System and method for the on-board production of reductants

The invention includes embodiments that relate to an emission treatment system, and more particularly to the on-board production and supply of reductants to an emission treatment system.

Current emission control regulations necessitate the reduction of pollutant species in diesel engine exhaust. NOx, principally NO and NO₂, contributes to smog, ground level ozone formation and acid rain. NO is produced in large quantities at the high combustion temperatures associated with diesel engines. NO₂ is formed principally by the post oxidation of NO in the diesel exhaust stream. Exhaust aftertreatment devices achieve NOx reduction by using a reductant agent. The reductant agent is added to the exhaust gas entering the aftertreatment device and reacts with NOx over a catalyst in a process of selective catalytic reduction (SCR). Typical reducing agents may include light hydrocarbons and oxygen bearing compounds like alcohols.

Known methods of supplying the reductants may involve supplying the reducing agents and the fuel separately or may involve chemically producing the reducing agent in situ from the fuel itself. Such methods typically employ complex subsystems such as special purpose pumps, filters, storage tanks and the like. Additionally, these systems also require valuable space and specialized materials, thereby involving additional expenses. Accordingly, there is need for an improved system and method for producing and supplying reductants to provide better overall economy and ease of operation.

Embodiments of the invention provide systems and methods for the on-board production and supply of reducing agents for use in hydrocarbon based SCR treatment. Briefly stated, in accordance with one embodiment of the invention, there is provided a system for the on-board production of reductants comprising a fuel tank adapted to directly or indirectly supply a first fuel stream and a second fuel stream; an engine in fluid communication with the fuel tank, wherein the engine is configured to receive the first fuel stream and create an exhaust stream; an emission treatment unit to treat the exhaust stream; a fuel conversion unit configured to receive the second fuel stream, and also receive a stream comprising oxygen to partially oxidize at least a portion of the second fuel stream thereby forming reductants, the fuel conversion unit also configured to supply a reductant stream comprising the reductants to the exhaust stream.

In accordance with another embodiment of the invention, there is provided a method for the on-board production of reductants comprising supplying a first fuel stream to an engine, wherein the engine is configured to create an exhaust stream; supplying a second fuel stream and a stream comprising oxygen to a fuel conversion unit; partially oxidizing at least a portion of the second fuel stream in the fuel conversion unit to form reductants; supplying a reductant stream comprising the reductants to the exhaust stream; and performing a selective catalytic reduction of NOx present in the exhaust stream.

FIG. 1 is a schematic diagram of an exemplary system 10 for the on-board production of reductants for treating NOx emissions from an engine. The system 10 includes an engine 12 that is directly supplied with a first fuel stream 14 from a fuel tank 16. An on-board fuel conversion unit 18 is directly supplied with a second fuel stream 20 from the fuel tank 16. If desired, the fuel tank 16 may be adapted to indirectly supply the first fuel stream 14 to the engine 12 and the second fuel stream 20 to the fuel conversion unit 18 via a single fuel stream 21 exiting the fuel tank that is split, or comprises a slip stream, to form the first and second fuel streams, as illustrated in FIG. 2.

Referring to FIGS. 1 and 2, the fuel tank 16 may be adapted to supply the first fuel stream 14 to a first fuel pump 22, wherein the first fuel pump is adapted to pump the first fuel stream to the engine 12. The fuel tank 16 is also adapted to supply the second fuel stream 20 to a second fuel pump 24. The second fuel pump 24 pumps the second fuel stream 20 to the fuel conversion unit 18. A portion of the first fuel stream 14 is burnt in the engine 12 during operation of the engine and an emission of exhaust gases containing NOx is produced thereby. The exhaust gases, thus produced, are discharged through an exhaust stream 30. The exhaust stream 30 carries the exhaust gases to an emission treatment unit 32 where the exhaust stream is treated by selective catalytic reduction. The resulting treated exhaust steam 38 is exhausted into the atmosphere.

The systems and methods of the invention allow for the use of one fuel tank 16 for carrying the fuel instead of requiring an extra storage tank for an SCR reductant. This is advantageous from an implementation and distribution point of view. For example, the system can be installed on existing locomotive engines.