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Article

Investigation of Water-in-Diesel Emulsion Behavior Formulated for Performance Conditions in a Single-Cylinder Diesel Engine

by
Pedro Oliveira
1,*,
Francisco Brójo
2,
Rogério Serôdio
3 and
João Serôdio
4
1
Centre for Mechanical and Aerospace Sciences and Technologies (C-MAST), University of Beira Interior, 6200-358 Covilhã, Portugal
2
Department of Aerospace Sciences, University of Beira Interior, 6200-358 Covilhã, Portugal
3
Department of Mathematics, University of Beira Interior, 6201-001 Covilhã, Portugal
4
Energy Safety Research Institute, Swansea University, Swansea SA1 8EN, UK
*
Author to whom correspondence should be addressed.
Energies 2025, 18(4), 934; https://doi.org/10.3390/en18040934
Submission received: 21 January 2025 / Revised: 4 February 2025 / Accepted: 13 February 2025 / Published: 15 February 2025
(This article belongs to the Special Issue Advances in Fuel Energy)
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Abstract

:
The search for alternative fuels is driven by increasing environmental and health concerns across the globe. Water-in-diesel emulsions (WiDEs) have been explored over the years as a potential fuel for diesel engines to mitigate emissions of greenhouse gases, especially nitrogen oxides and smoke. Researchers have been developing and testing different formulations of emulsified fuels with the common goal of stabilizing the mixture and minimizing pollutant emissions without significantly compromising engine performance. In this work, a novel approach is taken by developing a hydrophilic emulsion formulation optimized for engine operating temperatures, overcoming the storage-related stability issues that most studies focus on. Two different mixtures of WiDE were heated and supplied to a Hatz 1B40 single-cylinder diesel engine. The engine was coupled to an eddy current dynamometer to measure speed, torque, and power values. Emissions of carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HCs), nitric oxide (NO), and oxygen (O2) were measured by an AVL DiGas 1000 exhaust gas analyzer. Smoke emissions were measured by an AVL DiSmoke 480. This study represents a contribution to the field of alternative fuels for diesel engines by providing experimental evidence that formulating WiDE for operating temperatures can be advantageous and significantly improve thermal efficiency and reduce emissions of NO and smoke at specific engine operating conditions, with a maximum reduction of 46.86% for NO emissions and a maximum reduction of 83.67% for smoke emissions obtained when compared to diesel.

1. Introduction

Motivated by an inspiring lecture and since its invention by Rudolf Diesel in 1897 [1], diesel engines have been used as one of the most efficient options in the realm of internal combustion engines [2,3,4]. The reduced values of specific fuel consumption are, however, opposed by pollutant emissions that directly impact the environment and our health, especially nitrogen oxides (NOx), particulate matter, and smoke [5,6], mostly due to its heterogeneous combustion [7] leading to localized fuel-rich zones and higher temperatures [8]. Several emission reduction technologies have been implemented over the years [9]. Diesel particulate filters [10], selective catalytic reduction [11], diesel oxidation catalysts [12], and exhaust gas recirculation [13] are examples of some after-treatment systems significantly contributing to the reduction in pollutant emissions. However, not only do these systems increase the total weight of the engine, but they also significantly increase its cost [14]. Water-in-diesel emulsion (WiDE) is an alternative fuel capable of adapting to the thermodynamic cycle of compression-ignition engines (CI), while reducing fuel consumption and emissions [15,16]. For this alternative fuel, small water droplets are dispersed in a continuous diesel medium [15,17]. Due to surface tension and other actuating forces, these two phases are unable to remain static, and even though short time stability may occur, stability for longer periods is not attainable [18]. To solve this issue, two pathways can be followed [19]: producing the emulsion instantaneously and rapidly feeding it to the engine fuel system [20,21,22], or adding emulsifiers and having it stabilized for a longer period [23,24,25]. Even though the first option would eliminate any storage issues [26], it is more complex to achieve and overall less explored. The second option is more common and has been widely adopted by different researchers [27]. It involves the addition of surfactants, which are emulsifying substances responsible for lowering the interfacial tension of the system [28], making it easier for water droplets to disperse in the fuel, forming micelles [29]. These surface-active agents are labeled as amphipathic molecules due to their dual nature of hydrophilic and lipophilic parts [30]. The lipophilic tail of a surfactant is usually composed of a hydrocarbon and therefore turns towards the oil phase [31]. The polar head (hydrophilic) defines the ionicity of the surfactant and turns towards the water [18]. Based on their charge, they are classified as anionic, cationic, zwitterionic, or non-ionic (neutral charge) [32]. Non-ionic surfactants are often adopted for WiDE fuels as their ability to not dissociate into ions prevents the worsening of exhaust emissions, making them relatively non-toxic when compared to the other types [33]. By stabilizing the mixture, they allow the emulsion to be safely supplied to the fuel lines without risking phase separation and possibly shutting down the engine [34]. Emulsions can be divided into macroemulsions, kinetically stable nanoemulsions, and thermodynamically stable microemulsions [35,36,37]. Nanoemulsions and microemulsions are preferred for fuel applications as they exhibit higher shelf life, lower viscosity, and lower energy required to emulsify [37]. Several benefits have been found from utilizing WiDE fuels when it comes to performance and pollutant emissions. When sprayed into a hot combustion chamber, the surfaces of the fuel droplets start heating. As the boiling point of water is lower than diesel, the dispersed water molecules reach their superheated stage first, evaporating and splitting the parent droplet in violent processes known as puffing and micro-explosion [38,39]. An initial larger droplet of fuel is split into smaller ones, increasing the surface area in contact with the surrounding air [40], leading to better air/fuel mixing in the engine cylinder. This secondary atomization [41] can potentially lower the emission of some pollutants after combustion.
Many researchers have investigated the effects of WiDEs on CI engines; however, achieving a strong correlation between the different parameters remains challenging. Experimental conditions, such as engine type, equipment used, applied load, fuel properties, water properties, surfactants used, ratio of the mixture, mixing method [42], and others, significantly vary between the different studies. More recently, Tamam et al. [43] tested an emulsifier-free WiDE with water percentages of 3, 6, 9, 15, and 20 by mass at 20, 40, 60, and 80% engine loads in a 5900 cc common rail turbocharged diesel electric generator and found that increasing water content resulted in a reduction in brake-specific fuel consumption (BSFC), an increase in brake thermal efficiency (BTE), and a reduction in NOx emissions and smoke opacity. Okumuş, Kaya, and Kökkülünk [44] tested WiDEs with water percentages of 5, 10, and 15 by mass with a fixed surfactant ratio of 2% by mass of Tween 80 and Span 60 in a 510 cc single-cylinder diesel engine under full load conditions at engine speeds of 1500 and 2800 rpm and found a 5.22% and 5.46% respective power reduction with emulsified fuel usage, an increased BSFC of 7.42% and 8.96%, and lower NOx emissions, with a maximum reduction of 16.85% for the 10% water content emulsion, when compared to diesel. Woo and Lee [17] developed WiDEs composed of 10 and 20% water by mass and 2% surfactant content of polyglyceryl-4 oleate and tested them on a 2200 cc common rail diesel engine at brake mean effective pressures (BMEP) of 2, 4, 6, 8, and 10 bar at engine speeds of 1000, 1500, and 2000 rpm, adjusting injection timing to optimize pollutant emissions. They found increased exhaust gas temperatures with retarded injection timing and reduced NOx emissions. These emissions decreased with the increase in water content. For the 20% water content WiDE, PM emissions were almost non-existent by retarding the injection timing according to the amount of NOx emissions. They found that combustion duration is correlated with water content and not injection timing, decreasing the duration with the increase in water content. They also found that low-load conditions lead to ignition delay, requiring injection timing calibration to control the combustion process. Mondal and Mandal [25] prepared a WiDE with a 10% water and 2% surfactant ratio of Tween 80 and Span 80 by volume via ultrasonication and tested it in a 661 cc single-cylinder diesel engine at loads of 2, 4, 6, 8, 10, and 12 kg, injection pressures of 160, 190, 210, and 250 bar at a speed of 1500 rpm, and found reduced brake-specific energy consumption and a maximum BTE increase at 210 bar of 3.3% when compared to diesel. They found that NOx and smoke emissions were lower than diesel, increasing and decreasing, respectively, with the increase in injection pressure. Maximum reductions were also found at 210 bar with values of 32.6% and 51.9%, respectively. Emissions of carbon monoxide (CO) were higher for the emulsified fuels at every load condition.
Most of these studies target the utilization of WiDE fuels that are stable at ambient temperatures, therefore optimizing the formulation for storage purposes [45]. This often leads to an unbalanced emulsion formulation when temperature and pressure naturally increase from the fuel tank to the fuel injectors, affecting its thermodynamic stability and producing unoptimized results. As prior studies generally focus on storage stability, the surfactants and mixing methods utilized are aimed at preventing phase separation between the oil, water, and surfactant at room temperature. The increased temperatures, pressures, and shear forces encountered in the fuel system easily destabilize conventional formulations, deteriorating combustion and increasing emissions.
This study addresses this crucial gap by suggesting a novel WiDE formulation explicitly designed for engine operating states, ensuring stability at this condition rather than ambient storage. This approach not only mitigates the risk of phase separation in the fuel in the fuel tank but also improves secondary atomization effects as water droplets remain uniformly dispersed until fuel injection occurs, improving combustion and reducing some exhaust emissions. By offering an opposing alternative to ambient-stable emulsions, this work advances the field of WiDE beyond its current limitations by developing an emulsion formulation that is scalable and adaptable to emerging fuels to be used in diesel engine architectures.

