The Properties of Fuel and Characterization of Functional Groups in Biodiesel -Water Emulsions from Waste Cooking Oil and Its Blends

Studying biodiesel as an alternative fuel is important for finding the most suitable fuel for the future. Biodiesel from waste cooking oil is one of the alternative fuels to replace fossil oil. Waste cooking oil is the used oil from cooking and is taken from hotels or restaurants. The emulsion of waste cooking oil and water is produced by adding water to the oil, as well as some additives to bind the water and the oil. In this study, the fuel properties of 100% biodiesel waste cooking oil are compared to several blends by volume: 5% of biodiesel waste cooking oil blended with 95% diesel oil (BD5), 10% of biodiesel waste cooking oil blended with 90% of diesel oil (BD10), 5% of biodiesel waste cooking oil blended with 10% of water and 18.7% of additives (BDW18.7), and 5% of biodiesel waste cooking oil blended with 10% of water and 24.7% of additives (BDW24.7). The objectives of this study are to establish the properties and characteristics of the FTIR (Fourier-transform infrared spectroscopy) of biodiesel-water emulsions from waste cooking oil and to compare them to other fuels. The chemical properties of the fuels are analyzed by using the ASTM D Method and FTIR to determine the FAME (fatty acid methyl ester) composition of biodiesel in diesel oil. The results showed that the addition of additives in the water-biodiesel oil increases the viscosity, density, and flash point. However, it decreased the caloric value due to the oxygen content in the fuel. Article History: Received 27 Aug 2019  Revised 17 Dec 2019  Accepted 23 Jan 2020  Available online 29 Jan 2020  ____________________ Keyword: Biodiesel, Waste cooking oil, Water emulsion, Fuel properties, FTIR. Indonesian Journal of Science & Technology


INTRODUCTION
Biodiesel is a fuel that is produced from vegetable oil, such as jatropha oil, palm oil, coconut oil, and waste cooking oil. Biodiesel is one of the promising fuels to replace fossil fuels because it is a source of renewable energy (Nayaggy & Putra, 2019) and can reduce pollutants such as CO, NOx, and SOx (Farobie & Hasanah, 2016). Fossil fuels, on the contrary, are the biggest contributors in the global pollutions in the world. The pollutants may consists of CO, NOx, SOx, particulate matter, and non-burned hydrocarbons (Juan et al., 2011). Therefore, it is important to find alternative energy sources to reduce the pollution from fossil fuels and to improve the environment.
Water in diesel or biodiesel emulsion derives from the micrometer-sized droplets, which affects combustion (Lif & Holmberg, 2006). This experimental observation (Cook & Law, 1978) and theoretical insight were already made around 40 years ago (Ballester et al., 1996). In water emulsion diesel oil, water is homogeneously mixed with diesel oil. This mixing happens due to a surfactant that assists to create a balanced composition in the emulsion fuel. Moreover, the emulsion of water in the fuel can lead to a change in momentum, which may improve the mixing of air and fuel. In addition, the nanosize of the water particles may trigger microexplosions, which can also increase fuel atomization (Armas et al., 2005).
Many reseachers studied regarding to biodiesel water emulsion. It was found that 15% of water in biodiesel emulsions can decrease the NOx ,CO, and smoke emissions compared to diesel oil (Kinoshita et al., 2004;Lawson et al., 1986;Awang & May, 2008). However, another study found that CO emission in different loads was higher than diesel oil probably because of a lower combustion temperature (Subramanian et al., 2011). Moreover, a composition of 5% of water emulsion in palm oil blended with diesel oil can reduce CO, NOx, and black smokes (Narkpakdee et al., 2012). Furthermore, 30% of water emulsion with eucalypus oil biodiesel can reduce smoke and NOx emissions up to 30 to 32% (Senthur & Ravikumar, 2016). Yoshimoto et al. (2008) observed that 20, 40, 60% of water in biodiesel emulsions with used fying oil can reduce CO, NOx, and HC emissions as compared to diesel oil.
In this study, we investigated the fuel properties of biodiesel-water emulsions from waste cooking oil and compared these properties to those of other fuels. Some properties, such as density, kinematic viscosity, flash point, Cetane Index, and FTIR analysis, are explained.

