Experimental Investigation of Emission, Combustion, and Energy

Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX

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Experimental Investigation of Emission, Combustion, and Energy Performance of a Novel Diesel/Colza Oil Fuel Microemulsion in a Direct-Injection Diesel Engine Somaiyeh Heidari,†,‡ Reza Najjar,*,† Gaëtan Burnens,‡ Sary Awad,‡ and Mohand Tazerout‡ †

Polymer Research Laboratory, Faculty of Chemistry, University of Tabriz, 29 Bahman Boulevard, Tabriz 5166616471, Iran Departement des Systemes Energetiques et Environnement, Ecole des Mines de Nantes, 4 Rue Alfred Kastler, BP 20722, 44307 Nantes, Cedex 03, France

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‡

ABSTRACT: Formulation of a novel microemulsion (ME) fuel with a diesel/colza oil blend and investigation of its emission, combustion, and energy performance in a diesel engine with a direct-injection system is reported. The new ME was prepared using diesel/colza oil (4:1, 75%), water (5%), n-butanol (10%), Brij 30 (8%), and Tween 80 (2%). This blend is an economical formulation with acceptable physical properties with a high stability temperature. The results showed no significant difference between viscosity and density of new ME and diesel. The use of different surfactants in new ME formulation exerted an impressive effect on the highest stability temperature and water droplet size. All experiments were performed in a diesel engine with a direct-injection system, run under various loads at 1500 rpm speed. The fuel efficiency measurements were performed indicating that, in comparison to the neat diesel fuel, ME has a higher brake specific fuel consumption value in all engine loads and also a higher brake thermal efficiency value in medium engine loads. The level of emitted CO and unburned hydrocarbons was increased at full engine load. The CO2 emission value for ME and neat diesel was similar. Meanwhile, the amount of emitted NOx was decreased considerably, especially in the case of high loads of the engine for ME compared to neat diesel.

1. INTRODUCTION Diesel engines regarding their characteristic advantages of high thermal efficiency and driveability have received an increased world demand for use in major applications in power generation, industrial, transportation, and agricultural sections. However, high emissions of smoke and nitrogen oxide are their main problems.1−3 Use of a diesel engine increases harmful pollution, including carbon oxides (CO and CO2), oxides of nitrogen (NOx), hydrocarbon (HC), oxides of sulfur (SOx), and smoke. These pollutants are the main components, which increase greenhouse gases and damage the ozone layer, pushing the studies to discover a novel renewable energy source as a replacement for petroleum.4−6 Vegetable oils as renewable fuel based on sunflower, castor, soybean, and colza oils have good heating power and the potential to reduce carbon dioxide (CO2) emissions.7 For several reasons, colza oil is taken into consideration among the many other vegetable oils, because it can easily be converted to biodiesel or blended with petrodiesel and can be injected into the diesel engine directly.8 In the meantime, vegetable oils are considered as an appropriate choice for production of biodiesel, because they have similarities in some important properties with diesel fuels. Because of some features, such as biodegradability and eco-friendly and nontoxic nature, biodiesels are very important. The biodiesel with a lot of oxygen content improves the burning efficiency, decreases CO, CO2, particulate matter (PM), and HC, but has not desired effect on the NOx emissions.9−11 Emitted NOx react with ultraviolet radiation from sunlight and form photochemical smog harmful to the respiratory system, throat, and eyes.6 Because the viscosity of vegetable oils is high and their volatility is low, this make fundamental difficulties for employing them directly as a fuel in diesel engines. Hence, to overcome the problem of high viscosity © XXXX American Chemical Society

