Modeling of particulate matter creation and evolution in aircraft engines, plumes and particle sampling systems

Abstract

Environmental and health concerns have recently led to growing efforts to characterize the exhaust gas composition of aircraft engines. Besides major chemical species (N₂, 0₂, C0₂ and H₂0), aircraft engines also emit other species in much lower concentrations but that may also have significant impacts. Particulate Matter (PM) belongs to this category. This thesis presents a model of the microphysical processes leading to the creation of PM and its subsequent interactions with gas phase chemical species in thermodynamic environments typical of aircraft engines and exhaust plumes at ground level. The effects of the turbine and nozzle of an engine on non-volatile PM emissions are addressed first. Results suggest that limited opportunities exist for the modification of the microphysical properties of the non-volatile PM in these environments, leading to the conclusion that the characteristics of the turbine and nozzle of an aircraft engine have little or no influence on aircraft non-volatile emissions. The analysis is then extended downstream to the case of a plume at ground level. Direct comparisons are made to volatile PM measurements obtained from a recent test (APEX). Time-scale arguments are used to suggest that gas to particle conversion at ground level temperatures is a process too slow for volatile particles to exist before the plume reaches the sampling system and thus little if no modification of the PM characteristics should be measured. However, the residence times and temperatures within the sampling system used in APEX are such that significant modification of the PM characteristics within the sampling system is expected.

(cont.) Recommendations to improve the measuring techniques at ground level include lowering the residence time of gas samples inside the sampling system to avoid too large a modification of the flow microphysical characteristics before it reaches the measuring instruments, and careful monitoring of the temperature of the sample throughout the probe and sampling line.