2. Materials and Methods

EN590 diesel fuel from Galp (Lisbon, Portugal), deionized water, a hydrophilic surfactant (Cocamide DEA) from FarmaQuímica Sur (Malaga, Spain), and a lipophilic co-surfactant (Span 80) from TCI (Tokyo, Japan) were acquired to perform the different tests. Two different emulsions were prepared in the laboratory by mechanical homogenization, a low-energy mixing method. The goal was to obtain stable emulsions with different percentages of water at the temperature of 40 °C, similar to the temperature of the fuel in the fuel tank of high-capacity diesel engines during operation conditions, mostly due to heat transfer from the fuel return lines. After several trial-and-error attempts, and based on Serôdio’s work formulations [46], two different blends were obtained: an 8% WiDE and a 16% WiDE. The first one is composed of 89% diesel fuel, 8% deionized water, and 3% of total surfactant concentration (91% Cocamide DEA and 9% Span 80). The second one is composed of 78% diesel fuel, 16% deionized water, and 6% total surfactant concentration (95% Cocamide DEA and 5% Span 80). All percentages are by mass. Commonly used surfactants may degrade or be less efficient at higher temperatures found during engine operation, leading to phase separation and worse secondary atomization. If they are ionic, they are toxic, and, by dissociating into ions, they worsen emissions. Our formulation of Cocamide DEA and Span 80 addresses these limitations as the surfactants have high thermal stability, are non-ionic and therefore non-toxic, derive from renewable sources, aligning with current sustainability targets, and, in addition, they support higher shear stresses often found during fuel injection at higher pressures. During laboratory tests, it was also discovered that an increase in water concentration needed to be followed by a corresponding increase in surfactant concentration. The same happened for the hydrophilic–lipophilic balance of the surfactant mixture. These combined allowed to obtain two stable emulsions at the temperature of 40 °C. This stability was verified by pointing a flashlight on one side of the flask and observing the light on the other side after passing through the emulsion medium. This is an indication that the water droplet size is low enough and that the emulsion formulation used for each case was ideal and optimized for the temperature of 40 °C. Figure 1 shows diesel fuel and both emulsions in their initial state, prior to exposure to the thermostatic bath. The equipment and material used during the tests are shown in Figure 2.
After obtaining the different fuels, properties such as density, viscosity, and heating value were measured using a hydrometer, an Oswald viscometer, and a bomb calorimeter, model 6050 from Parr. These measurements are shown in Figure 3 and Figure 4, and Table 1.
A Hatz 1B40 single-cylinder from Hatz (Ruhstorf, Germany), naturally aspirated, direct-injection (DI) diesel engine was tested under different load conditions in an eddy current dynamometer. Its specifications are shown in Table 2. An AVL DiGas 1000 model 2301 exhaust gas analyzer and an AVL DiSmoke 480 opacimeter from AVL (Graz, Austria) were used to measure emissions of CO, carbon dioxide (CO2), hydrocarbons (HCs), nitric oxide (NO), oxygen (O2), and smoke. Table 3 summarizes its specifications.
The tests were performed at 25, 50, 75, and 100% of the maximum considered engine load at four different engine speeds (1500, 2000, 2500, and 3000 rpm) for the different fuels. As this diesel engine is composed of a governor (a mechanical device responsible for controlling fuel injection based on speed and load conditions), different fuel viscosities lead to different injection delays. To mitigate this and provide a fairer comparison between the fuels without modifying injection timings, a thermostatic oil bath was added for heating the emulsions to attain more similar viscosities to diesel fuel in the fuel tank during engine operation. The selected temperatures were 45 °C for the 8% WiDE and 55 °C for the 16% WiDE. Ambient conditions were also monitored during tests with temperature varying from 15.9 to 16.1 °C, relative humidity from 67 to 73%, and pressure from 937 to 942 hPa. Figure 5 shows the experimental setup during fuel testing.
For each operating condition, a run-up period was applied to warm the engine to reach its operating temperature. Performance data were collected from sensors every 250 ms via the Arduino 1.8.16 software, using the LabVIEW 2019 19.0f2 software to synchronize both microcontrollers. Emission data were collected every 50 ms with AVL DSS 2.0 software. The mean value of the different measured parameters was calculated for each condition of the total forty-eight experiments. Data analysis of the different results was conducted under R 4.1.3 software.

