EFFECTS OF WATER CONDENSATION AND EVAPORATION ON DIESEL CHAIN-AGGLOMERATE MORPHOLOGY

Diesel engines emit chain-agglomerate particles that can serve as clou d condensation nuclei. This research uses an Environment Scanning Elec tron Microscope (ESEM) to study the effect of cloud processing on morp hologies of individual diesel chain-agglomerates. Particles produced u sing a Caterpillar 3304 diesel engine from fuels with sulfur contents of 0.84%, 0.32% and 0.034% by weight were collected on silicon wafer s ubstrates. They were subjected to one to three water condensation-evap oration cycles in the ESEM. This process was recorded on video tape, a nd digitized images of individual particles were used to find the part icles fractal dimension before and after each condensation-evaporation cycle. Significant collapse occurred in particles generated from both the mid-range sulfur fuel (0.32% S) and the low sulfur fuel (0.034% S ). The average fractal dimension of the particle images increased from 1.56 to 1.76 and from 1.40 to 1.54 for particles from low and mid-ran ge sulfur fuel, respectively. We observed no significant morphological change in particles from high sulfur fuels. The experiments reflect l ower limits for the degree of collapse that diesel chain-agglomerate p articles undergo during atmospheric cloud processing.