A Methodology for Evaluation and Optimization of Three-Way Catalyst Based, Low NO _x Emission Control Systems

This paper presents a comprehensive and expanded system analysis methodology for evaluation and optimization of three-way catalyst (TWC) based, low NO_x emission control systems. Its relationship to previous work in engine control optimization is carefully reviewed. The expanded methodology is evolved from a synthesis of procedures, models, and empirical data. These include powertrain simulation, engine mapping data, transient air-fuel ratio analysis, three-way catalyst conversion maps, an oxidation catalyst model, a cold-start emission contribution procedure, and a tailpipe emission constraint level optimization of engine calibration. The methodology can be utilized to study the sensitivity of fuel economy and emission control capability to air-fuel control, catalyst activity, cold-start emissions, and hardware configuration. Examples are presented in the paper to illustrate quantitatively the fuel economy/emissions tradeoffs of 5.0L and 2.3L engine systems as well as effects of transient air-fuel control, cold-start emissions, and catalyst configuration on fuel economy.