im now doing a test on modified trucks and buses using wind tunnel. i have reached upto the drag force and power calculations. now im searching a formula or any other way to calculate the fuel efficiency. or is there any other way to calculate fuel efficiency in relation with drag coefficient or drag force.

is this calculation correct? is there any other parameters to be included for calculating fuel consumption?

C = fuel consumption

V = velocity or speed along road

t = time for your trip

S = SFC, specific fuel consumption (varies with engine, temp, and load, but usually about 0.4lb/HP)

r = density of fuel, 5.8lb/gal for gasoline, maybe 6.5? lb/gal for diesel

P = power from engine

F = total resisting force

Fd = drag force

Fr = rolling resistance

W = truck weight

G = grade in % (-% for downhill)

A = frontal area of truck

Cd = drag coefficient

C = Dist/Fuel used

= V * t / {[P] * S * r * t)}

Time cancels out, top and bottom:

C = V / {[F * V] * S * r}

Force is drag force + rolling resistance + force to go uphill:

C = V/{[Fd+Fr+W*(G/(√(1+G²)) * V] * S *r}

Now, where rho is air density,

Fd = (A * Cd * rho) * V²