Assessing the Impact of Ethanol/Biodiesel/Diesel Blends and Nanoparticle Fuel Additives on Performance and Emissions in a DI Diesel Engine with EGR Integration: An Experimental Study

Abstract

In this paper, the effect of nano-particles along with EGR rates was experimentally assessed on the performance and emission of a DI diesel engine fueled by biodiesel and ethanol. For this purpose, three levels of TiO₂ nanoparticles (0, 40, and 60 ppm) were added to biodiesel/diesel blends in the proportions of 0, 10, and 20% biodiesel with ethanol at levels of 0, 4, and 6%. EGR rates were used at 0, 20, and 30%. A total of 31 fuel samples with different ethanol, biodiesel, TiO₂ nano-additives, and EGR rates were tested at different speeds. The equation for this combination is B_xE_y + EGR_w + TiO_2z, where x, y, w, and z are the percentages of biodiesel, ethanol, EGR, and TiO₂. The results showed that the mixture of B10E4 + EGR20 + TiO₂60, reduced the amount of NO_x, CO, and HC by 10, 12.4, and 17%. Moreover, due to the significant reduction of emissions and performance improvement, the combinatory method of EGR–TiO₂ nano-additives can be used as an effective formula for diesel engines fueled with ethanol/biodiesel/diesel blends.

1. Introduction

Many researchers have recently become interested in the use of oxygenated fuels such as biodiesel and ethanol in diesel engines due to the implementation of severe limits on pollutant emissions [1,2,3]. Biodiesel, which is a high chain fatty acid monoalkyl ester, is obtained from renewable sources such as vegetable oils, waste, and animal fats [4]. Biodiesel, depending on the type of oil used in its production, contains 10 to 12 percent of oxygen approximately [5,6]. Ethanol as a renewable fuel can be produced by fermenting plant products that contain large amounts of sugar. Additionally, any compound that can be converted to sugar, such as starch and cellulose, is used in the production of ethanol [7]. Ethanol contains about 35% of oxygen, which helps to reduce soot and PM [8,9]. According to the studies, the mixtures of biodiesel and ethanol up to 20 vol% can be combined with pure diesel without any significant engine hardware modification [10,11,12]. In 2014, Karthikeyan et al. [13] investigated the performance, combustion, and emission characteristics of a single-cylinder engine for various mixtures of biodiesel and zinc oxide nanocatalysts. They also evaluated the properties of the prepared fuels, such as flash point, viscosity, cetane number, and calorific value. Their results showed that the addition of zinc oxide nanocatalysts accelerated the reaction rate and increased NO_x. In an experimental study conducted by Saravana in 2015 [14], the emissions and performance of a diesel engine fueled by pentanol were examined. Their results indicated that all prepared mixtures from pentanol had higher HC and CO emissions than pure diesel fuel. In 2017, Yilmaz et al. [15] experimentally evaluated the use of diesel, biodiesel, and pentanol fuels in a four-stroke single-cylinder diesel engine under different engine loads. The results showed that the use of biodiesel and pentanol increased NO_x and BSFC. In 2019, Devarajan et al. [16] investigated the combustion and emission characteristics of a single-cylinder diesel engine by adding the silver oxide nanoparticles at different particle sizes to biodiesel. The results showed that the use of biodiesel increases the amount of NO_x and the addition of nanoparticles reduces it. In 2020, Uyumaz [17] examined the combustion, performance, and emission characteristics of a diesel engine using linseed oil biodiesel. They concluded that with increasing the percentage of biodiesel, the amounts of NO_x, CO₂ emissions, as well as thermal efficiency, decreased. Disadvantages of oxygenated fuels include reducing power and torque and increasing fuel consumption, which has been reported in many references [18,19]. The nanoparticles can improve power and torque as well as reduce fuel consumption [20,21]. However, the addition of TiO₂ nanoparticles accelerates the reaction rate and increases NO_x emissions [22,23]. On the other hand, the EGR system is one of the methods that can be used to reduce NO_x emissions [24,25]. For this purpose, laboratory tests were applied to investigate the effect of TiO₂ nano-additive along with EGR rates on performance and emissions of a DI diesel engine fueled with ethanol and biodiesel.

2. Materials and Methods

2.1. Fuel

The high purity ethanol, pure diesel, and biodiesel were applied in this research.

Table 1. Properties of diesel, biodiesel, and ethanol.

