Production of sulfate aerosol precursors in the turbine and exhaust nozzle of an aircraft engine

Recent in-flight measurements of aircraft engine exhaust have suggested much higher conversions of fuel sulfur to sulfuric acid aerosols than can be explained by gasphase oxidation within the exhaust plume. This paper describes the effects of turbine and exhaust nozzle aerodynamics and chemical kinetics on the production of sulfate aerosol precursors in engine exhaust. Results from both one-dimensional (1-D) and two-dimensional (2-D) numerical simulations are presented for a range of flow and chemistry conditions. One-dimensional calculations for the entire postcombustor flow path of an advanced subsonic engine resulted in up to 6.3% sulfur oxidation through the turbine and exhaust nozzle. Results were most sensitive to species concentrations at the combustor exit, combustor exit temperature, and cooling flow mass addition in the turbine. Two-dimensional calculations for a representative turbine demonstrated that intraengine fluid mechanics can increase sulfur oxidation by a factor of 3 across a single blade row because of cooling-induced temperature nonuniformities. Comparisons of averaged 2-D results with 1-D simulations of the same blade row further showed that while 1-D simulations produce the correct trends, the magnitude of change in sulfur oxidation may be underpredicted by as much as 47% over a single blade row if spatial nonuniformities in flow field temperature are not included.