The objective of this work was to study the formation and evolutionary characteristics of aerosols, originating from the exhaust plume of a diesel engine operating in a ventilated mine tunnel. To extract these characteristics, precise cross-sectional scalar exhaust maps of CO₂, temperature, and aerosol concentration were generated and used to track the time averaged axial development of the plume. These maps were then used to position aerosol size distribution samples within critical regions of the plume. This approach was found to provide an efficient and thorough record of aerosol formation and evolution, as a result of naturally dispersed diesel exhaust in mine environments.

A diesel exhaust plume is made up of a complex spatial and temporally dependent array of various exhaust constituents. The state (i.e. temperature and partial pressures) of these constituents, as they travel through space, will depend on the nature of the plume and its environment. Laboratory studies usually simulate plume processes through sudden fully mixed systems. However, this approach compromises the complex path dependent processes present within natural plumes. This discrepancy can significantly affect the trends reported for the generation and transformation of diesel exhaust aerosols, which are dependent to a large extent on fuel sulfur level, temperature, species’ partial pressures, residence time, and dilution ratio. Some studies have been performed which preserve the natural evolution of the plume (i.e. vehicle chasing), but only demonstrate crude spatial development through the collection of relatively coarse and imprecisely positioned samples. As such, vehicle chasing studies result in relatively primitive descriptions of the formation and evolution of diesel exhaust aerosols. Consequently the following study was designed to efficiently extract detailed relationships that exist between the aerosols and other variables of a naturally occurring exhaust plume.

During this study, a digital three-axis probe placement device was developed and used to position time averaged exhaust samples precisely throughout the plume. Mapping software was also created and interfaced with the device, allowing a continued awareness of the relative probe positions with respect to the emerging plume. Scalar exhaust maps were extracted through the use of a NDIR CO₂ analyzer, K-type thermocouple, and a handheld TSI CPC3007 particle counter. These maps were used to strategically position aerosol size distribution samples measured by a TSI Scanning Mobility Particle Sizer (SMPS). This approach was employed to save time without incurring any losses in the quality of trends found from aerosol size distribution samples.

The results of this study reveal the intricate 3-dimensional paths traveled by developing aerosols under natural mixing. These paths are marked by continually changing exhaust states known to affect aerosol evolution. As such, spatial trends observed in aerosol data were found highly diverse over distances spanning as little as a few inches. These trends showed growth in the nuclei mode at distances as far as 20 feet from the exhaust source. Beyond 20 feet, the nuclei mode experienced considerable losses nearing 1 order of magnitude at a distance of ∼200 feet from the exhaust source. In spite of this loss, the accumulation mode was found virtually unaffected throughout the entire 200 foot test region of the tunnel.