3. Results and Discussion

The following figures represent the corrected data gathered during the experiments for the different engine and emissions parameters. For each case, a two-dimensional plot is displayed. For each load condition, four different engine speeds were tested. After analyzing how the different parameters behaved for each engine speed, their values were averaged, obtaining a mean value for BMEP and a mean value for BSFC, BTE, CO, CO2, HCs, NO, O2, and smoke for each load condition. As BMEP is calculated from engine speed, the following plots represent BMEP on the x-axis and the different parameters on the y-axis.

3.1. Brake-Specific Fuel Consumption

As can be seen in Figure 6, the BSFC of the 16% WiDE is higher when compared to the 8% WiDE at every load condition. It is also higher than diesel fuel in every condition except at the maximum load condition, where it is lower. The BSFC of the 8% WiDE is lower than diesel fuel at the lowest and highest load conditions, and higher in the 1.698 and 2.492 bar load conditions. For the 16% WiDE, the BSFC decreases with an increase in engine load. For diesel fuel, the BSFC decreases between 0.789 and 2.492 bar and then increases until 3.585 bar. For the 8% WiDE, BSFC remains constant between 0.789 and 1.698 bar and then decreases until 3.585 bar. The occurrence of puffing and micro-explosions in emulsion droplets may be responsible for increasing the force acting on the piston during the expansion stroke [47], increasing the burning rate, and reducing the fuel flow needed to achieve a certain power, reducing BSFC in some cases. In contrast, the increased spray penetration and injection duration due to different fuel properties and the lower energy content of the fuel may increase this parameter [48].

3.2. Brake Thermal Efficiency

Regarding BTE, as seen in Figure 7, the 8% WiDE exhibits higher values compared to the 16% WiDE at every load condition. The BTE of diesel fuel is lower than in the 8% WiDE and similar to the 16% WiDE at 0.789 bar, higher than both emulsions at 1.698 bar, lower than both emulsions at 3.585 bar, and higher than the 16% WiDE but lower than the 8% WiDE at 2.492 bar. For the 16% WiDE, BTE increases with engine load. For diesel fuel, it increases with engine load until 2.492 bar and then decreases until 3.585 bar. For the 8% WiDE, it remains constant between 0.789 and 1.698 bar and then increases until 3.585 bar. As BTE is inversely proportional to BSFC, the curves are oppositely similar. Due to the reduced lower heating values of the emulsions (less diesel and therefore less energy content) [49], BTE can also improve, as the lower potential energy of the emulsified fuel molecules is better harvested for producing useful work, and less energy is lost in the form of heat.

3.3. Carbon Monoxide Emissions

As shown in Figure 8, regarding CO emissions, they are always lower for diesel fuel compared to both emulsions. These results are in accordance with the most recent literature [50]. For the 8% WiDE, they are lower compared to the 16% WiDE at the minimum and maximum load conditions and higher at 1.698 and 2.492 bar. These emissions decrease for diesel fuel and the 16% WiDE with the increase in engine load and increase between 0.789 and 2.492 bar, followed by a decrease until 3.585 bar for the 8% WiDE. Higher CO emissions for the emulsions can be a result of the incomplete combustion of some fuel molecules, possibly due to the excess carbon atoms present in the surfactants that were not fully combusted, lack of mixture uniformity, lower combustion chamber temperature, cylinder pressure, slow soot burning, and lower O2 availability preventing CO from oxidizing to CO2, and different properties of the emulsified fuels leading to different spray characteristics after the injector [51]. On the other hand, a lower cetane number of diesel fuel due to its shorter ignition delay may reduce these emissions [52].

3.4. Carbon Dioxide Emissions

As seen in Figure 9, CO2 emissions, for every fuel tested, increase with increasing engine load. The CO2 emissions of diesel are always lower than the emulsions at every load condition. Similar to CO emissions, CO2 emissions for the 8% WiDE are lower than the 16% WiDE at the minimum and maximum load conditions and higher at both mid-load conditions. As a complete combustion of a hydrocarbon with O2 would only produce CO2 and water vapor, the higher CO2 emissions of the emulsions can be due to better combustion properties and favorable conditions for CO oxidation into CO2 [53]. Better burning characteristics can lead to a more complete combustion and therefore emit more CO2 [54], increasing with engine load for all cases as more fuel is being burned per engine cycle.

3.5. Hydrocarbon Emissions

As for HC emissions, as shown in Figure 10, they are lower for diesel at every load condition compared to the emulsions. These findings follow the most recent literature [55]. For diesel fuel, they remain overall constant throughout the different load conditions. For the 16% WiDE, they decrease between 0.789 and 2.492 bar and then increase until 3.585 bar. For the 8% WiDE, they increase between 0.789 and 1.698 bar, remain similar between 1.698 and 2.492 bar, and then decrease until 3.585 bar. Similar to CO emissions, these emissions are also a result of the incomplete combustion of fuel molecules, strongly influenced by the air–fuel ratio, combustion temperature [56], and cylinder pressure [57]. The higher HC emissions for the emulsions may also be due to increased hydrogen and carbon atoms in the emulsifiers. Puffing and microexplosions may also increase the spray penetration length, leading to spray wall impingement and spray wall wetting [58]. The production or breakdown of HC compounds resulting in the formation of intermediate products can also explain this increase [59].

3.6. Nitric Oxide Emissions

Regarding NO emissions, in Figure 11, for all fuels tested, they increase with increasing engine load. For diesel fuel, these emissions are always higher compared to the emulsions, except at 0.789 bar, where the NO emissions of the 8% WiDE are slightly higher, and 3.585 bar, where the NO emissions of the 16% WiDE are higher. The NO emissions of the 16% WiDE are lower than the 8% WiDE at 0.789 and 1.698 bar and higher at 2.492 and 3.585 bar. The reduction in NO emissions for WiDEs is in accordance with the most recent literature [60]. As the water molecules dispersed in the emulsified fuels need to absorb some of the heat produced during combustion to change their state from liquid to vapor, it was expected that the combustion temperature would drop as a consequence of this heat sink effect mechanism [61]. It was also expected that an increase in the water content of the emulsion would lead to a further reduction in the combustion temperature, which would prevent most of NO from being formed [62,63]. This only happened significantly for the 1.698 bar load condition, where NO emissions of diesel are higher, followed by the 8% WiDE, followed by the 16% WiDE. For the single case where NO emissions from diesel were significantly lower than the 16% WiDE, higher rates of premixed combustion and increased ignition delay may explain that occurrence [64]. An increased engine temperature, owing to different injection delays and ignition timings due to differences in fuel properties and the occurrence of intense micro-explosions in the combustion chamber, may also have contributed to increased burning rates and improved combustion, therefore increasing these emissions [65], as longer ignition delays lead to slower combustion and more time available for NO formation in the combustion chamber [64]. This can be confirmed by Figure S1 in the Supplementary Material describing the outer engine block temperature over different engine speeds for the three different fuels, which are significantly higher for the 16% WiDE. Increased engine temperatures lead to higher NO emissions as the increased heat facilitates the dissociation of molecular nitrogen, which then reacts with oxygen from the air, therefore increasing these emissions. The unique case where NO emissions for the 8% WiDE were higher than diesel at the lowest load condition also corresponded to the trends observed in [66], where a 25% engine load was the only condition reporting higher emissions of NO for the emulsified fuels compared to diesel.

