Diesel Particulate Measurement with Partial Flow Sampling: Systems A New Probe and Tunnel Design that Correlates with Full Flow Tunnels

Partial flow sampling methods in emissions testing are interesting and preferred because of their lower cost, smaller size and applicability to engines of all sizes. However the agreement of the results obtained with instruments based on this method to those obtained with the traditional, large tunnel full flow sampling systems needs to be achieved, and the factors of construction that influence this agreement must be understood. These issues have received more attention lately in connection with ISO and WHDC standardization efforts underway to achieve a world-wide harmony in the sampling methods for heavy duty diesel engines, and with the introduction of similar Bag-minidiluter techniques into light duty SULEV gaseous pollutant measurement.

This paper presents the theory and practice of a partial flow probe and tunnel design that addresses and minimizes the undesirable effects of the necessary differences between the two sampling methods. Data are presented to show the efficacy of the design changes and the attendant improvement in the correlation between full and partial flow systems. As a consequence, results from the partial flow system described can be compared with confidence to results from the more expensive full-flow equipment for development and homologation purposes.