of vegetable oils and also to reduce the high level of NOx gases emitted from them in diesel engines, various approaches have been examined.12−14 The following are the main approaches used to overcome the high viscosity problem of vegetable oil: (1) mixing of vegetable oil and diesel by microemulsification with surfactant and co-surfactant and adding water, (2) pyrolysis, (3) transesterification of vegetable oil to biodiesel, and (4) diesel microemulsification based on the vegetable oil.15 The microemulsification technique is regarded as a practical approach to use vegetable oils instead of diesel and also to add water to the fuel. Microemulsions (MEs) are known as a thermodynamically stable, macroscopically homogeneous mixture of two immiscible liquids, such as water, oil, and surfactant, mostly together with a co-surfactant.16,17 In these systems, which were obtained by mixing all of the components with required ratios,18 the surfactant was used to decrease the superficial tension of oil and water and form MEs.19 The co-surfactant was used to finetune the better fit as well as the motion of the surfactant at the oil/water interfaces and also to improve the stability of the ME system.20 The superiority of the microemulsification method to other techniques can be cited to its low price of the product, easy performance, and minimum need for fuel processing without chemical reactions. Another advantage of this method is that they have the possibility for direct application in diesel engines without the need for any modification of the engine system.21 The diesel composition and temperature have a significant effect on the solubility of vegetable oil in the diesel, and low temperatures cause phase separation. One way to solve the Received: October 16, 2017 Revised: August 31, 2018 Published: September 17, 2018 A

DOI: 10.1021/acs.energyfuels.7b03181 Energy Fuels XXXX, XXX, XXX−XXX

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Table 1. Composition and Some Physical Properties of ME Containing 75% Diesel/Colza Oil, 5% Water, 10% n-Butanol, and 10% Surfactant sample number

Tween 80 (%)

Brij 30 (%)

n-butanol (%)

stability

highest stability temperature (°C)

water droplet size at room temperature

1 2 3

0 1 2

10 9 8

10 10 10

S, clear S, clear S, clear

25 31 45

205 nm 5 μm 10 μm

torque.44,45 This phenomenon is called microexplosion, which helps to fuel atomization.46 The main objectives of the present work were to prepare a new water-in-oil (w/o) ME system with blending of diesel and colza oil as the oil phase and water as the aqueous phase and add additives to stabilize the phases, including Brij 30 and Tween 80 as non-ionic surfactants and n-butanol as a co-surfactant. This study formulates a single-phase ME with high stability. Here, the effect of the temperature on stability, physical properties, water droplet size, kinematic viscosity, and density of new ME systems is investigated and compared to the neat diesel fuel. Finally, the performance of the optimum ME system in terms of engine combustion, emission characteristics, and energy in a diesel engine with a direct-injection system was studied, and the results were compared to the values obtained for the neat diesel fuel.

immiscibility problem of vegetable oil and diesel is the microemulsification technique.22,23 Alcohol fuels can be used directly or in a mixture with diesel in the engine,24 and they can also act as a co-surfactant for microemulsification. Among the alcohols, n-butanol is advantageous compared to ethanol and methanol; therefore, this alcohol is used as one of the primary alcohols in diesel engines as an alternative fuel. Properties of n-butanol are similar to fossil fuels because its combustion in the engine is easy. These similarities allow for n-butanol to be used as a co-solvent in the diesel/oil blend with any proportions. Some of the outstanding features of n-butanol over other alcohols include low evaporation level, high energy release, high cetane number, high energy content, and ability to blend with diesel fuel without phase separation.25,26 In addition to resolving the high-viscosity problem of vegetable oil, the ME technique helps to reduce the level of NOx emitted from the diesel fuels, which is a drawback of the presence of water in the ME fuel. In recent years, emulsions of water and diesel fuel have been considered as a suitable way for reductions in NOx and PM emissions along with keeping engine thermodynamic efficiencies.27,28 The solubilizing of 5−20% (v/v) water-in-diesel fuel requires that the surfactants and co-surfactants be added to disperse and stabilize water as tiny droplets in the diesel matrix.29,30 Different factors, such as surfactants and their combinations, are affected on the solubility of water-in-diesel fuel to reach stable and single phases. Also, the amount of surfactant and co-surfactant and their chemical structure play a significant role in this issue.31,32 In general, the direct addition of water in the mixture of air and fuel is one of the common ways to add water to the diesel fuel. Also, the modified fuels as emulsions or MEs have been considered by many researchers and authorities because they have lower levels of emitted NOx and soot than neat diesel fuel.33−36 Regardless of the possibility of direct injection of water into the engine, the emulsion or ME route is prestigious because its application requires no fundamental change in diesel engines. Generally, water-in-diesel emulsions and MEs are simply produced by mixing of diesel and water and adding polymeric or low-molecular-weight surfactants to stabilize the system.37 A 35% reduction in NOx emission has been reported as a result of the addition of 15% water to the diesel by many authors.38−42 It has been observed that, with the use of fuels with a high nitrogen content, the amount of PM emission in the exhaust is reduced.14 A water-in-diesel emulsion with the Aquazole formulation has been reported to show a simultaneous reduction in NOx emission and black smoke up to 30 and 80%, respectively. It also reduces HC consumption and the emission level of CO in small quantities.41,42 Also, Daly and co-workers have reported that PuriNOx as a water−fuel emulsion has shown a significant reduction for NOx and particulate matter (PM) emissions by 19 and 16%, respectively, while the brake specific energy consumption was reduced by 0.7%.43 By injection of the ME fuel into the engine cylinder and heating, the water droplets start to vaporize; therefore, a highpressure steam is caused by the explosion of water droplets and HC phase. This pressure force on the piston improves the engine

