Abstract
The usage of petroleum fuels in IC engines is hazardous to humans, plants, and agriculture since they exhaust poisonous pollutants into the environment. Substantial research is now being conducted to identify an alternative to petroleum fuel and to enhance its quality. Nanoparticles are a relatively new technology that may be used to improve the properties of fuel. Engine tests were performed on conventional CI engines using a diesel and biodiesel blend under different running circumstances. The purpose of this study is to investigate the performance, emissions, and combustion characteristics of a pumpkin seed oil methyl ester diesel blend (PSOME20) in a diesel engine with the help of a copper oxide nanoparticle. CuO nanoparticles in varying concentrations (50 and 100 ppm) were dispersed in the PSOME20 fuel. The results showed that the BTE of the PSOME20CuO100 fuel is 2.3% higher than that of the PSOME20 fuel, but the reduction in BSFC is 6.4%. Engine HC, CO, and smoke emissions were being significantly minimized when CuO nanoparticles were mixed with PSOME20. The addition of CuO nanoparticles to PSOME20 enhanced combustion behaviors such as HRR and cylinder pressure.
1. Introduction
Because of their greater fuel efficiency, diesel engines are widely used in transportation, agriculture, and power generation. The use of petroleum fuels in engines endangers humanity by polluting the environment. Due of the probable depletion of resources and the degradation created by petroleum products, researchers are encouraged to search move in this direction [1, 2]. The utilization of alternative energy sources decreases reliance on fossil fuels and has a smaller influence on global fuel market volatility. Because of benefits such as higher lubricity and availability, biodiesel is a feasible diesel fuel alternative. Furthermore, as compared to diesel fuel, it has a lower calorific value and higher viscosity [3].
Numerous vegetable oil from feed stocks have been developed in recent years from nonedible oils and have been reported including Moringa oleifera biodiesel [4], rubber seed oil biodiesel [5], chicha oil biodiesel [6], lemon peel oil biodiesel [7], yellow oleander oil biodiesel [8], and Moringa oleifera oil biodiesel [9]. These biodiesels were synthesized by the process of transesterification, and these biodiesels were compounded with diesel in certain ratios and studied the working characteristics of diesel engine. They were reported that there is a reduction in all pollutants except NOx that are higher than diesel [10, 11].
Recently, researchers have focused on incorporating nanoparticles into various biodiesel mixes in order to minimize engine exhaust gas emissions. A nanosized metallic particle has activation energy, which results in increased reactivity, as well as a greater surface area, which promotes combustion. The high surface-to-volume ratio of nanoparticles increases the combustion by improving the interplay between fuel and oxygen in the cylinder. [12] evaluated the performance of a CI engine utilizing 100% biodiesel combined with alumina and titanium oxide nanoparticles in 25 ppm and 50 ppm dosage levels, respectively. The results showed that the engine’s brake thermal efficiency (BTE) and emissions were lower with nanoparticle-biodiesel mixture, except for NOx emissions, as compared to 100% biodiesel.
[13] investigated the influence of nanofluid additives on the performance and emissions of CI engines running on emulsified diesel and biodiesel. They concluded that nanofluid decreases the NOx emissions by 6.7% with improved engine performance. [14] explored the effects of copper oxide nanoparticle additions with soya bean biodiesel and determined that adding copper nanoparticle minimized the NOx emission of soya bean biodiesel. [15] conducted an exploratory investigation including the addition of nanoparticles to methyl ester and its mixes for CI engines. The outcomes demonstrate that thermal efficiency has increased, while NOx emissions have decreased. [16] investigated the diesel engine emissions and performance employing CuO nanoparticles with mahua biodiesel. They affirmed that the BTE was estimated to be lower than that of diesel due to the drop in exhaust emissions.
According to a thorough analysis of the literature, the addition of nanoadditive to biodiesel improves engine operating characteristics and emission characteristics. The usage of nanoparticle-infused biodiesel has decreased all the emissions, which were previously considered a major problem when running diesel engines, to a manageable level. In the current study, different dosage levels of CuO nanoparticle were added to pumpkin seed biodiesel-diesel mixture, and substantial improvement of overall, combustion, and emission were obtained and compared with base fuels.
