A Modular Numerical Simulation Tool Predicting Catalytic Converter Light-Off by Improved Modeling of Thermal Management and Conversion Characteristics 2001-01-0940

Strict legislation standards for automotive emission limits (e.g. ULEV, SULEV), which target for HC conversion rates beyond 99 %, impose the necessity to dramatically shorten catalyst Light-Off time and increase catalytic efficiency through improved catalytic converter heat-up. Especially, in early design stages, modeling thermal energy management is crucial to predict wether emissions standards can be met.

The CAE method (Computer Aided Engineering) presented in this study gives the flexibility composing the frontal exhaust system from modular numerical models, which describe heat transfer in single exhaust components, as e.g. takedown-pipes, flexible coupling element (FCE), flanges and conversion characteristics in catalytic converter. Each module upstream of the converter internally couples the energy equations of 1Dgas to 1D/2D-solid-structure, including heat transfer mechanism as radiation, natural and forced convection. An existing three way catalyst (TWC) program (1D) balances energy- and mass conservation in the converter, to model heterogeneous surface reactions and heat transfer in the solid, as well as mass and heat transfer in the gas phase. Transient emissions and temperature measurements required for inlet boundary conditions and validation of the composed model derived from dynamometer measurements of a 2.0 I - 2V SI engine in transient driving cycle.

Focused on improving the light-off and conversion behavior of the start-up brick in the first 30 seconds of the FTP 75 cycle, varying design parameters, as geometry changes, variations in engine out emissions, thermal capacities and insulation, have been investigated. It proves that in the converter underfloor position a major part of upstream heat losses occur in the FCE, resulting in decisive HC break-through during the light-off delay. Therefore, some effort has been put into developing and tuning a numerical model of the FCE, validated with temperature measurements on an engine test bench.