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Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)12976-3
10.1016/j.heliyon.2024.e36945
e36945
Research Article
Evaluation of physicochemical parameters as indicators of diesel adulteration
Dadson J.K. a
Arthur V. b
Asiedu N.Y. nasieducoe@gmail.com
c⁎
Akoto O. d
a Department of Biochemistry and Biotechnology, Kwame Nkrumah University of Science and Technology, Ghana
b Standards Directorate, Ghana Standards Authority, Ghana
c Department of Chemical Engineering, Kwame Nkrumah University of Science and Technology, Ghana
d Department of Chemistry, Kwame Nkrumah University of Science and Technology, Ghana
⁎ Corresponding author. nasieducoe@gmail.com
27 8 2024
15 9 2024
27 8 2024
10 17 e369455 1 2024
11 8 2024
25 8 2024
© 2024 The Authors
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
Diesel adulteration not only reduces engine performance and lifespan but also has a stiffening effect on the economy. Therefore, regulatory agencies and petroleum laboratories are constantly adopting various methods to ensure that commercial diesel is pure and of good quality. Despite the introduction of solvent tracer analysis as a reliable means of detecting adulteration, most laboratories still depend on the physicochemical parameters of diesel as an indicator of adulteration. This research aimed to document the feasibility of using quality parameters to detect diesel adulteration. Neat diesel samples were mixed with some common adulterants (kerosene, premix, and condensate) at varying concentrations. The quality of each admixture was analysed using the ERASPEC fuel analyser and physicochemical parameters including density, kinematic viscosity, cetane index, and flashpoint were recorded. A negative correlation was observed between adulteration and all quality parameters. At low levels of adulteration, physicochemical parameters were within the required range. However, diesel with adulterants above 20 % v/v had cetane index, density, and flashpoint values not conforming with quality standards. Kinematic viscosity of diesel remained within the required limits despite the levels of adulteration. Physicochemical parameters, though generally accepted as good indicators of fuel quality, were not reliable indicators of diesel adulteration, especially at low levels. At higher levels of adulteration, the type of adulterant present must be considered if physicochemical parameters are to be used to predict adulteration. However, it is recommended that physicochemical parameters be used in combination with other techniques to detect diesel adulteration.

Keywords

Diesel adulteration
Physicochemical parameters
Quality parameters
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pmc1 Introduction

With a higher density, diesel fuel produces more energy per unit volume compared to gasoline hence diesel engines are cost-effective in automobiles. In addition, diesel engines have become an apparent choice in heavy-duty vehicles and equipment due to their high thermal efficiency, torque capacity, low hydrocarbon and carbon monoxide emissions, versatility, and reliability Patil and Thipse, 2015. Africa is expected to have the fastest rise in fuel consumption amongst the continents of the world. It is predicted that over the next 30 years, diesel consumption will increase from about 2 million barrels per day (Mb/d) to approximately 6 Mb/d due to significant demographic and economic expansion Stratas Advisors, 2021.

Due to the high consumption of fuel and the continuous anticipated rise in demand, there is a tendency to increase fuel adulteration in an attempt to maximize profit while meeting consumer needs. In many developing countries, adulteration of fuel has become an issue of serious concern Gawande and Kaware, 2013. Adulteration is often attributed to the substantial price discrepancies between the fuels and the adulterants mostly as a result of subsidization Kulathunga and Mahanama 2013. There have been high levels of fuel adulteration recorded in most developing countries [1]. In Brazil, 40 % of fuel samples randomly selected from filling stations had varied degrees of adulteration [2]. Similarly in Morocco, fuel tests carried out in 2015 revealed an increasing trend in adulteration (Council, 2017). There have been reported incidences of fuel adulteration in Ghana where oil marketing firms and fuel station operators mix premium quality refined diesel fuel with substances such as kerosene, premix, condensate, and vegetable oils Boadu, 2019. Dadson et al. [3] sampled fuel at random from filling stations in a metropolis in Ghana and detected approximately 7 % of adulteration. A study conducted in Ghana also revealed 32 % of varying levels of fuel adulteration among retail outlets [4].

