DUAL CYCLE

In the dual cycle, part of the heat is supplied at constant volume and the rest at constant pressure. This is also called mixed or limited pressure cycle. The p–v and T–s diagrams are shown in Fig. 9.10. The various processes are:

Process 1−2: Isentropic compression of air

Process 2−3: Constant volume heat addition

Process 3−4: Constant pressure heat addition

Process 4−5: Isentropic expansion of air

Process 5−1: Constant volume heat rejection

Considering 1 kg of working fluid,

Heat supplied, q_s = c_v (T₃ − T₂) + c_p (T₄ − T₃)

Heat rejected, q_r = c_v (T₅ − T₁)

Work done per cycle, w = q_s – q_r = c_v (T₃ – T₂) + c_p (T₄ – T₃) – c_v (T₅ – T₁)

Let,  = compression ratio

Then from process 1−2, we have

T₂ = T₁r^γ−1

From process 2 – 3, 

Figure 9.10 Dual cycle: (a) p-v diagram, (b) T-s diagram

From process 3 – 4, 

From process 4 – 5, 

The variation of thermal efficiency of dual cycle is shown in Fig. 9.11.

Mean effective pressure,

Now 

Figure 9.11 Variation of thermal efficiency of dual cycle with compression ratio