Catalytic Converter Investigation

Author : Joshua Douglas Cowgill
Publisher :
ISBN 13 :
Total Pages : 510 pages
Book Rating : 4.:/5 (232 download)

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Download or read book Investigation of UEGO Deception and Other Challenges in Three-way Catalytic Converter Oxygen Storage Modeling written by Joshua Douglas Cowgill and published by . This book was released on 2007 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Three-way catalytic converter oxygen storage control is a topic which has gained increasing interest recently due to the potential additional emissions reduction benefits control could provide to reach SULEV emission standards. To further improve air-to-fuel ratio control strategies, however, accurate three-way catalytic converter models are required to optimally manage oxygen storage. A three-way catalytic converter model depends mostly upon two factors for success. The first of these is, of course, accurate model structure and parameter definition. The second, and possibly more problematic, is accurate measurement data to be used as model inputs. Despite a general trend of increasingly using universal exhaust gas oxygen (UEGO) sensors instead of switching exhaust gas oxygen (EGO) sensors, UEGO sensors are quite susceptible to sensor deception errors particularly present post-catalyst under dynamic conditions. Specifically, the response of the UEGO sensor is significantly effected by the not just the actual exhaust gas air-to-fuel ratio (AFR) but also the concentrations of different components which make up the exhaust gas. To characterize the effect of UEGO sensor measurement error, the specific processes by which measurement error developed was explored. Exhaust gas component concentrations were changed both artificially and through the use of a catalytic converter with the goal of better understanding the UEGO deception phenomenon as a standalone sensor and in its use in conjunction with a catalyst. From the data collected, steady state calibrations were created which allowed for more accurate predictions of true exhaust gas AFR. Furthermore, an ad hoc dynamic calibration was created to indirectly account for additional unmodeled catalytic converter dynamics which significantly affected the post-catalyst UEGO output. The knowledge of UEGO and three-way catalytic converter operation gained was applied to three- way catalytic converter modeling though many methods. Use of the corrected, and thus more accurate, exhaust gas AFR measurements allowed for the accurate determination of parameters necessary for three- way catalytic converter modeling. Understanding of the three-way catalytic converter operation allowed for a detailed analysis, calibration and subsequent improvements of a commonly available three-way catalytic converter model. From this work, the abilities and limitations of a standard three-way catalytic converter model were examined. Within the existing oxygen storage model framework, modified oxygen adsorption and release functions were suggested as well as a means of calibrating them. Furthermore, the work also shows that other unmodeled dynamics are present which are associated with the alteration of the magnitude of the change in hydrogen concentration from pre to post-catalyst possibly caused by catalytic converter deactivation. Unfortunately, while such unmodeled dynamics were noted, the extension of the three-way catalytic converter model to account for these dynamics was beyond the scope of this work. The sensitivity of a current oxygen storage model was numerically investigated by inducing plant and sensor faults and comparing the output of the model with faults against an ideal model output. It is shown in this work that effect of model or plant faults is the slow drifting of the predicted oxygen storage level, as would be expedited, since an integrator-type model is begin used. However it was also determined that, during this drift, the predicted post-catalyst AFR predicted is generally relatively unaffected. In a control application, this slow drift would not be of great concern, as the plant could be regulated around a operating condition which allowed information regarding the current oxygen storage level to be observed in the measurer post-catalyst AFR.