Fuel Property	Units	Diesel	Biodiesel	Ethanol	Method
Oxygen content	wt.%	0	11	35	D5293
Carbon content	wt.%	87	78	51	D5291
Hydrogen content	wt.%	13	11	14	D5292
Cetane number	-	55	62	7	D6890
Calorific value	MJ kg−1	43.37	34.35	27.52	D240
Flash point	°C	69.8	110.15	13	D93
Kinematic viscosity @ 40 °C	mm2 s−1	3.42	4.19	1.13	D445
Density @ 15 °C	kg m−3	847.7	887.3	794.9	D127

shows the properties of the fuels. Biodiesel was mixed with pure diesel (D100) at 10 and 20 vol% and named B10E0 and B20E0. Ethanol was mixed with pure diesel at two levels (4 vol% and 6 vol%) and was shown as B0E4 and B0E6. A mixture was also prepared by a simultaneous combination of biodiesel–ethanol and was named B10E4. Previous studies on the mixing of ethanol and diesel [19,26,27] showed that the phase separation in the ethanol–diesel mixture does not occur at temperatures above 10 °C. It should be noted that, in the present work, all operating conditions are at temperatures above 20 °C.

2.2. Preparation of Fuel Blends with TiO₂ Additive

Bandalin Sonopuls HD 3400 ultrasonic homogenizer has been used to add TiO₂ nanoparticles and prepare a homogeneous mixture. This process was performed for 30 min to provide the uniform distribution of nanoparticles and stability of the prepared mixtures. The average size of the nanoparticles is smaller than the diameter of the injector nozzle, so there will be no disturbance in the fuel flow path. TiO₂ nanoparticles were added to diesel–ethanol–biodiesel mixtures at 40 and 60 ppm levels. The main characteristics of TiO₂ are given in

Table 2. Properties of TiO₂.

Chemical Name	Titanium Dioxide
Purity	>99%
Form	Powder
Color	White
Average particle size	20 nm
Molecular weight	82.3 g/mol
Chemical abstract service (CAS) number	12188-41-9

.

2.3. Exhaust Gas Recirculation (EGR)

Recirculating some of the exhaust gases to the inlet manifold and combining it with fresh air is an effective way to reduce NO_x emissions. Numerous studies on the EGR system have shown that NO_x reduction cannot be achieved without cooling the exhaust gases. The high exhaust gas temperatures can increase NO_x formation [28]. For this purpose, an external cooled EGR system was used at two rates of 10 and 20%. This system reduces the maximum temperature and oxygen concentration and increases the specific heat of the mixture inside the combustion chamber. The EGR rate is controlled by the EGR valve and an orifice meter is used to measure the flow rate of the exhaust gas. Using Equation (1), the EGR value is expressed as a percentage [29]:

$$\%\mathrm{EGR}=\left(\frac{{\mathrm{CO}}_2 \mathrm{intake}}{{\mathrm{CO}}_2 \mathrm{exhaust}}\right)\times 100$$

(1)

2.4. Experimental Setup

A four-stroke six-cylinder diesel engine with the power of 62 kW was applied to investigate the combined effect of TiO₂ nano-additives and EGR rates on combustion and emission characteristics of biodiesel–ethanol–diesel blends. The engine specifications are given in

Table 3. Specifications of the test engine.

Manufacturer and Model	LOVOL 1006TG1A
Engine type	Six-cylinder, four-stroke, direct injection, turbocharged
Number of cylinders	6
Cylinder volume	5.99 lit
Bore and stroke	100 * 127 (mm)
Compression ratio	17.5:1
Maximum torque	337 Nm@1400 rpm
Maximum power	62 kW@2000 rpm
Number of holes in the nozzle	5

as well as the schematic of the testbed in Figure 1. To measure torque and power, a 400 kW hydraulic dynamometer with an accuracy of ±2 Nm is used, which creates a brake force against the rotation of the motor by creating a magnetic field. Eddy current dynamometer is equipped with a data collection system that is cooled by water. While no load is applied to the motor, the dynamometer rotates freely on the bearings. The SWPF-60A mass flowmeter with an accuracy of 0.01 kg/hr was used to measure fuel consumption. Temperature sensors are of the resistance thermometer (R) type, which can measure temperatures up to 1900 degrees. Their accuracy is ±1 degree and their coil is made of platinum with a base resistance of 100 Ω. A magnetic tachometer attached to the output shaft was used to measure the engine speed. Testo 350 was also used to measure the amounts of NO_x, CO, CO₂, and HC in all of the engine testing. It should be noted that the emissions analyzer is carefully calibrated before the tests to ensure the accuracy of the measurements. The variations range and calibration of this device are given in

Table 4. Specification of the Testo 350 emission analyzer.

Resolution	Range	Parameter
1 ppm	0–3000 ppm	NOx
1 ppm	0–5000 ppm	CO
0.1 vol%	0–50 vol%	CO2
1 ppm	0–40,000 ppm	HC

. The test result was analyzed and received in a computer system.

