Abstract
One of the excellent choices for compression ignition engines is emulsions. The current experimental analysis deals with transesterified Pongamia biodiesel. This work gives a substantial track to synthesize and to enhance fuel by including aluminium oxide nanoparticles. Emulsification is used to prepare fuel consisting of 88% of Pongamia biodiesel, 10% water, and 2% surfactants with series chemical emulsification techniques. This is then mixed with the ratio of 50 ppm and 100 ppm by mass with aluminium oxide nanoparticles by employing ultrasonication techniques. This work is carried out on compression ignition engines in different phases using biodiesel, nanoparticles, surfactants, and water. It was inferred from the results that there was a considerable enhancement in performance and decrease in emission when compared with diesel. It is found that the system exhibited 15% improvement in brake thermal efficiency and 45% reduction in oxides of nitrogen. The system exhibited considerable improvement in performance and reduction in emission.
1. Introduction
Compression ignition (CI) engines play a significant role in various sectors. Researcher’s efforts to reduce emission in diesel engines are ongoing. Though some of the methods show a reduction in the NOx level, they exhibit a significant increase in smoke and particulate matter. Simultaneous reduction of both smoke and NOx was achieved by the introduction of the water-diesel emulsification system. Injection of water decreases oxides of nitrogen emission but increases unburnt hydrocarbon and carbon monoxide emission [1]. A few changes made in CI engines decrease ignition delay [2–4]. Injection of water is an efficient manner for reducing oxides of nitrogen [5–8]. Water injection results in fuel contamination and wear of the engine. The above problems related to water injection makes it difficult to employ it for real-time applications. Due to this, emulsion fuels are considered as best alternatives for water injection in diesel engines. Emulsion fuels are developed to avoid problems caused due to injection of water, and they in turn form a dispersed uniform phase, which also avoids the need for storage of water. Addition of surfactants decreases oil and water surface tension, resulting in the formation of dispersed droplets. Due to the rise in cost and depletion of fossil fuels, biodiesel is the fine option for automotive fuel (especially Pongamia biodiesel) [9–13]. However, CI engines exhale toxic contents like HCs (hydrocarbons), NOX (nitrogen oxides), particulate matter, stench, and smoke. So researchers are trying to reduce emission by 3 ways: (i) modifying engine design, (ii) fuel modification/reformulation, and (iii) treatment of exhaust gas. However, these approaches are worn to scale down NOX [14]. Various works have shown that an inclusion of five to twenty percent of water can reduce oxides of nitrogen emission. This also may provide better vaporization due to microexplosion, which could also decrease oxides of nitrogen. This could also enhance combustion in engine cylinders [15]. Emulsion fuels could also prolong ignition delay [16]. Surfactants play a key role in mixing immiscible fluids. Surfactants and their significance of interfacial mechanisms were inferred in detail [17]. Depletion of fossil fuels makes it inevitable to look for an alternate replacement. The study on performance characteristics of a compression ignition engine fuelled with emulsion fuels showed that duration of ignition delay was prolonged with the employment of emulsion fuels [8, 18–21]. The employment of cerium oxide enhanced performance [22]. The review on the impact of hydrotreated vegetable oil in compression engines showed possibilities of employing vegetable oil in engines [23]. The impact of nanoparticles on performance characteristics of a compression ignition engine was studied in detail. It was seen that there was a significant improvement in performance and reduction in emission with the inclusion of nanoparticles [24, 25]. Biodiesel from Pongamia pinnata could act as a potential replacement for fossil fuels as fossil fuels are depleting at a faster rate. Inclusion of metal oxide nanoparticles along with biodiesel could show performance augmentation and reduction in emission. Metal oxide additives act as catalysts in water biodiesel emulsion, which activate molecular bonding between water and biodiesel. Enhanced properties of the nanoparticles resulted in the performance enhancement in the systems, in which they are employed. This work aims to examine the performance characteristics of a CI engine using nanoparticle-loaded water-biodiesel emulsion blend as a fuel. The inclusion of water in minor proportions could reduce the viscosity of the fuel and thereby could reduce potential frictional losses. The inclusion of water in minor proportions could also reduce emission of oxides of nitrogen. In the present work, the authors attempt to investigate the new combination of the water biodiesel blend with a higher concentration of nanoparticles, aiming to enhance performance and reduce emissions as nanoparticles have better properties due to which they enhance the performance of systems in which they are included.
2. Fuel Preparation
Emulsion fuels are prepared by employing an ultrasonicator and a stirrer. Surfactants Tween80 (hydrophilic) and Span80 (hydrophobic) were used as emulsifying agents. Span80 and Tween80 were chosen with appropriate HLB (15). A mixture of surfactants is used to get a stable mixture. Surfactants and fuels (by vol 88%) are mixed by using an agitator, and after that, distilled water is introduced to form water-biodiesel emulsion fuels. Aluminium oxide nanoparticles dispersed in the mixture by ultrasonication of the order of 50 ppm and 100 ppm result in the water-biodiesel emulsion fuel with 50 ppm and 100 ppm nanoparticles. Table 1 shows the necessary fuel properties.