2. MATERIALS AND METHODS 2.1. ME Preparation. Brij 30, Tween 80, and n-butanol (99% purity) were purchased from Aldrich. Colza or rapeseed oil is a nondrying oil extracted from the seeds of rapeseed colza (Brassica rapa L. and Brassica napus L.), which is cultivated in a very large scale in France. Colza oil was purchased from Awstrade Eurl Company (France), and its composition was analyzed by gas chromatography− mass spectrometry (GC−MS). An Agilent GC−MS system, model DB-35 MS, with a column at 30 m length and 0.25 mm inner diameter and stationary phase layer of 0.25 μm thickness was used. Colza oil was composed of oleic acid (87.3%), n-hexadecanoic acid (7.4%), and 10-octadecenoic acid (2.3%) ME as its main components. In all of the experiments, distilled water was used. Fuel MEs were produced from solubilization of water in the diesel/colza oil (4:1) mixture as the oily phase using Brij 30 or Tween 80 at room temperature (21−25 °C), and n-butanol was then added to obtain a single-phase system. The ME was formulated on a weight percent basis with the mentioned component. A mixture of diesel/colza oil (75%), water (5%), and 20% surfactant plus co-surfactant was stirred at room temperature for 5 min with an stirring speed of 500 rpm. The conversion of the white milky mixture into a homogeneous, transparent, and clear solution was considered as the formation of single-phase ME. The composition of investigated MEs are given in Table 1. It can be seen that ME 3 with 8% Brij 30 and 2% Tween 80 as the surfactant with economical formulation and acceptable physical properties is the best ME formulation with a high stability temperature compared to other ME systems. Therefore, ME 3 is chosen for more combustion and emission studies. The most important properties of ME 3 are given in Table 2. The level of emissions and also performance of the engine will be affected by the fuel properties of the ME with no need for any modification of the engine system. The addition of water into the diesel results in the decrease in the lower and higher heating values (LHV and HHV) of the ME fuel, and if used in an engine with a compression ignition system, it increases the ignition delay.47 2.2. Engine Test Procedure. A single-cylinder diesel engine equipped with a direct-injection system from Lister Petter Company, U.K., model TS1, is used for studying the engine performance of the samples. The engine is operated thoroughly at a speed of 1500 rpm. The detailed technical specifications of the engine can found elsewhere.5 Loading of the engine is performed by a dynamometer to transform the mechanical energy to the network output. The setup used for performing engine experiments is displayed schematically in Figure 1. B


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3. RESULTS AND DISCUSSION 3.1. Dynamic Viscosity. The viscosities of the three ME systems, i.e., samples 1, 2, and 3 (Table 1), as well as neat diesel are measured in various temperatures and plotted in Figure 2.

