Additional exercise

Pagina 1

Assignments # 1. The fuel consumption map of a four-stroke SI engine (RON 95) is given. To determine the aerodynamic resistance force the following equation is given: • FL= cw · A · ρ/2 · v2 The vehicle is operated at windless conditions during steady-state conditions in plane. Additional road resistances can be neglected. The following parameters are specified: - Drag coefficient · frontal area: cw·A = 0.855 m2 - Engine swept volume VH = 2.0 l - Effective wheel diameter Ddyn = 0.6 m - Overall transmission ratio in 4th gear i4 = 3.5 - Propulsion efficiency in 4th / 5th gear η = 0.8 - Air density ρa = 1.16 kg/m3 a) Evaluate the running re sistance points in 4 th gear at the engine speeds n = 2000, 4000, 5500 rpm and plot these points in the attached map. b) Sketch the running resist ance curve of the 4 th gear, qualitatively. Determine the maximal achievable vehicle speed in 4th gear under the given conditions. c) What overall transmission ratio should the 5 th gear have, designed as overdrive gear, if the same vehicle speed as at 4000 rpm in 4 th gear is to be reached, but with a 10% reduced specific fuel cons umption. Calculate the resulting route related fuel consumption in l/100 km. d) When driving with maximum speed in 4 th gear the driver shifts up to 5 th gear (constant vehicle speed during shifting). Directly after shifting the driver continues maintaining the pedal fully de pressed. Display the following requested operating points in the engine map. 1) directly after shifting and 2) after reaching a steady-state driving condition in 5th gear. Engine speed [rpm] bmep [bar] bsfc [g/kWh] 600 300 280 260 250 400 280 300 400 600 1000 2000 3000 4000 5000 6000 0 2 4 6 8 10 12