Performance and emission characteristics of a CI engine fuelled with carbon nanotubes and diesel-biodiesel blends
Introduction
Increased demand for energy, fluctuations in oil prices, global warming due to emission of greenhouse gases, environmental pollution, and fast depletion of fossil fuel reserves are the key factors underpinning the search for alternative sources of renewable energy, particularly biofuels derived from agricultural products [1], [2], [3]. Biodiesel is a class of renewable clean bioenergy as it can be produced from vegetable oils, animal fats and micro-algal oil. The properties of biodiesel are almost similar to those of diesel fuel; thus it is becoming a promising alternative to diesel fuel. Biodiesel consists of mono alkyl esters formed by a catalyzed reaction of triglycerides in the oil or fat with a simple monohydric alcohol [2], [3]. Biodiesel is similar to diesel fuel; however, it does not have unpleasant ingredients such as sulfur and polycyclic aromatics. It can be applied instead of diesel fuel without the need to make any special modifications to the components of combustion engines [3].
Many strategies have been adopted to reduce NOx and soot emissions simultaneously to achieve the emission targets in common diesel engines [4], [5]. Recently, research shows that using biodiesel in engines reduces the amount of unburned hydrocarbons (UHC), carbon dioxide (CO2), carbon monoxide (CO), sulfur oxides, and solid particles emitted from the exhaust. There is only an increase in nitrogen oxide emissions that can be reduced by adjusting the fuel-injection timing [1], [6], [7].
Fuel economy and emission characteristics in internal combustion engines are controlled by physical and chemical properties of the fuel. Various additives as catalyst are used for fuels in order to improve fuel quality, achieve better combustion and reduce exhaust emissions. During combustion, catalysts accelerate fuel instability reactions and improve engine performance [8]. In recent years, nano-catalysts or nano-additives in fuels have improved the thermo-physical properties such as high surface area-to-volume ratio, thermal conductivity, and mass diffusivity. Based on the literature review, it has been found that nano-additives along with diesel, biodiesel, and their blends enhance the flash point, fire point, kinematic viscosity, and other properties [9]. Most of the nanoparticles are made of ceramic, metallic, and polymeric materials. The most common nanoparticles are ceramics and mostly metal oxides such as titanium, carbon, aluminum, and iron [10]. Large surface and high energy level increase the catalytic performance of metal nanoparticles [11].
Many studies have been conducted on fuel additives and their effect on engine combustion, performance, and emission characteristics [12], [13], [14]. For example, Guru et al. empirically examined the effects of adding the synthesized magnesium, manganese, calcium, and copper to diesel fuel on emissions, efficiency, and quality of fuel ignition. They also studied the levels of pollutants like SO2, CO2, and CO and cetane number of fuels for diesel fuel with additives and pure diesel. It was observed that the organic based manganese drops the viscosity and flash point and improves the contents of the exhaust gases [15]. Gumus et al. examined the effects of alumina (Al2O3) and cupric oxide (CuO) nanoparticles added to diesel fuels on the engine performance and exhaust emissions. The storage and combustion characteristics were improved by adding nanoparticles. The engine torque and brake power output were slightly increased by the addition of alumina and cupric oxide to pure diesel. Since, added nanoparticles promote an increase in oxidation rate and a decrease in ignition temperature [16]. Shaafi and Velraj [13] investigated the combustion, performance, and emission characteristics of an engine running on two modified fuel blends, B20 (Diesel-soybean biodiesel) and diesel-soybean biodiesel-ethanol blends, with alumina as a nano additive (D80SBD15E4S1 + alumina), and their results were compared with those of pure diesel. The results showed that the cylinder pressure and the heat release rate during combustion were higher than those of the diesel fuel, which is due to the higher surface area exposure of the alumina nanoparticle supported by the inherent oxygen present in the soybean biodiesel, that helps in rapid combustion. The presence of oxygen in the soybean biodiesel and the better mixing capabilities of the nanoparticles reduce CO and UHC levels appreciably although there is a small increase in NOx under full load condition.
Sajith et al. [17] studied the effects of cerium oxide (CeO2) nanoparticles as additive to biodiesel fuel on engine performance, physicochemical properties of the fuel, and emissions resulting from the combustion. Different doses of cerium oxide with concentration of 20, 40, 60, and 80 ppm were used to achieve the optimal blend. The results indicated an increment of flash point and viscosity of biodiesel by adding cerium oxide nanoparticles. The values of NOx and UHC emissions are greatly reduced. It could be due to a complex interaction among factors such as the combustion temperature, reaction time, and the oxygen content [17]. Yetter et al. and Dreizin have critically reviewed the reports on the metal nanoparticle combustion, and observed that the nano-scale metallic powders possess high specific surface area and can cause high reactivity. They have also revealed that adding nano-additives to the hydrocarbon fuels (such as diesel) will reduce ignition delay and soot emissions [18], [19]. Ganesh et al. examined the effects of cerium oxide nanoparticles (the size ranging from 10 to 20 nm) as additives in Jatropha biodiesel, and found that there was an appreciable increase in the flash point, volatility, and viscosity of biodiesel [20].