Diesel adulteration is a deliberate contamination of diesel and is usually motivated by the desire to increase profit margins permitted to Oil Marketing Companies (OMCs) and fuel outlets. Hence it can be inferred that financial incentives resulting from differential taxes are the primary cause of adulteration. Diesel adulteration primarily is the blending of low-cost products with relatively high-cost diesel fuel. Factors such as easy miscibility, pricing, availability, and similar physicochemical qualities to diesel, influence the choice of adulterant. The most common diesel adulterants include kerosene, waste oils, vegetable oils, solvents, and alcohols [5]. In Ghana, adulteration with kerosene, premix fuel, naphtha, and condensate is mostly encountered Boadu, 2019.

Adulteration often results in non-conformance with regulatory requirements and degradation in the quality of the diesel which can negatively affect the efficiency of engines. Depending on the degree of adulteration, there may be obstruction of the fuel injection system, increased carbon deposition, and increased corrosion Gontijo et al., 2014. These can result in declined engine efficiency, damage to engine parts, vehicle component failure, increased emissions, and economic losses (Babu and Mani, 2017; [5]). An increase in the emission of harmful gases such as carbon monoxide, oxides of nitrogen, hydrocarbons, and particulate matter has a negative impact on air quality and may be detrimental to the environment and human health [6].

Detection of adulteration using fuel quality assessment remains a common practice of several laboratories and regulatory agencies globally. This is based on the assumption that physicochemical indices such as cetane index, density, flashpoint, and kinematic viscosity deviate from permissible ranges in contaminated fuel. A decrease in the kinematic viscosity of diesel fuel due to adulteration has been reported by Yadav et al. [7] and Boadu [8]. Flashpoint and opacity have been observed to also decrease with increasing diesel adulteration. According to Kadhim [9], the addition of adulterants to diesel can alter the cetane index of the diesel fuel. The cetane index indicates the fuel's auto-igniting capability and has a direct effect on ignition delay, a high cetane index implies shorter ignition delay and vice versa. Kerosene as a diesel adulterant can lead to the formation of sulphuric acid on combustion which has been identified as one of the factors known to cause significant engine damage and atmospheric acid pollution. However, it is also shown that some adulterants do not significantly affect the physicochemical properties of diesel. Yadav et al. [7] and Vempatapu et al. [10] reported no observable density differences at varying levels of adulteration hence suggesting that density may not be a useful indicator of diesel purity. Density and viscosity are important parameters for evaluating engine performance and tailpipe emissions. Variations in the density and viscosity of diesel fuel have been discovered to affect fuel injection timing which can result in changes in engine power and consequently, engine emissions and fuel consumption and eventually engine damage [11].

A sensitive method of detecting fuel adulteration that has been adopted by most developing countries is the solvent tracer analysis which employs unique identifiable markers. The marking system helps to distinguish between different petroleum products and exposes any modifications and/or adulterations [12]. Due to the tremendous cost of implementation amongst other limitations, most laboratories still rely on physicochemical quality assessment to determine adulteration. The addition of petroleum-based adulterants presents a challenge in detecting diesel adulteration. While there has been extensive research on diesel adulterated with kerosene, there is a paucity of information and documentation on how other common petroleum-based adulterants affect diesel quality. This study therefore sought to determine how physicochemical parameters change in response to the addition of such adulterants to diesel. The study demonstrates the potential of using physicochemical indicators to detect condensate- and premix-adulterated diesel.

2 Materials and method

2.1 Sample collection

Diesel samples as well as selected adulterants (kerosene, premix, and condensate) were obtained from CHASE (Bulk Distribution Company, BDC) and the Tema Oil Refinery (TOR) in Ghana and stored in sealed amber glasses before analysis. All samples were certified by the Ghana Standards Authority (GSA) and Ghana Oil Company (GOIL) to be in conformance with the required national quality standards.