Biodiesel and diesel oil
Biodiesel waste cooking oil was purchased from PT. Bali Hijau Biodiesel, Indonesia. Commercial diesel oil was produced by the Indonesian Oil Company, and the additives were obtained from the Mechanical Engineering Department, Trisakti University, Jakarta (Hafnan, 2008). The quality of the fuels was tested according to the ASTM D (American society for testing and materials) method.
In this study, biodiesel waste cooking oil was blended with diesel oil, water, or additives in several volume fractions: 5% of biodiesel waste cooking oil blended with 95% of diesel oil (BD5), 10% of biodiesel waste cooking oil blended with 90% of diesel oil (BD10), 5% of biodiesel waste cooking oil blended with 10% of water and 18.7% of additives (BDW18.7), and 5% of biodiesel waste cooking oil blended with 10% of water and 24.7% of additives (BDW24.7).
The properties were measured by the Petrolab Services Company in Indonesia. The FTIR (Fourier-transform infrared spectroscopy) spectra tests were done by Thermo Scientific Nicolet iS10.

The making of biodiesel water emulsions.
In this study, two samples of emulsions of biodiesel waste cooking oil and water were prepared by volume: 10% of Water, 5% of biodiesel waste cooking oil, 100% of diesel oil, and the additives were varied from 18.7% and 24.7%, respectively.
The additives in volume fractions of 18.7% and 24.7% were chosen to avoid the heterogeneity in the fuel. Whith these amounts, water, and diesel oil can be merged together. The fuels can be visualized in a 100 and 200x magnification (Bhikuning, 2008), as shown in Figure 3.

Density
Density is one of the most important properties of biodiesel. Density is defined as mass per unit of volume. Higher densities of biodiesel can cause problems in the engine, such as deterioration of the atomization of fuel (Xuea et al., 2011). The results of the density measurements are shown in Figure 1. The results are obtained by the ASTMD 1298-12b method. From Figure 1, it can be seen that more additives added to the diesel oil will increase the density of the fuel. The results show that pure biodiesel of waste cooking oil (BD100) has the highest density of about 881.6 kg/m 3 and that BDW24.7 has the second-highest density of 869.6 kg/m 3 . BD5 reached a density of 825.4 kg/m 3 while, BD10 was 833.6 kg/m 3 and BDW18.7 was 842.9 kg/m 3 . Awang andMay (2008), Abdurrahman et al. (2016), and Narkpakdee et al. (2012) showed that the density of biodiesel-water emulsions increased with an increasing percentage of water in the fuel. Figure 1 shows that more additives added to the diesel oil increased the density in the fuel. Kinematic viscosity of fuel is an important property to understand. In this study, kinematic viscosity was examined using ASTM D 445. The results are shown in Figure 2. shows that BDW24.7 has the highest viscosity of all the fuels tested. The high viscosity makes it difficult for a fuel to atomize and can affect combustion deterioration (Xuea et al., 2011). Fuel atomization and volatility are affected by viscosity (Borhanipur et al., 2014). The viscosity of pure biodiesel oil is higher than that of the blends. Blending pure biodiesel oil with diesel oil can decrease the viscosity of the fuel. Figure 2 also shows that additives in the fuel increase its viscosity. Similar trends were observed by Karim et al. (2014), in which biodiesel emulsion was found to have a higher viscosity than diesel oil. The viscosity of BDW24.7 is the highest volume among all the fuels tested (with a value of 8.805 cSt). Moreover, the viscosity of BDW18.7 reached a value of 7.217Cst. Narkpakdee et al. (2012) showed that the viscosity of biodiesel-water emulsions was increased by an increase in the composition of the fuel. In addition, Awang, and May (2008) demonstrated that the viscosity of biodiesel-water emulsions was increased by an increase in the concentration of water in the fuel.

