Particle number emissions are measured with two instruments
according to the upcoming European emission regulations for
light-duty diesel passenger vehicles and compared to data from
other methods, including the current regulatory total particulate
matter (PM) mass, photo-acoustic soot sensor (PASS) and engine
exhaust particle sizer (EEPS). At the very low emission levels of
diesel particulate filter (DPF) equipped vehicles, the solid
particle number data correlate well with soot mass and with
particle number measured by EEPS, if only those particles belonging
to the accumulation mode are considered in the latter case.
PN differences of ≻100% between tests of the same vehicle are
observed. Comparison of the two PN instruments and the
photoacoustic soot sensor show that these are systematic
differences which originate primarily with the vehicle and not from
instrument uncertainties. After accounting for this, a
repeatability of ≺8% and a reproducibility of ≺27% are estimated
for the particle number method.
A large body of new vehicle data is presented from tests carried
out immediately after production. The data show that nearly all
vehicles would be below the anticipated Euro-5/Euro-6 particle
number limit. The observed variability is significant and needs
further investigation.