3.7. Oxygen Emissions

As can be seen in Figure 12, regarding O2 emissions, for all fuels, they decrease with increasing engine load. At every load condition, O2 emissions for diesel are higher than the emulsions. For the 8% WiDE, these emissions are higher than the 16% WiDE at the minimum and maximum load conditions, similar at 2.492 bar, and lower at 1.698 bar. Lower values of O2 content measured by the gas analyzer in the exhaust system may be an indication that the extra O2 available in the emulsified fuels from the water molecules was used to react with fuel molecules and form other chemical compounds, assuring a more complete combustion [67]. If it was not used, it would be expected that O2 emissions measured in the exhaust would be higher.

3.8. Smoke Emissions

As for smoke emissions, shown in Figure 13, for the 8% WiDE, they increase with increasing engine load. For diesel, they increase between 0.789 and 2.492 bar and then decrease until 3.585 bar. For the 16% WiDE, these emissions increase between 0.789 and 1.696 bar and then decrease until 3.585 bar. The smoke emissions of diesel are always higher than the emulsions, similar to most recent studies [68]. These emissions are also always higher for the 16% WiDE compared to the 8% WiDE, except at the maximum load condition where these emissions are lower. As smoke is typically formed when the combustion is incomplete, producing soot, primarily composed of carbon particles, the reduction in fuel-rich zones, characteristic of diesel’s heterogeneous combustion due to the oxygenated fuels [69], an improved mixing rate due to puffing and micro-explosions [70], and a longer ignition delay due to slightly different properties of the emulsified fuels increasing the time for the emulsion to vaporize, mix, and auto-ignite initiating the combustion process [71] may explain these lower emissions. In addition, the decomposition of some water vapor into hydroxyl, atomic oxygen, and hydrogen radicals at high temperatures can oxidize soot in fuel-rich zones, reducing smoke emissions and improving fuel efficiency [72]. It was also expected that an increase in water content would further reduce the smoke emissions; however, this only happened at the maximum load condition. At lower load conditions, the engine is operating under lower temperatures and pressures, making the conditions less suitable for the additional water present in the higher water content emulsion to fully vaporize and be more effective at further reducing smoke emissions. For these cases, the mixture composed of reduced water content was found to be more efficient and adaptable to these conditions, therefore resulting in decreased smoke emissions. This trend was also observed in [43], who reported an increase in smoke opacity by increasing water content from 8% to 16% under certain load conditions.

4. Conclusions

This research evaluates the viability of utilizing water-emulsified diesel fuels stabilized with non-ionic surfactants formulated for operating temperatures of CI engines under hydrophilic surfactant formulations. After analyzing the different results regarding various engine and emissions parameters, some conclusions can be drawn.
At every load condition, oxygen and smoke emissions are reduced for both emulsions. At every load condition, CO, CO2, and HC emissions are increased for both emulsions. NO emissions are reduced for both emulsions at every load condition except during the minimum load for the 8% WiDE and the maximum load for the 16% WiDE. For the 8% WiDE, TE is improved at every condition, except during a 50% load. For the 16% WiDE, TE is only improved during maximum load conditions.
In addition, it is also expected that sulfur oxide emissions would be lower for WiDEs as less diesel, and therefore less sulfur, is present in the fuel. Possible changes in injection timing when utilizing WiDEs may also reduce some of the pollutant emissions from incomplete combustion, especially CO and HC. This possibility should be explored in future works.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/en18040934/s1.

Author Contributions

Conceptualization, P.O., F.B., R.S. and J.S.; methodology, P.O., F.B., R.S. and J.S.; software, P.O.; validation, P.O., F.B. and R.S.; formal analysis, P.O.; investigation, P.O., F.B. and J.S.; resources, P.O. and F.B.; data curation, P.O. and R.S.; writing—original draft preparation, P.O.; writing—review and editing, P.O., F.B., R.S. and J.S.; visualization, P.O., F.B., R.S. and J.S.; supervision, F.B.; project administration, F.B.; funding acquisition, P.O. and F.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by FCT through an individual PhD Grant 2021.07535.BD and C-MAST through projects UIDB/00151/2020 (https://doi.org/10.54499/UIDB/00151/2020) and UIDP/00151/2020 (https://doi.org/10.54499/UIDP/00151/2020).

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors would like to thank the University of Beira Interior, Center for Mechanical and Aerospace Science and Technologies and the University of Castilla—La Mancha, Department of Fuels and Engines for the space, equipment, and materials provided during the development of this work.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
BMEPbrake mean effective pressure
BSFCbrake-specific fuel consumption
BTEbrake thermal efficiency
CIcompression-ignition
COcarbon monoxide
CO2carbon dioxide
DIdirect injection
HChydrocarbons
LHVlower heating value
NOnitric oxide
NOxnitrogen oxides
PMparticulate matter
O2oxygen
WiDEwater-in-diesel emulsion

