Evaluation of Brazilian Fuel Quality by a Capacitive Microsensor

This work proposes a capacitive-type sensor to evaluate the quality o Brazilian automotive fuels (ethanol and gasoline). The sensor is processed on an alumina substrate and its electrodes are of interdigitated type. Because of its design, when it is placed in a gas tank or in a recipient containing the fuel, the gaps between its capacitors are filled by it. Then the fuel will become the dielectric of the capacitors of the sensor. A change on concentration of the fuel content results in a change of the dielectric constant. It can occur in case of mixtures gasoline-ethanol and ethanol-water (both used in Brazil). This change on dielectric constant changes the capacitance and others dielectric properties realizable by the sensor. In this way, the sensor can detect gasoline adulteration by alcohol, or by some solvents derived from petrol. In addition, it is possible to detect ethanol fuel adulteration by water (most common adulteration of this fuel). Several prototypes were processed and several tests were performed. During the tests, several adulteration cases have been simulated. The results show that the sensor is able to detect several types of adulterations of gasoline and alcohol fuel. Also, it is possible to use the sensor to detect the ratio alcohol-gasoline in flex-fuel vehicles.