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The transient, one-dimensional monolith model previously developed for gasoline emission control applications has been extended to study converter warmup behavior in the exhaust from a variable-fuel vehicle (VFV) running on mixtures of methanol and gasoline by including the catalytic oxidation of methanol which involves the formation of stable gaseous formaldehyde as a reaction intermediate. The model calculations show that the aldehyde formation increases gradually at the early stages of converter lightoff (when methanol conversions are low), peaks at ∼50% methanol conversion, and then declines rapidly with a further increase in methanol conversion. Consequently, for all cases of practical interest, the total amount of aldehyde produced during the converter warmup period correlates well with the time to converter lightoff, with lower aldehyde emissions predicted at faster converter lightoff.

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.

A transient three-dimensional model has been developed to simulate the thermal and conversion characteristics of nonadiabatic monolithic converters operating under flow maldistribution conditions. The model accounts for convective heat and mass transport, gas-solid heat and mass transfer, axial and radial heat conduction, chemical reactions and the attendant heat release, and heat loss to the surroundings. The model was used to analyze the transient response of an axisymmetric ceramic monolith system (catalyzed monolith, mat, and steel shell) during converter warm-up, sustained heavy load, and engine misfiring. The simulation indicates that high solid temperatures are encountered during sustained heavy load or engine misfiring, while steep temperature gradients are developed during the converter warm-up period. Flow maldistribution and radial heat loss are major sources for the thermal gradients.