I think the problem may be and error in the ln(D) terms.
The correct equations should be
Equation 2=exp(-2.289 + (2.649 ln(D)) – (0.021*(lnD)^2))
Equation 3= (d*exp(-1.499+(2.148*ln(D)) + (0.207*(lnD)^2 - (0.0281*(lnD)^3))*0.001
It is (lnD)^2, not ln(D^2)
It is (lnD)^3, not ln(D^3)
This is to say you take the ln of D FIRST, then you square or cube. Try this out and see if the numbers make more sense.