2. Materials and Methods
2.1. Pumpkin Seed Oil Extraction
Cucurbita pepe L. is the botanical name of the pumpkin plant. The pumpkin seed has a nice fragrance and is dark green in color. Pumpkin oil is produced at low temperature from raw pumpkin seeds. It is prepared by pressing toasted hull-less pumpkin seeds from a local pumpkin species. The oil content of pumpkin seeds fluctuates between 40 and 60%. There are numerous methods of producing pumpkin oil which are preexpelling and hexane extraction techniques. Pumpkin oil seems to be green in outer layers and red in hidden layers. It has an acid value of 1.2 and a specific gravity of 4.62. Because of its delicate nature, the oil must be stored in a dry and cool place.
2.2. Biodiesel Production
Pumpkin seed oil biodiesel is manufactured through the transesterification of raw pumpkin seed oil with the presence of a NaOH catalyst. To make a sodium methoxide solution, 1000 mL of raw oleander oil is placed in a round bottom conical flask, and 10 g of KOH crystal is properly dissolved with 200 mL of methanol in a beaker. The solution is then applied to raw pumpkin seed oil in a three-necked flask, heated to 65°C, and continuously stirred at 500 rpm for 1 hour. It is moved to a separating flask and allowed to settle for 8 hrs. In the flask, two layers appeared: the lower part is glycerol, and the top surface is biodiesel. Despite the fact that the glycerin process was mostly isolated, there was some glycerin and residual methanol in biodiesel phase. These compounds could be dissolved in water. Distilled water washing technique was utilized to remove and purify these compounds from the biodiesel.
During this process, the biodiesel was combined with one-third of its volume of warm distilled water and shaken. This procedure was replicated three times. After evaporation, the refined biodiesel was totally free of residual water and methanol. Filter paper was used in the filtration process. Pure B-100 fuel was on hand. Furthermore, PSOME fuel was combined with diesel at a 25 percent by volume ratio to produce PSOME20 fuel. The physicochemical properties are determined and listed in Table 1.
2.3. Experimental Test Engine
This study used a monocylinder Kirloskar diesel engine connected with dynamometer to simulate braking load. A test engine is depicted schematically which is illustrated in Figure 1. Instruments required for this study were calibrated and checked before being used to measure engine parameters and tail pipe emissions. Complete details of the experimental engine are given in Table 2. An AVL-444 gas analyzer had been used to assess exhaust emissions like CO, HC, and NO, and the AVL-437 smoke meter was used to measure the smoke opacity in the tail pipe. Engine was primarily fuelled by diesel and PSOME20 and then operated with PSOME20 at various injections pressures (200, 220, 240, and 260 bar) with original injection timing 23°bTDC to test the engine behaviors at 0-100 percent load in 25% increments. Every experiment was repeated three times, with the mean data utilized for computations. The experimental data were analyzed and compared to diesel at 200 bar normal injection pressure.
Injection pressure was changed in 20 bar increments from 200 to 260 bar pressure. Nozzle opening pressure was varied by adjusting the needle valve spring tension on the injector. The injector’s opening pressure (IP) is changed by adjusting the spring tension, which means that when the fuel line pressure exceeds the required pressure value, the injector’s nozzle valve opens, which is used to evaluate the fuel injection pressure after the necessary adjustments.
2.4. Copper Oxide Nanoparticles
Aldrich, a Bangalore-based vendor, provided the copper oxide (CuO) nanoparticle. The supplier provided black nanopowder that was 99.9% pure. Figure 2 is a photographic image of a CuO nanoparticle. The nanoparticles ranged in size from 40 nm to 50 nm. After adding CuO nanoadditive, the thermophysical characteristics of PSOME20 test fuel improved gradually. Copper oxide nanoparticle dosage levels were determined using a precision electronic balance and the situation frame in the base fuel, which ranged from 50 to 100 ppm. The copper oxide (CuO) nanoparticles were then distributed in the PSOME20 fuel sample at the dosage levels of 50 and 100 ppm using an ultrasonicator.
