Microstructural and loading characteristics of diesel aggregate cakes

Aggregates consisting of nanometer sized primary particles are ubiquitous in the atmosphere. Sources of these particles such as combustion and nanoparticle manufacturing require control by filtration. To further investigate how loading processes are impacted by aggregate characteristics, we evaluated the loading of diesel particulate matter (DPM) on membrane filters at ambient temperature. Experimental results indicated that the filtration face velocity, engine load, and the usage of a catalytic stripper (CS) impact the characteristics of the resulting aggregate deposit or "cake". Mode aggregate size and primary particle size were slightly higher at 75% load (63.8 and 44.9. nm, respectively) compared to 37.5% load (57.3 and 40.9. nm, respectively). In-situ direct measurements of cake thickness enabled calculations of the porosity of the aggregate cakes which indicated that porosity varied between 0.93 and 0.97. The CS removed condensed semi-volatile organic material from the aggregates, which in turn impacted the calculation of porosity. Modeling based on Endo, Chen and Pui (Powder Technology, 1998, 98, 241-249) [1] of the pressure drop was performed based on the observation that cakes formed by the aggregates could be regarded as formed by a uniform collection of primary particles and once deposited, the aggregates were indistinguishable. The sensitivity of this model to various analytical expressions for the void function depending on the porosity was investigated. Results showed that available expressions vary greatly, although some of them provided satisfactory fitting for the experimental data.