Sources of Vehicles Emissions in Three Day Diurnal SHED Tests - Auto/Oil Air Quality Improvement Research Program

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. The liquid fuel (seepage) contribution to SHED emissions for the 72-hour test was calculated to be 6 to 34% depending on the individual vehicle. The maximum mass of liquid fuel was about 11 g (0.5 fluid oz ) in three days.

Permeation rates of flexible fuel lines and vapor lines of four select vehicles were assessed in a separate laboratory investigation. Results indicated that permeation of fuel or fuel vapor through the hoses in three of the four cars was not a principal source of the SHED emissions. Tests of a fuel tank liquid fuel line of the fourth vehicle indicated that permeation could have accounted for about 40% of the seepage rate calculated for that vehicle.