Monitoring and Blending Biofuels Using a Microfluidic Sensor

Density measurements have long been used to monitor petrochemical distillation. The density of the petrochemicals decreases as one moves up the distillation column. Measuring the density or specific gravity of biodiesel has been reported to be the preferred method of blending biodiesel fuel for both accuracy and ease of use. To see widespread use, a measurement technology must not only be capable of accurately monitoring a parameter, but it must do so in an economical way. This paper explores the application of microelectromechanical systems technology to fuel monitoring, quality control, and blending. This microfluidic sensor has on-chip density/specific gravity, temperature, and viscosity measurement ca- pabilities, as will be demonstrated in the experimental results. The ability to differentiate between gasoline, ethanol, diesel, biodiesel, butanol, Fischer-Tropsch fuel, water, and air contamination with a density mea- surement and in some cases a viscosity measurement will be demonstrated. Using gravimetric measure- ments, based on fluid density, concentrations of fuel blends like ethanol-gasoline can be measured. Con- tamination levels of water in ethanol can also be measured in this manner. The density of fuel over temperature can be made with this sensing technology and applied to custody transfer. Potential microflu- idic clogging issues are addressed by filtration and by adding the capability of sensing flow through the sensor. Measuring fluids under high flow rates is accommodated with a bypass design. An intrinsically safe circuit has been developed to enable use of this technology with flammable liquids. Vibration testing has been undertaken to show that these micromachined devices, with their high resonant frequencies, are immune to vehicular and aviation vibration, unlike conventional density metres made using larger resonat- ing steel tubing.