The range for engine speed was 1000 to 1800 rpm. First, the engine warms up for about 10 min to reach a steady state in terms of inlet and outlet water temperature and oil temperature, and the tests were performed in an almost stable state. To prepare the engine setup, the oil level inside the oil pan is checked to be full. The water flow is then opened to the dynamometer and the needle valve is opened with the maximum water flow obtained, ensuring that the dynamometer seals are lubricated. The water flow is reduced to the point of dripping and the engine is started. The engine is allowed to run for about 10 min to warm up. The throttle control lever is then advanced to its maximum position and the maximum speed of the engine is recorded.

When the engine reached to the steady state conditions, the amounts of torque, inlet air temperature, fuel mass, amounts of NO_x, CO, CO₂, HC, and BSFC, and exhaust gas temperature and engine speed are recorded. This process was repeated for different operating conditions. After the test, the needle valve was closed. Allow the engine to run for a few minutes in this mode. The engine now turns off and closes the main water valve. It should be noted that the measurements were repeated three times for each sample and their mean value was recorded as the final data. All equipment is calibrated before the tests to avoid possible errors in the laboratory data.

2.5. Uncertainty Analysis

In experimental studies, the calculation of uncertainty is necessary. Uncertainty provides information about the quality of the measured parameters. Regardless of the accuracy of the test, there may be errors in the collection of experimental data for a variety of reasons. To identify these errors, statistical analysis of laboratory data, uncertainty has been used. Fixed and random errors may cause uncertainty in an experimental measurement. Fixed errors are usually eliminated by calibrating the measuring instruments, but random errors are detected through statistical analysis. In the present work, the uncertainty of the data is calculated from Equation (2):

$${\mathsf{\sigma }}_{\mathrm{m}}=\frac{\mathsf{\sigma }}{{\mathrm{n}}^{0.5}}$$

(2)

in which, σ_m is the standard deviation of the mean value, σ is the standard deviation of the set of measurements, and n is the number of measurements at each point (n = 3, for all laboratory results). The uncertainty of the laboratory data is also calculated from Equation (3):

$$\mathrm{X}=\frac{{\mathsf{\sigma }}_{\mathrm{m}}}{\overline{\mathrm{x}}}\times 100$$

(3)

that X is the uncertainty of the laboratory data. Additionally, the parameter X is calculated with the arithmetic mean of the data. Each test was repeated three times to avoid errors in the recording of laboratory data as much as possible. At each stage, a slight difference may be observed, which is characteristic of experimental work. Irrelevant data are removed to ensure the accuracy of the results and the percentage of uncertainty is obtained by using the obtained relations. For example, as the results show, the recorded data are acceptable for NO_x emissions with ±4%. In other words, in the results of NO_x = 100 ppm, this value will be in the range (96–104), i.e., 100 ± 4 ppm.

3. Discussion on Results

3.1. Brake Power

Figure 2 and Figure 3 show the power variation at different speeds for diesel–ethanol–biodiesel blends using TiO₂ nano-additive and EGR system.

Figure 2 shows the effect of EGR rates (20% and 30%) on the power for prepared fuel blends. It is observed that, with increasing the percentage of EGR, the output power decreases. The amount of output power when using B10E4 + EGR30 at the different speeds is between 13.8 to 19.2% less than when using B10E4 + EGR20. The minimum power was observed in B20E0 + EGR30, which reduced the power by an average of 27.8% at different speeds. B0E6 + EGR30 also reduced the output power compared to D100 at speeds of 1000, 1400, and 1800 rpm by 26, 27.7, and 21.1%. Reducing the amount of oxygen in the combustion chamber can be the main reason for reducing the power by using the EGR system [30,31,32].

The effect of simultaneous EGR = 20% and TiO₂ = 60 ppm on the output power of the diesel–ethanol–biodiesel blends is shown in Figure 3. It can be seen that the B0E4 + EGR20 + TiO₂60 mixture increased the output power by an average of 2.5% compared to the D100 at different speeds.

3.2. Torque

Torque variations at different speeds for prepared mixtures with TiO₂ nanoparticles and the EGR system are shown in Figure 4 and Figure 5. Variations of engine torque for diesel-ethanol–biodiesel blends due to the addition of TiO₂ nanoparticles at 40 and 60 ppm at different speeds are shown in Figure 4. It is observed that by increasing the percentage of nanoparticles, the brake torque increases. The B0E4 + TiO₂60 and B10E0 + TiO₂60 increased the torque by an average of 2.8 to 3% compared to D100 at different speeds. Using the B10E4 + TiO₂60 blend, increased the amount of torque compared to the B10E4 + TiO₂40 blend, by an average of 4.3% at the different speeds. The higher energy content and the surface-to-volume ratio of TiO₂ can be the main reasons for increasing the torque [33,34].

