For Maximum Specific Output of a Constant Volume Cycle (Otto Cycle)

Question:

For maximum specific output of a constant volume cycle (Otto cycle):

a) The working fluid should be air
b) The speed should be high
c) Suction temperature should be high ✅
d) Temperature of working fluid at the end of compression and expansion should be equal

Correct Answer: (c) Suction temperature should be high

Explanation:

The Otto cycle is the ideal cycle for spark ignition (petrol) engines.
Specific output means the power produced per unit engine displacement.

• When the suction temperature increases, the temperature after compression also increases.

• This raises the pressure after combustion, leading to higher mean effective pressure (MEP) and more work output per cycle.

Why not the other options?

• (a) – The cycle already assumes air as the working fluid; it does not affect maximum specific output.

• (b) – Higher engine speed can increase total power but does not directly maximize specific output for a given displacement.

• (d) – Equal temperatures at the end of compression and expansion are unrealistic and not linked to maximum output.