The air-standard Otto, Dual and Diesel cycles are drawn on common p-v and T-s diagrams for the same maximum pressure and maximum temperature, for the purpose of comparison.
Otto 1-2-3-4-1, Dual 1-2′-3′-3-4-1, Diesel 1-2″-3-4-1 (a).
Slope of constant volume lines on T-s diagram is higher than that of constant pressure lines
Here the otto cycle must be limited to a low compression ratio (r) to fulfill the condition that point 3 (same maximum pressure and temperature) is to be a common state for all the three cycles.
The construction of cycles on T-s diagram proves that for the given conditions the heat rejected is same for all the three cycles (area under process line 4-1). Since, by definition,
η = 1 – \(\cfrac{Heat ,rejected,Q_r}{Heat,supplied,Q_s}\) = 1 - \(\cfrac{const.}{Q_s}\)
the cycle, with greater heat addition will be more efficient. From the T-s diagram,
