Multi-stage diesel particulate collector system with combined processes of inertial impaction, virtual impaction, and filtration

The invention relates to diesel particulate collectors for controlling exhaust emissions from a diesel internal combustion engine.

In the control of diesel particulate emissions, wall flow filters have been widely used. The restriction of the filter increases with time due to the increasing amount of soot deposited in the filter. The limited soot loading capacity requires the filter to be regenerated through either passive or active processes. During each cycle of regeneration, however, a filter can never be recovered to its initial restriction level due to ash accumulation. A filter has to be discarded if it cannot be regenerated to meet back pressure requirements specified by the diesel engine manufacturer. A system with high soot loading capacity is thus desired, for less frequent regeneration, longer operating time, and longer service intervals.

The present invention provides a multi-stage diesel particulate collector combining in preferred form various principles including inertial impaction, virtual impaction, and filtration. A series of inertial impactors form a cascade to trap diesel soot particles. The inertial impactor accelerates the particle laden exhaust gas flow through an array of orifices or nozzles, and then forces the flow to change direction, causing the larger particles to impact on a collector. Low pressure behind the porous impactor generates secondary flow causing smaller soot particles to be virtually impacted and then captured through a filtration process. As the flow moves through further stages, even smaller particles are carried with the exhaust gas flow stream and are removed at following stages of collectors.

FIG. 1 is a schematic side sectional view of diesel particulate collector in accordance with the invention.

FIG. 2 is a sectional view taken along line 2 — 2 of FIG. 1 .

FIG. 3 is an enlarged sectional view taken along line 3 — 3 of FIG. 2 and showing an enlarged portion of FIG. 1 .

FIG. 4 is a sectional view taken along line 4 — 4 of FIG. 1 .

FIG. 5 is a sectional view taken along line 5 — 5 of FIG. 1 .

FIG. 6 is a sectional view taken along line 6 — 6 of FIG. 1 .

FIG. 1 shows a diesel particulate collector 10 for controlling exhaust emissions 12 from a diesel internal combustion engine 14 . A housing 16 has an upstream inlet 18 for receiving exhaust from the diesel engine, and a downstream outlet 20 for discharging the exhaust. The housing conducts exhaust axially therethrough as shown at 22 . A first plate 24 receives exhaust flow from inlet 18 and has a first set of nozzles 26 , FIGS. 1-3, directing exhaust flow therethrough. A first inertial impactor 28 is provided in the housing downstream of plate 24 and in the path of exhaust flow from nozzles 26 and causes particle separation and a change of flow direction. A second plate 30 is provided in the housing downstream of impactor 28 and receives exhaust flow therefrom and has a second set of nozzles 32 , FIGS. 1 , 5 , directing exhaust flow therethrough. A second inertial impactor 34 is provided in the housing downstream of plate 30 and in the path of exhaust flow from nozzles 32 and causes particle separation and a change of flow direction.

Plate 24 is a metal plate with holes drilled therethrough with tapered upstream ends 36 , FIG. 3, to provide jet nozzles accelerating exhaust flow against impactor 28 and creating a low pressure zone 38 downstream of impactor 28 . Impactor 28 is a porous impactor passing some of the exhaust flow therethrough as shown at arrow 40 , and reflecting some of the exhaust flow and causing a change of direction as shown at arrow 42 . The porous impactor is provided by porous media 44 , FIG. 3, for example high temperature non-metallic or metallic porous material such as ceramic fibers or sintered metal, having an upstream face at a metal screen or mesh 46 . The upstream face is a collector for particles separated from the exhaust flow upon the noted change of direction. Low pressure zone 38 creates secondary flow through the porous impactor causing virtual impaction of particles smaller than the noted particles separated upon the change of direction, which smaller particles are captured by filtration in porous media 44 .

Plate 24 has a central section 48 surrounded by an outer section 50 . Central section 48 has the noted nozzles 26 therethrough. Outer section 50 blocks exhaust flow. Central section 48 and outer section 50 have the same area, i.e. the circular area of section 48 is the same as the annular area of section 50 . A frusto-conical shroud 52 extends axially between plate 24 and impactor 28 . The shroud has an upstream end at outer section 50 of plate 24 , and tapers outwardly to a wider downstream end at impactor 28 . Shroud 52 is perforated and passes exhaust flow therethrough as shown at arrows 54 , including exhaust flow reflected from porous impactor 28 . Porous impactor 28 is axially aligned with the set of nozzles 26 and has an upstream face having an area larger than the area of central section 48 of plate 24 . Narrow passage 55 enhances acceleration of the exhaust flow, further reducing the pressure at low pressure zone 38 behind impactor 28 .

Plate 30 has a central section 56 blocking exhaust flow and surrounded by an outer section 58 having the set of nozzles 32 therethrough, which nozzles are formed by drilling a set of holes through the plate, comparably to the drilling of nozzle holes 26 . Outer section 58 and central section 56 have the same area, i.e. the annular area of section 58 is the same as the circular area of section 56 . Impactor 34 is comparable to impactor 28 including porous media 60 comparable to media 44 , and metal screen 62 comparable to screen 46 ; however impactor 34 defines an annulus with a hollow interior 64 . The area of hollow interior 64 of impactor 34 is smaller than the area of central section 56 of plate 30 . A frusto-conical shroud 66 extends axially between plate 30 and impactor 34 , and has an upstream end at central section 56 of plate 30 , and tapers inwardly to a narrower downstream end at impactor 34 . Shroud 66 is perforated and passes exhaust flow therethrough as shown at arrows 68 , including exhaust flow reflected from porous impactor 34 .

Central section 48 of first plate 24 , first impactor 28 , and central section 56 of second plate 30 are axially aligned, with first impactor 28 being axially between central section 48 of first plate 24 and central section 56 of second plate 30 . Outer section 50 of first plate 24 , outer section 58 of second plate 30 , and second impactor 34 are axially aligned, with outer section 58 of second plate 30 being axially between outer section 50 of first plate 24 and second impactor 34 .

Third plate 72 , third impactor 74 , fourth plate 76 , fourth impactor 78 , third frusto-conical shroud 80 , and fourth frusto-conical shroud 82 are identical respectively to first plate 24 , first impactor 28 , second plate 30 , second impactor 34 , first frusto-conical shroud 52 , and second frusto-conical shroud 66 , except for decreasing nozzle size and porosity to increase the jet momentum for capturing smaller particles as the exhaust flow continues downstream. A modular multi-stage serially axially cascaded structure is provided. The housing includes an inlet section 84 having inlet 18 , an outlet section 86 having outlet 20 , and a plurality of intermediate sections such as 88 and 90 having respective mating flanges such as 92 secured to each other by bolts such as 94 . Housing section 88 houses a first stage provided by plates 24 and 30 and impactors 28 and 34 . Housing section 90 provides a second sequential stage provided by plates 72 and 76 and impactors 74 and 78 . Further stages may be added as desired. Pressure transducers (not shown) can be placed at various upstream, downstream and intermediate locations along the housing to monitor restriction. When one or more collectors reach maximum capacity, the soot filled porous media can be replaced and/or its respective stage can be replaced and/or the device can be cleaned. The multi-stage collector is particularly well suited as a pre-collector with other primary diesel particulate filters in order to increase the system soot loading capacity, resulting in less frequently required regeneration.

It is recognized that various equivalents, alternatives and modifications are possible within the scope of the appended claims.