Question

1. Air standard dual cycle. Compression starts with in-cylinder conditions of T = 20°C and P = 85 kPa. The compression ratio is 18. The cut-off ratio  is 1.46. The pressure ratio  is 2.60.

a) Determine the total specific heat addition [kJ/kg, 3].

b) Determine the total heat rejection [kJ/kg. 3].

c) Determine the net work of the cycle [kJ/kg, 3].

d) Determine the indicated thermal efficiency [unitless, 3].

e) What fraction of the fuel burned under constant volume conditions? Assume that all of the fuel is present at the start of combustion (that is, neglect the fact that the mass is constantly changing due to fuel injection). Also, assume that the combustion efficiency is the same during constant-volume and constant-pressure combustion.

Answer 1

In this question we will first draw the PV Diagram and T S Diagram and take its help and help of thermodynamic equations to find out parameters at different points. This will help us at arriving at the answer.

We have found out the Value of efficiency as approximately 31 % which is accurate. However it is smaller than expected as pressure ratio (2.6) is very high.

Note : I have solved it using Cv =0.7 KJ/KgK. You can use Cv=0.718 Kg/KgK if you want.

Hope you like my solution and give me a ??. Happy Chegging.