Air-Standard Otto Cycle – Process Composition and Idealization The ideal Otto cycle (spark-ignition engine model) consists of four internally reversible processes: two constant-volume heat-transfer processes (isochoric heat addition and isochoric heat rejection) and two isentropic processes (compression and expansion).

Introduction / Context:
The Otto cycle is the standard air-standard model for spark-ignition (SI) engines. Knowing the exact sequence of idealized processes helps in deriving thermal efficiency, mean effective pressure, and the effects of compression ratio on performance.

Given Data / Assumptions:

• Air-standard assumptions (ideal gas with constant specific heats).
• Internally reversible processes (no friction or pressure losses).
• Heat addition and rejection are idealized to occur at constant volume.

Concept / Approach:

The four processes are: isentropic compression, constant-volume heat addition, isentropic expansion, and constant-volume heat rejection. This pairing (CV + isentropic) is distinctive and differentiates Otto from Diesel (which has constant-pressure addition) and from Dual cycles (mixed CP and CV addition).

Step-by-Step Solution:

Verification / Alternative check:

Typical p-v and T-s diagrams show vertical lines (CV) and adiabatic curves (isentropic) for the Otto cycle. Thermal efficiency derived from this sequence depends only on compression ratio and gamma, matching textbook results.

Why Other Options Are Wrong:

Constant-pressure segments belong to Diesel/Ericsson/Brayton; isothermal segments belong to Carnot/Stirling, not Otto. Mixed CP/CV with two isentropics describes the Dual cycle, not Otto.

Common Pitfalls:

Confusing real engine valve events with idealized heat-transfer steps; thinking isothermal appears in SI cycle models (it does not in Otto).

Final Answer:

two constant volume and two isentropic processes