Evolution of deep-bed filtration of engine exhaust particulates with trapped mass

Size-resolved particle mass and number concentrations were obtained from different operating conditions using a spark-ignition direct-injection engine and a heavy-duty diesel engine. Particle mass versus mobility diameter results obtained for the engines showed weak dependence on the operating condition. The particle mass–mobility data enabled the use of an integrated particle size distribution method to estimate the particulate matter mass concentration in the exhaust stream. Average mass concentrations determined with the integrated particle size distribution method were 77 − 32 + 47 % of the gravimetric measurements performed using Teflon filters. Despite the relatively low elemental carbon fraction (∼0.4 to 0.7), the integrated particle size distribution mass for stoichiometric spark-ignition direct-injection exhaust was 83% ± 38 % of the gravimetric measurement. Exhaust from the spark-ignition direct-injection engine was also used to perform wall-scale filtration experiments on identical cordierite filter samples with properties representative of diesel particulate filters. The filters were sequentially loaded with particulate matter from four spark-ignition direct-injection engine operating conditions, in order of increasing particulate matter mass concentration. Simultaneous particle size distribution measurements upstream and downstream of the filter sample were used to evaluate filter performance evolution and the instantaneous trapped mass within the filter for two different filter face velocities. The filtration experiments focused on the filter wall loading stage where the estimated trapped mass was < 0.3 g/m². The evolution of filtration performance at a fixed filtration velocity was found to only be sensitive to the trapped mass, despite using particulate matter from different operating conditions. Higher filtration velocity resulted in a more rapid shift of the most penetrating particle size toward smaller mobility diameters.