Modeling of sulfur gases and chemiions in aircraft engines

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 H2SO4 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 C2H3O+ 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.