Measurement of no and no2 for control of selective catalytic reduction

Various embodiments relate to selective catalytic reduction systems, and in an embodiment, but not by way of limitation, to the measurement of nitrogen oxide and nitrogen dioxide in the control of such selective catalytic reduction systems.

Selective Catalytic Reduction (SCR) systems normally receive as input a gas, and catalytically convert undesirable components in that gas into less noxious components. An example of such an SCR system is a catalytic reduction system in a diesel engine powered vehicle. One aspect of an SCR system is the conversion of nitrogen oxide (NO) and nitrogen dioxide (NO₂) into nitrogen and water. In such SCR systems, a urea solution (which converts to ammonia—NH₃) or other ammonia source is used to react with the nitrogen oxide and nitrogen dioxide. It is known that dosing the urea so that the ammonia is in a 1:1 ratio with the combined amount of both the nitrogen oxide and the nitrogen dioxide (referred to in the art as NO_x) is conducive to the effectiveness of the system.

In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. Furthermore, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views.

Embodiments of the invention include features, methods or processes embodied within machine-executable instructions provided by a machine-readable medium, such as an in electronic control unit (ECU). A machine-readable medium includes any mechanism which provides (i.e., stores and/or transmits) information in a form accessible by a machine (e.g., a computer, a network device, manufacturing tool, any device with a set of one or more processors, etc.). In an exemplary embodiment, a machine-readable medium includes volatile and/or non-volatile media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.), as well as electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.)).

Such instructions are utilized to cause a general or special purpose processor, programmed with the instructions, to perform methods or processes of the embodiments of the invention. Alternatively, the features or operations of embodiments of the invention are performed by specific hardware components which contain hard-wired logic for performing the operations, or by any combination of programmed data processing components and specific hardware components. Embodiments of the invention include digital/analog signal processing systems, software, data processing hardware, data processing system-implemented methods, and various processing operations, further described herein. As used herein, the term processor means one or more processors, and one or more particular processors can be embodied on one or more processors.

One or more figures show block diagrams of systems and apparatus of embodiments of the invention. One or more figures show flow diagrams illustrating systems and apparatus for such embodiments. The operations of the one or more flow diagrams will be described with references to the systems/apparatuses shown in the one or more block diagrams. However, it should be understood that the operations of the one or more flow diagrams could be performed by embodiments of systems and apparatus other than those discussed with reference to the one or more block diagrams, and embodiments discussed with reference to the systems/apparatus could perform operations different than those discussed with reference to the one or more flow diagrams.

In an embodiment, in a Selective Catalytic Reduction (SCR) system, the molar flows (e.g., moles/sec) of nitrogen oxide (NO) and nitrogen dioxide (NO₂) are determined and/or measured, and a dosing of a urea solution is metered based on these molar flows of nitrogen oxide and nitrogen dioxide. While it is generally more practical to dose a urea solution, in other embodiments, other ammonia sources could be used, including the direct injection of ammonia into the SCR system.

Specifically, the SCR system takes into account the molar flows of nitrogen oxide and nitrogen dioxide molecules that are available for a standard reaction and a fast reaction in a catalyst. There is also another reaction, besides the standard reaction and the fast reaction, referred to as a slow SCR reaction in which only NO₂ is converted. However, as the name indicates, the slow SCR reaction is very slow, has only a minor effect on the overall NO_x conversion rate, and therefore will not be discussed further. The fast SCR reaction (Equation No. 1) and the standard SCR reaction (Equation No. 2) and can be represented by the following equations: