The quality of automotive fuels—gasoline, diesel, biodiesel, and ethanol—is discussed in the light of their specifications in different countries and regions and in terms of their adulteration, which has such a prejudicial effect on the production chain, distribution chain, tax revenues, the environment, and end consumers. Different ways of adulterating automotive fuels are analyzed, as are the procedures for their detection. Several analytical methods for monitoring quality and detecting adulteration have been addressed in the literature, emphasizing the determination of properties such as density, distillation curve, octane rating, vapor pressure, etc., by means of physicochemical methods and chromatographic and spectrographic techniques, to the detriment of colorimetric methods. This chapter looks at colorimetric techniques designed for quality monitoring and the detection of adulteration in fuels, especially simple, quick, low-cost procedures with potential to be used in the field.
The failure of a fuel to meet any of its specifications is referred to as a nonconformity, which means the fuel is not fit for use. Nonconformity is not always due to adulteration, which is the deliberate and illegal addition of lower-cost substances to a fuel, usually with tax evasion, all with the purpose of increasing the profit margin by illicit means, resulting in reduced tax revenues, unfair competition, harm to the environment, and increased wear and tear of vehicle engines In fact, a fuel may be adulterated and yet stay within its specifications, in which case the only detrimental effect is on tax revenues. It is a challenge to detect the adulteration of fuels because adulterants usually include compounds that are already present in the fuels themselves
The illegal practice of fuel adulteration may impair the fuel’s quality while also resulting in increased environmental contamination by polluting gases and particulate matter because the combustion process is affected, leading to higher emissions of pollutants and compounds that cause acid rain, like NOx and SOx, as well as CO, which is highly asphyxiating.
The biggest detrimental effect of fuel adulteration is on the performance of the vehicle. In 2006, around 95% of vehicle repairs in São Paulo city, Brazil, were directly or indirectly attributable to poor fuel quality. Indeed, it has been estimated that fuel adulteration cost Brazil over 1 billion dollars that year, including 400 million dollars in lost tax revenues, affecting both local and federal budgets [9]. According to the Brazilian newspaper Estadão, a study done in 2017 by the Getúlio Vargas Foundation found that 4.8 billion reais is lost in the fuel sector every year to money laundering and tax evasion, with serious knock-on effects on the economy as a whole