Thanks. I already found the solution. This was exactly what I did.

@MichaelBrown I know a kg is 2.2 lbs. That's why there is a 2.2 in the numerator for a kg in the denominator which is afterwards converted to newton and a 2.2 in the denominator for the kg in the numerator. $1lbs=1/2.2kg$

@MichaelBrown first the reason the lbs falls out is because the use of the same unit for mass and force in the imperial system. If you use kg-force instead of newton it will also fall out and leave only the second. Do you really think you could express the SFC in hertz. This is why the metric system is much clearer, it prevents these confusions. If you want just split the lbs-force in mass and acceleration. You will come to the same.