An ultrasonicator with a capacity of 200 W and a frequency of 40 kHz was used to generate a homogenous dispersion of CuO nanoparticles in PSOME20 test fuel. At a temperature of 70°C, the ultrasonicator was agitated at 350 rpm. The operation was carried out for 1.5 hours to ensure appropriate dispersion. The fuel qualities of diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 fuel samples were tested in accordance with ASTM standards. Because the attentiveness of the nanoparticles in the test biofuels enhanced, the density of the test fuels containing CuO nanoparticles improved. When CuO nanoparticles were extra to the PSOME20 improper fuel, the kinematic viscosity improved somewhat. Due to the increased O2 concentration of the CuO nanoparticles, with PSOME20 fuel, the CuO nanoaddition biodiesel blends’ fire point and flash were found to be lower. Table 1 lists the characteristics of all of the test fuel samples. CuO Nanoparticles characterization was done in the research work.
Scanning electron microscope (SEM) and X-ray diffraction (XRD) methods were used to characterize the CuO nanoparticles. The average particle size and shape of CuO nanoparticles were found out by SEM. Figure 3 shows a 10,000 magnification SEM picture of CuO nanoparticles. XRD may be used to identify the phase and crystal structure existing in CuO nanoparticles. XRD may also be used to calculate the phase fractions and crystallite size of CuO nanoparticles. The XRD pattern of CuO nanoparticles was measured using an X-ray diffractometer with a radiation source (=1.55080 Ao) in the 200–1000 range. Figure 4 depicts the XRD spectra of CuO nanoparticles [17].
3. Results and Discussion
3.1. Performance Characteristics
3.1.1. Brake Thermal Efficiency
The change in BTE with brake power for the fuels used for this experiment is shown in Figure 5. The BTE was increased with an increase in engine load due to a reduction in heat dissipation from the combustion chamber. Because of its lower calorific value and higher viscosity and density of biodiesel mixture, PSOME20 fuel has a lower BTE than diesel fuel. This is also owing to greater viscosity and lower BTE caused by inadequate fuel breakdown inside the combustion chamber. When PSOME20 biodiesel is mixed with CuO nanoparticles, the BTE is higher than when PSOME20 is used alone. It occurs as a result of improved combustion caused by the CuO nanoparticles’ high surface-volume ratio, which results in superior fuel oxidation [12]. Nanoparticles work similarly to oxygen buffers in that they increase the mixing rate of A/F, resulting in improved fuel combustion. CuO increases the attributes of PSOME20 test fuel by reducing ignition delay and fuel evaporation time. BTE increases as the number of CuO nanoparticles increases, which is related to rapid heat liberation during the combustion process. Maximum BTE were obtained as 31.4%, 28.6%, 30.2%, and 30.9% for the diesel, PSOME2020, PSOME20CuO50, and PSOME20CuO100 test fuels at maximum engine load. The BTE of PSOME20CuO50 and PSOME20CuO100 were increased by 1.6% and 2.3% as compared to PSOME20 at maximum load.
3.2. Brake-Specific Fuel Consumption
The change in BSFC with BP for diesel and PSOME20 with various CuO nanoparticles is given in Figure 6. Because of the lower heating value, the BSFC for PSOME20 fuel was greater than that of diesel fuel. Improved combustion of the PSOME20CuO50 and PSOME20CuO100 test fuels resulted in a decreased BSFC at all loads. Another theory is that by improving the surface area/volume ratio and decreasing the ignition delay, CuO mixing improved the combustion process and reduced BSFC. Because of the enhanced fuel quality, the BSFC for the synthesis of nanoparticles to the PSOME20 fuel was lower than the BSFC for the PSOME20 fuel (i.e., more oxygen molecules) [12]. At maximum engine load, the BSFC for diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 fuel samples is 0.28, 0.31, 0.3, and 0.29 kg/kW-hr, respectively. The BSFC were decreased by 3.2% and 6.4% as compared to PSOME20 at maximum load.
