Classification of prime movers: A steam engine burns fuel in a separate boiler and admits steam to the cylinder for expansion. State whether the following is correct: “Steam engines are external combustion engines.”

Introduction:
Prime movers are broadly divided into internal combustion (combustion inside the working cylinder) and external combustion (combustion outside the working cylinder). Understanding this distinction is foundational to thermodynamics and power plant engineering.

Given Data / Assumptions:

• Steam engine uses steam produced in a boiler.
• Fuel is burnt in the boiler furnace, not inside the engine cylinder.
• Steam expands in the engine cylinder doing work on the piston.

Concept / Approach:
In external combustion engines, the working fluid (steam) is heated by combustion occurring in a separate chamber. The engine cylinder never experiences combustion; it only receives high-energy steam as the working medium. This is in contrast to internal combustion engines (e.g., Diesel, Otto) where the fuel–air mixture ignites within the cylinder itself.

Step-by-Step Solution:
1) Identify the location of combustion: in a boiler furnace, external to the engine.2) Recognize the working fluid path: boiler → steam line → engine cylinder.3) Note that energy conversion in the cylinder is purely due to steam expansion, not combustion.4) Conclude that a steam engine is an external combustion engine.

Verification / Alternative check:
Historical and modern references consistently classify steam engines and steam turbines as external combustion due to separate combustion chambers (boilers).

Why Other Options Are Wrong:
“No” and conditional variants contradict the clear definition; fuel type, compounding, or pressure level do not change the combustion location.

Common Pitfalls:
Confusing steam engines with internal combustion reciprocating engines due to similar piston–crank mechanisms.

Final Answer:
Yes