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The steady-state reduction of NOx at temperatures between 150-300°C has been investigated under simulated lean-burn conditions using a two-stage transient flow reactor system consisting of non-thermal plasma in combination with a sodium Y zeolite catalyst. Reactivity comparisons were made with and without plasma operation in order to identify the plasma-generated hydrocarbon species necessary for the selective catalytic reduction (SCR) of NOx. With propene as the hydrocarbon in the feed, NO is completely oxidized to NO2 in the plasma and the formation of oxidized carbon-containing species include formaldehyde, acetaldehyde, carbon monoxide, carbon dioxide, and methanol. Fourier transform infrared (FTIR) measurements indicate a close carbon balance between plasma inlet and outlet gas feed concentrations, signifying the major species have been identified.

The automotive clean-air catalyst system from Engelhard Corporation (PremAir™) consists of a catalyst-coated vehicle radiator and air-conditioning condenser designed to catalytically remove ground-level ozone and carbon monoxide (CO) from ambient air. Although initial on-road testing of the PremAir™ system showed reasonably high ozone conversion activity and satisfactory catalyst durability during the course of relatively low mileage accumulation, the long-term durability of the catalyst coating, its potential negative impact on cooling efficiency and corrosion characteristics, and incompatibility with the existing radiator manufacturing process remain among the issues of some concern. This paper describes an alternative approach to the problem of on-road pollutant destruction, which involves placing a thin catalytic monolith brick immediately behind the uncoated vehicle radiator.

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.

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.

The thermal response characteristics of automobile monolithic converters during sustained engine misfiring have been studied using a mathematical model which accounts for the simultaneous processes of heat transfer, mass transfer, and catalytic reaction. Particular attention was given to the effects of converter properties and inlet exhaust conditions on the location and magnitude of the temperature peak developed during the transient. Our simulation results show that the temperature excursions in typical monolith converters during engine misfiring are generally characterized by an ignition zone (where a steep exothermic temperature rise occurs as a result of rapid reaction) preceded by a relatively short, unreactive region near the inlet. Also, the predicted maximum wall temperature correlates well with the adiabatic reaction temperature, and the melting point of the monolith substrate would not be exceeded unless the extent of engine misfiring is 40% or higher.

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.

A mathematical model has been developed to describe the initial performance of fibrous filters for diesel exhaust particulates. In addition to the basic mechanisms of particle deposition on fibers, the size distributions of both diesel particulates and fibers were incorporated into the model in order to account for the polydispersity of particles and fibers encountered in realistic diesel particulate filters. Filtration experiments with a single-cylinder diesel engine were conducted to test the validity of the model, and the calculated filter efficiencies agreed very well with the experimental data.