The effect of simultaneous EGR = 20% and TiO₂ = 60 ppm on the engine torque for diesel–ethanol–biodiesel blends is shown in Figure 5. The B10E4 + EGR20 + TiO₂60 at 1000, 1400, and 1800 rpm reduced torque by 3, 7.7, and 6.2% compared to D100.

3.3. BSFC

The fuel consumption characteristics of an engine are generally expressed in terms of fuel consumption in kg of fuel per kW-hr. It is an important parameter that reflects how good engine performance is. It is inversely proportional to the thermal efficiency of the engine. Brake-specific fuel consumption (BSFC) is the specific fuel consumption on the basis of the brake power (P_b). In other words, BSFC is the measurement of efficiency of fuel by the engine that combusts the fuel–air mixture and produces the rotational motion of the crankshaft. This is used for comparing the efficiency of the engine. BSFC is the ratio of the rate of fuel consumption and the effective power produced from the engine. Mathematically it is expressed as:

$$\mathrm{BSFC}=\frac{\mathrm{Fuel} \mathrm{mass} \mathrm{flow} \mathrm{rate} ({\dot{\mathrm{m}}}_{\mathrm{f}})}{\mathrm{Brake} \mathrm{power} ({\mathrm{P}}_{\mathrm{b}})}$$

(4)

Variations in BSFC at different speeds for prepared fuel blends using TiO₂ nanoparticles and EGR are shown in Figure 6 and Figure 7. The effect of adding TiO₂ nanoparticles at 40 and 60 ppm on the BSFC of diesel–ethanol–biodiesel blends at different speeds is shown in Figure 6. It is observed that with increasing the percentage of nanoparticles, the BSFC decreases. The B10E0 + TiO₂60 and B0E4 + TiO₂60 decreased BSFC by an average of 11.7% and 12%, at different speeds compared to diesel. Also, the B10E4 + TiO₂60 blend reduced the BSFC by 13.5, 13.2, and 16.5%, compared to the B10E4, at 1000, 1400, and 1800 rpm. Improving the combustion process as a result of TiO₂ addition can be the main reason for BSFC reduction [35,36].

The effect of simultaneous use of EGR = 20% and TiO₂ = 60 ppm on BSFC for different blends is shown in Figure 7. B10E4 + EGR20 + TiO₂60 at 1000, 1400, and 1800 rpm increased BSFC by 4.7, 2.5, and 2% compared to pure diesel.

3.4. Exhaust Gas Temperature

Figure 8 and Figure 9 show the variations of the exhaust gas temperature for the prepared mixtures using the EGR system and TiO₂ nanoparticles. Figure 8 shows that as the percentage of EGR in diesel–ethanol–biodiesel fuels increases, the exhaust gas temperature decreases. The lower oxygen content of the inlet air and the decreasing of the peak combustion temperature can be the reasons for decreasing of the exhaust gas temperature [37]. The minimum exhaust gas temperature was observed for B0E4 + EGR30, which reduced the exhaust temperature by 15, 21, and 13% at 1000, 1400, and 1800 rpm. In addition, the B10E4 + EGR30 blend, reduced the exhaust gas temperature by 15.8% in the different speeds compared to the B10E4 blend.

The effect of simultaneous use of EGR = 20% and TiO₂ = 60 ppm on exhaust temperature for different blends is shown in Figure 9. The maximum temperature was observed for B20E0 + EGR20 + TiO₂60 with a 3.6% increasing in temperature compared to D100. The minimum temperature was recorded for B0E4 + EGR20 + TiO₂60, which showed an average reduction of 7% in the exhaust gas temperature compared to D100 at different speeds.

3.5. NO_x

Variations of NO_x at different speeds for prepared blends are shown in Figure 10 and Figure 11. As can be seen, NO_x emission decreases with increasing speed. Figure 10 shows that with increasing the percentage of TiO₂ in the mixture, the amount of NO_x increases. The maximum amount of NO_x was recorded for B20E0 + TiO₂60, which increased the NO_x by 27.5, 26.7, and 35.8% at 1000, 1400, and 1800 rpm. Also, the B10E4 + TiO₂60 blend, increased NO_x emission by 2.9% compared to the B10E4 + TiO₂40 at different speeds. With increasing of the percentage of TiO₂ in the mixture, more oxygen atoms are available to react with nitrogen atoms in the combustion chamber, increasing the combustion temperature, which can be the main reason for increasing of NO_x emission [38,39,40].

