In a two-spool axial flow jet engine, N2 represents the rotational speed of the high-speed spool. This spool includes the high-pressure compressor and the high-pressure turbine, which are connected by a concentric shaft. In contrast, in a three-spool engine, N2 refers to the rotational speed of the intermediate-speed spool. This spool consists of the intermediate pressure compressor and its corresponding turbine. Understanding these components is key to grasping how jet engines operate efficiently.