3.3. Exhaust Gas Temperature
Figure 7 shows the EGT variations with brake power for the test fuels. The graph shows that as the engine load increases, so does the EGT because more energy is released from the fuel. It is observed that there is an increase in EGT for PSOME20 blend owing to its high viscosity, resulting in slow combustion, which reflects in the higher exhaust gas temperatures. CuO nanoparticles promote combustion and raise cylinder temperature, resulting in higher EGT than PSOME20 fuel [12]. The mixing of CuO nanoparticles enhanced the number of the sample fuel contains oxygen molecules. As a result of these tests, the exhaust gas temperature of the engine was determined to be somewhat higher using diesel fuel. At maximum load, the average EGT values of diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 fuel samples are 376°C, 392°C, 412°C, and 436°C, respectively.
3.4. Emission Characteristics
3.4.1. CO Emissions
Figure 8 depicts the change in CO emissions with engine load for the test fuels. From the engine test, CO emissions were shown to be lower at 75% load for the test fuels. CO emission for PSOME20 is decreased because biodiesel includes more oxygen molecules, which aid in the oxidation of the fuel-air combination, resulting in improved combustion. The graph shows that CO emissions were found to be lower than diesel and PSOME20 at all loads. Because biodiesel contains more oxygen and the CuO nanoparticle increases surface area, the fuel burning process is improved and CO emissions are reduced [14]. The mixing of CuO nanoparticles, which improves the oxygen concentration in test fuels, allowing lower CO emission and improved chemical stability, could be one of the reasons for the lower CO emission. When under maximum load circumstances, CO emissions for diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 fuels are 0.12%, 0.09%, 0.07%, and 0.05%, respectively.
3.4.2. HC Emissions
Figure 9 shows the HC with BP for PSOME20 with CuO nanoparticle mixtures. The PSOME20’s HC emissions were reported to be lower than that of the diesel. It might be owing to the biodiesel’s high oxygen concentration in the fuel, which results in improved combustion. Further, the HC emission was diminished with the inclusion of CuO nanoparticles with PSOME20 fuel owing to excess oxygen present in the fuels. CuO nanoparticle results in a shorter ignition delay time, a better fuel explosion cycle, and a higher HRR during combustion, supporting full combustion inside the combustion chamber. It could also be attributed to the catalytic activity of the metal-based nanoadditive during the combustion process. By incorporating CuO nanoparticles into biodiesel blends, the calorific value improves, the viscosity reduces, and the fuel burns completely, lowering HC emissions [14]. HC emissions obtained for diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 fuels are 48 ppm, 43 ppm, 38 ppm, and 32 ppm, respectively, at fill load.
3.4.3. NOx Emissions
Change in NOx emissions with BP for diesel biodiesel blend and with CuO nanoparticle blends is illustrated in Figure 10. NOx generation is primarily caused by high temperatures, abundant oxygen availability, and the accessible reaction time during combustion. PSOME20 with nanoadditive emits less NOx than PSOME20 blends without addition. NOx emission for PSOME20 was found slightly more than diesel. The primary cause for increased oxygen availability in biodiesel fuel mixes was found during the test. The amount of NOx emitted is affected by the exhaust gas temperature and the cetane number of the test fuel. Because nanoparticles pick up on the fuel burning and result in full combustion, the application of a CuO nanoadditive reduced NOx emissions [16]. Another purpose for using CuO nanoparticles into PSOME20 base test fuel is to reduce ignition delay and increase heat release during the combustion stage. NOx emissions obtained for diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 fuels are 868 ppm, 936 ppm, 1036 ppm, and 1160 ppm, respectively, at maximum load.
3.5. Smoke Opacity
Smoke opacity changes with BP for diesel and PSOME20 and with CuO nanoparticle fuel blends are presented in Figure 11. Smoke opacity was decreased for PSOME20 when compared with diesel at maximum power output. It can be attributed to biodiesel blend PSOME20 which contains more O2 content present in it and leads to complete combustion. Further, the smoke opacity was decreased by adding nanoparticle additive with PSOME20 fuel blend. This is attributed to high surface to volume ratio of nanoparticle added with PSOME20 blend resulting in improved evaporation with better combustion characteristics leading to decrease in smoke opacity [16]. It is observed that NOx emissions obtained for diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 fuels are 32%, 28%, 24%, and 20%, respectively, at maximum load conditions.
