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A one-dimensional carbon canister adsorption model (CANMOD) has been developed to assist in the prediction of the performance of carbon bed canisters in vehicle evaporative emissions control systems. The model accounts for mass transfer and transient thermal phenomena, both of which are found to be essential in accurately describing canister behavior. The model assumes the vapor above the carbon to be in equilibrium with the adsorbed mass while the local temperature is determined by the dynamic balance between the heat of adsorption, carbon heat capacity and heat loss to ambient. The results of the model compare well with laboratory data on a 1L canister under load and purge conditions typical of vehicle operation. Variables investigated include: load level, feedgas concentration, and purge rate. The model accurately predicts the hydrocarbon mass adsorbed by the canisters, as well as breakthrough times, and hydrocarbon removal rates.

The elimination of water condensation is a familiar challenge to exhaust sampling system design and operation. The Constant Volume Sampler (CVS), commonly used to sample automotive exhaust, uses ambient air to dilute raw exhaust in order to keep water vapor, produced by the combustion process, in suspension. Without sufficient dilution, the water vapor will condense on the surfaces of the CVS and sample bags, absorbing water soluble compounds. These compounds are left unanalyzed resulting in nonrepresentative emissions and fuel economy measurements. Furthermore, condensation in the bag sampling system (pump, filter, lines, etc.) will increase all emissions measurements. Overdilution of the raw exhaust, on the other hand, produces low-level diluted concentrations which are more difficult to accurately measure.