Influence of Material Properties and Pore Design Parameters on Non-Catalyzed Diesel Particulate Filter Performance with Ash Accumulation 2012-01-1728

Diesel particulate filters (DPF) are a common component in emission-control systems of modern clean diesel vehicles. Several DPF materials have been used in various applications. Silicone Carbide (SiC) is common for passenger vehicles because of its thermal robustness derived from its high specific gravity and heat conductivity. However, a segmented structure is required to relieve thermal stress due to SiC's higher coefficient of thermal expansion (CTE). Cordierite (Cd) is a popular material for heavy-duty vehicles. Cordierite which has less mass per given volume, exhibits superior light-off performance, and is also adequate for use in larger monolith structures, due to its lower CTE. SiC and cordierite are recognized as the most prevalent DPF materials since the 2000's.

The DPF traps not only combustible particles (soot) but also incombustible ash. Ash accumulates in the DPF and remains in the filter until being physically removed. Several studies have confirmed that a small amount of ash accumulation in the DPF (until a certain level) improves DPF performance, both in terms of filtration efficiency and sooted back pressure [1, 2, 3, 4]. On the other hand, it has also been confirmed that too much ash accumulation increases exhaust back pressure, leading to a reduction in engine efficiency, as the ash occupies space and plugs the DPF. In some cases, periodic ash cleaning, which requires removal of the DPF from the vehicle, is needed to ensure appropriate DPF performance, especially for heavy-duty diesel vehicles which accumulate high mileage. Thus, accumulation of ash in the DPF is a common and considerable issue for long-term vehicle operation, regardless of the filter material. Improved understanding of the phenomena of ash accumulation in the DPF is valuable for further improvement of the emission-control system.

In this study, four different non-catalyzed DPF materials (three different porosities and two different pore sizes) of rectangular configuration 38mm × 38mm × 152mm, made of SiC were subjected to accelerated ash loading. In addition, a non-catalyzed cordierite DPF was also evaluated to determine the influence of the DPF material. Ash loading at five different levels from 0 to 20 g/L was conducted. Twenty five ashed DPF samples in total were prepared for this investigation. The DPF back pressure response to soot loading was verified by a soot generator for all samples. The phenomenon of ash accumulation and its effects on the sooted DPF back pressure response was investigated, resulting in the formulation of DPF design criteria to reduce ash-related impact on lifetime DPF performance.