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The aggressive reduction of future diesel engine NOx emission limits forces the heavy- and light-duty diesel engine manufacturers to develop means to comply with stringent legislation. As a result, different exhaust emission control technologies applicable to NOx have been the subject of many investigations. One of these systems is the NOx adsorber catalyst, which has shown high NOx conversion rates during previous investigations with acceptable fuel consumption penalties. In addition, the NOx adsorber catalyst does not require a secondary on-board reductant. However, the NOx adsorber catalyst also represents the most sulfur sensitive emissions control device currently under investigation for advanced NOx control. To remove the sulfur introduced into the system through the diesel fuel and stored on the catalyst sites during operation, specific regeneration strategies and boundary conditions were investigated and developed.

Three-day diurnal SHED evaporative emissions were measured in a fleet of ten Auto/Oil current (1989) and 2 older (1984) vehicles using Auto/Oil Industry Average fuel. SHED temperature cycled each 24-hour period from 72 to 96 F (22.2 to 35.5C). Measurements included speciation of individual hydrocarbons in the SHED as well as total mass emissions at the end of each of the three 24-hour test periods. Previous evaporative emission studies provided evidence that permeation and/or fuel seepage could contribute significantly to the mass of diurnal and hot soak emissions. Data from this investigation were used to quantify the contribution of liquid fuel to total SHED emissions during diurnal testing. A calculation method, based on the concentration of 29 select hydrocarbons in the SHED, is presented to apportion SHED emissions between those associated with liquid fuel losses and those associated with fuel tank head space vapor losses.