- #1

marellasunny

- 255

- 3

From Heywood,E2.11

You are designing a 4 stroke CI to provide a brake power of 300kW,Naturally aspirated at its max rated speed.Based on typical values for brake mean eff.pressure(bmep){700kPa to 900kPa} and max mean piston speed,estimate the required engine displacement,and the bore and stroke for sensible cylinder geometry and number of engine cylinders. What is the maximum rated engine speed(rpm) for your design? What would be the brake torque and the fuel flow rate(g/h) at this max speed?Assume a max mean piston speed 12 m/s is typical of good engine designs.

I use the usual equations which relate bmep to max power(i.e max rpm) and bmep to max torque(i.e max bmep)

bmep=Pb(max)∗nR∗10^3/Vd∗N(max) ; nR=2 for 4 strokes

bmep(max)=6.28∗nR∗T(max)/Vd

where, Vd is the displacement volume=number of cylinders*3.14/4*B^2*L

where B-bore,L-stroke

**The problem I have is that once I have found the bore dimension,I have no other way of finding the stroke length i.e I just have to assume the stroke=bore and continue the problem. To solve for fuel flow rate,I have to assume that the sfc for NA diesels is usually 200(g/kWh)**