Question

Consider a 4-cylinder, 4-stroke square engine running on octane, CH18 (1) at an equivalence ratio of 0.8. The volumetric efficiency is measured as 90% at an ambient temperature and pressure of 25°C and 100 kPa, respectively. The engine produces 100 kW (brake) at 3000 rpm with a bsfc value of 290 g/kWh. a) What are the air and mass flow rates? b) What are the bore and stroke dimensions? c) Estimate the torque that this engine can produce at this operating condition.

Answer 1

Volumetric Effeeleney, y = 0.90 Giren: Four stroke Engine running on octanel(214) Number of cylinder, Equivalence Ratio, & = 0.8 n = 4 298K T= 25e P = 100 kPa. Brake power, BP = 100 kW. N=3000rpm. bsfc=290 g/kWh = 0.29 kg/kWh. solution :- a Mass flow rate of air, (ma): Since Octane (Catie is need as a fuel. The Combustion equation is given as follows, & 418 + 12.5 02 + 47N2 8 CO2 + H2O +47 Ny. The stopchiometric ass-fuel ratio can be obtained from the above equation, mass of air mass of fuel (12.5*32) + ( 47*28) 400t 1316 (12x8 + 1x 18) - (A/P etichiometric = 114 = 15.05 ( 9/7 odchiometrie We know that, equivalence Ratio, o (A/F) store@semitis (A/Factural d = 15.05 (A/Fact 15.05 Actual als fuel Ratio = =0.8 18.8125. 0.8 . Au fuel Ratio can also be given by. obsac bsal 18-8125 (A/F) aut = bsfc 0.290 bsac = 5.4556 kg/kWh. Mass flow rate of air, ina=bsac & BP ma = 5.455645 x loo 545.56 kg/hr Mass flow rate of air, ma- 545.56 kg/hr (0) ma=9.093 kg/min. b) Bore and stroke dimensions: Volume flow rate of air at intake Condition, va ma RT Р 9.093x287x 298 100 x 103 Va = 7.776 m/min. Swept volume per minute, Us = II d ² L x W x since the given engine is a square engine. Hence the Bore diameter and length should be equal L=d Ve = II d x x n = II d ² x 3000 x 4 The volumetric Efficiency is We also know that W = given as Mr = 901 va is is = 8. 641 m/min. va nu 7.776 0.9 8.641 Also, I d3x 3000x4 = 4 8.641 x 2 x 4 1.8336 x 103 d3 i こ TT X 4x 3000 d = 0. 1223m. = L Bore and stroke dimension d=L=0. 1223m (or 122.39 mm c) Torque Produced, We know that Brake Power, BP = QTINT bo BP xbo Torque, T= 100x10360 2TX 3000 QIN T 318.31 Nm. Torque produced by the engine T= 318.31 Nm