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This paper presents the use of a fixed volume, open-loop (FVOL) mini SHED (Sealed Housing for Evaporative Determination) for the measurement of evaporative emissions of fuel systems components. Because of tighter government emissions standards for vehicles, more stringent requirements are being made for emissions testing at the component level. Component suppliers need to provide accurate and repeatable emissions test data as well as more extensive testing to show compliance with customer requirements. In light of these demands, improving accuracy and reducing costs for component emissions testing is becoming more important. In this paper, we present a method for using open-loop sampling in conjunction with a fixed volume mini SHED system for emissions testing of automotive components. The advantage of this system is improved accuracy at reduced cost. We also present a simple method for validation of SHEDs using fuel based hydrocarbon vapors.

During the fall of 1992, the Michigan Roadside Study was conducted. During this study IM240 tests were conducted on vehicles that had also been emissions tested during on-road operation via two remote sensors that were separated by 100 feet. The use of two remote sensors provided an indication of the short-term real-world emissions variability of a large number of on-road vehicles. This data was used to determine the frequency of flippers, i.e. vehicles that are sometimes high emitters (>4% CO) and at other times low emitters (<2% CO). The data show that the flipper frequency increases for older model year vehicles. Also, the correlations between remote sensor readings of emissions concentrations and IM240 mass emissions rates were determined. The data show that the correlation between remote sensing and IM240 improves with increasing numbers of remote sensing readings. For three remote sensor readings, CO correlates with an r2 of 0.69 and HC correlates with an r2 of 0.54