Flow maldistribution measurements in wall-flow diesel filters

Abstract

Understanding the flow maldistribution phenomena inside porous ceramic diesel particulate filters and their effects on the pressure drop and regeneration characteristics is important for the successful design and modelling of this class of exhaust aftertreatment system. In this paper the results from an experimental study of flow distribution in wall-flow diesel filters are presented. The experiments were performed on a specially designed cold flow test rig, under steady state flow conditions. The flow distribution at the exit of cordierite and SiC filters were measured with a hot film velocity sensor under low and medium mass flowrate conditions. The system configuration was varied to incorporate tests with and without the installation of an oxidation catalyst before the filter in order to investigate the effect of the catalyst honeycomb structure to the measured flow distribution. Flow distribution in filters loaded with various levels of particulate mass was also measured using the same device. The filters were loaded in a modern diesel engine run on catalyst-doped fuel up to different backpressure levels. A flow uniformity index was adopted in order to quantify the measured flow maldistribution by a single number for each case. The velocity distribution at the exit of the filters is found to be significantly affected by certain design and operating parameters of the system: diffuser-catalyst-filter. The results of this work aim to give a better assessment of the magnitude of flow maldistribution in diesel filters, which severely distort their pressure drop characteristics and affect the distribution of collected soot mass. In this way, a previously neglected aspect of the complex three-dimensional filter regeneration behaviour is better understood.