Techniques for measuring wall flow along the channels of a diesel particulate filter

This paper presents two novel tracer gas based techniques that have been developed to measure the axial variation of wall flow through the porous channel walls of a diesel particulate filter. The first technique is based on measuring the dilution of a tracer gas, introduced at the upstream end of the 'outlet' channel, due to the wall flow. A second technique was developed overcoming some of the drawbacks of the first technique. In this improved technique, a single traversable probe aspirates all the gas available in front of it with a controllable flow sink. The flow control is achieved by detection of a tracer gas, injected just downstream of the probe tip. Typical results from clean filters, loaded filters and filters with known wall blockages are presented. It is suggested that these techniques could be easily extended to interpret the soot loading in the filter channels in a non-intrusive way.