Motion and deposition of particulate matter in monolithic reactors - modeling and numerical simulations

Övrigt konferensbidrag, 2011

Particulate matter is formed during incomplete combustion in modern diesel and gasoline engines. These particulates start to grow from tiny carbonaceous structures or condensed volatiles and eventually form larger porous agglomerates. When emitted to the ambient air, they may end up in human lungs and eventually cause premature deaths among susceptible individuals. It is therefore imperative to remove as much (on a mass basis) and as many (on a number basis) of these particles before the exhaust exits the tailpipe. In the continued development and optimization of exhaust gas aftertreatment systems for the removal of diesel and gasoline particulate matter, computer-aided simulations can help both to cut the design and development time and to provide information that is otherwise difficult to access by direct measurements. In the present work, detailed mathematical models are used to investigate the motion and deposition of particulate matter in generic exhaust gas aftertreatment systems. It is shown that particulate matter from internal combustion engines can be divided into three groups depending on their size, and that these groups are transported differently in the aftertreatment system. This is reflected in the extent and location of particle deposition, and can be taken advantage of in emission control engineering. Furthermore, it is shown that the different sensitivity of the particles to the range of transport phenomena present have important consequences for the construction of computationally efficient models for describing the particle motion. In addition, the effects of turbulence on the motion of particulate matter are discussed. It has often been suggested that the turbulent-to-laminar flow transition in the first part of the channels enhance the mass transfer characteristics of a monolithic reactor. With the aid of comprehensive numerical models, the effects of the upstream turbulence on the extent of particle deposition inside the channels can be quantified. It is also shown that the flow field – and thus the particle motion – inside the channels can be significantly affected by ageing and deposit accumulation in the areas surrounding the channel inlets.