Ceramic Foams as Catalyst Substrates: Pre-catalyst Application Homogenising the Exhaust Flow upstream of Aftertreatment Devices

Abstract

Non-homogeneities in the exhaust line regarding flow distribution and mixing of exhaust gases upstream of catalytic converters or particulate filters are a major source of conversion efficiency reduction due to partial volume utilization. Current supports for catalytic converters use a honeycomb monolithic substrate with only a limited potential for increased wall contacts of the gas molecules due to their laminar channel flow profile. Non homogeneities of the flow distribution at the entering cross section of the catalytic converter prevail also inside the converter channels since no momentum exchange is possible perpendicular to the main flow direction. The ceramic based foams developed and patented by Empa are a promising alternative. In the upstream of exhaust aftertreatment devices they ceramic foams redistribute the exhaust gases homogenizing the flow, enhancing turbulence and species mixing, without increasing flow resistance to prohibitive levels. Catalytically coated, they even can initiate, facilitate or even complete oxidation of unburnt HCs and CO and oxidize a substantial fraction of particulates while generating required species for the following aftertreatment step. In this paper we present some material development aspects as well as flow field investigations performed in the up and the downstream of the ceramic foams, demonstrating their potential.

Ceramic Foam Catalyst Substrates for Diesel Oxidation Catalysts: Pollutant Conversion and Operational Issues

“…The foams have been in-house manufactured based on antecedent development, [11,12]. Composed out of A1 2 O 3 the chosen foams had a porosity of 10ppi.…”

“…Following a systematic development process, our laboratory has extensively investigated material issues, [11], the fluid dynamic behavior, [12,13], reactivity in the exhaust gas of natural gas engines [4,5], while using simulation for analyzing the underlying phenomena, [14]. In this study the focus was the realization of a foam based DOC for a small heavy duty truck.…”

Ceramic foam substrates for automotive catalyst applications: fluid mechanic analysis

“…The optical access areas consist of a detachable quartz glass window on all sides. For a more detailed description of the test flow rig the interested reader is referred to (Dimopoulos et al 2007).…”

“…The optimal interrogation window size was a further investigation item and was found to be 32 9 32 pixels (Dimopoulos et al 2007). In combination with a 50% overlap of the interrogation windows (and the optical imaging) one velocity vector per 0.908 mm was obtained.…”

“…Similar mixing devices have also been proposed to achieve uniform flow distribution and proper mixing upstream of selective catalytic reduction (SCR) catalysts (Kaiser and Rusch 2007), where a small amount of liquid urea is injected in the exhaust line to help the reduction of nitrogen oxides. Initial investigations on the potential of achieving uniform flow distribution upstream of DPFs and SCR catalysts by using foam substrates upstream of these devices have already been performed (Dimopoulos et al 2007).…”