2.2 Sample preparation and analysis

Diesel-kerosene admixtures were prepared by adding varying concentrations (5–40 % v/v) of kerosene to diesel. The same procedure was used to prepare diesel-condensate and disel-premix admixtures. The final volume for each admixture was 100 mL. Analysis of fuel quality was done using the Eralytics fuel analyser machine, ERASPEC shown in Fig. 1. ERASPEC provides a simple and fast approach to determining fuel component concentrations and complex properties by direct measurement or using chemometrical models based on fuel libraries. All measurements by the ERASPEC fuel analyser are done in accordance or correlation with ASTM, EN, and ISO standards.Fig. 1 ERASPEC fuel analyser.

Fig. 1Source: Kareem et al. [13].

The prepared samples were placed in a sample container of the fuel analyser and the sample inlet tube was inserted. Samples were run in triplicates and fuel quality parameters recorded were density at 15 °C, cetane index, kinematic viscosity at 40 °C, and flashpoint. These parameters were selected as they are indicators of key fuel properties. Density and kinematic viscosity are indicative of flow and injection quality whereas the cetane index serves as a measure of performance and efficiency. Flashpoint relates to the handling and transportation safety of the fuel.

After each run, there was an automatic rinsing with the next sample. With a temperature-controlled U-tube density meter, ERASPEC can measure density in full compliance with ASTM D4502. Cetane index, kinematic viscosity. and flashpoint, as measured and reported by the analyser, were in correlation to ASTM D976, ASTM D445, and ASTM D93 respectively. Experiments were carried out in the laboratories of Ghana Oil Company (GOIL).

2.3 Data analysis

Microsoft Excel was used to calculate the mean and standard deviation for each triplicate measurement. The PAST statistical software was used to compare the differences between measurements using ANOVA. Correlation analysis was performed using the SPSS software to determine the relationship between the quality parameters and the levels of adulteration.

3 Results and discussion

3.1 Effect of adulteration on density of diesel

From Fig. 2A, it can be observed that there was a decrease in density upon addition of the different adulterants (Kerosene, Premix, and Condensate). Fig. 2B showed that about 99 % of the variation in density recorded was a result of increasing concentration of the adulterants. There was a strong negative correlation between diesel density and the selected adulterants (Kerosene, Premix, and Condensate). Adulteration with kerosene decreased the density of the diesel fuel from 827.5 to 815.6 kg/m3. This decrease could be attributed to kerosene being a lighter hydrocarbon mixture than diesel. Premix and condensate which are lighterweight hydrocarbons decreased the density to 788.5 and 770.1 kg/m3 respectively. Based on this observation, it could be assumed that the lighter the weight of the adulterant, the greater the magnitude of the decrease in density. According to the quality standards for diesel fuel in Ghana set by the Ghana Standards Authority (GSA), the density for diesel fuel should range between 820 and 850 kg/m3.Fig. 2 (2A) Effect of varying levels of adulteration on density of diesel (2B) Correlation between level of adulterant and diesel density.

Fig. 2*[Datapoints for a specific adulterant with different alphabets are significantly different (p < 0.05); Short dash lines indicate upper and lower required limit of density for diesel fuel in Ghana]

Diesel adulterated with kerosene (up to 30 % v/v) complied with the standard requirement as shown in Fig. 2A. However, the addition of 40 % v/v of kerosene to the diesel significantly decreased the density below the required permissible limit. For premix and condensate, the density of the diesel was shifted below the limit upon the addition of more than 5 % v/v adulterants. Since modern injectors are designed to supply the right amount of fuel into the combustion chamber based on volume, a decrease in density will result in less mass of diesel reaching the injectors and hence less energy released upon combustion. The observed decrease in the density of the diesel fuel after adulteration is consistent with work by Boadu [8]. He reported a decrease in the density of diesel from 850 to 838 kg/m3 after adulteration with 40 % v/v kerosene. Yadav et al. [7] also reported a decrease in density of adulterated diesel. They further indicated that the density remained within the prescribed range even at higher adulteration levels.

