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Ion Concentration in Gasoline and Diesel Engine Exhaust

Measurements of Ion Concentration in Gasoline and Diesel Engine Exhaust

  • Fangqun Yu, Atmospheric Sciences Research Center, State University of New York at Albany
  • Thomas Lanni, Brian P. Frank, Division of Air Resources, New York State Department of Environmental Conservation

Summary

The nanoparticles formed in motor vehicle exhaust have received increasing attention due to their potential adverse health effects. It has been recently proposed that combustion-generated ions may play a critical role in the formation of these volatile nanoparticles. In this paper, we design an experiment to measure the total ion concentration in motor vehicle engine exhaust, and report some preliminary measurements in the exhaust of a gasoline engine (K-car) and a diesel engine (diesel generator). Under the experimental set-up reported in this study and for the specific engines used, the total ion concentration is ca. 3.3×106 cm-3 with almost all of the ions smaller than 3 nm in the gasoline engine exhaust, and is above 2.7×108 cm-3 with most of the ions larger than 3 nm in the diesel engine exhaust. This difference in the measured ion properties is interpreted as a result of the different residence times of exhaust inside the tailpipe/connecting pipe and the different concentrations of soot particles in the exhaust. The measured ion concentrations appear to be within the ranges predicted by a theoretical model describing the evolution of ions inside a pipe.

Graph of measured and calculated tailpipe ion concentrations vs. exhaust age

Theoretically calculated evolution of total ion concentrations inside the tailpipe or connecting pipe at two different ion-ion recombination coefficients (Kr = 2×10-7, 1×10-8 cm3 s-1) and four ion loss time constants (t = 0.05, 0.2, 1.0, 5.0 s). The observed ion concentrations in the exhaust of the K-car (U<250 V) and the diesel generator (U=250 V and U=2900 V) are also indicated. The initial total ion concentration at the end of expansion stroke (~ 0.01 s exhaust age) is assumed to be 2×109 cm-3

The complete manuscript is published in Atmospheric Environment, 2004, 38, 1417-1423.