Table 2. Main Properties of Diesel and ME 3 property

diesel

ME 3

density (g/cm3) kinematic viscosity at 21 °C (mm2/s) flash point (°C) cloud point (°C) pour point (°C) cetane number HHV (kJ/kg) LHV (kJ/kg)

0.84 3.1 58 2 −4 51.3 45.74 42.73

0.89 3.98 45.5 −2 −9 49.52 40.75 38.03

For control and signal measurement acquisition, two systems are embedded inside of the test bench. The first system can control and perform measurements that are very fast and is mostly installed to measure the pressure of the fuel injection and cylinder. The measurement of the crankshaft angular position is another function of this system. For the purpose of control and measuring slow measurements of the setup, the second acquisition system is installed. This system is responsible for the control of some feed parameters, such as flow rates of air and fuel. Also, it controls the engine dynamometer, engine speed, measure torque, and amount of emitted pollutants from the exhaust.5,48,49 The type and accuracy of the sensors5 employed in the setup and the method for estimating uncertainty in measured data are detailed elsewhere.48 2.3. Test Method. ME 3 on the formulation of diesel/colza oil (4:1, 75%), water (5%), n-butanol (10%), Brij 30 (8%), and Tween 80 (2%) is subjected to more engine tests with various values of brake power. The values of investigated brake power include 0.83, 1.8, 2.6, 3.5, and 4.5 kW, which correspond to engine loads of around 20, 40, 60, 80, and 100%, respectively (in comparison to the engine full load). The engine calibration is performed considering the instructions and values provided by the manufacturer before every experiment. The running condition obtained from the dynamometer control system is implemented on the brake torque during experiments.

Figure 2. Comparison of viscosity of ME systems (Table 1) to neat diesel at different temperatures.

The results indicated no significant difference between the viscosity of samples 1, 2, and 3. As expected, 1−2% variation in the amount of Tween 80 in these samples cannot impose a significant difference in the viscosity of these three ME samples (1, 2, and 3). 3.2. Study of the Particle Size. The preparation of ME was performed by different speeds of stirring at 500, 1000, and

Figure 1. Schematic representation of the experimental setup of the direct-injection diesel engine system. C


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the injection and shortens the ignition delay period.51 For a 0.83 and 4.5 kW engine power output (20 and 100% of the engine load), a higher pressure peak was obtained for ME than neat diesel fuel. The same trend of changes is obtained for the medium engine load (60% of the engine load). The fraction of fuel combusted in the premixed burning phase in the engine determines the peak cylinder pressure. The pressure of the cylinder influences the fuel capability to blend well with air and combust. The cylinder pressure versus crank angle diagrams for the experiments using diesel and ME fuel at various engine loads are plotted in panels a−c of Figure 4. Figure 4 show that, when the engine load is low, a higher peak pressure of the cylinder is observed for ME fuel than neat diesel fuel, but by increasing the engine loads to medium loads (about 60%), it become almost identical for both of the fuels. Meanwhile, by increasing the engine load to 100%, the peak cylinder pressure for ME is higher than that for diesel fuel. The fast combustion of ME components (being oxygen in the ME formulation) and short ignition delay (Figure 5) can be mentioned as the reasons for these results. Ignition delay is one of the most influential parameters, which has significant effect on the combustion duration and cylinder pressure. Because the ignition delay period is longer for neat diesel fuel than ME fuel at low engine loads, the start of combustion has occurred later for diesel fuel than ME fuel. At the low engine loads, because the piston is in a position that is far from the top dead center (TDC), consequently, the cylinder pressure is at a low value. Also, the pressure peak of the cylinder appeared earlier for ME than neat diesel fuel at the low engine loads. With the increase of the engine load, the pressure of the cylinder increases more rapidly for ME than neat diesel fuel, which is attributed to the increased amount of fuel combusted in the premixed step. With the use of ME fuel, the microexplosion of water droplets causes the enhancement of spray atomization results to a more rapid combustion of ME fuel than neat diesel; therefore, the ignition delay is reduced.52 Also, it is well-known that the size and size distribution of water droplets have a significant effect on fuel atomization,53 and there is an optimum size for the water droplets to be more effective in microexplosion. The net heat release rate (HRR) plot versus crank angle is displayed in panels a, b, and c of Figure 6 for the experiments with engine loads in low, medium, and high regions, respectively. HRR analysis is an effective measure made in framework of the first law of thermodynamics, showing the change in parameters, such as the volume, mass loss at the cylinder pressure, and heat transfer, when the intake and exhaust valves are in the closed positions.54 At the start of the HRR plot for all tested fuels, a negative HRR can be noticed, which is attributed to the vaporization of the injected fuel in the ignition delay time. After the beginning of the combustion, a positive value for HRR is observed; afterward, a process appeared that is normal for a diesel engine with a direct-injection system. As seen in Figure 6a, the combustion started earlier and also the intensity of the HRR peak of premixed combustion decreased at a low engine load (20%) for ME compared to diesel fuel. These observations are attributed to the cetane number and the effects of the oxygen content of ME components on the ignition delay at the same time that the higher viscosity of ME can decrease mixing fuel/air during injection. As in panels b and c of Figure 6, for ME at medium and high engine loads (60 and 100%), a heat release peak with higher intensity was obtained for the premixed combustion step compared to neat diesel fuel, which is most likely due to the short ignition delay. According to Figure 5, at