The effect of EGR = 20% and TiO₂ = 60 ppm on NO_x emission for different blends is shown in Figure 11. The B20E0 + EGR20 + TiO₂60 increased NO_x by an average of 6.2% compared to D100 at different speeds. Additionally, the minimum amount of NO_x was recorded for B0E4 + EGR20 + TiO₂60 with a 13% reduction compared to D100.

3.6. CO Emission

Figure 12 and Figure 13 show the variations of CO emission for the different mixtures with EGR system and TiO₂ nanoparticles. As can be seen the B10E0 + EGR30 blend increases the amount of CO by 6.7% compared to the B10E0 + E,GR20, at the different speeds. The B10E4 + EGR30 blend also increased CO emission by an average of 4.8% compared to B10E4 + EGR20.

The effect of EGR and TiO₂ in the prepared mixtures on the amount of CO is shown in Figure 13. It is observed that the B10E4 + EGR20 + TiO₂60 at 1000, 1400, and 1800 rpm reduces CO by 5.9, 10, and 12.5% compared to D100.

3.7. CO₂ Emission

Variations of CO₂ emission for diesel–ethanol–biodiesel mixtures by using TiO₂ and EGR are shown in Figure 14 and Figure 15. The effect of adding TiO₂ nanoparticles at 40 and 60 ppm on the CO₂ emission of different blends is shown in Figure 14. It is observed that with increasing of TiO₂ in the blends, the amount of CO₂ increases. Improving the combustion process can be the main reason for the increase in CO₂ [41]. In addition, the B20E0 + TiO₂60 at 1000, 1400, and 1800 rpm increased CO₂ by 17.1, 28, and 11.4% compared to D100.

Figure 15 shows the effect of the simultaneous use of EGR and TiO₂ on CO₂ emission. The maximum amount of CO₂ was observed for B0E6 + EGR20 + TiO₂60 by 17.2% at 1800 rpm compared to D100.

3.8. HC Emission

Figure 16 shows the variations of HC emission for the prepared mixtures. As can be seen in all of the prepared mixtures, HC emission is reduced with increasing speed. Incomplete combustion is one of the main reasons for HC formation [42].

The higher oxygen content of biodiesel and ethanol than pure diesel, which improves the combustion process, as well as the lower carbon-to-hydrogen ratio of biodiesel and ethanol, can be the main reasons for HC reduction. As can be seen in Figure 16, the minimum HC emission was produced in B20E0 + EGR20 + TiO₂60, which reduced HC by 20% at 1800 rpm.

4. Conclusions

In the present study, the performance and emission parameters of a direct injection diesel engine have been experimentally investigated by using different levels of TiO₂ and EGR system in prepared diesel–ethanol–biodiesel blends. The most important results are:

• The minimum power was observed in B20E0 + EGR30, which reduced the power by an average of 27.8% at different speeds.
• With increasing of the EGR rate as well as increasing the percentage of ethanol and biodiesel in the mixture, the brake power and engine torque decreased. While increasing the percentage of TiO₂ in the mixture, the amount of power and torque increased.
• BSFC increased with increasing the EGR rate, as well as increasing the percentage of ethanol and biodiesel in the mixture. However, with increasing the percentage of TiO₂ in the mixture, the amount of BSFC decreased.
• The B10E4 + EGR20 + TiO₂60 at 1000, 1400, and 1800 rpm increased BSFC by 4.7, 2.5, and 2% compared to pure diesel.
• Increasing the EGR rate reduced the exhaust gas temperature. While an increase in the percentage of biodiesel, ethanol, and TiO₂ in the mixture increased the exhaust gas temperature.
• The minimum exhaust temperature was recorded for B0E4 + EGR20 + TiO₂60, which showed an average reduction of 7% in the exhaust gas temperature compared to D100 at different speeds.
• The amounts of HC and CO emissions increased with increasing of the EGR rate, while the addition of TiO₂, as well as increasing the percentage of biodiesel and ethanol in the mixture, reduced the amounts of these emissions.
• NO_x emissions increased with an increase in the percentage of biodiesel, ethanol, and TiO₂. While increasing the EGR rate reduced NO_x emissions. The minimum amount of NO_x was recorded for B0E4 + EGR20 + TiO₂60 with a 13% reduction compared to D100.
• The B10E4 + EGR20 + TiO₂60 reduced the emissions of HC, CO, and NO_x by 17, 12.4, and 10% compared to D100. The amounts of brake power and torque were also generated near to pure diesel, while BSFC values increased by an average of 3%.