3.2 Effect of adulteration on cetane index of diesel

Although there was an overall reduction in the cetane index, diesel adulterated with kerosene and premix at higher adulteration levels remained above the minimum requirement of 50, as illustrated in Fig. 3A. However, at 30 % v/v and 40 % v/v addition of condensate, a significant reduction in the cetane index resulting in non-compliance with the required minimum value was observed. At 40 % v/v diesel adulteration, the cetane index reduced from 54.0 to 51.5, 52.1, and 46.7 for kerosene, premix, and condensate respectively. From Fig. 3B, it could be observed that there was a strong negative correlation between the cetane index and adulteration levels. Correlation coefficients (R2) recorded for the selected adulterants were higher than 0.92 signifying that the observed decrease in cetane index was actually due to the increasing addition of adulterants.Fig. 3 3A) Effect of varying levels of adulteration on cetane index of diesel 3B) Correlation between level of adulterant and cetane index of diesel.

Fig. 3[Datapoints for specific adulterant with same alphabets are not significantly different (p < 0.05); Short dash lines indicate minimum required cetane index for diesel fuel in Ghana]

A high cetane index is indicative of good quality and shorter ignition delay. Therefore, addition of adulterants to diesel fuel affects the ignition properties and performance of the fuel. Cetane index also directly relates to engine performance, efficiency, noise production, and emissions Kalligeros et al., 2003. The reduction in the cetane index aligns with research by Chikwe et al. [14]. They observed that the addition of condensate to diesel fuel from some reservoirs in Nigeria significantly reduced the cetane index of the fuel. Similarly, Vempatapu et al. [10] reported a decrease in cetane index from 55 to 48.5 after adding 40 % v/v kerosene.

3.3 Effect of adulteration on kinematic viscosity of diesel

A decrease in kinematic viscosity was recorded with increasing levels of adulteration for all the adulterants. The kinematic viscosity decreased from 4.5 to 3.5 cSt after adulteration with 40 % v/v kerosene. A decrease to 3.2 and 3.9 cSt was also recorded for premix and condensate respectively. The reduction in kinematic viscosity may be attributed to the low viscosity of the adulterants compared to diesel. Fig. 4A shows that there was no significant decrease in kinematic viscosity even at 20 % v/v adulteration levels. However, a significant decrease was observed after the addition of 30 % v/v of each of the adulterants. Despite the decrease, kinematic viscosity remained within the permissible range of 2.0–4.5 cSt at 40 °C according to the diesel fuel standards in Ghana. It can be deduced from Fig. 4B that over 90 % of the observed variation was due to varying levels of adulteration. This implies that there is a strong negative correlation between the kinematic viscosity of diesel and adulteration with kerosene, premix, and condensate.Fig. 4 4A) Effect of varying levels of adulteration on kinematic viscosity of diesel: 4B) Correlation between level of adulterant and kinematic viscosity of diesel.

Fig. 4[Datapoints for specific adulterant with same alphabets are not significantly different (p < 0.05); Short dash lines indicate upper limit for kinematic viscosity of diesel in Ghana]

The adulterated diesel fuel may not provide enough lubrication to injectors and plungers as low kinematic viscosity affects the lubrication properties of diesel fuel Boadu, 2019. According to Das [15], decrease in kinematic viscosity may potentially lead to leakage in the fuel system. A similar decrease in kinematic viscosity has been reported by Vempatapu et al. [10]. Their research revealed a decrease from 2.86 to 1.95 cSt at 40 °C with increasing kerosene concentration. Work done by Yadav et al. [7] also showed a decrease in kinematic viscosity from 2.63 to 1.89 cSt when diesel fuel was adulterated with kerosene.

