hjmin:

Look in your burner operation manual and find the manufacturer's name, phone number, and burner type.  Call them and ask them the same question.

With the sparse and meager basic data you give, we don't know the type of burner, the atomizing fluid, the manufacturer, year, application, etc., etc.   I hope you don't believe that all liquid fuel burners are the same and that there is one, solitary magic formula for calculating the combustion air pressure drop.  Most burners I've used have no combustion air "nozzle"; some burners aspirate the combustion air through induced draft - with little or nil pressure drop.

Now atomizing air, that's another story....