3. Experimental Work
This work has been performed in a setup consisting of a water-cooled, 4-stroke single-cylinder CI engine. The engine is run at the rated speed. The fuel is injected by using a fuel injector, which is controlled by using a camshaft. The injection timing is 23 degrees before the Top Dead Centre. Cylinder pressure is also monitored. Emission is measured by using an exhaust gas analyzer. The schematic diagram of engine specifications is shown in Figure 1 and Table 2, respectively.
4. Result and Discussion
The emulsion fuel is tested for performance and emission characteristics, and results are shown in the graph.
4.1. Engine Combustion Analysis
Figures 2 and 3 show the pressure of the cylinder and release of heat. There will be shortened ignition delay due to alumina nanoparticles which improve ignition by early combustion. The inclusion of nanoparticles improves the properties of fuel including the thermal conductivity and calorific value. This improvement in properties results in the decrease in the ignition delay period and thereby results in early initiation of combustion. This decrease in ignition delay improves antiknocking characteristics of the engine, which is in line with the results in [1, 2]. Further, the peak cylinder pressure is less for fuel samples with nanoparticles, when compared to normal biodiesel due to reduced ignition delay and early initiation of combustion. This can be augmented due to comparatively short duration of uncontrolled combustion when compared with normal biodiesel, which is in line with the results in [9, 18].
4.2. Engine Performance Analysis
In Figure 4, comparatively fuel consumption decreases for fuel containing aluminium oxide nanoparticles since nanoparticles exhibits catalytic effect during combustion. This decrease in fuel consumption is due to an increase in the calorific value. The inclusion of nanoparticles enhances the calorific value of the fuel, which in turn reduces specific fuel consumption. Figure 5 also displays 15% improvement in thermal efficiency due to secondary atomization that results in microexplosion of nanoparticles, which is due to inclusion of nanoparticles, which in turn improves the calorific value and thermal conductivity.
Figure 6 depicts the variation of exhaust gas temperature. Water having a lower boiling point leads to adequate evaporation during the main combustion phase. The inclusion of water in emulsion fuels and the decrease in the duration of uncontrolled combustion reduce exhaust gas temperature considerably. This reduction in exhaust gas temperature also reduces oxides of nitrogen by 45% significantly. This resulted in a lower exhaust gas temperature for emulsion fuels. Addition of nanoparticles is also one of the reasons for lower exhaust gas temperature.
4.3. Engine Emission Analysis
In engine emissions, Figure 7 shows the NOX variation, where alumina nanoparticle-blended fuel has drastic reduction in NOX due to the heat sink effect. The decrease in NOX emission is due to reduction in exhaust gas temperature and addition of aluminium oxide nanoparticles. Furthermore, the decrease in the duration of ignition delay and uncontrolled combustion further reduces the peak cylinder pressure. It further reduces exhaust gas temperature, which in turn reduces NOX emission.
Figure 8 shows that the alumina nanoparticle-blended fuel has less smoke density compared to biofuels since it has a higher concentration of OH radical, which is due to improvement in the thermal conductivity and calorific value.
Figures 9 and 10 show that the alumina nanoparticle-blended fuel has lower CO emission than water emulsion biofuels, which is due to enriched oxygen content wherein carbon combines with enriched oxygen content to form carbon monoxide. Hence, nanoparticles lead to the catalytic effect, and it creates secondary atomization during combustion. This secondary atomization further reduces carbon monoxide emission. However, unburnt hydrocarbon emission is very low for diesel and maximum for emulsion fuel. With the addition of alumina nanoparticles, unburnt hydrocarbon emission reduces. However, it is slightly higher than that of diesel.
5. Conclusion
From the experimental work, following conclusions have been made:(i)Cylinder pressure and heat release are minimum for the emulsion fuel with nanoparticles because of the reduced delay period. This reduced delay period initiates combustion early. The consumption of fuel is minimum for emulsion fuels in comparison with normal fuels.(ii)NOX emission is reduced to an extent of 45% for fuel containing aluminium oxide nanoparticles because ignition delay is reduced for fuel containing nanoparticles. This further reduces exhaust gas temperature, which in turn reduces NOX emission. The reduction in flame temperature reduces emission of NOX. NOx formation increases with temperature. So here, reduction in temperature decreases NOx.(iii)The smoke density is reduced significantly for water-biodiesel emulsion fuels blended with nanoparticles.(iv)CO emission for emulsion fuels blended with nanoparticles is lower when compared with biodiesel due to oxygen enrichment which is caused by addition of aluminium oxide nanoparticles.(v)HC emission is very less, nearly 40% for emulsion fuel containing aluminium oxide particles when compared with emulsion fuels but still slightly higher than that of diesel.(vi)Since the viscosity of the fuel is only slightly higher, it does not have a significant impact on the life of the engine. The microemulsion enhances the mixing of nanoparticles with fuels and improves the calorific value, which in turn improves performance characteristics significantly, i.e., improvement in a brake thermal efficiency of 15%.
Data Availability
Data are available on request.
Conflicts of Interest
The authors declare that they have no conflicts of interest.