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Author Topic: Table Top Engine Expo - Heritage Park of North Iowa  (Read 1494 times)

RedRyder

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This AI looks smart but a little ignorant too. 
The BDC port is aways open and has no valve or flap.
It only let's out exhaust when the piston moves past it to BDC exposing the port. As soon as the piston moves moves up near an inch from BDC, it is "closed".
This AI is also confusing the intake stroke with the compression stroke. intake stroke is always downward. 
Most interesting is that AI writes in good English that is easy to understand.

CBWho

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While not perfect the ai helps

* **Incomplete exhaust:**
I think the ai text is stating that the port at bdc must take away from the total stroke. If it's open at the last 1% then that engine is only 99% as efficient as one that doesn't have a port.

Also that port stops the scavenging effect of the valved exhaust. Although perhaps that could be mitigated by routing both to a common exhaust pipe.

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* **Fresh air loss:**
Indeed it was clumsy on its wording for the intake stroke. Basically on the bdc of the intake/compression stroke some of the intake charge will be lost to the open exhaust port.

RedRyder

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While not perfect the ai helps

* **Incomplete exhaust:**
I think the ai text is stating that the port at bdc must take away from the total stroke. If it's open at the last 1% then that engine is only 99% as efficient as one that doesn't have a port.

Also that port stops the scavenging effect of the valved exhaust. Although perhaps that could be mitigated by routing both to a common exhaust pipe.

.
* **Fresh air loss:**
Indeed it was clumsy on its wording for the intake stroke. Basically on the bdc of the intake/compression stroke some of the intake charge will be lost to the open exhaust port.
Good points. 

However regarding exhaust port taking away a bit of the power stroke, there likely would not be a noticeable efficiency or power loss given that the the bottom 5-10% of the power stroke provides a miniscule amount of power/torque given the limited amount of piston travel. This open port design clearly did not grow much over time with the exception being 2 cycle engines. As for scavenging, the intake valve on a Gade is atmospheric and doesn't let in any fuel/air until the piston is traveling downward and creates a vacuum. On non-hit & miss engines (without any open ports) the intake cam lobe could be timed to begin opening before top dead center on the exhaust stroke which allows for some scavenging.