Flash Point
The flash point was calculated using the ASTMD 93-16a method. The flash point is defined as the lowest temperature of the fuel that can provide a combustible mixture between fuel and air (Borhanipur et al., 2014). The values of the flash point for diesel oil were in the range of 55-66 o C, and for biodiesel between 110 and 180 o C (Bhikuning et al., 2018).
From Figure 4, it can be seen that the amount of biodiesel blended in the fuel can affect the value of the flash point. The higher concentration of additives resulted, the higher the flash point of the fuel. The flash point of BDW24.7 is 80 o C, which is higher than that of BDW18.7 at 77 o C. Similar results were obtained by Senthur and Ravikumar (2016) who showed that the flash point of emulsified biodiesel is higher than that of diesel oil but slightly lower than that of biodiesel. The cetane index is calculated based on the density and the volatility from the fuel (Anggono et al., 2018). The ignition quality of diesel oil can be described on the Cetane Number (Knothe, 2003).
The value of cetane number should not be too high nor too low. The incomplete combustion and smoke can appear if the cetane number is too high because the combustion can occur before the fuel and air are properly mixed (Knothe, 2003).
The incomplete combustion can also occur if the cetane number is too low because the engine warms up too slowy, resulting in engine roughness, higher air temperature, and misfiring (Knothe, 2003). The cetane index in BDW18.7 is 17.30 to 18.86%, which is lower than BD5 and BD10. Moreover, the cetane index of BDW24.7 is the lowest among all fuels tested. The addition of additives in the fuel can decrease the value of the cetane index. Figure 6. Caloric values from various fuels Figure 6 shows the caloric values of several fuels. From Figure 6, it can be seen that the biodiesel-water emulsions BDW18.7 and BDW24.7 have a low caloric value. Adding water and additives (BW18.7) in biodiesel can cause a decrease of 12.08% in caloric value as compared to BD5. The caloric values of BDW18.7 and BDW24.7 are nearly the same with that of BD100. As can be seen in Figure 6 the caloric value of BDW24.7 is 11.89% which is, lower than that of BD5. The low caloric value of biodiesel and biodiesel-water emulsion is due to their high oxygen content. Nevertheless, the combustion efficiency of biodiesel and biodiesel-water emulsion will be high because of the oxygen content in the fuel. Similar results were found by Awang and May (2008) who found that the caloric value can be decreased up to 5.46% by adding 15% of water to biodiesel emulsion. Narkpakdee et al. (2012) and Senthur & Ravikhumar (2016) showed that adding water to biodiesel emulsions can decrease the caloric value of biodiesel-water emulsions compared to diesel oil.  Figure 7. This figure shows that BD100 has the highest volatility among all fuels tested. This can indicate that BD100 has poor spray characteristics as compared to other fuels. As seen in Figure 7, the distillation of BDW18.7 is nearly the same as that of BD10. This can be indicated that BDW18.7 has better in spray characteristics than BDW24.7.
The composition of the fuel can affect the infrared spectroscopy. BD5, BD10, BDW18.7, and BDW24.7 were blended with diesel oil; therefore, the organic sulfate stretch can be found in the FTIR figures. BDW18.7 and BDW24.7 included water additives; therefore, the O-H hydrogen bond could be found in the infrared spectroscopy figures.

CONCLUSION
The addition of additives in waterbiodiesel oil increases the viscosity, density, and flash point. However, it lowers the cetane index and the caloric value. The distillation of BDW18.7 is nearly the same as that of BD10. This can signify that BDW18.7 has better spray characteristics than BDW24.7. The infrared spectroscopy figures of BDW24.7 and BDW18.7 indicated strong O-H hydrogen bonds from water additives. The organic sulfate stretch can be found in BD5, BD10, BW24.7, and BW18.7 because the oils were blended with diesel oil. The different compositions of the fuels can affect the infrared spectroscopy figures.

ACKNOWLEDGEMENTS
The first author would like to thank for Directorate General of Higher Education of the Ministry of Education and culture of Indonesia, Doshisha University and Dr. Muhammad Hafnan of the Mechanical Engineering Department, Trisakti University that have supported this research.

AUTHORS' NOTE
The authors declare that there is no conflict of interest regarding the publication of this article. The authors confirmed that the data and the paper are free of plagiarism.