Study of particulate matter formation and evolution in near-field aircraft plumes using a one-dimensional microphysical model

Abstract

Environmental concerns have led to a growing effort to investigate and characterize the particulate matter (PM) emissions from aircraft engines. This thesis presents a one-dimensional microphysics and chemical kinetics model that is used to study the formation and evolution of particulate matter in near field aircraft plumes at ground level. The initial exhaust properties were obtained from engine data and plume mixing profiles were generated using FLUENT®. The initial gas species concentrations were estimated based on a two-step constrained equilibrium process. Parametric studies of the effects of ambient temperature, ambient relative humidity, engine operating conditions and engine design parameters on the aerosol formation were investigated using the one dimensional model following a centerline trajectory up to lkm downstream of the engine exit plane. PM formation and evolution characteristics along trajectories from several radial locations were also investigated and compared to the results from the centerline study. The results from this study show that binary homogeneous H2SO4-H20 nucleation strongly depends on ambient conditions such as ambient temperature and relative humidity whereas the condensational growth of soot particles is most dependent on engine power settings.

(cont.) For example, the nucleation mode sulfur emissions index varies from 0.01 mg/kg-fuel at 299 K and 80% relative humidity to 9 mg/kg-fuel for the same level of relative humidity at 288K. The nucleation mode sulfur Elm increased from 0.01 mg/kg-fuel at 10% relative humidity and 7% engine power setting to about 9 mg/kg-fuel at 80% relative humidity for the same power setting and ambient temperature. The amount of SvI condensed on soot particles changes from around 2 mg/kg-fuel to around 8 mg/kg-fuel as the engine power increases from 7% to 100% for the same 10% relative humidity. Engine design parameters such as engine bypass ratio as well as core and bypass total temperature also play important roles in both the homogenous nucleation and heterogeneous condensation processes in the plume. It was found that at 80% relative humidity and 100% power settinig, the'sulfur emission index increased from 1.8 mg/kg-fuel at the high BPR of 9 to a value of 2.5 mg/kg-fuel for the limiting case of zero BPR. The sulfur emission index for the nucleation mode increased from around 0.7 mg/kg-fuel at the higher core and bypass total temperature (15 K. above the CFM56-2C1 values) to 3.5 mg/kg-fuel at the lower temperature (15 K below the CFM56-2C 1 engine values).The study sheds light on the PM formation mechanisms in near field aircraft plumes and provides guidance on the improvement of future experimental measurement techniques.