Question
An air standard Otto cycle has thermal efficiency of 0.5 and the mean effective pressure of the cycle is 1000 kPa. For air, assume specific heat ratio γ = 1.4 and specific gas constant R =0.287 kl/kg-K. If the pressure and temperature at the beginning of the compression stroke are 100 kPa and 300 K, respectively, then the specific net work output of the cycle is ---------- kJ/kg (round off to two decimal places).
Answer :
As per given data,
ηotto = 0.5
v1 = RT1/P1 = 0.287•300/100 = 0.861 m³/kg
ηotto = 1 - 1/(r)γ-1
0.5 = 1- 1/(r)γ-1
r0.4= 2
r = 5.65
v1/v2 = 5.65
v2 = 0.861/5.65
v2 = 0.1524 m³/kg
Specific work output = Pmep × vS
= 1000kPa•(v1-v2 )
= 1000•(0.861 - 0.1542)
= 708.6 kJ/kg
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