References

  1. Jayabal, R. Ammonia as a Potential Green Dual Fuel in Diesel Engines: A Review. Process Saf. Environ. Prot. 2024, 188, 1346–1354. [Google Scholar] [CrossRef]
  2. Jin, C.; Wei, J. The Combined Effect of Water and Nanoparticles on Diesel Engine Powered by Biodiesel and Its Blends with Diesel: A Review. Fuel 2023, 343, 127940. [Google Scholar] [CrossRef]
  3. Sonachalam, M.; Manieniyan, V.; Senthilkumar, R.; Ramis, M.K.; Warimani, M.; Kumar, R.; Kedia, A.; Khan, T.M.Y.; Almakayeel, N. Experimental Investigation of Performance, Emission, and Combustion Characteristics of a Diesel Engine Using Blends of Waste Cooking Oil-Ethanol Biodiesel with MWCNT Nanoparticles. Case Stud. Therm. Eng. 2024, 61, 105094. [Google Scholar] [CrossRef]
  4. Liao, J.; Wang, Z.; Hu, J.; Yan, F.; Wu, Y.; Cai, Z.; Zheng, S.; Li, S.; Peng, H. Investigation of the Effect of Different Structure Parameters and Operating Factors on the Integrated Exhaust Aftertreatment System for Diesel Engines and Parameter Importance Analysis. J. Clean. Prod. 2024, 447, 141257. [Google Scholar] [CrossRef]
  5. Bhagat, R.N.; Sahu, K.B.; Ghadai, S.K.; Kumar, C.B. A Review of Performance and Emissions of Diesel Engine Operating on Dual Fuel Mode with Hydrogen as Gaseous Fuel. Int. J. Hydrogen Energy 2023, 48, 27394–27407. [Google Scholar] [CrossRef]
  6. Kim, J.; Vallinmaki, M.; Tuominen, T.; Mikulski, M. Variable Valve Actuation for Efficient Exhaust Thermal Management in an Off-Road Diesel Engine. Appl. Therm. Eng. 2024, 246, 122940. [Google Scholar] [CrossRef]
  7. Farzam, R.; McTaggart-Cowan, G. Hydrogen-Diesel Dual-Fuel Combustion Sensitivity to Fuel Injection Parameters in a Multi-Cylinder Compression-Ignition Engine. Int. J. Hydrogen Energy 2024, 49, 850–867. [Google Scholar] [CrossRef]
  8. Nadimi, E.; Przybyła, G.; Løvås, T.; Adamczyk, W. Effects of Biodiesel Injector Configuration and Its Injection Timing on Performance, Combustion and Emissions Characteristics of Liquid Ammonia Dual Direct Injection Engine. J. Energy Inst. 2024, 114, 101605. [Google Scholar] [CrossRef]
  9. Nguyen Manh, D.; Tran Quang, V.; The Luong, N.; Nguyen The, T.; Duy, T.N.; Duc, K.N.; Pham Minh, T. A Simulation and Experiment Study on the Emission Reduction Potential of Light-Duty Diesel Engine Retrofitted with an after-Treatment System: A Case Study. Energy Sources Part A Recover. Util. Environ. Eff. 2024, 46, 674–688. [Google Scholar] [CrossRef]
  10. Zhang, Z.; Dong, R.; Tan, D.; Duan, L.; Jiang, F.; Yao, X.; Yang, D.; Hu, J.; Zhang, J.; Zhong, W.; et al. Effect of Structural Parameters on Diesel Particulate Filter Trapping Performance of Heavy-Duty Diesel Engines Based on Grey Correlation Analysis. Energy 2023, 271, 127025. [Google Scholar] [CrossRef]
  11. Zhang, Y.; Xia, C.; Liu, D.; Zhu, Y.; Feng, Y. Experimental Investigation of the High-Pressure SCR Reactor Impact on a Marine Two-Stroke Diesel Engine. Fuel 2023, 335, 127064. [Google Scholar] [CrossRef]
  12. Liu, W.; Gao, Y.; You, Y.; Jiang, C.; Hua, T.; Xia, B. Nonlinear Model Predictive Control(NMPC) of Diesel Oxidation Catalyst (DOC) Outlet Temperature for Active Regeneration of Diesel Particulate Filter (DPF) in Diesel Engine. Energy 2024, 293, 130658. [Google Scholar] [CrossRef]
  13. Sekar, M.; Selim, M.Y.E.; Saleh, H.E.; Elgendi, M. Utilization of Hydrogen and Methane as Energy Carriers with Exhaust Gas Recirculation for Sustainable Diesel Engines. Energy Convers. Manag. X 2024, 23, 100618. [Google Scholar] [CrossRef]
  14. Bui, K.Q.; Perera, L.P.; Emblemsvåg, J. Life-Cycle Cost Analysis of an Innovative Marine Dual-Fuel Engine under Uncertainties. J. Clean. Prod. 2022, 380, 134847. [Google Scholar] [CrossRef]
  15. Shen, S.; Liu, H.; Liu, Y.; Liu, X.; Hu, H.; Hu, Z.; Wang, T. Dynamic Details inside Water-in-Oil (W/O) Emulsion Droplet and Its Impact on Droplet Evaporation and Micro-Explosion. Fuel 2023, 338, 127254. [Google Scholar] [CrossRef]
  16. Gowrishankar, S.; Rastogi, P.; Krishnasamy, A.; Basavaraj, M.G.; Kaisare, N.; Aidhen, I.S. Synthesis and Characterization of Emulsion Fuels –Implications to Spray and Engine Studies. Prog. Energy Combust. Sci. 2024, 101, 101133. [Google Scholar] [CrossRef]
  17. Woo, S.; Lee, K. Effect of Injection Strategy and Water Content on Water Emulsion Fuel Engine for Low Pollutant Compression Ignition Engines. Fuel 2023, 343, 127809. [Google Scholar] [CrossRef]
  18. Ali, A.; Aziz, A.R.A.; Ismael, M.A.; Alqaed, S. Biosurfactants as an Alternative Eco-Friendly Solution for Water-in-Diesel Emulsions-A Review Paper. Heliyon 2024, 10, e37485. [Google Scholar] [CrossRef] [PubMed]
  19. Vellaiyan, S. Recent Advancements in Water Emulsion Fuel to Explore Efficient and Cleaner Production from Various Biodiesels: A Retrospective Review. Renew. Sustain. Energy Rev. 2023, 187, 113704. [Google Scholar] [CrossRef]
  20. Tamam, M.Q.M.; Yahya, W.J.; Abdul Rahman, H.; Ithnin, A.M.; Abd Kadir, H.; Rahman, M.M.; Noge, H.; Koga, T.; Sugeng, D.A. Application of an Inline Mixer to Produce Surfactant-Free Biodiesel-Diesel/Water Emulsion Fuel: An Analysis of Water Droplets Characteristics and Drive Cycle Emissions. Arab. J. Sci. Eng. 2024, 1–14. [Google Scholar] [CrossRef]
  21. Mahdi, W.N.I.W.; Ithnin, A.M.; Yahya, W.J.; Rashid, M.A.A.; Kadir, H.A.; Sugeng, D.A.; Eiji, K. The Effect of Different In-Line Mixers Producing Emulsifier-Free Bio-Diesel Emulsion on the Diesel Engine Combustion Performance and Exhaust Emission. Fuel 2023, 337, 126886. [Google Scholar] [CrossRef]
  22. Mohd Tamam, M.Q.; Omi, M.R.T.; Yahya, W.J.; Ithnin, A.M.; Abdul Rahman, H.; Rahman, M.M.; Abd Kadir, H.; Noge, H.; Koga, T.; Hong, C.; et al. Engine Performance and Emissions Evaluation of Surfactant-Free B30 Biodiesel–Diesel/Water Emulsion as Alternative Fuel. Sci. Rep. 2023, 13, 10599. [Google Scholar] [CrossRef] [PubMed]
