Search Results

Until now no results have been available regarding the composition of evaporative emissions in a SHED test. In particular, for alcohol containing fuels, it is important to assess the relative percentage of alcohols and hydrocarbons in view of their different environmental impacts. This paper presents the results of a study conducted to determine the composition of the emissions from a number of multilayer coextruded plastic fuel tanks soaked in IE10 and CM15 test fuels. These emissions were analyzed for composition using a gas chromatography analytical method which employs a vapor trap and desorb sampling technique. In the case of CM15, methanol was found to account for as much as 50% of the overall evaporative emissions. This speciation method also allows estimation of how leakage and permeation contribute separately to the overall emissions.

Using the results of Constant Temperature (CT) Permeation Measurements to estimate Real Time Diurnal (RTD) permeation emissions has a number of practical advantages. In particular, Constant Temperature measurements are easier to set up and control in a laboratory environment, and Constant Temperature measurements provide for data checks using simple self-consistency tests that are not possible with Real Time Diurnal measurements. Furthermore, there is no need to repeat permeation measurements for each separate real-time temperature profile of interest. The same two Constant Temperature measurements can be used to estimate permeation performance for many different temperature cycles - for example, the temperature cycles prescribed by CARB, EPA, and EEC, or the different temperature profiles experienced by separate fuel system components during a vehicle SHED test.

Liquid fuels and the fuel vapors in equilibrium with them typically differ in composition. These differences impact automotive fuel systems in several ways. Large compositional differences between liquid and vapor phases affect the composition of species taken up within the evaporative emission control canister, since the canister typically operates far from saturation and doesn't reach equilibrium with the fuel tank. Here we discuss how these differences may be used to diagnose the mode of emission from a sealed container, e.g., a fuel tank. Liquid or vapor leaks lead to particular compositions (reported here) that depend on the fuel components but are independent of the container material. Permeation leads to emissions whose composition depends on the container material. If information on the relative permeation rates of the different fuel components is available, the results given here provide a tool to decide whether leakage or permeation is the dominant mode of emission.