Cycle identification: Which ideal cycle consists of two constant-pressure (isobaric) processes and two isentropic processes?

Introduction / Context:
Identifying cycles by their process sequence is crucial for analyzing gas turbines, internal combustion engines, and refrigeration systems. The air-standard Brayton (Joule) cycle models the simple gas turbine engine used in power generation and aviation.

Given Data / Assumptions:

• Air-standard analysis, constant specific heats.
• Two isentropic legs (compressor and turbine).
• Two constant-pressure legs (combustor heat addition and cooler/stack heat rejection).

Concept / Approach:
The Brayton cycle sequence is: 1→2 isentropic compression, 2→3 constant-pressure heat addition, 3→4 isentropic expansion, 4→1 constant-pressure heat rejection. This distinguishes it from the Otto cycle (constant-volume heat addition), Diesel cycle (constant-pressure heat addition and constant-volume heat rejection), Carnot (isothermal and isentropic), and Stirling (isothermal with regeneration).

Step-by-Step Solution:

Verification / Alternative check:
p–V or T–s diagrams show two vertical isentropes and two near-horizontal CP lines for Brayton, consistent with gas turbine operation.

Why Other Options Are Wrong:

• Carnot: Isothermal + isentropic, not constant-pressure.
• Stirling: Isothermal with regeneration, not isentropic legs.
• Otto: Constant-volume heat addition and rejection at constant volume.

Common Pitfalls:
Confusing Brayton with Diesel; Diesel's heat rejection is at constant volume, not constant pressure.

Final Answer:
Brayton (Joule) cycle