prticle emissions from a turbo-charged diesel off-road engine were hcaracterized with DMA+CNC and electron microscopy for comparison of differetn sampling and dilutiion systems.Four differetn samplign methods were used:(1) two ejector diluters,(2) partial flow and ejector diluter,(3) porous tube and ejector diluter,and (4) porous tube diluter.Number size distributions for partial flow an dejector dilution hadmodes at 25-30 nm and at 45-50 nm independent of the dilution ratio.The modej at 25-30 nm indicated nucleation durign dilution in these experiments and was clearly most significant for the partial flowj and ejector diluter exhaust gas,sample line,and partial flow diluter and cold dilution air.Forj other dilution systems the main mode was at 45 nm and indications of a model at 15-20 nm were observed dependin gon the dilution ratio.Especially for the porous tube diluter,the main mechanism for particlej growth was condensation on the surfaces of the existing particles.According to this study thebest dilution system for obtaining a number size distribution without any significant nucleation effects was the porous tube dilution setup.
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