New Trends in Automobile Fuel Analysis Sensors

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Abstract:

There is a great interest in fuel qualification since adulteration is a common practice with harmful consequences for the vehicle, such as engine malfunctioning, higher environmental pollution and tax evasion [1]. Two types of fuel are used in automotive vehicles in Brazil: gasohol and alcohol. Gasohol is a blend of anhydrous ethanol fuel and gasoline. Anhydrous ethanol may contain a maximum of 0.4% water by volume. The ethanol content in gasohol should be in the range of 18-27.5% v/v. The typical adulteration of gasohol occurs by the addition of a greater amount of alcohol than that one established by the government through the Brazilian National Petroleum Agency (ANP) [2]. This adulteration can damage some engine parts, e.g. diaphragms and rubber seals. Gasohol adulteration also occurs by the addition of organic solvents and aromatic hydrocarbons, such as alkanes, toluene, benzene, xylenes, hexane, complex hydrocarbon mixtures, mineral spirits, petrochemical naphtha, kerosene, rubber solvent, diesel, and thinner. These solvents present lower taxation in comparison to gasoline [3]. The other important fuel in the Brazilian energy matrix is the hydrous ethanol fuel, which should have purity ranging from 94.5 to 96.3% ethanol by volume and may contain a maximum of 4.9% water by volume [4]. Despite undergoing rigorous inspection, this type of fuel is usually altered by the addition of water above the allowed amount. One of the trends in the coming years is the increased embedding of electronic systems in modern cars [5], including those capable of qualitatively evaluating the presence of adulterants in the fuel. This work presents some new trends for qualifying fuel systems and sensors. First, analytical methods for determining automotive fuel composition are reviewed [6], such as nuclear magnetic resonance (NMR) spectroscopy [7], chemometric tools [8], high-performance liquid chromatography (HPLC) [9] and spectroscopic [10] methods. These usual analytical methods have some drawbacks: they must be made in a laboratory environment and they are expensive, complex and often apply sample-destructive techniques. Thus, greater attention is given to new approaches for detecting fuel quality based on new low-cost sensors, e.g. optical fiber sensors, infra-red (IR) and near IR (NIR) sensors [11], and nanomaterial-based sensors [12, 13]. A more detailed presentation is made for electromagnetic sensors methods [14], specially electrical impedance-based methods and the time domain reflectometry (TDR) technique [12]. These kinds of sensors can analyze the electromagnetic properties of fuels enabling in-situ and real-time monitoring while the vehicle engine is working. Besides, they can be combined with intelligent computation techniques [3, 15] to detect fuel adulteration and to allow the self-tuning of the engine for the best working conditions. The main results show the possibility of detecting fuels adulterants as well as the ability to analyze and to quantify ethanol/water and gasoline/ethanol/water mixtures. Through current research, we can predict, in the years to come, the use of embedded fuel qualification smart sensors will allow monitoring the fuel quality in real time, in-situ or remotely, increasing the lifespan of cars, enhancing their performance, and reducing the emission of pollutants in the environment.

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