Non-reactive Working Fluids for Reliably Sensing Nanoparticles in Automotive Exhaust Gases

Nanoparticles in the exhausts of automotive internal combustion engines are routinely measured using condensation nuclei counting (CNC) sensors. Traditionally, n-butanol is used as working fluid for sensing combustion aerosols. However, when used on combustion engines burning modern, (partly) biogenic fuels, strong system drifts and reduced saturator lifetimes occur. This effect could be traced to non-volatile reaction products of acidic exhaust components with the alcoholic working fluid that poison the sensor, creating an immediate need for alternatives. Following fundamental theoretical considerations of the CNC principles, n-alkanes were identified as a new, advantageous class of working fluids. The materials have favourable thermal and diffusion properties, are chemically inert and condense efficiently on the carbonaceous nanoparticles of combustion aerosols and can be used with standard CNCs under standard conditions. Subsequent tests with linear alkanes in the C9 - C14 range proved their practical applicability as well as the validity of the underlying models.