Generation and characterisation of reactive and inert aerosols
FILTECH 2019 - The Filtration Event
J. Thieringer, H. Werling, J. Meyer, A. Dittler
Particle filters, such as diesel or gasoline particle filters (DPF/GPF), are applied to reduce emissions of combustion engines and have become a standard component in many exhaust aftertreatment systems. The emission standards regarding PM (particulate matter) and PN (particulate number) concentrations are getting stricter hence a better understanding is essential for the further optimisation of the exhaust treatment. Due to particle deposition and the resulting layer formation in the filters, the pressure drop and energy consumption increase during operation. In order to reduce the influence of particle deposition and resulting particle layer on operating conditions, various process parameters and their effects on the filtration process of reactive-inert particle systems have to be known.
In order to investigate the operational behaviour of wand-flow-filters, test aerosols are used to characterise the formation of particle layers and to determine structural layer changes due to break-up and rearrangement of deposited particulate matter. Due to the variety of reactive and inert aerosols, various particle size distributions (PSD) and morphologies need to be identified and have to be replicated. For the generation of aerosols, consisting of reactive and inert particles, two different generation methods are used to produce different compositions of aerosols. The inert particles (ash) are generated with an oil-mist and a subsequent thermal conversion. The process para- meters, oil and oven temperature, are varied. The method for the generation of reactive particles (soot) is based on a soot generator where soot is formed with propane and a subsequent diffusion flame pyrolysis. In this process, stable operating points for the reactive particles were measured.
The properties of the inert aerosol, such as particle size and concentration, depend on the process parameters and are analysed with SMPS and OPC measurements. The PSD is adjusted by oil and oven temperature. With an increase of oven temperature and decrease of oil temperature, the PSD shifts in the fine fraction (10 - 200 nm) to smaller particle diameters. The appearance of inert and reactive particles are visualised with SEM-images. The soot generator produces replicable reactive particles with constant particle diameters that are been analysed and controlled with SMPS measurements.