Otto Cycle: Understanding the Constant Volume Cycle

The Otto cycle is a fundamental thermodynamic cycle that describes the workings of a spark-ignition internal combustion engine, commonly found in gasoline cars.

It is also widely referred to as the constant volume cycle. This name comes from the key processes within the ideal Otto cycle where heat is assumed to be added and rejected instantaneously.

• Heat Addition: In the ideal Otto cycle, the combustion process (adding heat to the system) is modeled as occurring rapidly while the volume remains constant.
• Heat Rejection: Similarly, the exhaust process (removing heat from the system) is idealized as happening instantaneously at constant volume.

These two processes, occurring at constant volume, are characteristic features that give the cycle its alternative name.

Why Other Options Are Incorrect

• Constant Pressure Cycle: This type of cycle is more representative of the Diesel cycle or Dual cycle, where heat addition occurs partly or wholly at constant pressure, not the Otto cycle.
• Constant Temperature Cycle: Cycles involving constant temperature processes (isothermal processes) are different and not characteristic of the basic Otto cycle, which involves significant temperature changes during compression and expansion.
• Constant Temperature and Pressure Cycle: This combination does not describe the primary processes of the Otto cycle.

Therefore, the most appropriate alternative name for the Otto cycle, based on its idealised heat transfer processes, is the constant volume cycle.