1500 rpm and different stirring time durations of 5, 10, and 20 min at 21 °C to obtain an optimum formulation with a proper water droplet size as well as preparation conditions. It was seen that, by stirring with 500 rpm, fairly uniform and small water droplets were obtained. The water droplet sizes were measured using the optical microscope. The optical microscope image of water droplets for ME 3 prepared by 5 min of stirring at 500 rpm and room temperature is shown in Figure 3. The sizes of water

Figure 3. Optical microscope image of ME 3 prepared at room temperature by 5 min of stirring at 500 rpm.

droplets are in the range of 5−15 μm, and almost 90% of droplets have sizes smaller than 10 μm, with a highly uniform size distribution. 3.3. Combustion Characteristics. The results for cylinder and injection pressure reported in this part are provided for three engine power outputs, 0.83, 2.6, and 4.5 kW, related to 20, 60, and 100%, respectively, of the full engine load. These results are used to compare the final stable ME system to diesel fuel in the characterization of combustion. During the cycles in every 0.2° crank angle (CA), a variation in the pressure of the injection system and cylinder is obtained. The reported values for the pressure are the average for 200 successive cycles at each load. The amount of fuel combusted in a compression ignition engine before the premixed combustion directly affects the pressure peak. The mixing in the ignition delay cycle controls the premixed combustion.49,50 Panels a, b, and c of Figure 4 show the cylinder pressure versus crank angle plots at 20, 60, and 100% loads for ME and diesel fuel, respectively. Higher peak pressures of ME at 20% load vary from 67.5 to 77.5 bar at 60% load to 87.5 bar at full load. Also, the results presented for diesel fuel at 20, 60, and 100% loads vary from 66.5 to 77 and finally to 84.5 bar, respectively. As predicted in internal combustion engines, with an increasing engine load, the pressure peak increases too. The cause of this increase is the result of increased amounts of fuel injected into the engine system, which produces more combustion products as well as vapors, resulting in a higher pressure than injection of lower loads. Also, this can be a result of the decrease of the ignition delay period by increasing the engine load. When the engine load is low, the ignition delay period becomes longer, and hence, the combustion of the neat diesel starts later than ME fuels. The delay in the start of combustion results in the attainment of a lower value for the cylinder pressure peak when operating in low engine loads compared to high loads. An increased value of the cylinder pressure peak is observed by the increase of the engine load for diesel and ME fuel. As a result of the increase of the engine load, the temperature of the engine walls and residual gas increase, and this leads to a high temperature in filling the cylinder during D


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Figure 4. Cylinder pressure variation with crank angle at (a) 20%, (b) 60%, and (c) 100% loads of ME and neat diesel.

