this engines have no pressure
an ignition system would be cool. some rockets utilise a spark-ignition system, others use volatile chemicals, some use tiny pyrotechnic charges... it's all pretty cool stuff - https://blogs.nasa.gov/J2X/tag/ignition/
These aren't meant to be fully realistic tho
Looks fine, but where is the throat or any form of a combustion chamber?
You should also check out my starship rocket it has some smaller engines.
I've been experimenting with making a similiar small type of engine but have had no luck so far. This is becausse when you go smaller it is harder to control when the rocket is on or off. And the output of the engine is small so it doesn't provide a lot of thrust.