>>510834340
Ignited expanding gas inside the engine bell is the green P in the image
It is exerting a force in all directions
If the engine bell was closed nothing would happen - pressure equalizes
But when it is open, the gas escapes and a force imbalance is created
The force to the right is no longer countered by the left, so thrust is produced.

There is no outer gas required for this - the expanding gas is pushing against the right wall of the engine bell
https://www.youtube.com/watch?v=kAZMBAVRsCo
Also https://youtu.be/_18RZDwnX4U?t=406
Also https://youtu.be/yRfDwkHPVeg?t=294

>>22959268
Ignited expanding gas inside the engine bell is the green P in the image
It is exerting a force in all directions
If the engine bell was closed nothing would happen - pressure equalizes
But when it is open, the gas escapes and a force imbalance is created
The force to the right is no longer countered by the left, so thrust is produced.

There is no outer gas required for this - the expanding gas is pushing against the right wall of the engine bell
https://www.youtube.com/watch?v=kAZMBAVRsCo
Also https://youtu.be/_18RZDwnX4U?t=406
Also https://youtu.be/yRfDwkHPVeg?t=294