From a large number of experimental data, an equation was developed for prediction of the smoke number as measured in gas turbine exhaust according to the well established SAE standard. Two different scales of combustors were used with inlet temperatures and pressures ranging from 300 to 600 K and from 0,1 to 0,9 MPa respectively. The formulation is based on the residence time which is calculated from the mass flow rate, density and volume of the primary and secondary zones of the combustor. The reaction rate has an Arrhenius form with the global equivalence ratio to account for the air and fuel flow rates. All these parameters can be evaluated from desired operating conditions. Nineteen different types of fuel were used varying from a paraffinic mixture to a pure aromatic compound. The fuel is characterized by its calorific value and hydrogen mass fraction.
With the wide range of fuels burned in the experiment giving a smoke number variation from 0 to 100, the accuracy of the equation (Standard Deviation of 40%) is acceptable for most purposes. The formulation should be particularly useful in assessing the efficiency of new systems for smoke reduction or in calculating the smoke number from older experimental data where it was not measured.