Measurement of Fuel Evaporative Emissions From Gasoline Powered Passenger Cars and Light Trucks Using the Enclosure Technique
This SAE Recommended Practice describes a procedure for measuring evaporative emissions from fuel systems of passenger cars and light trucks. Emissions are measured during a sequence of laboratory tests that simulate typical vehicle usage in a metropolitan area during summer months: 1.) A 1 h soak representing one diurnal cycle in which temperature of fuel in the vehicle's tank is raised from 15.6 to 28.9 degrees C (60 to 84 degrees F). 2.) A 17.9 km (11.1 mile) run on a chassis dynamometer. 3.) A 1 h hot soak immediately following the 17.9 km (11.1 mile) drive. The method described in this document, commonly known as the SHED (Sealed Housing for Evaporative Determination) technique, employs an enclosure in which the vehicle is placed during the diurnal and hot soak phases of the test. Vapors that escape from all openings in the fuel system--both expected and unexpected--are retained in the enclosure, and the increase in hydrocarbon (HC) concentration of the atmosphere in the enclosure represents the evaporative emissions. Emission values measured by the enclosure method can, therefore, be significantly different than those obtained by the former trap method, depending on fuel system configuration and component design.