Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants can include, among other things, gaseous compounds such as the oxides of nitrogen (NOX). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NOX emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to ensure compliance with the regulation of these compounds, some engine manufacturers have implemented a process called Selective Catalytic Reduction (SCR).
SCR is a process where a reductant (most commonly a urea/water solution) is injected into the exhaust gas stream of an engine and adsorbed onto a catalyst. The reductant reacts with NOX in the exhaust gas to form water (H2O) and elemental nitrogen (N2), both of which are unregulated. Care should be taken so that the amount of reductant injected into the exhaust gas stream corresponds with the amount of NOX in the exhaust gas stream. If too much reductant is injected, some of the reductant may pass through the exhaust system and be discharged into the atmosphere. This can be costly and violate regulations in some areas. If too little reductant is injected, the NOX may not be adequately reduced and some may pass through the exhaust system and be discharged into the atmosphere.
Despite the need for accurate control, reductant injection systems are limited in their functionality. For example, overall reductant injection flow rate is often the only adjustable input. Therefore, in response to exhaust flow fluctuation and exhaust system irregularities, it can be difficult to fine tune reductant injection in order to efficiently maintain the exhaust within regulatory limits.
One method of addressing this problem of limited control functionality is described by U.S. Patent Publication No. 2012/0204542 of Norris et al. that published on Aug. 16, 2012 (“the '542 publication”), which discloses an exemplary aftertreatment system. Specifically, the '542 publication describes a system having two exhaust legs configured to receive parallel flows of exhaust from an engine, and a controller configured to selectively adjust exhaust flow through the legs via a throttle to compensate for uneven flow distribution. The system includes a particulate filter disposed within each leg at a location upstream of an SCR catalyst. A hydrocarbon doser is positioned between each particulate filter and the corresponding SCR catalyst, and a sensor (e.g., an ammonia sensor, a NOX sensor, a temperature sensor, and/or a pressure sensor) is located downstream of each catalyst. The controller is configured to determine clogging of the particulate filters based on signals from the sensor, calculate uneven flow distribution through the legs based on the clogging, and selectively adjust exhaust flow to compensate for the uneven flow distribution. In addition, operation of the hydrocarbon dosers is controlled based on feedback from the sensor.
While the system of the '542 publication may have increased functionality that helps to maintain dosing accuracy during uneven exhaust flow, the system may still be less than optimal. For example, the system may not be capable of detecting or accommodating certain exhaust flow fluctuations and aftertreatment system irregularities.
The present disclosure is directed at overcoming one or more of the shortcomings set forth above and/or other problems of the prior art.