Why does a turbojet engine send most of its turbine power to the compressor?

In a turbojet engine, the turbine must extract energy from the high-pressure, high-temperature gas stream to drive the compressor because the engine's operation relies on a continuous cycle of air compression.12

The engine functions by ingesting ambient air and compressing it to a high pressure—typically 10 to 40 times the inlet pressure—before it enters the combustion chamber. This compression process is essential for the engine's thermodynamic efficiency and power generation. Because the compressor requires significant mechanical energy to achieve these high pressure ratios, it is linked by a torque shaft to the turbine.12

The turbine acts as the engine's power source, extracting the necessary energy from the expanding combustion gases to keep the compressor rotating. Once the turbine has powered the compressor, the remaining energy in the high-velocity exhaust stream is then harnessed to produce thrust as it exits through the nozzle.12