Abstract
Monolith-type substrates are extensively used in automotive catalytic converters and have gained popularity in several other industrial processes. Despite their advantages over traditional unstructured catalysts, such as large surface area and low pressure drop, novel monolith configurations have not been investigated in depth. In this paper, we use a detailed computational model at the reactor scale, which considers entrance length, turbulence dissipation and internal diffusion limitations, to investigate the impact of using a dual cell substrate on conversion efficiency, pressure drop, and flow distribution. The substrate is divided into two concentric regions, one at its core and one at its periphery, and a different cell density is given to each part. According to the results, a difference of 40% in apparent permeability is sufficient to lead to a large flow maldistribution, which impacts conversion efficiency and pressure drop. The two mentioned variables show a positive or negative correlation depending on what part of the substrate—core or ring—has the highest permeability. This and other results contribute relevant evidence for further monolith optimization.
Highlights
The catalytic converter forms the basis of the automotive exhaust gas after treatment systems (EGATS) used on most passenger vehicles in Europe, North America, and other regions to control emissions such as carbon monoxide, hydrocarbons, and oxides of nitrogen
The catalyst formulation varies depending on the mode of engine operation, the heart of the catalytic converter is the multichannel honeycomb monolith substrate, the walls of which are covered with the catalytic washcoat
In view of the literature extant on the subject of the effect of flow distribution and cell density on the light-off performance, and recent commercial developments, this paper presents a computational study of the effects of using dual-cell-density structures in monolith catalytic converters
Summary
The catalytic converter forms the basis of the automotive exhaust gas after treatment systems (EGATS) used on most passenger vehicles in Europe, North America, and other regions to control emissions such as carbon monoxide, hydrocarbons, and oxides of nitrogen. When the cell density is changed, a number of other properties including the flow distribution are affected, so it is necessary to include all of these effects in a model [20] Another idea that has been proposed is to use composite monoliths composed of rings of various cell densities to improve the light-off performance [21]. In view of the literature extant on the subject of the effect of flow distribution and cell density on the light-off performance, and recent commercial developments, this paper presents a computational study of the effects of using dual-cell-density structures in monolith catalytic converters The effects of such structures on the velocity and temperature distributions, and subsequently, on the chemical conversion is demonstrated for a variety of dual-cell configurations
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