Exemplary embodiments of the present disclosure are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts.
The filter 20 illustrated in
In an exemplary embodiment, the filter media 26 may define a plurality of filter passages 30. The filter passages 30 may be arranged in any configuration known in the art. For example, the filter passages 30 may be substantially parallel channels extending in an axial direction. The filter passages 30 may be, for example, flat, cylindrical, square tube-shaped, or any other shape known in the art. The filter passages 30 may also be configured to allow exhaust gas to pass between adjacent filter passages 30 while substantially restricting the passage of particulate matter. The flow of exhaust through the filter passages 30 is illustrated by arrows 32 in
In an exemplary embodiment, a plurality of filter passages 30 may be substantially blocked or closed proximate the inlet 16 of the filter 20 such that gas may not enter certain filter passage 30 at the inlet blocked end 33, but rather be directed to particular inflow surfaces of the filter media 26. A plurality of filter passages 30 may also be substantially blocked or closed proximate the outlet 34 of the filter 20 such that gas may not exit the filter passage 30 at the outlet blocked end 36, but rather be directed to other portions of the filter media 26.
Any fluid (liquid or gas) that will donate an oxygen atom may be used as the chemical species 40. For example, nitrogen dioxide (NO2) gas may used as the chemical species 40. The NO2 molecules may donate an oxygen atom to soot and undergo a change in composition to nitrous oxide (NO). The NO may then take an oxygen atom from the oxygen in the exhaust flow to convert back to NO2.
Any process known in the art may be used to attach the chemical species 40 on the filter media 26. The molecules of the chemical species 40 may be attached to the filter media by adsorption. Adsorption is a phenomenon whereby molecules of the chemical species 40 stick to the external and internal surfaces 38, 42 of the filter media 26 due to the attractive force (Van der Waals force) between the surfaces and the molecules of the chemical species 40. In some cases, there may also be some chemical bonding between molecules of the chemical species 40 and the molecules of the filter media 26. For adsorption to occur, the filter media 26 may be soaked in an atmosphere containing the chemical species material 40. In the case of a gaseous chemical species 40, the filter media 26 may be soaked in the gaseous material for adsorption to occur. In the case of a liquid chemical species 40, the filter media 26 may be immersed in the liquid chemical species 40 or in a solution containing the chemical species 40. Droplets of the liquid chemical species 40 may get attached to the external surface 38 or entrapped in pores 54 of the filter media 26. The temperature and pressure of the atmosphere may be controlled or varied to facilitate the attachment of the chemical species 40 on the filter media 26. In some cases other energy sources, such as a high pulse laser, may be used to facilitate attachment.
The disclosed filter system 50 comprising a filter 20 and a filter media 26 with a chemical species 40 attached to its external and/or internal surfaces 38, 42, may be used with any type of engine system 100 that exhausts pollutants including diesel engines, gasoline engines, or gaseous fuel driven engines. The operation of an engine system 100 having a filter media 26 chemically functionalized with a gaseous chemical species 40 of NO2 will now be explained.
The engine system 100 may be a part of any mobile or stationary machine that generates exhaust containing various regulated species like soot, soluble organic fraction (SOF), sulphates, and ash. The engine exhaust is passed through the filter 20 comprising the filter media 26 with chemical species 40 of NO2 molecules attached to its external and/or internal surfaces 38, 42. As the exhaust flows through the filter media 26, particulate matter including soot and SOF gets accumulated on or within the filter media 26. The collected particulate matter increases the resistance to exhaust flow through the filter 20, thereby increasing the pressure drop within the filter 20. When the filter pressure drop exceeds a set value, regeneration of the filter 20 is carried out.
Regeneration is the process by which the collected solid particulate matter in the filter 20 is burned to form gaseous and liquid products, which are carried along with the gases exiting the filter 20. As soot particles gets accumulated on the external and internal surface 38, 42 of the filter media 26, a soot particle may receive an oxygen atom from the molecules of NO2 attached to the external and internal surface 38, 42 of the filter media 26. This gain of an oxygen atom by the soot particles activates the soot particle for combustion using oxygen in the exhaust flow 14. Activation of the soot particle allows it to undergo combustion at a lower temperature. Thus, the NO2 chemical species 40 may function as a catalyst by reducing the regeneration temperature of the filter. In some cases, the regeneration temperature may be reduced to below 600° C.
Filter regeneration temperature is the temperature at which combustion of the soot occurs. Reduced regeneration temperatures may increase the durability of the filter 20. For regeneration to occur, the temperature of the soot collected on the filter media 26 should exceed the regeneration temperature. The temperature of the filter media 26 can be increased by enriching the air to fuel mixture, or actively heating the filter media 26, or by any other technique used in the art. This filter temperature may be increased periodically to periodically regenerate the filter 20 when the pressure drop within the filter 20 exceeds a preset limit, or by the occurrence of any other triggering event. Using NO2 chemical species 40 to activate the soot may decrease the regeneration temperature sufficiently for regeneration to occur at the normal operating temperature of the filter 20, thereby enabling continuous regeneration. Continuous regeneration is the process whereby the combustion of soot occurs continuously.
After donating an oxygen atom, the molecule of NO2 which is bonded to the solid surface, may undergo a change in chemical composition to NO. This surface-bonded molecule of NO then regains its original composition (NO2) by taking an oxygen atom from oxygen in the exhaust flow 14. The NO2 attached to the filter media 26 may thus be replenished by the oxygen in the exhaust flow 14. This cycle, where the NO2 changes to NO by donating an oxygen atom to a soot particle and changes back to NO2 by taking an oxygen atom from the exhaust flow 14, may continue indefinitely.
Rather than a solid catalyst coating, the chemically functionalized filter media 26 uses particles of a fluid chemical species 40 attached to the external and internal surfaces 38, 42 of a filter media 26 as the catalyst for soot regeneration. Unlike a solid catalyst coating, the particles of the chemically functionalized species 40 will not restrict exhaust flow nor significantly increase the pressure drop within the filter 20, thereby improving engine efficiency. In addition to improving efficiency, the operating cost of the engine 100 may also be reduced by use of the chemically functionalized filter system. Since the chemical species 40 replenishes itself taking oxygen from the exhaust flow 14, the useful lifetime of the filter media 26 is also extended. In addition, since the catalyst of the present disclosure is not made of expensive noble materials, the original cost of the filter 20 may also be reduced.
It will be apparent to those skilled in the art that various modifications and variations can be made to the shape and size of the chemical species 40, the deposited pattern of these particles 40 on the filter media 14, and the process used to deposit them. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed chemically functionalized filter system. It is intended that the specification and examples be considered as exemplary only, with the true scope being indicated by the following claims and their equivalents.