Test: Air Standard Cycle of IC Engine - 2 - Mechanical Engineering MCQ

Mean effective pressure (mep) of Otto cycle: Let clearance volume be unity 

Work done - area of the P-V'diagram

Hence mean effective pressure is directly proportional to pressure ratio (α) i.e., P₁/P₂

As compression ratio increases, the thermal efficiency of cycle increases and for the same heat input workout put increases.

Air standard efficiency of Otto cycle

Hence thermal efficiency or air standard efficiency of Otto cycle is proportional to the compression ratio.

Thermale fficiency of an Ottocycle is proportional to the compression ratio only and increase in compression leads the higher thermal efficiency and for same heat input higher workout put. Hence increase in mean effective pressure.

With increase in heat addition for same power output efficiency of diesel engine decrease but with increase in cutoff ratio thermal efficiency decreases.

Correct answer is A. mep will be greater with increase in r_p and decrease in r_c

Otto cycle => 1-2-3-4
Diesel cycle =>1-2-3'-4'
Dual cycle => 1-2-2"-3"-4"-1 

All the cycles starts from the same initial state 1 and the air is reversible adiabatically compresed to state 2, as the compression ratio is same. For the same compression ratio and heat input, minimum heat is rejected in the Otto cycle arid the maximum heat is rejected in the Diesel cycle. Consequently, the Otto cycle has largest work area hence highest efficiency, the Diesel cycle has least efficiency, the Dual cycle having efficiency between these two.
Hence

For the same compression ratio and heat rejection, heat supplied is more in Otto cycle and hence it will be more efficient than Diesel and Dual will be in between these two.
Hence