In a porous body, a surface layer thickness Ts takes a relatively small value satisfying P≧0.54 Ts (formula (1)), the surface layer thickness Ts being derived by a microstructure analysis using the porous-body data that is prepared through three-dimensional scanning of a region including a surface (inflow plane 61) of the porous body. Here, P denotes a porosity [%] of the porous body, and 0%<P<100% and 0 μm<Ts are assumed. The surface layer thickness Ts is derived as a distance in a thickness direction (X direction) between a surface-layer region start plane 92 in which a straight-pore opening ratio becomes 98% or less for the first time and a surface-layer region end plane 93 in which the straight-pore opening ratio becomes 1% or less for the first time.

An exhaust gas purification filter is configured to he disposed in an exhaust passage in a gasoline engine. The exhaust gas purification filter includes partition walls including a plurality of pores, a plurality of cells partitioned by the partition walls, and sealing portions alternately sealing ends of a plurality of the cells in the exhaust gas purification filter. The partition walls each have an average pore diameter of more than 16 μm and less than 21 μm, and have a ratio of an average surface opening diameter of the pores in a partition wall surface to the average pore diameter of the partition wall of 0.66 or more and 0.94 or less.

A porous ceramic honeycomb body (10) including intersecting walls that form channels (22) extending axially from a first end face to a second end face and layered plugs (62) comprised of a first layer (64) disposed on channel walls and a second layer (66) disposed inward toward an axial center of each respective channel on the first layer. The plugs seal at least one of a first portion of the channels at the first end face and a second portion of channels at the second end face of the porous ceramic honeycomb body.

A honeycomb filter includes a pillar-shaped honeycomb substrate including a porous partition wall that defines a plurality of cells extending from an inflow end face to an outflow end face, an inflow side plugging portion disposed at the inflow end face of the honeycomb substrate to plug open ends of outflow cells; and an outflow side plugging portion disposed at the outflow end face of the honeycomb substrate to plug open ends of inflow cells other than the outflow cells. The honeycomb substrate includes the partition wall that defines two of the inflow cells by division. An average of the plugging length L.sub.OUT of the outflow side plugging portions disposed in the inflow cells of the honeycomb substrate is larger than an average of the plugging length L.sub.IN of the inflow side plugging portions disposed in the outflow cells of the honeycomb substrate.

A honeycomb structure includes a honeycomb structure body including porous partition walls defining a plurality of cells serving as fluid passages extending from an inflow end face to an outflow end face. A porosity of the partition walls is from 45 to 65%, an open frontal area of pores having an equivalent circle diameter of 10 um or more is from 20 to 40%, a pore density of pores having an equivalent circle diameter of 10 μm or more is from 350 to 1,000 pores/mm.sup.2 and a median opening diameter of the pores having an equivalent circle diameter of 10 μm or more is from 40 to 60 μm, where the median opening diameter is the median value of the equivalent circle diameters.

An aftertreatment system comprises a SCR system, a first filter, and a second filter disposed downstream of the first filter and a bypass conduit providing a flow path bypassing the second filter. A valve is operatively coupled to the bypass conduit and is moveable between a closed position in which the exhaust gas flows through the second filter, and an open position in which at least a portion of the exhaust gas flows through the bypass conduit. A controller is operatively coupled to the valve configured to adjust the valve based on a first filtration efficiency of the first filter to cause the exhaust gas expelled into the environment from the aftertreatment to have a particulate matter count meeting particulate matter emission standards.

In a method for operating a urea dosing system in an exhaust aftertreatment system (EATS) of an engine, an ambient temperature is measured in an environment in which the EATS is disposed, one or more temperatures associated with the EATS to which there is a relationship to a temperature of area in the urea dosing system are monitored. After turning off the engine, whether urea in the urea dosing system is subject to freezing is determined based on the measured ambient temperature and the one or more monitored temperatures. A reversion operation is performed after turning off the engine with a delay until one or more events occur, the one or more events including determining that urea in the urea dosing system is subject to freezing. An engine system is also provided.

A honeycomb filter includes a honeycomb structure having a porous partition wall disposed to surround a plurality of cells; and a plugging portion provided at one end of the cell, wherein the honeycomb structure has an inflow side region including a range of up to at least 30% with respect to the total length of the honeycomb structure with the inflow end face as the starting point and an outflow side region including a range of up to at least 20% with respect to the total length of the honeycomb structure with the outflow end face as the starting point, in the extending direction of the cell of the honeycomb structure, an average pore diameter of the partition wall in the inflow side region is 15 to 20 μm and an average pore diameter of the partition wall in the outflow side region is 9 to 14 μm.

A honeycomb filter includes a honeycomb structure body having a porous partition wall disposed to surround a plurality of cells and a plugging portion disposed at one end of the cells, wherein the plurality of cells are arranged in a square grid pattern along a first direction and a second direction in a section orthogonal to an extending direction of the cells, the shape in the section is a deformed square having a specific corner, the specific corner includes a first curved portion, a second curved portion, and a connecting portion, a radius of curvature R1 of the first curved portion and a radius of curvature R2 of the second curved portion are 40 to 80 μm, respectively, and a center distance between a center of curvature O1 of the first curved portion and a center of curvature O2 of the second curved portion is 80 to 200 μm.

A ceramic honeycomb structure comprising a ceramic honeycomb body having pluralities of longitudinal flow paths partitioned by square-lattice-cross-sectioned cell walls, and an outer peripheral wall formed on an outer periphery of the ceramic honeycomb body; the outermost peripheral cell wall of the ceramic honeycomb body having an outer peripheral surface shape reflecting the square lattice shapes of the cell walls; the thickness of the outer peripheral cell wall being larger than the thickness of the cell walls; and the outer peripheral wall being formed to cover an outer peripheral surface of the outer peripheral cell wall.