Development of a cost-effective micro-SHED system for determining fuel evaporative emissions of components

Regulations regarding evaporative emissions have set more and more stringent limits over the last years. To fulfill these specifications, original equipment manufacturers (OEMs) now tend to break down the sum value of evaporative emissions for the whole car onto single parts or components. Especially small, fuel-containing components (fuel lines, pressure sensors, injection systems, etc.) are challenging. Very low emission rates (<1 mg/24 h) must be measured precisely, and also the stability of these values must be verified due to fuel equilibration effects. Standard SHED (sealed housing evaporative determination) systems or test chambers for measuring volatile organic compound (VOC) emissions are often too big and have too high background levels to achieve reliable results. In addition they are quite expensive which affects the costs per measurement. Our aim was to develop a low-cost Micro-SHED system which fulfills the above mentioned requirements. Commercial gas-tight aluminum boxes with a volume of about 73 L were modified using a Tedlar bag and a fan. Four of those boxes can be put in a standard 1 m3 VOC emission test chamber for temperature control. Measurements are performed by one flame ionization detector (FID), which samples the boxes successively. Parameters such as repeatability, recovery, and retention were determined. Results show that the performance regarding these parameters is within the requirement range given by the California Air Resources Board (CARB) Standards and Test Procedures with few exceptions. Background emission rates are less than 0.1 mg/24 h over the CARB Diurnal Soak temperature profile. The parallel measurement of four parts using only one 1 m3 SHED reduces the costs per part considerably. The new Micro-SHED system allows testing more parts in the same time or measuring up to four identical samples in parallel to get more reliable results. This setup was used for the determination of emission rates of fuel hoses, pressure sensors, and injector seals.