This project was a multi-component effort to understand volatile contributions to particulate matter (PM) emitted from military aircraft engines. Volatile PM, formed when condensable gases emitted in the exhaust form new particles or add coatings to emitted soot particles, is getting increasing attention due to potential environmental and health effects, and is coming under increasing regulatory control. Military operations can be constrained if local air quality limits are exceeded. Improved understanding is sought of volatile PM and the factors that control its formation and evolution for these environmental reasons and for the potential impact on aircraft signatures.
This project was structured to have interplay between modeling and several experimental measurement efforts. The project was divided into four components, one focused on modeling and three focused on experimental explorations. Modeling work focused on the development of an advanced particle evolution model considering microphysics involving soot, sulfur, water, and condensable hydrocarbons (HC). Experimental work included a laboratory study on soot interaction with organic species, an oil emissions field study, and a combustor sector rig study of condensation on soot. Experimental and modeling efforts were integrated with experiments providing key parameters needed for model simulations and with model simulations aiding in the interpretation of experimental results.
An existing particle evolution model, which included soot and sulfur/water microphysics, was extended to include HC condensable species. The inclusion of a wide range of HC species and their capability to condense on soot surfaces was successfully finalized and the participation of HCs in forming new, volatile particles in concert with sulfuric acid and water was also completed. Upgrades to the microphysical code are complete and the upgraded code was applied in analyzing measurement data and planning of experiments. The extended microphysical model was used in helping to plan a series of laboratory studies. A key finding of the experiments carried out in the first year was the need to include a thermal denuder to remove HCs from the soot surface and make soot more representative of military aircraft engine soot. This was achieved and subsequent laboratory studies examined several key condensable HCs in a controlled environment, interacting with the stripped combustion generated soot particles. The coupling between the experimental data and experiment-model evaluation has been greatly improved.
In parallel with the laboratory studies, measurements were performed on operating engines to understand the role that lubrication oil has in contributing volatile HCs to the particle phase. The first measurements of their kind were performed in the project’s first year on the oil breather vent of several turbofans being operated at the manufacturing facility and at an 'endurance testing facility'. These results show that nanometer size particles are being vented from engines, and that their composition is the lube oil used in the turbofan engine lubrication system. In the second year, additional oil emissions measurements were performed on turbofans operated in endurance testing in which improved determination of the sample dilution by oxygen depletion allowed better quantification of the absolute emissions amounts. In the third year, a field study focusing on lubrication oil emissions from in-service commercial aircrafts was performed at Chicago Midway Airport and O’Hare International Airport. Lubrication oil was identified in the organic PM emissions from engine exhaust plumes. The contribution from lubrication oil to total PM organic ranges from 5% to 100%.
Accomplishments for the project have resulted in significant advances in understanding and in state-of-the-art-modeling tools, which will be documented in archival journal publications.