Smoke trace as a porting aid.

[SchmidtMotorWorks]

For those that are interested to understand the relationship between a flow bench test and a CFD test that is concerned with the trajectory of particles; any moderately capable, modern CFD program is capable of simulating suspended particles, moreover CFD allows specification of the particle size and density. For those that are interested in heat transfer involved with the particles, that can be modeled as well.

In steady-state flow, generally the trajectory of the particles is influenced by its inertia and gravity in ways that are intuitive.
If you simulate with gravity force up vs down, the difference is much more noticeable when the particles are large and density is high, the point is that particle size and density are important (also, the angle of the head relative to gravity).
As anyone that has sprayed a garden hose in the wind has seen; the larger the particle, the less it is influenced by the surrounding wind.

Before drawing any conclusions from a steady-state simulation, it is important to remember that air motion in a port not only stops, it reverses after the intake valve closes. Generally, the greater the reversal, the greater the amount of fuel that will fall out of suspension.

[GARY C]

For those that are interested to understand the relationship between a flow bench test and a CFD test that is concerned with the trajectory of particles; any moderately capable, modern CFD program is capable of simulating suspended particles, moreover CFD allows specification of the particle size and density. For those that are interested in heat transfer involved with the particles, that can be modeled as well.

In steady-state flow, generally the trajectory of the particles is influenced by its inertia and gravity in ways that are intuitive.
If you simulate with gravity force up vs down, the difference is much more noticeable when the particles are large and density is high, the point is that particle size and density are important (also, the angle of the head relative to gravity).
As anyone that has sprayed a garden hose in the wind has seen; the larger the particle, the less it is influenced by the surrounding wind.

Before drawing any conclusions from a steady-state simulation, it is important to remember that air motion in a port not only stops, it reverses after the intake valve closes. Generally, the greater the reversal, the greater the amount of fuel that will fall out of suspension.

Thats been known and written about for as long as I have read about engines but the question still remains, what do you change in a port to improve it?
Wet flow testing is done in the forward motion because that is when it is entering the cylinder, reverse motion is only going to back up left over fuel and add it to the incoming fuel so the focus is how to better atomize it as it enters the cylinder so it will burn.

[SchmidtMotorWorks]

Thats been known and written about for as long as I have read about engines but the question still remains, what do you change in a port to improve it?
Wet flow testing is done in the forward motion because that is when it is entering the cylinder, reverse motion is only going to back up left over fuel and add it to the incoming fuel so the focus is how to better atomize it as it enters the cylinder so it will burn.

Knowing where and when the fuel fuel drops out is the first step to designing an improvement.
The only practical way I know of to do that is to simulate the entire duct (port and manifold) through the entire cycle.
Every CFD simulation, shows surprises that challenge intuition.
The more comprehensive the simulation, the more surprises are found.

In the current era, fuel injector positioning is readily improved with knowledge gained form CFD simulation.

In carburetor engines, design of plenum and transition to runners generally have the largest opportunities for improvement.

[GARY C]

Clear plenum and runner video.
Video OP...

This is a compilation of some videos shared by Jon Kaase during his presentation at the 2015 AETC that I attended.

https://www.youtube.com/watch?v=7Iq1B-2paCs

In Cylinder Video ( How a 4 stroke engine works ) https://www.youtube.com/watch?v=sEf8va1S7Sw