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Theoretical Investigation of Volatile Removal Efficiency of Particle Number Measurement Systems
Abstract:
Euro 5/6 light-duty vehicle emissions regulation introduced non-volatile particle number emission measurements. The particle number measurement system consists of a volatile removal unit followed by a particle number counter with a 50% cut-point diameter at 23 nm. The volatile removal unit must achieve a >99% concentration reduction of a monodisperse aerosol of tetracontane (CH
3
(CH
2
)
38
CH
3
) particles of diameter ≥30 nm with inlet concentration ≥10
4
cm
−3
.
In this paper the evaporation of tetracontane particles in the volatile removal unit is investigated theoretically. The temperature and the residence time in the evaporation tube are discussed, as well as the possibility of nucleation events of evaporated particles at the exit of the evaporation tube. In addition, sulfuric acid nucleation at the evaporation tube exit is analyzed. Theoretical calculations are, finally, compared to experimental data.
Our main conclusion is that the volatile removal efficiency requirements of the legislation can be easily met. However, as some experimental measurements showed, the removal efficiency might differ for large particle sizes and high concentrations; thus, the results of particle number counters with a 50% cut-point diameter less than 23 nm should be interpreted with care.