Air-standard cycles – alternate name for the Otto cycle In air-standard analysis, the Otto cycle (modeling spark-ignition engines) is also referred to as which of the following?

Introduction / Context:
Air-standard cycles simplify internal combustion engine analysis by modeling heat addition and rejection as idealized processes. The Otto cycle is the canonical model for spark-ignition (SI) engines such as gasoline engines. Knowing its alternate descriptive name helps connect PV-diagram intuition with thermodynamic process labels.

Given Data / Assumptions:

• Air-standard assumptions: working fluid is air with constant properties; combustion and exhaust are replaced by heat addition/removal.
• Compression and expansion are isentropic (adiabatic and reversible).
• Heat addition and heat rejection occur as idealized processes at either constant volume or constant pressure depending on the cycle.

Concept / Approach:

In the Otto cycle, heat addition occurs at constant volume (between the end of isentropic compression and the start of isentropic expansion), and heat rejection also occurs at constant volume. Therefore, the Otto cycle is often called the “constant volume cycle.” By contrast, the Diesel cycle features heat addition at constant pressure (“constant pressure cycle”), and the Brayton cycle has heat addition at (approximately) constant pressure in open systems like gas turbines (with different compression/expansion devices).

Step-by-Step Solution:

Verification / Alternative check:

PV and TS diagrams for the Otto cycle show vertical heat-addition and heat-rejection lines on the PV diagram (volume fixed), confirming the constant-volume characterization.

Why Other Options Are Wrong:

Constant pressure cycle: Describes the Diesel cycle, not Otto.Constant temperature or constant enthalpy cycle: Not standard labels for reciprocating-engine cycles.Constant temperature and pressure: Physically inconsistent for finite heat addition in a closed cycle.

Common Pitfalls:

Confusing Otto and Diesel cycles due to real-engine combustion phasing; in the air-standard idealization, the distinction is strictly about the constraint during heat addition.

Final Answer:

constant volume cycle