure...

Atmospheric pressure is 14.7 psi... or 14.7 pounds PER SQUARE INCH. Let's say a hand is 4" wide and 6" tall... That's 24 square inches... Multiply this by 14.7 pounds PER SQUARE INCH, and you get a force of 353 pounds... just on ONE side of your hand! Of course, since we are at the bottom of this big ocean of air, we feel this as PRESSURE. Our hand doesn't go flying, as it has equal pressure on the other side, so it's at equilibrium.

Let's look at a 4 barrel carburetor with 1.5" venturis. That's 1.77 square inches each, for a total of 7.07 square inches. This provides 14.7 x 7.07 = 104 pounds of force driving the air into the engine... assuming the pistons could pull a complete vacuum.

The above is simple, idealized pressure differential. If you're going to look at the gravitational weight of the fuel... It's pretty damn insignificant. lol
As was said earlier, the weight of the air mass is not a factor, as it is at equilibrium before entering the engine. ZERO net downward effect from gravity there.
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Re: Simple Tunnel ram Question

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Gravity is an acceleration force (a1) . When there is another acceleration force (a2) the vectors (directions) of the acceleration forces combine (a1 + a2) and the resultant apparent acceleration force and equal reaction force vector (direction) is located between the two at an angle proportionate to the ratio of the applied forces. Gravity's 1g acceleration vector is always present and affects any other acceleration of any mass in any direction, proportionate to the combined vectors, positive or negative (toward or away from each other). Evidence of this is seen in the 45° angle of a liquid subject to 1g horizontal acceleration, such as fuel in a float bowl. The horizontal acceleration vector and vertical acceleration vector of gravity are 90° apart and the apparent acceleration vector acting on the liquid is 45°.

Because the air in an intake port runner is accelerated from at rest to what ever is runner velocity, if the runner is vertical, such as in a tunnel ram, gravity adds 1g to whatever other acceleration force is acting to accelerate the air. If it is an updraft runner, gravity's 1g is subtracted.
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