Engine Cycles — Which thermodynamic cycle models a Diesel engine? Select the idealized thermodynamic cycle that represents the working of a compression-ignition (Diesel) engine.

Introduction / Context:
Ideal cycles provide simplified models for heat-engine behavior. While real engines deviate, identifying the appropriate ideal cycle helps predict trends and compare efficiencies.

Given Data / Assumptions:

• Compression-ignition engine (Diesel).
• Air-standard assumptions for ideal cycles.
• Comparison against Otto, Rankine, and Carnot cycles.

Concept / Approach:
The ideal Diesel cycle features heat addition at constant pressure, representing fuel injection over a portion of the expansion after high compression of air alone. The Otto cycle models spark-ignition engines with constant-volume heat addition. The Rankine cycle describes vapor power (steam) plants, not internal combustion. Carnot is an unattainable ideal with isothermal and adiabatic processes, not a practical engine model.

Step-by-Step Solution:
Identify CI trait: air is compressed; fuel is injected and burns while the piston moves — approximated as constant-pressure heat addition.Match to cycle: Diesel cycle fits this description.Therefore, select “Diesel cycle.”

Verification / Alternative check:
Textbook p-v diagrams show the Diesel cycle with a horizontal (constant-pressure) heat-addition line versus the vertical (constant-volume) line of Otto.

Why Other Options Are Wrong:
Otto: constant-volume heat addition (SI engines).Carnot: reversible ideal benchmark, not engine-specific.Rankine: external-combustion steam cycle.Dual cycle: closer to real Diesels but not the canonical “Diesel cycle” asked here.

Common Pitfalls:
Assuming real Diesels match constant-pressure perfectly; many are better approximated by the dual cycle, but the standard answer remains “Diesel cycle.”

Final Answer:
Diesel cycle