Question

what is diagram efficiency in otto cycle

Answer 1

An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical spark ignition reciprocating piston engine,[1] the thermodynamic cycle most commonly found in automobile engines.



Pressure-Volume diagram


Temperature-Entropy diagram
The idealized diagrams of a four-stroke Otto cycle Both diagrams:
the intake (A) stroke is performed by an isobaric expansion, followed by an adiabatic compression (B) stroke. Through the combustion of fuel, heat is added in an isochoric process, followed by an adiabatic expansion process, characterizing the power (C) stroke. The cycle is closed by the exhaust (D) stroke, characterized by isochoric cooling and isobaric compression processes.
The Otto cycle is constructed out of:

Top and bottom of the loop: a pair of quasi-parallel adiabatic processes
Left and right sides of the loop: a pair of parallel isochoric processes.
http://en.wikipedia.org/wiki/Otto_cycle

Answer 2

The efficiency of Otto cycle can be found by using following formula...
\[\eta =1-\left(\begin{matrix}Hrejected \\ Hsupplied\end{matrix}\right)\]
Here I attach the efficiency diagram of Otto Cycle drawn with reference of Compression ratio and Ideal efficiency