Comparison of Otto, Diesel and Dual Cycles

The comparison of Otto, Diesel and Dual cycles can be made on the basis of compression ratio, maximum pressure, maximum temperature, heat input, work output etc.

(a) For same compression ratio and same heat input:
When compression ratio is kept constant process (1-2) remains the same for all the three cycles. But process (2-3), which shows the heat addition is different for those cycle. If same heat is transferred in all three cycles, the temperature attained is maximum for Otto cycle and minimum for Diesel cycle.

The work done during the cycle is proportional to the area inside the bounded region. The area is maximum for Otto cycle and minimum for Diesel cycle. Thus, for same heat input, efficiency of Otto cycle will be the maximum while that of Diesel cycle will be the minimum.

(b) For same maximum pressure and same heat input:
For the same maximum pressure 3.3’. and 3” must be on same pressure line and for the same heat input the area 2-3-a-d-2, 3’ -3’ –c-d-2 and 2”3”4” b – d – 2” should be equal. It is obvious from figure that heat rejected by otto cycle 1-4 – a – d – 1 is more than 1-5” – b – d – 1 and 1 – 4’ – c – d – 1.

Since     ∏_thermal = Q_s – Q_R / Q_s

The Diesel cycle is more efficient that Dual cycle, which in term is more efficient that Otto cycle.

(iii) For same pressure and temperature:
It is clear from the figure that the heat rejected by all three cycles, Otto, Diesel and Dual cycle remains the same (area 4-a – b - 1 - 4). But the heat supplied is

 

 different for all three cycles. Maximum heat is supplied during diesel cycle (area 2’-3-a-b-2’) and minimum for Otto cycle (area 2 – 3 – a – b - 2) while for Dual cycle it is in between the two (area 2’ – 3” – 3 – a – b – 2”)

since,      ∏_thermal = 1 – Heat rejected / Heat supplied

Hence, for the above conditions the Diesel cycle is more efficient than Dual cycle, which in turn is more efficient than Otto cycle.(Internet)