In Figure 7 for the injection pressure peaks, the same results can be observed. The injection duration grows with an increasing engine load in all tests. The fuel pressure plots for ME and diesel follow a similar injection pressure pattern at three load conditions (20, 60, and 100%). A small shift delay (around 1° CA) is observed in the peak location on the ME fuel compared to neat diesel, which is a consequence of the bulk modulus of fuel that affects the density and injection process.55 3.4. Engine Performance. The change of the total brake specific fuel consumption (BSFC) versus power output for ME and diesel fuel is plotted in Figure 8. Considering the relative ratio of the mass of fuel transferred and brake power output of the engine, the value of BSFC was calculated. The calculated value of BSFC for ME fuel at power output values of 1.13 kW (25% load) and 4.5 kW (100% load) are 17.6 and 9.7% higher than the values for neat diesel fuel, respectively. For the whole range of engine loads, noticeably higher BSFC values are obtained for ME than neat diesel. In the diesel engine, a BSFC depends upon the heating value and engine efficiency.2 In the ME system with the adding additives (vegetable oil and surfactant) in the mixture, the heating value of fuel decreases to reach 90% of that diesel fuel. ME showed a noticeably lower heating value than neat diesel fuel. The relative ratios of the parameters, such as fuel viscosity,

Figure 5. Ignition delay variation with power output for ME and neat diesel.

medium and high range loads (50−100%), the ignition delay for ME is higher than that for neat diesel fuel. In the case of a high ignition delay, more fuel is supplied for combustion; hence, in the premixed combustion step, the HRR is increased. E


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Figure 6. HRR variation to crank angle diagram for (a) 20%, (b) 60%, and (c) 100% loads of ME and neat diesel.

3.5. Exhaust Emissions. The CO2 emission with respect to power output of ME and diesel fuel is displayed in Figure 10. CO2 emission values for ME and diesel fuel are similar. This could be attributed to their similar C/H ratio. Figures 11 and 12 depict higher levels of CO and HC emissions for ME compared to diesel values. No significant difference between CO emission of ME and neat diesel fuel is observed in low engine load experiments. However, when the engine load increases, ME fuel emitted a higher level of CO than neat diesel fuel, so that at the maximum engine load (4.5 kW power output), ME emitted 23% CO higher than neat diesel fuel. This is attributed to the fact that, in comparison to the neat diesel fuel, in using ME fuel, the combustion occurred at lower temperatures, which results in the decomposition of water molecules and the formation of a high level of OH radicals, that finally react with and oxidize carbon to CO.58 Also, the high level of emitted CO at increased engine loads is partially due to the incomplete combustion of the mixture of n-butanol−air. Figure 12 shows that ME fuel emitted at a higher level of HC than neat diesel fuel in all engine load ranges. For example, at maximum engine load conditions, the HC emission for ME was higher than that for diesel fuel by 34%. The main reason to increase HC emission is that vaporization of water at a high latent heat resulted in a lower gas temperature that prevented the oxidation of resulting HC.2 These findings are in line with the results of studies led by numerous researchers using water-in-diesel42,58 and w/o3,15 emulsions. They have attributed these observations to several reasons, from

density, volume-based fuel injection system, and lower heating value, have significant influence on the diesel engine BSFC value. The presence of oxygen-containing components, such as vegetable oil, water, surfactant, and co-surfactant, in ME fuel has a lowering effect on the heating value.56 Therefore, to obtain the same value of energy in output, a larger amount of ME is needed to be injected at different loads; hence, the value of BSFC increases to balance the reductions in the fuel chemical energy. The brake thermal efficiency (BTE) to power output is seen in Figure 9. It can be observed that the BTE of ME has comparable levels to diesel fuel at low loads; it slightly increases between 40 and 80% loads and decreases beyond. At mid-range loads (40−80%), ME has indicated a BTE of 3% higher than neat diesel fuel, which can be due to the enhanced premixed combustion phase. ME fuel sprayed as big droplets has many very tiny water droplets, which cause thorough microexplosion of the big oil droplets to explode and break down to smaller oil droplets. This phenomenon improves the fuel mixing with air, increases the evaporation rate of fuel, and consequently results in a more rapid combustion and a better BTE. However, at the high power outputs (4.5 kW), ME indicated a BTE that is 93% of the value for neat diesel fuel. In fact, the premixed combustion increase reaches a critical value beyond which BTE decreases as a result of the increase in engine pumping work. At higher loads, combustion starts earlier before TDC, and a further increase in premixed combustion creates a counter pressure on the piston during the compression stroke.48,57 F


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Figure 7. Injection pressure variation with crank angle in (a) 20%, (b) 60%, and (c) 100% loads of ME and neat diesel.

