A computational model based on the flow, filtration, heat transfer and reaction kinetics theory in a porous ceramic diesel particulate trap.

摘要

A 2-D computational model was developed to describe the flow, filtration processes, heat transfer, and reaction kinetics in a honeycomb structured ceramic diesel particulate trap. This model describes the steady state trap loading, as well as the transient behavior of the flow and heat transfer during the trap regeneration processes.; The trap temperature profile was determined by numerically solving the 2-D unsteady energy equation including the convective, heat conduction and viscous dissipation terms. The convective terms were based on a 2-D analytical flow field solution derived from the conservation of mass and momentum equations. The reaction kinetics were described using a first order Arrhenius function. The 2-D term describing the reaction kinetics and particulate matter conservation of mass was added to the energy equation as a source term in order to represent the particulate matter oxidation. The filtration model describes the particulate matter accumulation in the trap. This model includes the diffusion, direct interception. and inertia mechanisms, and are linked together to capture the overall filtration characteristics of the trap.; A general semiheuristic power law approach for determining the particulate matter properties was developed. This relationship relates the particulate layer porosity to the amount of mass present in the trap and the trap pressure drop. Based on the calculated particulate layer porosity, analytical relationships can be used to determine the particulate layer permeability and density.; A general analytical solution for the trap pressure drop was developed. This analytical relationship can be used to determine the clean trap pressure drop. The loaded trap pressure drop can also be determined using this analytical relationship in conjunction with knowledge about the trapped particulate matter and its properties as given by the power law relationship for particulate layer porosity.; The parametric study indicated that the trap wall porosity, pore size, thickness, and trap material thermal conductivity density and specific heat are the main parameters controlling the trap pressure drop, filtration processes, temperature profile and regeneration efficiency.; The effect of trap material properties on trap regeneration behavior was studied with and without a Cu fuel additive for controlled and uncontrolled regeneration tests. The theoretical results compared well to the experimental data.