A cold air standard gas turbine engine with a thermal efficiency of 56.9 % has a minimum pressure of 100 kP a. Calculate the pressure at the inlet to the expansion process in the turbine. Enter your answer in kPa to one decimal place.
b. Calculate the thermal efficiency of a cold air standard Otto cycle engine with a compression ratio of 10.9. Enter your answer in percent with one decimal place.

a) 5.2 kPa

b) 49.3%

Explanation:

Given data:

Thermal efficiency ( л ) = 56.9% = 0.569

minimum pressure ( P1 ) = 100 kpa

a) Determine the pressure at inlet to expansion process

P2 = ?

r = 1.4

efficiency = 1 - [ 1 / (rp) ]

   0.569   = 1 - [ 1 / (rp)^0.4/1.4

1 - 0.569  = 1 / (rp)^0.285

∴ (rp)^0.285 = 0.431

rp = 0.0522

note : rp = P2 / P1

therefore P2 = rp * P1 = 0.0522 * 100 kpa

                                   = 5.2 kPa  

b) Thermal efficiency

Л = 1 - [ 1 / ( 10.9 )^0.285 ]

   = 0.493 = 49.3%