Question

The air standard cycle involving constant pressure heat addition and constant volume heat rejection corresponds to

• A. Otto Cycle
• B. Diesel Cycle
• C. Brayton Cycle
• D. Atkinson Cycle

Hint:

The Diesel cycle features constant pressure heat addition (combustion) and constant volume heat rejection (exhaust), distinguishing it from Otto and Brayton cycles.

Answer 1

The Correct Option is B

Step 1: Understand air-standard cycles.
Air-standard cycles are idealized thermodynamic cycles used to model internal combustion engines. We need to identify the cycle with:
Constant pressure heat addition,
Constant volume heat rejection.
Step 2: Analyze each cycle.
Otto Cycle: Used in spark-ignition engines (gasoline engines). Processes: Isentropic compression, constant volume heat addition, isentropic expansion, constant volume heat rejection.
Heat rejection: Constant volume (matches), but heat addition is also constant volume (does not match constant pressure).
Diesel Cycle: Used in compression-ignition engines (diesel engines).
Processes: Isentropic compression, constant pressure heat addition, isentropic expansion, constant volume heat rejection.
Heat addition: Constant pressure (matches), heat rejection: Constant volume (matches).
Brayton Cycle: Used in gas turbines.
Processes: Isentropic compression, constant pressure heat addition, isentropic expansion, constant pressure heat rejection.
Heat addition: Constant pressure (matches), but heat rejection is also constant pressure (does not match constant volume).
Atkinson Cycle: A modified cycle for higher efficiency.
Processes: Isentropic compression, constant volume heat addition, isentropic expansion, constant pressure heat rejection (or variations).
Heat addition: Typically constant volume, heat rejection: Often constant pressure (does not match).
Step 3: Identify the matching cycle.
The Diesel cycle has:
Constant pressure heat addition (during combustion),
Constant volume heat rejection (during exhaust at the end of the cycle).
Step 4: Select the correct answer.
The cycle with constant pressure heat addition and constant volume heat rejection is the Diesel cycle, matching option (2).