Fuel sold in Ecuador

Fuel is any material capable of releasing energy when burned and then changing or transforming its chemical structure. The term fuel is limited to those substances that burn easily in air or oxygen by emitting substantial amounts of heat. It involves the release of an energy from its potential form into a usable form (because it is a chemical reaction, it is known as chemical energy) (^{Encalada & Ñauta, 2010}). The gasoline sold in the city of Guayaquil comes from the La Libertad refinery (^{Montero Mosquera, 2020}). This refinery around 45.000 barrels per day of derivatives with an average annual load of 14´850.000 barrels (^{Coral Guerrero & Encalada Rojas, 2017}).

The commercialization of petroleum and its derivatives in Ecuador is carried out by EP Petroecuador through the National and International Marketing Departments, following internal processes to meet local demand, with optimal quality standards with social and environmental responsibility (^{Coral Guerrero & Encalada Rojas, 2017}). The supply and marketing of fuels at the local level is summarized in Figure 1 below (^{Coral Guerrero & Encalada Rojas, 2017}).

Source: ^{Coral Guerrero & Encalada Rojas, 2017}

Figure 1 Supply & fuel chain  

The most used fuels in the automotive industry are gasoline, diesel, and liquefied petroleum gas. Gasoline is a product obtained through the fractional distillation of crude oil, which means that depending on the crude oil being processed, it can either be a single fraction or a blend of several fractions. Gasoline consists of a mixture of hydrocarbons with relatively low molecular weight. It must be volatile enough to burn easily and improve cold starts, but not so volatile that it generates excessive vapor in hot weather conditions (^{ICCT, 2011}). In Ecuador, the predominant fuels for taxis and motorcycles are Extra and Ecopaís gasoline. Notably, 70% of the motorcycles in the country are of Chinese origin (^{AEADE, 2023}), meaning their emission regulations adhere to China’s National Stage III standard, equivalent to Euro 3. This standard imposes significantly lower emission requirements compared to those for automobiles (^{Deng et al., 2019}).

Gasoline sold in Ecuador

The most important parameter of our gasoline is the octane number. Three types of gasoline are used in the country: Super, Eco-País and Extra (^{Fernández Mora & Mideros Mora, 2023}; ^{Herrera-Franco et al., 2022}). The octane number of the engine correlates with the anti-knock performance of commercial internal combustion engines under severe operating conditions. This engine octane number is used by engine manufacturers, petroleum refiners and retailers, and in commerce as a related primary specification measurement for the pairing of fuels and engines (^{Instituto Ecuatoriano de Normalización, 2013a}).

Eco-País gasoline, a biofuel composed of 5% bioethanol (from sugar cane) and 95% base gasoline (^{Terneus-Páez & Viteri-Salazar, 2023}). Eco-País has the same octane rating (87 octane) and price of Extra gasoline. For the production of Extra gasoline with 87 octanes, it is necessary to mix 76% of high-octane naphtha (NAO), which is imported, with 24% of low-octane naphtha (NBO); while for the production of ECOPAÍS, with the same amount of octane, 62% of NAO, 33% of NBO and 5% of bioethanol are required (^{Castillo-Hernández et al., 2012}). Super gasoline is the highest quality fuel found in the city of Guayaquil for use in high-performance vehicles. It is used in engines that have a high compression ratio. Mainly the isoparaffinic and aromatic hydrocarbons (benzene chains that raise the octane index) found in super gasoline resist high pressures and temperatures (^{INSST, 2013}).

Importation and sales of motorcycles in Ecuador

Figure 2 shows the number of motorcycles that were imported from 2019 to 2021 according to reports from the Association of Automotive Companies of Ecuador.

Source: ^{AEADE (2021)}

Figure 2 Importing motorcycles in Ecuador 

Regulations for indicating the technical characteristics of fuel

In Ecuador there is the NTE INEN 935 Standard (^{Instituto Ecuatoriano de Normalización, 2021}) (^{Diario Oficial de las Comunidades Europeas, 1998}), which is responsible for establishing what value according to parameter the gasoline that is being sold must meet, in Table 1 below you can see these mandatory characteristics (^{Freepik, 2022}; ^{Tribologik, 2013}; ^{Motorgiga, 2000}).

Selection of petrol stations

We proceed to investigate which selected gas stations are operational in the province of Guayas, which includes Guayaquil, Samborondón and Durán, to place them in a list as shown in Table 2, after this we have the purpose of choosing fuel samples for their respective analysis.

A market analysis is carried out at these gas stations and the method used was the counting of motorcycles (^{Motorecambios VFerrer, 2020}; ^{Toledo Montaleza, 2016}) at each service station in such a way that it can be achieved to have an idea of the influx, this is detailed in Table 3.

