A Simplified Catalytic Converter Model for Automotive Coldstart Control Applications

Abstract

More than three-fourths of the unburned hydrocarbon (HC) emissions in a typical drive cycle of an automotive engine are produced in the initial 2 minutes of operation, commonly known as the coldstart period. Catalyst light-off plays a very important role in reducing these emissions. Model-based paradigm is used to develop a control-oriented, thermodynamics based simple catalyst model for coldstart purposes. It is a modified version of an available model consisting of thermal dynamics and static efficiency maps, the critical modification being in the thermal sub-model. Oxygen storage phenomenon does not play a significant role during the warm-up of the engine. The catalyst is modeled as a second-order system consisting of catalyst brick temperature and temperature of the feedgas flowing through the catalyst as its states. Energy balance of an unsteady flow through a control volume is used to model the feedgas temperature, whereas energy balance of a closed system is used to model the catalyst brick temperature. Wiebe profiles are adopted to empirically model the HC emissions conversion properties of the catalyst as a function of the catalyst temperature and the air-fuel ratio. The static efficiency maps are further extended to include the effects of spatial velocity of the feedgas. Experimental results indicate good agreement with the model estimates for the catalyst warm-up. It is shown that the model represents the system more accurately as compared to the previous model on which it is based and offers a broader scope for analysis.

A Physics-Based Integrated Model of a Spark Ignition Engine and a Three-Way Catalyst

“…Unlike phenomenological catalyst models (e.g., Brandt et al, 2000;Fiengo et al, 2002;Sanketi et al, 2006b;Shaw et al, 2002), physics-based catalyst models commonly consider a reaction mechanism and a description of substrate dynamics. Voltz et al (1973) appear to have formed the basis for most developments in the modeling of the chemical behavior.…”

Simplified Models of Engine Hc Emissions, Exhaust Temperature and Catalyst Temperature for Automotive Coldstart

“…The simplified catalyst model has a structure similar to that described in (Sanketi et al 2006a). Here, a thermal diffusivity calculation is used to show that the gas comes in equilibrium with the solid before it leaves the catalyst, thus making unnecessary the use of different states for the catalyst solid temperature and the gas temperature.…”

“…It employs a parameter adaptation algorithm that uses the T cat measurement to finḋ Q ev throughQ out . Readers are encouraged to read (Sanketi et al 2006a) for details. Fig.15 shows the comparison of the model versus experimental data for an engine coldstart run.…”

“…It is not straightforward to findQ ev directly. Hence, it is calculated implicitly using a method that is similar to that used in (Sanketi et al 2006a). It employs a parameter adaptation algorithm that uses the T cat measurement to finḋ Q ev throughQ out .…”

“…These range from very complex ones to simplified ones which are more suitable for closed-loop control. Some of the important contributions are (Ohsawa et al 1998), (Shen et al 1999), (Chan and Hoang 1999), (Jones et al 2000), (Brandt et al 2000), (Fiengo et al 2002), , (Koltsakis and Tsinoglou 2003), (Sanketi et al 2006a) and references therein. The catalyst model presented here is an improved version of the model developed in (Sanketi et al 2006a).…”