3.4 Effect of adulteration on flashpoint of diesel

The flashpoint of diesel decreased from 80.9 °C to 58.2 °C, 49.3 °C and 44.2 °C after the addition of 40 % v/v of kerosene, premix, and condensate respectively. Correlation coefficients greater than 0.89 were recorded for selected adulterants as shown in Fig. 5B. This suggests that there is a significant correlation between flashpoint and adulteration: increasing adulterants decreases the flashpoint of diesel. The reduction in the flashpoint of the diesel fuel could be a result of the lightweight hydrocarbon fractions of the added adulterants. As per specifications, diesel fuel is expected to have a minimum flashpoint of 55 °C. Even at higher adulteration levels, the flashpoint of diesel adulterated with kerosene still complied with the minimum standard limit as observed in Fig. 5A. However, for premix and condensate adulterations, higher adulteration levels above 30 % v/v shifted the flashpoint below the minimum threshold.Fig. 5 5A) Effect of varying levels of adulteration on flashpoint of diesel 5B) Correlation between level of adulterant and flashpoint of diesel.

Fig. 5[Datapoints for specific adulterant with different alphabets are significantly different (p < 0.05); Short dash lines indicate minimum required flashpoint for diesel fuel in Ghana]

The decrease in flashpoint to a level below the standard requirement is indicative of a higher risk of potential fire hazard. Flashpoint is the lowest temperature at which a fuel can ignite in the presence of an ignition source. Therefore, a reduction in the flashpoint of diesel fuel due to adulteration threatens the handling and transportation safety of the fuel which could lead to explosions and accidents. The observed decrease in the flashpoint is consistent with the findings by Boadu [8]. He reported a decrease from 73 to 58 °C after the addition of 40 % v/v kerosene to diesel.

4 Conclusion

Increasing levels of adulterants (kerosene, premix, and condensate) resulted in a decline in all quality parameters assessed. The density of diesel adulterated with more than 5 % premix or condensate did not conform to the requirement. All other quality parameters were within the required range upon addition of low levels of adulterants though these adulterants may affect engine performance and cause environmental pollution.

Adulterating diesel with more than 20 % condensate reduced the cetane index below the required limit. Similarly, the density of diesel-kerosene mixtures (above 30 % v/v) did not conform to the quality standard. High levels (>30 % v/v) of condensate and premix in diesel resulted in non-compliance with the set standard for flashpoint. However, kinematic viscosity conformed to the criteria for diesel regardless of the adulterant present.

From the results, it can be inferred that no single quality parameter was a good indicator of diesel adulteration. It can also be concluded that at low levels of adulteration, physicochemical parameters are not reliable indicators of diesel purity. At high levels of adulteration, it is prudent to consider the type of adulterant if quality parameters are to be used to detect adulteration in diesel. It is therefore recommended that more sensitive, reliable, and cheaper methods should be developed for the detection of diesel adulteration.

Data availability statement

The authors confirm that processed data supporting the findings of this study are available within the article. Raw data were generated at the laboratory of Ghana Oil Company, and are available from the corresponding author, Asiedu, N. Y., on request.

CRediT authorship contribution statement

J.K. Dadson: Writing – original draft, Visualization, Validation, Methodology, Formal analysis, Data curation, Conceptualization. V. Arthur: Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. N.Y. Asiedu: Writing – review & editing, Supervision, Methodology, Conceptualization. O. Akoto: Writing – review & editing, Supervision, Data curation, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors would like to express their sincere gratitude to Mr. Kofi Amo-Asante of the Tema Oil Refinery, Ghana and Mr. Francis Bonsu of the Ghana Oil Company (GOIL) for providing the fuel samples used in the research. Sincere gratitude to the management and staff of GOIL for providing laboratory space and instrument used in the analysis of samples.
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