Can you expound on what part of that qualifies it as an “engine”?
Well, the engine is actually the turbine that expands the steam to produce power. The boiler burns the fuel and generates the high pressure working fluid — akin to combustion of fuel and air in the ICE cylinder. The expansion in the Rankine cycle is done in a separate machine (the turbine) while in the Diesel cycle the combustion and expansion are in the same location.