Figure 8. Variation of the total BSFC to power output for ME and neat diesel. Figure 9. Variation of BTE to power output for ME and neat diesel.

which the following can be listed: higher viscosity and lower volatility of triglycerides, lack of homogeneity, slow burning of soot, lower cycle temperature because of latent heats of evaporation of water and alcohol, and increase in ignition delays.59,60

The level of NOx emitted in application of the diesel fuels is one of the most important issues in this field. According to the G


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Figure 12. Variation of the HC emission to power output for ME and neat diesel. Figure 10. Variation of CO2 emission to power output for ME and neat diesel.

Figure 13. Variation of the NOx emission to power output for ME and neat diesel. Figure 11. Variation of the CO emission to power output for ME and neat diesel.

Meanwhile, the presence of oxygen in the n-butanol structure can be effective in reducing the flame temperature, and consequently, these can be partially effective in the reduction of NOx emissions.63

emitted NOx versus power output diagrams for ME and neat diesel in Figure 13, it is observed that ME has been more effective in decreasing NO levels. For both of the ME and diesel fuels, with the increase of engine loads, the level of emitted NOx increases. ME fuel showed a lower level of emitted NOx than neat diesel fuel. At the highest engine loads, the level of emitted NOx with neat diesel fuel is 758.8 ppm, whereas with ME, it is 601 ppm. According to the results, at the highest engine load (4.5 kW power output), ME fuel exhibited an emitted NOx level of approximately 21% lower than neat diesel. The added water is considered as the reason for the reduction of NOx emission from ME fuel. The added water absorbs a relatively huge amount of heat to evaporate (vaporization heat) and reduces the flame peak temperature, and consequently, the level of emitted NOx decreases.61,62 Also, considering the presence of 10% n-butanol with a high heat of evaporation, a considerable amount of thermal energy will be consumed for evaporation of n-butanol.

4. CONCLUSION Here, the physicochemical parameters, combustion, emission characteristics, and performance of the designed ME fuel and neat diesel fuel in an engine with a direct-injection system are investigated and compared together. Nevertheless, no cost effectiveness analysis has been made, and the formulated systems here have obvious advantages of long-term stability, the possibility to use vegetable oils without any expensive processes, such as pyrolysis, transesterification, etc., and simple and easy preparations without having to design and use any new emulsification accessories. Meanwhile, a few fuel ME formulations have been reported with a very low surfactant content, but they have used different emulsification methods.64 In fact, the maximum time that they have studied the emulsion H


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stabilities has been 24 h, but our MEs have been proven to be stable up to 9 months.65,66 The experiments are performed in different engine loads, and the following important conclusions can be made by this work: (1) The new w/o ME system was produced with the blending of diesel/colza oil, water, and adding additives to stabilize the phases, including Brij 30, Tween 80, and n-butanol. Here, a single-phase ME with high stability and acceptable physicochemical properties is formulated. (2) The BTE and BSFC for ME are higher than those for diesel fuel in medium engine load for BTE and all engine load ranges for BSFC. The high BSFC as a result of adding colza oil and additives had a direct effect on the heating value and BSFC. (3) ME fuel exhibited higher HC emission levels than neat diesel fuel at the entire range of engine loads. (4) CO emission of ME fuel is higher than that of neat diesel fuel when the engine load is high. (5) For the whole range of engine loads, the level of emitted NOx from ME fuel is lower than that from neat diesel fuel.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +98-41-33393101. Fax: +98-41-33340191. E-mail: [email protected]. ORCID

Reza Najjar: 0000-0003-2292-2746 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been supported by the Center for International Scientific Studies & Collaboration (CISSC). Also, the authors acknowledge the Ecole des Mines de Nantes, France, for the research facilities.

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REFERENCES

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Experimental Investigation of Emission, Combustion, and Energy

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