How can one achieve supersonic cruise capabilities without afterburners?
A normal jet engine has subsonic flow throughout. This avoids shock problems such as choking or excessive acoustic noise.
A conventional afterburner accelerates the exhaust flow to supersonic speed, allowing it to push the plane past the speed of sound. It is placed after the turbines in order to avoid those shock problems.
A supercruise engine must deliver supersonic exhaust flow without using an afterburner. Luckily, in a hot gas the speed of sound is much higher than in a cold gas. So as long as the exhaust is not cooled before exit, its high exit velocity stays subsonic within the engine and only &quot;looks&quot; supersonic relative to the outside air.
The problem with this is that you cannot obtain the usual benefits of mixing bypass air with it to increase its mass flow and thermodynamic efficiency, because that would cool it and create a standing shock wave across it, slowing it to subsonic speeds.
The end result is a bit of a design compromise; relatively high mass flow through the core, relatively low bypass ratio, some sacrifice of efficiency.