On the applications of CNTs, Selvan et al. studied the performance, emission and combustion characteristics of a diesel engine using cerium oxide nanoparticles (CERIA) and CNTs as fuel-borne nanoparticles (combined) additives in diesterol (diesel–biodiesel–ethanol) blends. The addition of CERIA and CNT to diesterol blend was increased the cylinder gas pressure as comparing with the pure diesterol blends. The combination of CERIA and CNT as additives to the diesterol fuel blend was led to cleaner combustion and significantly was reduced the harmful exhaust gas emissions [21].
Recently, several studies have been conducted on the effects of fuels on performance and emission characteristics of engines. With a focus on nano-fuels, many studies have been carried out on the engine performance and emissions. However, there are still many shortcomings about the effects of CNTs and diesel-biodiesel blends on these characteristics of engines. The literature reviews show that no research have been reported on performance and emission characteristics of diesel engines using CNTs, biodiesel, and its blends with pure diesel. Due to the potential properties of CNTs and the lack of studies focusing on diesel-biodiesel blended fuels, the present work is aimed to establish the effects on performance and emissions of a single-cylinder diesel engine. So, both advantages of combustion accelerator additives (CNTs) and oxygenate fuel (biodiesel) are used.
Section snippets
Materials and methods
In this research, the biodiesel was produced from the waste cooking oil, using the trans-esterification reaction based on the ASTM D6751 standard. The carbon nanotubes (CNTs) with doses of 30, 60, and 90 ppm were then mixed with B5 (5% biodiesel and 95% diesel) and B10 fuel blends.
Multi-walled carbon nanotubes (MWNTs) were provided from the Iranian Research Institute of Petroleum Industry (RIPI) with 90–95% purity. The average diameter of the nanotubes varied from 10 to 20 nm and their length
Results and discussion
Table 4 shows some characteristics measured based on the ASTM standard for tested fuels. The density, kinematic and dynamic viscosity, HHV, LHV, dissolved oxygen, and cetane index of each fuel blend are represented in this table. In B5Cx (x = 30, 60, and 90) and B10Cx blends, the kinematic and dynamic viscosities slightly drop with increasing the CNT dosages (Fig. 3-a and b). It seems that development of carbon nanotubes in intermolecular gaps of the fuel causes them easier to slip and
Optimal fuel
In all cases, addition of CNTs to diesel-biodiesel fuel blends (B5 and B10) increased the amount of torque. It can be seen that the larger torque and BTE belong to B5C90, B10C90, and B0 fuel blends, respectively. Regardless of CNT additives, B5 and B10 fuels have less torque and BTE than those of pure diesel fuel (B0). Similarly, the power trend follows the torque chart and has the same results. The minimum level of SFC belonged to B5C90, B5C60 and B10C90.
According to these results, the highest
Cost analysis
The cost of CNTs additives used in present study is about 400 US$ per kg in Iran, and dosages of 30, 60, and 90 ppm are respectively 0.03, 0.06, and 0.09 g per kg of B5 or B10 fuel blends. The specific cost of which are 0.012, 0.024, and 0.036 US$ per kg of B5 or B10 fuel blends. In addition, diesel fuel costs about 0.18 $ per kg in Iran. Adding CNTs with mentioned dosages to B5 and B10 blends, the fuel price increases by 6.67, 13.33, and 20%, while, by adding CNTs additives, the SFC is reduced
Conclusion
In the present study, the B5 and B10 fuel blends mixed with carbon nanotubes (CNTs) were used to characterize performance and exhaust emissions of a single-cylinder engine. The CNTs with dosages of 30, 60, and 90 ppm were applied to the fuel blends. The experiments were conducted at three engine speeds of 1800, 2300, and 2800 rpm under full load mode. The results showed that the power, BTE, SFC, and EGT of the B5C90 fuel blend vary by +3.67%, +8.12%, −7.12%, and +5.57%, respectively, compared
Acknowledgments
The authors would like to express their gratitude to Gorgan University of Agricultural Science and Natural Resources, and Iran Nanotechnology Initiative Council for their supports.
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