Comparison of Water and Butanol Based CPCs for Examining Diesel Combustion Aerosols

The introduction of condensation particle counters (CPCs) utilizing water as the condensing fluid provides an alternative to traditional butanol based CPCs. Previous evaluations, using atmospheric and laboratory test aerosols, have verified performance. This study compares the performance of multiple water and butanol based CPC models using a diesel engine exhaust challenge aerosol. A total of 5 CPCs used in a scanning mobility particle sizer (SMPS) configuration were compared. TSI models 3786, and 3782 use water as the condensing fluid while models 3010, 3025A, and 3775 use butanol. The test aerosol was generated by a turbocharged, direct injection diesel engine running at constant speed and load, with two fuels, a low sulfur diesel and 99% soy methyl ester biodiesel fuel. Tests were conducted using a single SMPS platform and switching CPCs for each set of tests. In addition, the tests were repeated with long and nano differential mobility analyzer (DMA) columns. Four of the five CPCs agreed well, giving a standard deviation of the overall average geometric mean diameter of less than 1 nm between the 4 CPCs. The fifth CPC, TSI model 3782 did not agree well with the others. The cause of this disagreement is thought stem in part from the use of water as a condensing fluid, but primarily from a lack of sheath air in the 3782 design. The performance of the TSI 3786, an ultrafine water-based CPC with sheath flow showed far better agreement with the butanol CPCs throughout most mobility diameters.

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