1997-10-01

Mathematical Modeling of Electrically Heated Monolith Converters: Meeting European Emissions Regulations Proposed for 2000 and 2005 972852

After the EC93 and EC96, the next European emissions regulations are the EC2000 and the EC2005. The use of an Electrically Heated Catalyst (EHC) is considered to be one possible strategy to meet the new limits. One potential difficulty with the EHC is the electrical power level required to obtain the desired emission level. Ideally the power level should be kept as low as possible to avoid the use of a secondary battery or larger alternator. To examine the possible use of the EHC in meeting these new regulations a numerical model is used to optimize the several parameters influencing the electrical power requirements for a 4 cylinder European engine undergoing the new ECE+EUDC driving cycle. An analysis of the heater element volume shows that the prototypes in use are properly sized (about 0.04 liters) and a further reduction in volume may not be an important source of improvement. The idea that reduction in the volume of the lightoff brick behind the heater reduces emissions through faster warm-up is not confirmed by our simulations. By optimizing the heating power and timing, the secondary air injection amount and timing it is possible to achieve HC emissions of 0.02 g/test km during the first super cycle using 1.5 kW of electrical power for 10 s and 2 g/s of supplemental air for 55 s. This represents a substantial reduction from the unheated system baseline of 0.09 g/test km. The model also demonstrates that, due to the very rich engine calibration, no significant emissions reduction is possible, even at high heating power levels, without also adding supplemental air.

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