  23. Wang, Z.; Yuan, B.; Cao, J.; Huang, Y.; Cheng, X.; Wang, Y.; Zhang, X.; Liu, H. A New Shift Mechanism for Micro-Explosion of Water-Diesel Emulsion Droplets at Different Ambient Temperatures. Appl. Energy 2022, 323, 119448. [Google Scholar] [CrossRef]
  24. Gowrishankar, S.; Krishnasamy, A. Emulsification–A Promising Approach to Improve Performance and Reduce Exhaust Emissions of a Biodiesel Fuelled Light-Duty Diesel Engine. Energy 2023, 263, 125782. [Google Scholar] [CrossRef]
  25. Mondal, P.K.; Mandal, B.K. Effect of Fuel Injection Pressure on the Performances of a CI Engine Using Water-Emulsified Diesel (WED) as a Fuel. Energy Sustain. Soc. 2024, 14, 12. [Google Scholar] [CrossRef]
  26. Ayad, I.; Ghannam, M.T.; Selim, M.Y.E. Experimental Stability Investigation of Different Water-in-Jojoba Biodiesel Emulsions. Fuel 2024, 357, 129782. [Google Scholar] [CrossRef]
  27. Patel, K.R.; Dhiman, V.D. A Review on Emission and Performance of Water Diesel Micro-Emulsified Mixture-Diesel Engine. Int. J. Environ. Sci. Technol. 2022, 19, 8027–8042. [Google Scholar] [CrossRef]
  28. Han, D.; Mao, J.; Zhao, J.; Zhang, H.; Yang, X.; Lin, C. Effect of Surfactant Hydrophobic Chain Equivalence on the Oil-Water Interface and Emulsion Stability: A Dissipative Particle Dynamics and Experimental Study. J. Mol. Liq. 2023, 382, 121781. [Google Scholar] [CrossRef]
  29. Attar, A.; Waghmare, J.; Mane, S. Water in Diesel Emulsion Fuel: Production, Properties, Performance, and Exhaust Emission Analysis. Int. J. Energy Environ. Eng. 2022, 13, 729–738. [Google Scholar] [CrossRef]
  30. Saha, U.; De, R.; Das, B. Interactions between Loaded Drugs and Surfactant Molecules in Micellar Drug Delivery Systems: A Critical Review. J. Mol. Liq. 2023, 382, 121906. [Google Scholar] [CrossRef]
  31. Vieira, A.; Simonelli, G.; Carlos, L. Review of the Application of Surfactants in Microemulsion Systems for Remediation of Petroleum Contaminated Soil and Sediments. Environ. Sci. Pollut. Res. 2023, 12, 32168–32183. [Google Scholar] [CrossRef]
  32. Bello, A.; Ozoani, J.; Adebayo, A.; Kuriashov, D. Rheological Study of Nanoparticle-Based Cationic Surfactant Solutions. Petroleum 2022, 8, 522–528. [Google Scholar] [CrossRef]
  33. Sazdanić, D.; Krstonošić, M.A.; Ćirin, D.; Cvejić, J.; Alamri, A.; Galanakis, C.M.; Krstonošić, V. Non-Ionic Surfactants-Mediated Green Extraction of Polyphenols from Red Grape Pomace. J. Appl. Res. Med. Aromat. 2023, 32, 100439. [Google Scholar] [CrossRef]
  34. Ali, A.; Aziz, A.R.A.; Ismael, M.A.; Alqaed, S. The Investigation of Lecithin and Cocamide DEA Biosurfactant Concentrations on Emulsified Biodiesel Fuel Stability, Properties, and the Micro-Explosion Phenomenon. Results Eng. 2024, 23, 102482. [Google Scholar] [CrossRef]
  35. Marhamati, M.; Ranjbar, G.; Rezaie, M. Effects of Emulsifiers on the Physicochemical Stability of Oil-in-Water Nanoemulsions: A Critical Review. J. Mol. Liq. 2021, 340, 117218. [Google Scholar] [CrossRef]
  36. Deepak, B.; Ibrahim, M.M. Microemulsion Fuel Formulation from Used Cooking Oil with Carbinol as the Dispersion Phase. Energy Sources Part A Recover. Util. Environ. Eff. 2023, 45, 4107–4126. [Google Scholar] [CrossRef]
  37. Czerniel, J.; Gostyńska, A.; Jańczak, J.; Stawny, M. A Critical Review of the Novelties in the Development of Intravenous Nanoemulsions. Eur. J. Pharm. Biopharm. 2023, 191, 36–56. [Google Scholar] [CrossRef]
  38. Kumar, A.; Chen, H.; Yang, S. Modeling Microexplosion Mechanism in Droplet Combustion: Puffing and Droplet Breakup. Energy 2023, 266, 126369. [Google Scholar] [CrossRef]
  39. Antonov, D.V.; Kuznetsov, G.V.; Razumov, D.S.; Fedorenko, R.M.; Yanovskiy, L.S.; Strizhak, P.A. Puffing and Micro-Explosion Effects in Composite Liquid Fuels in Different Heating Arrangements. Int. J. Heat Mass Transf. 2024, 223, 125273. [Google Scholar] [CrossRef]
  40. Zhang, H.; Lu, Z.; Wang, T.; Che, Z. Mist Formation during Micro-Explosion of Emulsion Droplets. Fuel 2023, 339, 127350. [Google Scholar] [CrossRef]
  41. Ismael, M.A.; Aziz, A.R.A.; Mohammed, S.E.; Zainal A, E.Z.; Baharom, M.B.; Hagos, F.Y. Macroscopic and Microscopic Spray Structure of Water-in-Diesel Emulsions. Energy 2021, 223, 120040. [Google Scholar] [CrossRef]
  42. Sartomo, A.; Santoso, B.; Ubaidillah; Muraza, O. Recent Progress on Mixing Technology for Water-Emulsion Fuel: A Review. Energy Convers. Manag. 2020, 213, 112817. [Google Scholar] [CrossRef]
  43. Mohd Tamam, M.Q.; Yahya, W.J.; Ithnin, A.M.; Abdullah, N.R.; Kadir, H.A.; Rahman, M.M.; Rahman, H.A.; Abu Mansor, M.R.; Noge, H. Performance and Emission Studies of a Common Rail Turbocharged Diesel Electric Generator Fueled with Emulsifier Free Water/Diesel Emulsion. Energy 2023, 268, 126704. [Google Scholar] [CrossRef]
  44. Okumuş, F.; Kaya, C.; Kökkülünk, G. NOx Based Comparative Analysis of a CI Engine Fueled with Water in Diesel Emulsion. Energy Sources Part A Recover. Util. Environ. Eff. 2020, 3, 6710–6729. [Google Scholar] [CrossRef]
  45. Vasistha, V.; Bharj, R.S. Analyzing the Storage Stability of Diesel Emulsified Fuels: A Comparative Standpoint. Energy Sources Part A Recover. Util. Environ. Eff. 2022, 44, 5527–5544. [Google Scholar] [CrossRef]
  46. Fernandes Serodio, J.C. Method, System, Apparatus and Formulations for Producing Oil-Based Blends and Microemulsions and Nanoemulsions. Worldwide Application No. WO2021090010A1, 14 May 2021. [Google Scholar]
  47. El Shenawy, E.A.; Elkelawy, M.; Bastawissi, H.A.E.; Shams, M.M.; Panchal, H.; Sadasivuni, K.; Thakar, N. Investigation and Performance Analysis of Water-Diesel Emulsion for Improvement of Performance and Emission Characteristics of Partially Premixed Charge Compression Ignition (PPCCI) Diesel Engines. Sustain. Energy Technol. Assess. 2019, 36, 100546. [Google Scholar] [CrossRef]
