Diesel Engine Theoretical Efficiency

Air standard diesel engine cycle

Since the compression and power strokes of this idealized cycle are adiabatic, the efficiency can be calculated from the constant pressure and constant volume processes. The input and output energies and the efficiency can be calculated from the temperatures and specific heats: It is convenient to express this efficiency in terms of the compression ratio rC = V1/V2 and the expansion ratio rE = V1/V3.

The efficiency can be expressed in terms of the specific heats and temperatures.

Now using the ideal gas law PV=nRT and g= C_P/C_V, this can be written

Now using the fact that V_a=V_d=V₁ and P_c=P_b from the diagram

Dividing the numerator and denominator by V₁P_c

Now making use of the adiabatic condition PV^g = constant,

the efficiency can be written

Calculation