PM Measurement with Partial Dilution Tunnel - Influence of Sampling Line on PM Measurement -

The full-flow dilution tunnel (hereinafter referred to as full tunnel) measurement method has become the de facto standard for the evaluation of particulate matter (hereinafter referred to as PM) emitted from diesel-powered vehicles. However, due to its drawbacks such as bulkiness and expensiveness, a method that uses a very small partial dilution tunnel (hereinafter referred to as micro tunnel) has been developed, mainly in Europe, nearly to the level of practicality. With this method, a higher degree of freedom in controlling sampling flow and temperature can be obtained. Another advantage of the micro tunnel is that the system is compact.

However, the micro tunnel's measurement accuracy remains uncertain because the accumulation of measurement data is not yet sufficient. Measuring PM while varying micro tunnel operating parameters permitted a check on the equivalency with a full tunnel system. Although no errors were found in sampling flow rate and dilution ratio control, the resulting PM measurements were observed with some bias errors. This tendency has also been reported by researchers in many other laboratories. The cause is speculated to be the longer sampling line of the micro tunnel in proportion to the tunnel itself and the impact of temperature control on the composition of PM. On this basis, a sampling line system was modified for further measurement. The influence of the sampling line system on equivalency to full tunnel results was shown very clearly from the measurements and analysis.