  48. Wang, Z.; Wu, S.; Huang, Y.; Huang, S.; Shi, S.; Cheng, X.; Huang, R. Experimental Investigation on Spray, Evaporation and Combustion Characteristics of Ethanol-Diesel, Water-Emulsified Diesel and Neat Diesel Fuels. Fuel 2018, 231, 438–448. [Google Scholar] [CrossRef]
  49. Khanjani, A.; Sobati, M.A. Performance and Emission of a Diesel Engine Using Different Water/Waste Fish Oil (WFO) Biodiesel/Diesel Emulsion Fuels: Optimization of Fuel Formulation via Response Surface Methodology (RSM). Fuel 2021, 288, 119662. [Google Scholar] [CrossRef]
  50. Hassan, Z.U.; Usman, M.; Asim, M.; Kazim, A.H.; Farooq, M.; Umair, M.; Imtiaz, M.U.; Asim, S.S. Use of Diesel and Emulsified Diesel in CI Engine: A Comparative Analysis of Engine Characteristics. Sci. Prog. 2021, 104, 00368504211020930. [Google Scholar] [CrossRef] [PubMed]
  51. Zhang, W.; Zhang, Z.; Chen, H.; Ji, Z.; Ma, Y.; Sun, F. A Review on Performance, Combustion and Emission of Diesel and Alcohols in a Dual Fuel Engine. J. Energy Inst. 2024, 116, 101760. [Google Scholar] [CrossRef]
  52. Kim, K.; Lee, W.; Wiersema, P.; Mayhew, E.; Temme, J.; Kweon, C.B.M.; Lee, T. Effects of the Cetane Number on Chemical Ignition Delay. Energy 2023, 264, 126263. [Google Scholar] [CrossRef]
  53. Liu, J.; Booma Devi, P.; Chinnathambi, A.; Ali Alharbi, S. Mitigating Fossil Fuel Deficiency and Environmental Impacts: Performance Analysis of Scenedesmus Obliquus Microalgae Biodiesel in a Diesel Engine. Fuel 2024, 364, 131033. [Google Scholar] [CrossRef]
  54. Abdollahi, M.; Ghobadian, B.; Najafi, G.; Hoseini, S.S.; Mofijur, M.; Mazlan, M. Impact of Water–Biodiesel–Diesel Nano-Emulsion Fuel on Performance Parameters and Diesel Engine Emission. Fuel 2020, 280, 118576. [Google Scholar] [CrossRef]
  55. Rahman, H.A.; Rahman, M.M.; Yahya, W.J.; Kaonain, T.E.; Kadir, H.A. Implementation of a Non-Surfactant Water-in-Diesel Emulsion Fuel in a Common Rail Direct Injection Diesel Vehicle. Int. J. Automot. Technol. 2023, 24, 1349–1358. [Google Scholar] [CrossRef]
  56. Cengiz, C.; Ozen Unverdi, S. Effect of Early Intake Valve Closing, Exhaust Gas Recirculation and Split Injection on Combustion and Emissions Characteristics of a HDDI Diesel Engine Operating in PCCI Combustion Mode. Fuel 2023, 353, 129079. [Google Scholar] [CrossRef]
  57. Ağbulut, Ü.; Sarıdemir, S. Synergistic Effects of Hybrid Nanoparticles along with Conventional Fuel on Engine Performance, Combustion, and Environmental Characteristics. Energy 2024, 292, 130267. [Google Scholar] [CrossRef]
  58. Gowrishankar, S.; Krishnasamy, A. Experimental Investigations on Biodiesel-Water Emulsion as a Potential Fuel for Early and Late Injection Based Premixed Lean Combustion. Energy Convers. Manag. 2022, 273, 116386. [Google Scholar] [CrossRef]
  59. Neha; Prasad, R.; Singh, S.V. A Review on Catalytic Oxidation of Soot Emitted from Diesel Fuelled Engines. J. Environ. Chem. Eng. 2020, 8, 103945. [Google Scholar] [CrossRef]
  60. Gautam, P.S.; Vishnoi, P.K.; Gupta, V.K. The Effect of Water Emulsified Diesel on Combustion, Performance and Emission Characteristics of Diesel Engine. Mater. Today Proc. 2022, 52, 1041–1047. [Google Scholar] [CrossRef]
  61. Vigneswaran, R.; Balasubramanian, D.; Sastha, B.D.S. Performance, Emission and Combustion Characteristics of Unmodified Diesel Engine with Titanium Dioxide (TiO2) Nano Particle along with Water-in-Diesel Emulsion Fuel. Fuel 2021, 285, 119115. [Google Scholar] [CrossRef]
  62. Ramlan, N.A.; Yahya, W.J.; Ithnin, A.M.; Abd Kadir, H.; Abu Kassim, K.A.; Abdul Rahman, H.; Ezzat Chan, A.F.; Mazlan, N.A.; Abdul Rashid, M.A.; Sugeng, D.A. Emissions and Performance Analysis of Diesel Powered Road Vehicle Equipped with Real-Time Non-Surfactant Emulsion Fuel Supply System. Fuel 2020, 273, 117257. [Google Scholar] [CrossRef]
  63. Vellaiyan, S. Enhancement in Combustion, Performance, and Emission Characteristics of a Biodiesel-Fueled Diesel Engine by Using Water Emulsion and Nanoadditive. Renew. Energy 2020, 145, 2108–2120. [Google Scholar] [CrossRef]
  64. Su, X.; Chen, H.; Gao, N.; Ding, M.; Wang, X.; Xu, H.; Zhang, P. Combustion and Emission Characteristics of Diesel Engine Fueled with Diesel/Cyclohexanol Blend Fuels under Different Exhaust Gas Recirculation Ratios and Injection Timings. Fuel 2023, 332, 125986. [Google Scholar] [CrossRef]
  65. Veza, I.; Irianto; Tuan Hoang, A.; Yusuf, A.A.; Herawan, S.G.; Soudagar, M.E.M.; Samuel, O.D.; Said, M.F.M.; Silitonga, A.S. Effects of Acetone-Butanol-Ethanol (ABE) Addition on HCCI-DI Engine Performance, Combustion and Emission. Fuel 2023, 333, 126377. [Google Scholar] [CrossRef]
  66. Oh, J.; Im, M.; Oh, S.; Lee, C. Comparison of NOx and Smoke Characteristics of Water-in-Oil Emulsion and Marine Diesel Oil in 400-KW Marine Generator Engine. Energies 2019, 12, 228. [Google Scholar] [CrossRef]
  67. Elumalai, P.V.; Nambiraj, M.; Parthasarathy, M.; Balasubramanian, D.; Hariharan, V.; Jayakar, J. Experimental Investigation to Reduce Environmental Pollutants Using Biofuel Nano-Water Emulsion in Thermal Barrier Coated Engine. Fuel 2021, 285, 119200. [Google Scholar] [CrossRef]
  68. Mondal, P.K.; Mandal, B.K. A Comprehensive Review on the Feasibility of Using Water Emulsified Diesel as a CI Engine Fuel. Fuel 2019, 237, 937–960. [Google Scholar] [CrossRef]
  69. Yin, Z.; Liu, S.; Tan, D.; Zhang, Z.; Wang, Z.; Wang, B. A Review of the Development and Application of Soot Modelling for Modern Diesel Engines and the Soot Modelling for Different Fuels. Process Saf. Environ. Prot. 2023, 178, 836–859. [Google Scholar] [CrossRef]
  70. Chen, X.; Xi, X.; Zhang, L.; Wang, Z.; Cui, Z.; Long, W. Experimental Study on Nucleation and Micro-Explosion Characteristics of Emulsified Heavy Fuel Oil Droplets at Elevated Temperatures during Evaporation. Appl. Therm. Eng. 2023, 224, 120114. [Google Scholar] [CrossRef]
  71. Wang, X.; Bu, H.; Chen, H.; Liu, J.; Chen, Z.; Gao, J. Numerical Investigation of Diesel Spray Combustion Characteristics in the Ammonia/Air Atmosphere. J. Energy Inst. 2024, 116, 101718. [Google Scholar] [CrossRef]
