Mathematical Modeling of Electrically Heated Monolith Converters: Power and Energy Reduction Strategies

A transient heated converter model, coupled with vehicle emission testing with a prototype Park Avenue, has been used to develop strategies for reducing electrical power and energy requirements for electrically heated monolith converters (EHCs). The following two strategies were examined in detail: open-loop fuel-rich engine operation and use of low-thermal-mass electric heaters. It is found that although effective individually, a combination of these strategies provides even greater reductions in electrical power and energy requirements. For example, using a small-volume electric heater with fuel-rich engine calibration is predicted to give a 3-fold reduction in power and a 5-fold reduction in energy required to meet a cold-start HC emission target, compared to early prototype EHC systems operating with the baseline (fuel-lean) engine calibration. It is also found that a small-volume heater in an optimized EHC system serves primarily as a heat transfer medium/ignitor rather than a catalytic conversion device. This function of a small electric heater can be augmented by coupling it with an unheated “lightoff” catalyst containing high concentrations of noble metals.