Primary standard for traceability in low liquid hydrocarbon fuel flow rates

Abstract

We developed a primary standard for low liquid hydrocarbon flow rates that works on light oil (diesel), kerosene and industrial gasoline. To achieve a calibration accuracy of below 0.1% over a wide flow range from 0.02 L h−1 to 100 L h−1 as required by the industry, this primary standard adopts the gravimetric calibration method performing static weighing with flying-start-and-finish, incorporating a compactly designed conical rotating double-wing diverter for the upper flow range (1 L h−1 to 100 L h−1) and a pair of high-speed switching valves as a diverter for the lower flow range (0.02 L h−1 to 6 L h−1). The uncertainty of liquid mass measurement (in which the evaporation error is a dominant factor) as well as the uncertainty of liquid collection time (in which the diverter timing error is a major factor) are minimized to a level that curbs their dominance to the overall mass flow uncertainty. On the other hand, the uncertainty due to the estimation of liquid density at the flowmeter under test, which is a significant contributing factor to the overall uncertainty of volumetric flow, is being reduced by temperature control measures through a self-developed thermostatic chamber. Intra-facility and inter-facility comparisons within NMIJ were performed, all showing a good agreement, and hence providing supporting evidence for the calibration and measurement capability (CMC), which are 0.020%–0.044% for the mass flow rates and 0.044%–0.066% for the volumetric flow rates as claimed by the facility.