Question

An Air standard otto cycle has a compression ratio of 8. At the start of compression process the temperature is 26ºC and the pressure is 1 bar. If the maximum temperature of the cycle is 1080K. Calculate 

(1) Net out put 

(2) Thermal efficiency. Take C_V = 0.718

Answer 1

Compression Ratio (R_c ) = 8

T₁ =26°C = 26 + 273 = 299K = 1 bar

T₃ =1080 k

(i) Net output = work done per kg of air

Process (1 – 2) Isentropic compression process 

Process (1 – 2) Isentropic compression process

Net output = work done per kg of air = ∮δw

∮∫ = C_v (T₃ – T₂) – C_v (T₄ – T₁)

= 0.718 (1080 – 686.92) – 0.718 (471.62 – 299)

= 0.718 × 393.08 – 0.718 × 172.62 = 282.23 – 123.94

Net Output = 158.28 KJ/Kg

η thermal =56.08%