Study on a New Gasoline Particulate Filter Structure Based on the Nested Cylinder and Diversion Channel Plug

Abstract

Increasingly stringent emission regulations have imposed strict requirements on the particulate matter (PM) from gasoline direct injection (GDI) engines, and the gasoline particulate filters (GPFs) are considered one of the most promising devices for meeting these requirement. To reduce the flow resistance of the GPF, a type of nested cylinder and diversion channel plug (NC-DCP) GPF is designed. It is composed of nested foam metal cylinders and annular diversion channel plugs. The pressure drop and its influencing factors were theoretically studied. The results show that the structural parameters, such as the cylindrical layer spacing and the length-to-diameter ratio, and the pressure drop have trade-off relationships. Moreover, the filtration efficiency is analyzed, and the calculation formula is summarized. The internal flow field distribution and its influencing factors are discussed based on a 2-D axisymmetric simulation. The results show that the exhaust velocity affects the flow field uniformity but does not affect the flow field structure. The pressure drop gradually decreases as the number of nested layers increases, and the positive direction is beneficial to reduce the overall pressure drop. Under different velocities, there is an optimal length-to-diameter ratio to minimize the pressure drop, and the simicircular diversion plug greatly improves the flow uniformity index for the internal flow field of the filter element. ]. Actually, for GDI engines, the emissions may be low on a mass basis (mg/km) but can be very high on a number basis, 10 11 -10 13 #/km (number of solid particles emitted per kilometer), much more than PFI engines, exceeding the particulate number (PN) limit of 6 × 10 11 #/km in China and Europe. Compared with diesel engines equipped with diesel particulate filters (DPFs), modern gasoline engines can emit more PM [12,13].Gasoline particulate filters (GPF) are effective devices for reducing PM emissions. With increasingly stringent emission regulations, research regarding the application of PM filters in GDI engines will become an inevitable trend. The particulate filter must have high filtration efficiency and a long life and satisfy other requirements, and the flow resistance (pressure drop) must be small. The physical characteristics of DPFs have been fully understood and documented [14,15], and these insights can be applied to GPFs. Initially, soot is captured in the wall, known as "deep-bed" filtration. When the filter is fresh, the filtration efficiency (the proportion of particles trapped) is not 100%, but it increases with the mileage. Soot and ash accumulation forms a layer on the filter wall to prevent further penetration of soot into the wall, which is helpful to improve the filtration efficiency. The regeneration of soot can lead to breakage of the soot cake layer, which will reduce the filtration efficiency. However, in most driving conditions and life periods of a vehicle, the filtration efficiency of the GPF is expected to be very high (>90%) [16].The filter element is th...

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