DUAL CYCLE

For same compression ratio, Otto cycle is more efficient but delivers less power than the diesel cycle. Therefore, in dual cycle partly heat is added at constant volume and partly at constant pressure as shown in Figure 6.17.

Figure 6.17 ρ−V and T−s Diagrams for Dual Cycle  

Example 6.6: An air standard dual cycle has a compression ratio of 18 and compression starts at 0.1 MPa and 300 K. The maximum pressure is 8 MPa. The heat transferred to air at constant pressure is equal to that at constant volume. Determine (i) temperatures and pressures at the end points of all the processes, (ii) cycle efficiency, and (iii) mean effective pressure. C_p = 1.005 kJ/kg, C_v = 0.718kJ/kgK, γ_air = 1.4.

Solution:

Given: r_k =  = 18, P₁ = 0.1 MPa, T₁ = 300K, P₃ = P₄ = 8MPa, Q₁ = Q₂ where Q₁ is heat added at constant volume and Q₂ is heat added at constant pressure

Hence,