Effects of hydrothermal aging on SiC-DPF with metal oxide ash and alkali metals

Characterizing Diesel Particulate Filter Failure During Commercial Fleet Use due to Pinholes, Melting, Cracking, and Fouling

“…of the DPF outlet face, but its presence was not observable prior to cutting the DPF and exposing the cross section. The crack pattern is most likely attributed to the difference of the thermal expansions among these crystalline phases [8,15,16,22]. Fouling failures were DPFs with layers of agglomerated ash on the inlet face that the DPF no longer was permeable via exhaust.…”

“…The incombustible ash remains following DPF regeneration and accumulates in the substrate channels and walls [13,14]. During uncontrolled on-board regeneration temperatures, DPF substrates may suffer thermal damage due to excessive temperature peaks, above 1200°C, which occur due to exothermic combustion of soot and the limited heat capacity of the exhaust gas and DPF substrate material [7,8,[15][16][17]. Pinholes, melts, and cracks have been found within cordierite and silicon carbide substrate materials after exposure to uncontrolled regeneration conditions [15,16].…”

“…During uncontrolled on-board regeneration temperatures, DPF substrates may suffer thermal damage due to excessive temperature peaks, above 1200°C, which occur due to exothermic combustion of soot and the limited heat capacity of the exhaust gas and DPF substrate material [7,8,[15][16][17]. Pinholes, melts, and cracks have been found within cordierite and silicon carbide substrate materials after exposure to uncontrolled regeneration conditions [15,16]. While previous laboratory controlled studies have confirmed the corrosive impact ash imparts on DPFs, the underlying mechanisms responsible for DPF failure and the interaction between ash/substrate is not well understood.…”

“…DPF failure due to ash/substrate interaction has been successfully modeled using catastrophe theory and diffeomorphism transformation considering flow resistance due to ash deposition, yet this model does not identify the specific underlying mechanisms causing failure [18]. Several hypotheses exist to explain DPF substrate failure, where interaction between substrate materials and alkali compounds significantly reduced the melting point of the cordierite and silicon carbide, with average melt temperatures lowered to about 700-900°C [7,8,15,17]. This temperature range is within the maximum peak temperatures experienced by the filter under controlled regeneration conditions.…”

“…With respect to specific compounds, sodium-rich ash was shown as corrosively damaging to both cordierite and silicon carbide materials [7,17]. Interaction between substrate materials and alkali compounds in the presence of additional ash materials, including Ca, Mg, and Zn in phosphate-sulfateoxide forms, was observed to act more aggressively on the substrate materials than the alkali materials alone [8,15]. Merkel et al found the presence of large amounts of iron oxide tends to promote greater reaction of the ash with the cordierite filter material as well [16].…”