Mathematical modeling of catalytic converter lightoff. Part II: Model verification by engine‐dynamometer experiments

Abstract

A transient mathematical model has been developed which describes the behavior of packed-bed catalytic converters during warmup. Model predictions agree very well with the results of enginedynamometer experiments for three Ptalumina catalysts of widely different properties, thus demonstrating the validity of the model. General Motors Research LaboratoriesWarren, MI 48090 SCOPEUnited States federal regulations of automobile exhaust emissions are based on pollutant emissions measured while driving a vehicle over a prescribed driving schedule referred to as the Federal Test Procedure (FTP). This standardized emission test procedure requires that the vehicle under test be at room temperature for a minimum of 12 h before the test. For a short period of time after the cold start, emissions of hydrocarbons and CO from the engine are quite high due to the operation of the choke. To compound the problem, the catalyst is relatively cold at this time and thus is not fully operational. As a result of the combination of the high engine-out emissions and the low catalyst efficiencies, CO and hydrocarbon emissions during the first few minutes of the ETP (i.e., warmup period) account for a large fraction of the overall FTP tailpipe emissions (Pozniak, 1980;Kummer, 1980). Consequently, improving the warmup performance of catalytic converters is an effective means of reducing CO and hydrocarbon emissions on the FTP test.As is evident from the results of engine-dynamometer experiments presented here, catalyst properties have a strong influence on converter warmup performance. The converter models previously reported in the literature (e.g., Kuo et al., 1971;Harned, 1972;Bauerle and Nobe, 1973;Ferguson and Finlayson, 1974) were not designed to include details about the catalyst pellets and thus are not well-suited for studying the effects of the parameters associated with catalyst design. In our previous paper (Oh et al., 1980), a detailed mathematical model was developed which describes the behavior of a single catalyst pellet under transient conditions encountered during the warmup period of automobile exhaust catalytic converters. The singlepellet model treated catalyst pellets as composite porous media composed of concentric shells of differing physical and chemical properties. Such a multilayered configuration was found to be especially convenient for examining how the lightoff behavior of a catalyst pellet is influenced by its properties, such as the poison penetration depth, and the location and width of the noble metal band.In this paper, the second part of our converter modeling studies, we couple the single-pellet model with a mixing cell scheme to develop a mathematical model which is capable of predicting the warmup performance of the entire catalytic converter. Some of the results of model calculations presented provide useful insights into the dynamic behavior of packed-bed catalytic converters during warmup. In addition, the validity of the converter model is tested by comparing model predictions with the results of e...

Development and application of a computer aided engineering methodology supporting the design optimization of automotive exhaust treatment systems

“…has been studied extensively in the past over several catalyst formulations [94] and is considered to proceed according L-H mechanism, where adsorbed CO and oxygen react in a rate-determining surface step [95] . The detailed reaction mechanism is not part of this study and can be found elsewhere [96] .…”

“…The model of this thesis originates from the milestone works of Voltz [93] and Oh and Cavendish [94] and belongs to a large group of models sharing similar practically remained unsolved while the storage submodels were identified to be responsible for the major inaccuracies of the model.…”

“…Cavendish [94] , based on the apparent kinetics formulated by Voltz [93] , has been widely used as the basis of several models and it has been further developed to follow changes in the catalytic technology [77,78,113] . The most common modeling approach is 1-D, uses simple balance equations to model the transport phenomena and apparent kinetics expressions for the description of the catalytic reactions.…”

“…Based on the milestone work of Oh and Cavendish [94] , the model has been extensively validated [1,119] and recently extended with an analytical oxygen storage submodel [3] . In a short, the model is a one-dimensional catalytic converter model, which uses semi-empirical coupled equations and simple mechanisms for the gas properties, the heat and the mass transfer.…”

“…Shamim et al [77] have presented a model that incorporates transient terms at channel level modeling. On the other hand, Young & Finlayson [126] and Oh & Cavendish [94] argue about the validity of the quasi-steady approximation. They provide justification on the basis of the large ratio of thermal to mass time constants of the problem.…”