Extended isothermal equilibration tests at 75 deg F (approx=24 degC) and 94 deg F (approx =34 deg) were conducted on a 1988 GeneralMotors (GM) Corsica fuel system in a sealed housing for evaporativedetermination (SHED) using pure methanol fuel (M100). An initialcondition of evaporation canister brakthrougth loading was chosen toavoid hysteresis effects, and assure experimental repeatability. HotFlame Ion Detection (HFID) analysis of air samples from the SHED wereperformed during 6-hour experiments. The concentration of methanolwas found to increase continually over the duration of theexperiments, but at less than a linear rate. A temperature dependentmodel was developed assuming that evaporation rate is proportional toa finite mass of fuel available for evaporation and diffusion fromthe fuel system. This study suggests that the hot soak emissionsprocess, with concurrent thermal and nonequilibrated fuel systemvapor concentration gradients, is unlikely to stabilize within anominal one hour period.
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