a question for simonizer.

[donnyman]

This question is for an engineers mind.I know that you most have takeing it in class at some time.My question is, does air travel better though a oval hole or a round hole.Also witch hole would have the most air trbulance on the outlet side of the hole.Also how are things in the cambell,I got a nehew liveing there he and his wife work for one of the forestry companys.Hes a cartogerfer,hope I spelled that right.eg.Map maker.By trade.Thanks in advance for your reply.Don.

 

[Simonizer]

This question is for an engineers mind.I know that you most have takeing it in class at some time.My question is, does air travel better though a oval hole or a round hole.Also witch hole would have the most air trbulance on the outlet side of the hole.Also how are things in the cambell,I got a nehew liveing there he and his wife work for one of the forestry companys.Hes a cartogerfer,hope I spelled that right.eg.Map maker.By trade.Thanks in advance for your reply.Don.

This is actually a very complex question. As with fluids, there is a point at which laminar changes to turbulent flow. Air temperature, humidity, dimensions of passageway, surface finish, all play important roles.

 

[donnyman]

Thanks for the reply.Ok were talkin saw cylinder ports, intake and exhaust.Oil and gas mixed wth air.ok. Thanks Don.

 

[Fish]

Yes the laminar flow gets disrupted even with minor market fluctuations, and the
party in control of the senate. But remember, an oval is just a circle "puckering".
I beat the crap out of an engineer once, and he told me everything he knew.
So I am qualified to field any questions you have as well. I have a big shovel too.
Sorry all, just doin' my job, which pays quite well.
Let's have a sawbuilder's contest. Let Lambert judge the event. Not any of that
Walt Galer "type" complications. No feeling sorry for anyone.

 

[donnyman]

Thanks for the reply.Mr Fish.How are things in Kintuk.Don

 

[Fish]

John, Is that you?

 

[Gypo Logger]

Hi Fish, no that's not me. Could it be Walt or Tundraotto?
John

 

[PLAYINWOOD]

its neither.unless they have moved to Bobcaygeon.jeff

 

[bwalker]

You also have to take into account that flow through a two stroke is unsteady.

 

[jokers]

Simon,

I understand that we would want laminar flow to keep the velocity of the fuel charge up, but is there any reason that we would want any turbulent flow, say for atomization? Say for example in the intake port area. The fuel is atomized at the nozzle in the carb but it`s velocity immediately drops in the carb throat. This has a tie in to volumetric efficiency, no?

donnyman,

It`s my belief that because of the port time/area relationships necessary for a two stroke to run efficiently, a round port would not have the open area necessary for optimal performance. In other words, because of the time/area relationship the top and bottom heights of the ports are limited which also limits the widths of the ports in a circular port. An oval port could have more area and thus more flow. Poor turbulent flow is better than no laminar flow.

This is speaking strickly in the sense of port efficiency. Piston ring life is another area worthy of serious consideration. A round or oval port has a ramp effect on pushing the ring back into it`s groove after it has expanded into the open area on it`s way by vs square or rectangular ports with flat tops and bottoms which abruptly force the ring back. This is called ring clipping. This is why proper chamfer on port edges is critical. There are sometimes valid reasons why square or rectangular ports would be used and a level of acceptable ring life needs to be established.

Sorry to hop in for Simon. I`ll return the thread to his care for further response.

Russ

 

[timberwolf]

Air flows better through a circle, than an oval of the same area. The issue is that the majority of friction and non laminar flow is at the edges. Because an oval has a greater circumference than a circle of the same area there is more exposure to the edge of the hole and hence more friction to flow.

Ideal for performance would be a square or rectangle to maximize the port area, however rings dont like squares so we come up with a compromise half way between a circle and a rectangle. this suits the rings, offers a fairly flat top so the ports open and close quickly, while giving a decently large port area with good flow characteristics.

Some engines do use a more squared port shape with a tapered nub in the middle of the top of the port to push the ring back into the piston and prevent the ring from catching.

 

[jokers]

Air flows better through a circle, than an oval of the same area. The issue is that the majority of friction and non laminar flow is at the edges. Because an oval has a greater circumference than a circle of the same area there is more exposure to the edge of the hole and hence more friction to flow.

Ideal for performance would be a square or rectangle to maximize the port area, however rings dont like squares so we come up with a compromise half way between a circle and a rectangle. this suits the rings, offers a fairly flat top so the ports open and close quickly, while giving a decently large port area with good flow characteristics.

Some engines do use a more squared port shape with a tapered nub in the middle of the top of the port to push the ring back into the piston and prevent the ring from catching.

Sounds pretty similar to what I said, translated in Canadian. Thanks for the affirmation Timberwolf.

Russ

 

[Fish]

And no one shoveled in the word "viscosity"!

 

[jokers]

And no one shoveled in the word "viscosity"!

No...... but Simonizer said "humidity" which could be taken as related to viscosity when speaking of flow, of course all bets are off if the operator were to use full synthetic fish oil, say Amsoil, at 16:1.

Russ

 

[Simonizer]

Simon,

I understand that we would want laminar flow to keep the velocity of the fuel charge up, but is there any reason that we would want any turbulent flow, say for atomization? Say for example in the intake port area. The fuel is atomized at the nozzle in the carb but it`s velocity immediately drops in the carb throat. This has a tie in to volumetric efficiency, no?

donnyman,

It`s my belief that because of the port time/area relationships necessary for a two stroke to run efficiently, a round port would not have the open area necessary for optimal performance. In other words, because of the time/area relationship the top and bottom heights of the ports are limited which also limits the widths of the ports in a circular port. An oval port could have more area and thus more flow. Poor turbulent flow is better than no laminar flow.

This is speaking strickly in the sense of port efficiency. Piston ring life is another area worthy of serious consideration. A round or oval port has a ramp effect on pushing the ring back into it`s groove after it has expanded into the open area on it`s way by vs square or rectangular ports with flat tops and bottoms which abruptly force the ring back. This is called ring clipping. This is why proper chamfer on port edges is critical. There are sometimes valid reasons why square or rectangular ports would be used and a level of acceptable ring life needs to be established.

Sorry to hop in for Simon. I`ll return the thread to his care for further response.

Russ

Actually you supplied very accurate insight.

 

[jokers]

Actually you supplied very accurate insight.

Thanks Simon, I have the occassional moment of lucidity.

Russ

 

[Simonizer]

Thanks Simon, I have the occassional moment of lucidity.

Russ

Me too but the duration and frequency are becoming a concern ha ha.

 

[Fish]

Maybe, you 2 should get a room.

 

[jokers]

Hey Fish, we got a California King, there`s room for one more! :Eye::Eye:

 

[Fish]

OOOOOooo, which one of you will bring the champagne? A good domestic brand works for me, you girls bring the glasses!!!
If you all just mumble "engineer talk", I am quite happy.
Just say it sllllooooowwwwwly.