Considering that the Dixon statistical analysis (^{Statologos, 2022}), it lets us know if there is an outlier in a dataset that should be discarded. That said, we relied on this criterion to be able to select the number of gas stations that are going to be chosen to sample, it was determined that it had to be a minimum of 3 gas stations since, to apply Dixon to the results obtained. It determines that the number of samples to apply this theory is from a minimum of 3 to 30 samples maximum (^{Rorabacher, 1991}), as shown in Table 4.

This selection of 3 gas stations is due to the excessive cost of the laboratories to analyze the fuel of approximately $2.500 for each sample. The gas stations selected are Gómez Rendón, Portete and vía Durán Tambo according to Dixon's analysis.

Selection of laboratories

For the selection of laboratories, the difficulty in Ecuador is to find a laboratory where all the necessary tests are carried out.

Below is the list of laboratories that carry out these tests, however, for this project we only worked with 2, which are the laboratory of the Department of Petroleum, Energy and Pollution of the Central University and the laboratory of Fuels, Biofuels and Lubricating Oils of the National Polytechnic School. Table 5 shows the list of laboratories that were investigated to make the respective quotation.

Each laboratory has its fundamental requirements for the correct collection and transport of samples. The fuel is stored in an amber glass jar and moved to a temperature of no more than 30 degrees.

Another requirement is to place a label on the bottle indicating where they come from, the date of the sample and the type of gasoline, in this way we can avoid confusion at the time of analysis.

Figure 3 shows 4 amber containers, 2 of 250 milliliters, which are the smallest, these were delivered to the laboratory of the Central University of Ecuador, and the other two of 1 liter were delivered to the National Polytechnic School.

Figure 3 Storing Samples in Amber Bottle 

The results of the selected laboratories are placed in Table 6 to visualize the difference in the values obtained according to the ASTM D86 standard (^{Laboratorios DPEC y LACBAL, 2022}; ^{Universidad Internacional del Ecuador, 2021}).

As shown in the results, there are variations in each of the parameters, so the Minitab application is used to know the normality criterion, which is a determining detail to apply the Dixon method and thus establish the gas station that provides the best parameters.

Application of Dixon's theory in parameter vehicles

Minitab software is used, to know the criterion of normality and then apply Dixon's theory in each parameter of the results obtained in the laboratory of Super gasoline, to determine the feasibility of each of the 3 gas stations established and thus validate the results. To be able to apply Dixon to the values obtained by the laboratories, it is essential to know that the data set follows a normal distribution. The Minitab program was used to find out if it effectively complies with the analysis of knowing how much the distribution of the data obtained differs based on the expected data.

Placing Data in Minitab Sheet

The values obtained are placed on the worksheet (Figure 4), it is necessary to include a title to keep a correct order.

Figure 4 Worksheet in Minitab 

Normalcy Test Selection in Minitab

You look for the stats tab (Figure 5), where you select basic stats, then normality test (^{Rodó, 2006}).

d en Minitab

Figure 5 Normality test in Minitab 

Anderson-Darling Test Selection

A screen is displayed with the different tests that can be performed to check normality, in this case Anderson-Darling was selected (^{Flores Tapia & Flores Cevallos, 2021}). Select the dataset that belongs to C1 on the left and click OK (Figure 6).

Figure 6 Normality tests available 

Obtaining a graph of the Normality Criterion

As can be seen in Figure 7, a p-value is obtained, which serves as a criterion to determine whether the set of results for Super gasoline follows a normal distribution.

Figure 7 Chart to check Normality 

Normality test results applying Anderson-Darling in Minitab

Below is a breakdown of normality testing by applying Anderson-Darling in Minitab software (^{Closas et al., 2010}), of each of the parameters investigated, i.e. octane number, distillation temperature at 10%, 50%, 90%, boiling endpoint, vapour pressure, gum content and sulphur content.

Octane Normality Test

Analyzing the octane parameters in Minitab shows that the obtained value of P = 0,472 > 0,05 (Figure 8). Since the p - value is greater than the significance value of 0,05, the probability that the data obtained at the three gas stations follows a normal distribution cannot be rejected. In the case of this parameter, the highest-octane parameter, which is the Portete gas station, will be taken as a base.

Figure 8 Octane probability graph 

Figure 9 shows the histogram of how this dataset follows a normal distribution.

Figure 9 Octane histogram 

Results for all parameters applying Dixon

As can be seen in Table 9, Dixon is applied for each parameter (number of octanes, distillation temperature at 10%, 50%, 90%, boiling endpoint, vapor pressure, gum content and sulfur content) for each parameter there is a population of 3 samples, for the calculation of the outlier value was considered for both the maximum and the minimum value of the data set.

After applying the respective formula, the values detailed in the calculated Q column were collected, because all the values shown in Table 7 do not exceed the critical Q (0,97), it is determined that there are no outliers (^{Chorro, 2010}), that said, it is concluded that all values within this population can be selected for analysis.

As shown in Table 9, the gas station that complies the most is La Portete, therefore it is verified with the INEN 935 standard (^{Instituto Ecuatoriano de Normalización, 2013b}).