3.6. Combustion Characteristics
3.6.1. Cylinder Pressure
Figure 12 depicts cylinder pressure fluctuations versus CA with diesel, PSOME20, and its nanoparticle combinations. It is revealed that increasing the quantities of CuO nanoparticles in the PSOME20 combination results in a considerable improvement in cylinder pressure. This spike in cylinder pressure was responsible for increased surface area of CuO nanoparticles and the presence of excessive O2 in the biodiesel, which increases the oxidation of the biodiesel mixture. Furthermore, as compared to diesel and biodiesel mixtures, combining copper oxide nanoparticles with biodiesel blends resulted in a significant boost in cylinder pressure. Furthermore, better air-fuel mixture boosts the rate of fuel combustion inside the cylinder [14]. At maximum power, the cylinder pressure for diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 at full load conditions is 67.2 bar, 65.7 bar, 68.3 bar, and 70.2 bar, respectively.
3.6.2. Heat Release Rate
Figure 13 depicts the heat release rate variations with crank angle for all the test fuels. Addition of CuO nanoparticles combined with PSOME20, which increases biodiesel oxidation, results in efficient burning, which limits carbon deposit on the cylinder wall [14]. When comparing to PSOME20, it was determined that the heat release rate was enhanced at all CuO nanoparticle concentrations with PSOME20. This increase in HRR may be due to the improvement in premixed combustion phase by the CuO nanoparticle mixed with PSOME20 blend. Because of better fuel atomization, the use of CuO nanoparticles reduces the delay period. The high cetane number of biodiesel blends and the catalytic activity of nanoparticles might be the cause. This improvement was attributable to improved blended fuel burning characteristics during the duration of the premixed and diffusion stages, which raises the maximum cylinder temperature. HRR obtained for diesel, PSOME20, PSOME20CuO50, and PSOME20CuO100 at full load conditions are 70 J/°CA and 65.3 J/CA, 72 J/°CA and 74 J/°CA, respectively, at maximum power.
4. Conclusions
The experiments were carried out in a diesel engine to demonstrate the operating characteristics with the effect of CuO nanoparticles as additions to a 20% pumpkin seed oil methyl ester mixture with diesel. PSOME20 with different dosage levels of 50 and 100 ppm CuO nanoparticle was added to the biodiesel mixture. The major results are summarized here as follows.
CuO nanoparticle with PSOME20 shows somewhat significant improvements in BTE. BTE of PSOME20CuO50 and PSOME20CuO100 were increased by 1.6% and 2.3% as compared to PSOME20 at maximum load, while the BSFC of PSOME20CuO50 and PSOME20CuO100 were decreased by 3.2% and 6.4% as compared to PSOME20 at maximum load.
Addition of the 100 ppm of CuO nanoadditive with PSOME20 blend decreases the CO, HC, and smoke emissions by 44%, 26%, and 36%, respectively, as compared to PSOME20 fuel sample. CuO nanoadditive with biodiesel blend emits somewhat more NOx emission than PSOME20 fuel.
Maximum engine cylinder pressure and HRR were observed for PSOME20CuO50 and PSOME20CuO100 compared to PSOME20 at maximum load. The cylinder pressure and HRR for PSOME20CuO100 are 70.2 bar and 74 J/°CA, respectively, at maximum load conditions.
Finally, it is possible to achieve that biofuel combined with CuO nanoparticle additions would improve engine combustion and minimize the hazardous exhaust emissions.
Data Availability
The underlying data supporting the results of this study were included in the paper.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgments
The authors are obliged to Aarupadai Veedu Institute of Technology, Vinayaka Mission Research Foundation, Deemed to be University, Tamil Nadu, India, for providing laboratory facilities.