Additive manufactured open cell structures: Promising substrates for automotive catalysts

Abstract

Catalyst technologies for automotive after-treatment systems require constant developments to comply with the latest regulations concerning real driving emissions. Apart from the current benchmark in catalyst substrates of honeycombs (HCs), the research is focusing on open cell structures, which show promising properties [1]. The network of solid struts of the open cell lattices overcomes the limits of laminar flow in HCs and enhances higher conversion efficiencies [2][3], lower cold start emissions and higher flow uniformity, which is a key factor for catalyst durability [4][5][6][7]. Open cells allow more flexibility in the geometrical configuration of the reactor [8], but they show also a higher pressure drop per unit of length [9][10], decreasing engine efficiency. Thus, to have a fair comparison between HC and open cells, the performance index I has been introduced [2], which evaluates catalyst efficiency by weighting conversion and pressure drop. CFD analysis suggested that the trade off is in favour of open cell structures when the porosity is high enough [11][1]. Here open cells are studied as regular polyhedral structures, which literature have shown to be more performant than randomized foams [12]. Several works conducted numerical analysis of open cell foams consisting of regular cells [2] [13] [14]. Regular structures are easier to handle because they require only two parameters (for example the characteristic pore dimension and its ratio with the strut diameter) to be defined and mathematical expressions allow the derivation all the other geometrical properties [1]. Often the Kelvin cell has been used as a typical elementary cell.