A Review on the Morphological Properties of Non-volatile Particulate Matter Emissions from Aircraft Turbine Engines

Accurate assessment and effective mitigation of the impacts of non-volatile Particulate Matter (nvPM) emissions from aircraft turbine engines require a detailed understanding of its morphological properties. This review summarizes the state of knowledge for the key morphological properties of nvPM emitted from aircraft turbine engines, i.e., aggregate structure, primary particle size, aggregate size and size distribution, effective density, mass mobility exponent, and internal structure. The morphological data for nvPM emitted from 20 different types of thrust producing and non-thrust producing aircraft turbine engines reported in the literature is reviewed. The objective of this review is to support the improvement of measurement techniques and inform the development of evidence-based regulatory standards for nvPM emitted from aircraft turbine engines. The impacts of sampling configuration and protocols, particle line-loss correction methods, measurement instruments, fuel composition, engine power setting, and engine type on the measured morphological properties are discussed. The relationships between various properties are examined and areas requiring further research are identified. Some of the major trends observed in the data are as follows: The nvPM emitted from aircraft turbine engines is composed of branched-chain fractal aggregates of multiple primary particles. The structure of aggregates, characterized by fractal dimension and mass-mobility exponent, depends on engine power setting. Primary particle diameter, aggregate diameter, and effective density generally increase with engine power setting. The use of alternative aviation fuels reduces the size and increases the effective density of nvPM. Correlations between morphological properties and engine characteristics are less consistent for non-thrust producing engines. There is inconsistency in the literature for the reported variation of nvPM internal structure with engine power settings.