Basic Mechanical Engineering (3110006)

Question-3b-OR

BE | Semester-1 Summer-2019 | 04-06-2023

Q3) (b)

A comparison of the cycles (Otto, Diesel and Dual) on the p-v and T-s diagrams for the same compression ratio and heat supplied is shown in the Figure.
We know that, $η = 1 - \frac{Heat rejected}{Heat supplied}$
Since all the cycles reject their heat at the same specific volume, process line from state 4 to 1, the quantity of heat rejected from each cycle is represented by the appropriate area under the line 4 to 1 on the T-s diagram.
It is seen from the T-s diagram for the same heat input, the heat rejection in Otto is minimum and heat rejection in Diesel cycle is maximum. Consequently, Otto cycle has the highest work output and efficiency. Diesel cycle has the least efficiency.
It is the evident from the above equation that the cycle which has the least heat rejected will have the highest efficiency.
Thus, the efficiency of Otto cycle is greater than that of Diesel cycle for the same compression ratio.