Question

(12 points) An ideal Otto cycle operates with a compression ratio of 10. At the beginning of the compression process, the air is at 101 kPa and 27°C. During the constant volume heat addition process, 790 kJ/kg of heat is transferred to the air. Accounting for variable specific heats with temperature, determine: the maximum temperature during the cycle 1266.862 °C the maximum pressure during the cycle 6239.424 kPa the specific net work output 475.495481 kJ/kg the mean effective pressure (MEP) for the cycle kPa the thermal efficiency 60.189281 % What is the thermal efficiency of this Otto cycle if we use the cold-air standard assumption?

Answer 1

given at 1 T= 27'2- P= Jook Pa 3001 t vilo - Compi ratto tat 1 Ti = 300, Now Usiy ideal gas property Chart ) luble for air. h,= 300.19 A 4 Now Vy, a 62112 Very V at 1: B-101 ICRA, TE 30 K usin Pe=RT . (v in mhes) 10 Tolx = 0.287 x 360 a = 0.8525 m Ivy: 62.12 | :. Ten 73014 The 745.62 lei + V D =10 Ve=0lv, - Swept volume Vs VV Vs- V-010, Vs = 0'90, 1 790- The h-745.42 1535.62 kg T3= 1417K ITs - 1144°C J + Vq = Ug = 0,10 = 0.18 0:0525 01085 25 m Tman

:.6131 4 Whet Vs Prean Tz=14171 Tma) Vz= 0.08525 m/ ¢ Pz = Pmay 143194 - 0.90, x Rmean 431.94 = 0.98 0.8525 x P mean PV = RT3 Prmane x 0:00S 15 = . Pmean = 562-97 Kg 0.2870 1417 I Pmax = 4770.567 kPa 1 Heat Rejected heat added Chy-hi ) Smo Thy ha) 58.25 -30:19) Vory 790 4 at 3? Vr: 8.5885 Vry . To soil Vry= Lovrs Vry = 85.885) shq = 658.25 ks | THE 648.5k? Ima 0,54676 Mma 54.676% for Cold air anomphing, Yma ("? Net Work and pr. Weet = Heat added – Heat Rejected (hy he ) = (ha-hi) Whele (790) – (658, 25 – 3019) Weet a 431.34 ks Wheres 1210 rhy 11 -4-1 S. 16) Ime 0: 601 89 mm 60-189 %