TEM analysis of gas turbine and diesel particles

David Kittelson

New regulations on emissions of non-volatile particle mass (nvPM) and non-volatile particle number (nvPN) from aircraft (gas turbine) engines are being developed. The work described here is part of a larger study of the response of instruments used to measure nvPM and nvPN from aircraft engines. It examines the range of particle structures and size expected from combustion sources using a transmission electron microscope (TEM) and compares sizing results with measurements made with a scanning mobility particle sizer (SMPS). Several particle sources have been examined: a gas turbine auxiliary powers unit (APU), two diesel engines, and an aircraft turbojet engine. Test were run using a variety of fuels, petroleum and bio based and blends. Particles were sampled onto TEM grids with an electrostatic precipitator. The role of semi-volatile material was examined by sampling with and without a catalytic stripper (CS).

A variety of particle sizes and shapes were observed. A new technology diesel engine and the APU produced the largest, highly aggregated structures, equivalent area diameter (EAD) ~ 100 nm, while the turbojet engine produced the smallest, less aggregated particles, EAD ~ 40 nm. Particles sampled from an old technology diesel engine without the CS were compact aggregates with uniform images showing little evidence of overlap, while with the CS, primary particles were smaller, and aggregates were more dendritic with less uniform images suggesting particle overlap. Fuel tests using the APU gave the largest aggregates and primary particles with Jet A and smallest with a 50% biofuel / Jet A blend. For the APU and the turbojet TEM EAD closely agreed with SMPS arithmetic mean diameter (AMD) but for the diesel engines AMD’s were usually larger.

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