**1. Introduction**

The quality of a fuel is associated with its fitness for use, the minimum requirements for which are given by its specifications, defined as a set of characteristics and their respective limits, which are required to ensure its good performance in engines. A comparison of the specifications for gasoline, ethanol, diesel, and biodiesel in different countries and regions is provided in the **Supplementary Material** to this chapter.

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 [1–5]. In fact, a fuel may be adulterated and yet stay within its specifications, in which case the only detrimental effect is on tax revenues [6]. It is a challenge to detect the adulteration of fuels because adulterants usually include compounds that are already present in the fuels themselves [2, 6].

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 [4, 7, 8].

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 [10].

According to ANP, the agency responsible for monitoring fuel quality in the country, gasoline can be adulterated in multiple ways, such as by the addition of ethanol over the maximum permitted limit or the illicit addition of light and heavy aliphatic and aromatic solvents, which are themselves constituents of gasoline [6].

Gasoline and ethanol are both adulterated with methanol in Brazil, which is not allowed to exceed 0.5% v/v due to its toxicity, but whose low price makes it an attractive adulterant [11]. Meanwhile, the main nonconformity found in diesel in Brazil is a failure to comply with the correct quantity of biodiesel, which is set by ANP at 10% v/v [12]. Petroleum products like fuels are extremely important inputs for economies, industries, and basic everyday activities all around the world. Their importance to governments—whether for geopolitical reasons or because of armed conflicts or economic factors—means they tend to be taxed heavily, which raises their cost to consumers. As a result, adulteration has become a common practice in regions as diverse as South America and South Asia [13].

In India, kerosene is subsidized, which makes it particularly popular for adulterating gasoline, along with other products like naphtha, rubber solvents, aromatics, ethanol, light and heavy aliphatic solvents, and lubricants [2, 14, 15]. In 2018, the Petroleum Institute of East Africa announced that up to 75% of the 33 million liters of kerosene consumed every month ends up contaminating diesel and gasoline: only 5 million liters is actually used every month for lighting and cooking [16].

Cases of gasoline adulteration with acetone and sec-butyl acetate were reported in Vietnam and China in 2016, although this practice is less widespread in Vietnam now with the introduction of new limits for ketones in its gasoline specifications. In China, gasoline is often adulterated with substances like naphtha, ethanol, methanol, and even silicon oil or waste chemicals containing silicon [17].

In France, the most common form of adulteration consists of the addition of soybean oil or used cooking oil to diesel. In the last 5 years, the European Commission has invested heavily in preventing fuel adulteration [18].

According to Mani et al. (2017), the parameters that affect which adulterants are used in fuels—including considerations such as profitability, availability, and chemical compatibility—vary from place to place. The main adulteration methods are blending small quantities of middle distillate fuels like diesel and kerosene in gasoline; blending waste lubricants in gasoline and diesel, because the lubricants are expensive to dispose of in compliance with environmental standards; and adding small quantities of heavier fuel oils to diesel [3].

In Australia, the Department of the Environment and Energy regulates the Fuel Quality Standards Act 2000, which legislates and provides the standards on fuel quality in the country. In Europe, mandatory quality requirements for automotive gasoline and diesel are laid down by Directive 98/70/EC.

**87**

**Table 1.**

*Gasoline specification.*

*Fuel Quality Monitoring by Color Detection DOI: http://dx.doi.org/10.5772/intechopen.86531*

**Supplementary Material**.

the Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants. Meanwhile, in Japan there are two standards for fuels: the mandatory standards set by the Central Environment Council, under the Ministry of the Environment, and the Japanese Industry Standards. The former are statutory requirements and regulate the Act on Quality Control for Gasoline and Other Fuels, which has been enforced since April 1996 [19]. **Tables 1**–**4** showing the gasoline, diesel, ethanol, and biodiesel specifications for each country or region are included in the

In the United States, ASTM International publishes standards on each type of fuel. Responsibility for setting the standards for fuel quality lies with