  72. Shen, S.; Sun, K.; Che, Z.; Wang, T.; Jia, M.; Cai, J. Mechanism of Micro-Explosion of Water-in-Oil Emulsified Fuel Droplet and Its Effect on Soot Generation. Energy 2020, 191, 116488. [Google Scholar] [CrossRef]
Energies 18 00934 g001
Figure 1. Diesel fuel (a), 8% WiDE (b), and 16% WiDE (c) at ambient temperature (T = 15 °C).
Figure 1. Diesel fuel (a), 8% WiDE (b), and 16% WiDE (c) at ambient temperature (T = 15 °C).
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Figure 2. Laboratory equipment and material: diesel fuel (a), deionized water (b), beakers (c), pipette (d), surfactants (e), analytic balance (Radwag AS 310/C/2, Radwag, Macclesfield, UK) (f), magnetic stirrer (Stuart Scientific SM3, Salford Scientific, Salford, UK) (g), and thermometer (Enviro-Safe, SP Bel-Art, Wayne, NJ, USA) (h).
Figure 2. Laboratory equipment and material: diesel fuel (a), deionized water (b), beakers (c), pipette (d), surfactants (e), analytic balance (Radwag AS 310/C/2, Radwag, Macclesfield, UK) (f), magnetic stirrer (Stuart Scientific SM3, Salford Scientific, Salford, UK) (g), and thermometer (Enviro-Safe, SP Bel-Art, Wayne, NJ, USA) (h).
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Figure 3. Density of the different fuels.
Figure 3. Density of the different fuels.
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Figure 4. Kinematic viscosity of the different fuels.
Figure 4. Kinematic viscosity of the different fuels.
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Figure 5. Test-bench layout: (a) emission data acquisition; (b) performance data acquisition; (c) Arduino 1; (d) Arduino 2; (e) Hall effect sensor (speed); (f) test-bench; (g) load cell for torque measurement; (h) HX711 load cell amplifier; (i) eddy current dynamometer; (j) diesel engine; (k) fuel filter; (l) load cell and fuel tank balance for fuel consumption measurement; (m) heating unit; (n) thermostatic oil bath for emulsion fuel tank; (o) diesel fuel tank; (p) fuel temperature sensor; (q) opacimeter; (r) gas analyzer; (s) fuel return; (t) type K thermocouple; and (u) MAX6675 thermocouple amplifier.
Figure 5. Test-bench layout: (a) emission data acquisition; (b) performance data acquisition; (c) Arduino 1; (d) Arduino 2; (e) Hall effect sensor (speed); (f) test-bench; (g) load cell for torque measurement; (h) HX711 load cell amplifier; (i) eddy current dynamometer; (j) diesel engine; (k) fuel filter; (l) load cell and fuel tank balance for fuel consumption measurement; (m) heating unit; (n) thermostatic oil bath for emulsion fuel tank; (o) diesel fuel tank; (p) fuel temperature sensor; (q) opacimeter; (r) gas analyzer; (s) fuel return; (t) type K thermocouple; and (u) MAX6675 thermocouple amplifier.
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Figure 6. Average BMEP vs. BSFC.
Figure 6. Average BMEP vs. BSFC.
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Figure 7. Average BMEP vs. BTE.
Figure 7. Average BMEP vs. BTE.
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Figure 8. Average BMEP vs. CO.
Figure 8. Average BMEP vs. CO.
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Figure 9. Average BMEP vs. CO2.
Figure 9. Average BMEP vs. CO2.
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Figure 10. Average BMEP vs. HC.
Figure 10. Average BMEP vs. HC.
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Figure 11. Average BMEP vs. NO.
Figure 11. Average BMEP vs. NO.
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Figure 12. Average BMEP vs. O2.
Figure 12. Average BMEP vs. O2.
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Figure 13. Average BMEP vs. smoke.
Figure 13. Average BMEP vs. smoke.
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Table 1. Heating value of the different fuels.
Table 1. Heating value of the different fuels.
FuelsLower Heating Value (MJ/Kg)Lower Heating Value (MJ/L)
Diesel42.5335.77
8% WiDE38.7733.15
16% WiDE35.4230.89
Table 2. Hatz 1B-40 specifications.
Table 2. Hatz 1B-40 specifications.
Engine SpecificationsParameters Values
Operation cycle4-stroke
Cylinders1
Valves per cylinder2
Bore [mm]88
Stroke [mm]76
Displacement [cm3]462
Injection systemDI
Injection pressure [bar]200
Compression ratio20.5:1
Cooling systemAir cooling
Rated torque [Nm]23.4
Rater power [kW]7.3
Table 3. AVL DiTest gas 1000 model 2301 and AVL DiSmoke 480 opacimeter specifications.
Table 3. AVL DiTest gas 1000 model 2301 and AVL DiSmoke 480 opacimeter specifications.
Measuring RangesAccuracy
CO: 0–15% vol.±0.03% vol.
CO2: 0–20% vol.±0.5% vol.
HCs: 0–30,000 ppm vol.±10 ppm vol.
O2: 0–25% vol.±5% of Maximum
NO: 0–5000 ppm vol.±1% vol.
Opacity±0.1%
Absorption: 0–99.99 m−1±0.01 m−1
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Oliveira, P.; Brójo, F.; Serôdio, R.; Serôdio, J. Investigation of Water-in-Diesel Emulsion Behavior Formulated for Performance Conditions in a Single-Cylinder Diesel Engine. Energies 2025, 18, 934. https://doi.org/10.3390/en18040934

AMA Style

Oliveira P, Brójo F, Serôdio R, Serôdio J. Investigation of Water-in-Diesel Emulsion Behavior Formulated for Performance Conditions in a Single-Cylinder Diesel Engine. Energies. 2025; 18(4):934. https://doi.org/10.3390/en18040934

Chicago/Turabian Style

Oliveira, Pedro, Francisco Brójo, Rogério Serôdio, and João Serôdio. 2025. "Investigation of Water-in-Diesel Emulsion Behavior Formulated for Performance Conditions in a Single-Cylinder Diesel Engine" Energies 18, no. 4: 934. https://doi.org/10.3390/en18040934

APA Style

Oliveira, P., Brójo, F., Serôdio, R., & Serôdio, J. (2025). Investigation of Water-in-Diesel Emulsion Behavior Formulated for Performance Conditions in a Single-Cylinder Diesel Engine. Energies, 18(4), 934. https://doi.org/10.3390/en18040934

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