How does an engine decompression brake (Jake brake / Dekompressionsbremse) operate, and at what engine speed (RPM) does it achieve its MAXIMUM braking performance?

1. It opens exhaust valves near top dead center of the compression stroke, releasing trapped compressed air so it cannot push the piston down; maximum braking power is achieved at HIGH engine speeds (1,800 to 2,200 RPM)
2. It shuts off the fuel supply at idle speed (600 RPM)
3. It works only at low engine speeds (under 1,000 RPM) to prevent engine over-revving
4. It sprays water into the combustion chambers to quench combustion pressure