Characteristics of Three-way Catalyst during Quickly Start-up Process in a PFI Engine for HEV Application

The characteristics of three-way-catalyst during engine start process were investigated based on a simulated start/stop test system for HEV application. Although the catalyst has already reached its light-off temperature, the conversion efficiency is poor during engine start process due to the deviation of lambda from stoichiometric. The high concentration hydrocarbon emission spike can be stored by catalyst substrate temporarily, then it is released. This dynamic process decreases the conversion efficiency for the following exhaust hydrocarbon emission. When the initial temperature of catalyst substrate before engine start increased from 150°C to 400°C, the conversion efficiency for both the hydrocarbon and NO are increased. For the engine investigated in this study, in order to convert the hydrocarbon efficiently (conversion efficiency >50%) from the beginning of engine start, the catalyst substrate temperature should be maintained at least at 350°C, as well as the lambda should be controlled at its optimal range throughout the start transient process.