system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: How does a Jake Break work?
gpt
So, you know how an engine works, right? Roughly speaking.

A fuel-air mixture is drawn into the cylinder, compressed, then ignited; the force of the expanding gas as a result of that ignition drives the piston down and imparts energy to the crankshaft.

In a diesel engine, though, even if you let off the gas pedal, the engine will still draw a full charge of air into the cylinders, and that air acts as a spring; because the engine is still turning, it's still compressing the air, and the air then rebounds when the piston falls back down.

What a Jake brake does is it opens the exhaust valve as the piston reaches the top of the cylinder, bleeding some of that air off and robbing the crankshaft of power.