Question

The Carnot cycle has maximum efficiency for:

• A. Reversible engine
• B. Irreversible engine
• C. Petrol engine
• D. Diesel engine

Answer 1

The correct option is A

Reversible engine

Correct Option:

Option A: Reversible engine

• A reversible heat engine is one in which the process can be retraced by reversing the boundary conditions.
• Carnot Cycle: It is an ideal reversible closed thermodynamic cycle consisting of four stages, namely, isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.
• In isothermal expansion, the air expands at a constant temperature $T_1$ from $V_{1}to{V}_2$.$Q_1$ is the heat supplied which is used to do external work, therefore they are equal.
• In adiabatic expansion, air expands without emitting or accepting heat.
• In isothermal compression, the air is compressed at a constant temperature $T_2$,.$Q_2$ is the heat emitted by the air which is equal to work done on air.
• In adiabatic compression, the air is furthermore compressed. Internal energy increases since temperature increases and eventually work done on air is equal to an increase in internal energy
• No other engine has an efficiency greater than a reversible heat engine.

Carnot Cycle

Incorrect Options:

• Correct B: Irreversible engine: The efficiency of an irreversible heat engine is always less than that of a reversible heat engine working between the same two reservoirs.
• Correct C: Petrol engine: A petrol engine is less efficient than a reversible heat engine.
• Correct D: Diesel engine: A diesel engine is less efficient than a reversible heat engine.

Hence, the correct option is option A.