A Sensing Method for Quality Assessment of in-Vehicle Liquid Fluids

Abstract: This thesis studies a sensing method for assessing the quality of liquid fluids used invehicles such as fuel, urea, break oil and coolant, etc. Dielectric constant is one of the important indicators of liquid fluids quality. When the dielectric constant is measured, comparison between the dielectric constant of used fluid and unused one can indicate the presence of contaminants such as water or particles, or changes in chemistry of the fluid such as additive depletion or oxidation happening by time. There are different methods for estimating dielectric constant of liquids. In the literature study for this project after studying physical and mathematical principles of different methods the Method of Time Domain Reflectometry (TDR) is chosen for measuring dielectric constant of the liquid fluids. Applying Time Domain Reflectomety method, the reflections result from a signal generated by signal generator, traveling through study sensor which is partially submerged into the liquid under test is investigated. The reflected signal together with the incident one plotted in time domain received via oscilloscope, is then being analyzed. A measurement of the reflection from and/or transmission through a material along with the knowledge of its physical dimensions provides information to characterize the refractive index or dielectric constant of that material. Transmission line is best way to investigate the signal which travels form one point to another point. The prototype sensor forms a coaxial transmission line, and the theory behind it is very helpful to understand the form, amplitude and timing of the reflected wave. The literature on this theory supports finding the sensitivity of study sensor with respect to a small change in dielectric constant of the liquid under test and its helpful to approach the long term goal of installing a sensor on-board to satisfy the strong desire in automotive industry and monitor the quality of in-vehicle used fluids in real-time.