The Number Concentration of Non-Volatile Particles - Design Study for an Instrument According to the PMP Recommendations 2004-01-0960

The increasing use of diesel particulate filters (DPF) as the most effective exhaust after-treatment method to reduce particle emissions from internal combustion engines emphasises the need for new particle measurement methods beyond gravimetric. Following a guideline of the Swiss EPA to extend particle measurement to particle size, number concentration and surface concentration, a group of European countries, joined by Japan, have initiated a large-scale investigation of particle metric and measurement methods, the “Particulate Measurement Programme” (PMP). Under the auspices of the UNECE Group of Experts on Pollution and Energy (GRPE), PMP aims at finding a particle metric that is more sensitive to the toxicologically relevant sub-micron particles and that is to supplement, or even replace, gravimetric as future certification standard for particle emissions.

The particle metric and corresponding measurement system recommended after phase I and II of GRPE-PMP is the number concentration of non-volatile exhaust particles, to be measured with a combination of thermo-diluter and condensation particle counter (CPC). This paper presents a design study for an integrated instrument according to the PMP recommendations. Thermo-dilution as particle conditioning concept is explained and compared to alternative methods such as hot diluter and thermo-desorber. Particle number as preferred metric is discussed as well as the suggested instrument, CPC, and some of its challenges. Along with issues of principal and scientific interest, the measurement system must fulfil very practical usability criteria when used as certification instrument, such as robustness, ease of use, and moderate cost.