Question

As compared to air standard cycle, in actual working, the effect of variation in specific heats is to ______________

(a) increase maximum pressure and maximum temperature

(b) decrease maximum pressure and maximum temperature

(c) increase maximum pressure and decrease maximum temperature

(d) decrease maximum pressure and increase maximum temperature

I had been asked this question at a job interview.

My question comes from Engine Efficiencies in section Measurements and Testing/Performance Parameters and Characteristics of IC Engine

Answer 1

The correct answer is:

(a) increase maximum pressure and maximum temperature

In actual working conditions, the specific heats of the working fluid (such as air or a fuel-air mixture) vary with temperature. This variation leads to a higher maximum pressure and maximum temperature compared to the idealized air standard cycle (like the Otto or Diesel cycle), where specific heats are assumed to be constant. This is due to the real thermodynamic processes and properties of the engine's operating medium, which result in greater energy being absorbed and released, thus increasing pressure and temperature.