Question

Which of the following processes is/are used for heat addition in an air-standard dual cycle?

• A. Isochoric
• B. Isobaric
• C. Isentropic
• D. Isothermal

Hint:

Think about the two-stage heat addition in a dual cycle, one part at fixed volume and one at fixed pressure.

Answer 1

The Correct Option is A, B

The air standard dual cycle is built to model a real diesel engine better than the plain Otto or Diesel cycle. It has two heat addition stages instead of one, and this question checks if you remember what those two stages are.

1. Isochoric: correct. After isentropic compression, the cycle first adds heat at constant volume, so pressure jumps up sharply while volume stays fixed. This is the same idea as the Otto cycle part of the dual cycle.
2. Isobaric: correct. Once the peak pressure is reached, the rest of the heat is added at constant pressure, so the gas expands while pressure stays fixed. This is the Diesel cycle part of the dual cycle.
3. Isentropic: wrong. The two isentropic legs of the dual cycle are the compression and the expansion strokes, and no heat crosses the boundary during either of them by definition.
4. Isothermal: wrong. A dual cycle has no constant temperature process at all, that process belongs to cycles like the Carnot or Stirling cycle, not the dual cycle.

So heat addition in the dual cycle happens in two parts, first at constant volume and then at constant pressure, which makes options A and B correct.