Modeling of Sulfur Gases and Chemiions in Aircraft Engines

Kurzfassung

The formation of sulfur-containing gases and chemiions in the combustor and their evolution in the turbine of aircraft-engines between combustor exit and engine exit are computed including the conversion fraction of fuel sulfur into SO₃ and H₂SO₄. The combustion is approximated by an adiabatic time-dependent box-model. The temperature and pressure evolution in the flow between combustor exit and engine exit is modeled using a quasi one-dimensional (Q1D) model. New kinetic models for S-containing gases and chemiions are used. About 1% of the sulfur molecules are computed to be converted into SO₃ within the combustor and about 10% into SO₃ and ₂SO₄ before engine exit. Box models agree with the Q1D results for the same initial and thermodynamic conditions, but underestimate sulfur conversion by a factor of 3 if using a linear temperature profile. The number of positive and negative ions formed within the combustor, mainly NO⁺ and HSO₄^-, , depends strongly on the fuel/air ratio and on recombination reactions, mainly with ₂H₃O⁺ ions. The model computes a total ion emission of 2·10¹⁵ per kg of fuel burned at cruise. Far larger ion concentrations close to values observed behind engines at ground, are computed for higher combustor inlet pressure and higher fuel/air ratio.