Kinematic Viscosity

The kinematic viscosities of the fuel samples can be measured w'ith a Redwood viscometer. As per the ASTM D445 standard, the experiment should be maintained at 40°C. In a Redwood viscometer, the biodiesel was filled into a heat chamber and it was heated to 40°C. The viscometer stopper was removed to drain out the heated biodiesel, and the drained biodiesel was collected with a graduated beaker placed below' the stopper. When 50 mL of biodiesel was bought into the beaker, the flow of the biodiesel was stopped using the stopper. The time period for the collection of 50 mL of biodiesel was noted. For calculating the viscosity of the biodiesel, the following equation is used (Karmakar, Kundu, and Rajor 2018).

where A and В are constants for the specific Redwood viscometer, A = 0.26, В = 179 (for times less than 100 s) or A = 0.24, В = 50 (for times more than 100 s).

Kinematic viscosity affects the ease of engine start and the spray pattern of the fuel; as the viscosity becomes higher, the bigger will the fuel droplets be, which results in excessive mixing of air and fuel, resulting in low combustion and high PM emissions (Nabi et al. 2015). On the other hand, when the norm is bigger than the viscosity, the heat release rate of the peak is decreased, and there is a decrease in the degree of fuel impingement, and the air-fuel mixing rate is also reduced (Hellier, Ladommatos, and Yusaf 2015). According to ASTM D6751, the range of the biodiesel viscosity is from 1.9 to 6.0 mm2/s with biodiesel dropping from 1.9 and 6.0 mm2/s; if there is very low viscosity, the outflow would result in a loss in power of the engine, but if it happens to be high, there are low'er possibilities that the injection pump will be able to provide sufficient fuel to seal the pumping chamber, resulting in powder loss once again (Sani et al. 2018). It is found that the viscosities of AMC biodiesel, Karanja biodiesel, and Jatropha biodiesel are 3.6, 5.60, and 4.84 centistokes, respectively. The Calophyllum inophyllum methyl ester and palm methyl ester kinematic viscosities are found to be 5.21 and 4.18 centistokes, respectively (Silitonga et al. 2016). It is seen that there is a factor of two between the biodiesels’ viscosities, which is often greater than petroleum diesel; as the biodiesel level decreases, the viscosity decreases.

Density

As per the ASTM D1298 and IS 1448: Part 32: 1992 standard at 15°C, determination of the density of oil, diesel, and biodiesel was done. A 60 mL empty vessel was taken and it was taken and weighed, and the fuel sample to be tested was transferred into the vessel up to the graduated marks and weighed. The testing fuel was kept at 15°C by placing it in the defreezer chamber. By subtracting the empty vessel weight of the taken fuel sample from the filled one, the weight of the sample fuel was calculated. The following equation was used for finding the density of the fuel sample.

The density or specific gravity data are critical for the various operations of chemical engineering units. In industries related to oleochemistry, lipid density data are required for preparing the reactor’s design for fatty acid spilling or converting fatty acids into their derivatives, for distillation units for fatty acid separation, for storage tanks, and for process piping. Biodiesel density data are required for modeling the combustion processes and other applications as a function of the temperature. The injection systems (pump and injectors) of the engine are designed for the production of a specified fuel volume, while the main parameter in the combustion chamber is mass air-fuel ratio (Veny et al. 2009). The density of the Jatropha biodiesel was estimated to be 884.2 kg/m3 (Pramanik 2003) and the density of the AMC oil was found to be 880 kg/m3 (Thangarasu, Siddharth, and Ramanathan 2020).

Carbon Residue

As per the ASTM D4530 method, the carbon residue experiment was done to measure the presence of the quantity of carbon residue in the fuel sample. Presence of the quantity of carbon residue in the fuel sample after pyrolysis method was measured. In the Conradson carbon residue experiment, a moisture-free sample of 5 g was placed in an iron crucible. The crucible was then kept in the middle of a Skidmore crucible apparatus. After placement of the crucible, the crucible was closed with a lid with an exit portal for allowing formed vapors to escape. The oven was heated electrically. The oven temperature was raised to 500°C slowly at a 10°C /min rate, and it was kept for 15 min for pyrolyzing the fuel sample. With a rate of flow of 600 mL/min, the nitrogen gas was purged for the pyrolysis process. After the pyrolysis of fuel sample, the power supply for the oven was shut down the nitrogen flow was continued until the temperature reached 150°C. After the oven temperature reached 150°C, the crucible was shifted out and the sample temperature was reduced to 30°C by placing it in a desiccator. After this, carbon residue was weighed using a precision weighing balance, and the mass percentage of carbon residue was calculated according to the following equation.

where CR, carbon residue, g; w, weight of sample, g.

One of the important indicators for calculating the propensity is the carbon residue which is used for the formation of the deposits of carbonaceous materials in engines, causing several problems associated with operation like nozzle blockage, corrosion, and part cracking. In the case of biodiesel, the indication of the carbon residue is not only the quantity of material remaining next after the process of vaporization and pyrolysis but also the amount of glycerides which are free glycerol, partially reacted, or unreacted glycerides along with added residues which remain in the biodiesel product (free fatty acids and catalyst residues) (Phan and Phan 2008).

Increasing a volume of unconverted/partially converted glycerides increased the amount of carbon residue according to Fernando et al. Hence, the development of a large amount of residue may be attributed to the polymerization of unsaturated alkyl chains (about 10 wt.%) and the degradation of glycerides and free fatty acid remaining at a high temperature in the biodiesel (Fernando et al. 2007). Additionally, glyceride degradation at high temperatures can also serve as a catalyst for the polymerization of unsaturated fatty acids (Nas and Berktay 2007). The percentages of carbon residue for the Jatropha biodiesel and diesel are 0.22% and 0.10%, respectively (Pranab 2011). The Karanja biodiesel percentage of carbon residue was estimated to be 0.07% (Dhar and Agarwal 2014). The AMC biodiesel was found to be 0.025%. The degree of unsaturation in the case of Jatropha biodiesel was found to be 77.2%. Biodiesel for Karanja was found to be 73.93%. The degree of saturation for AMC biodiesel was found to be 66.6%.

Copper Strip Corrosion

Corrosion of metals happens due to the presence of water molecules in it. Fuel flows through various metallic and non-metallic parts of the engine system. Copper strip corrosion is a qualitative method used to determine the level of corrosion in fuel samples such as gasoline, diesel fuel, and other hydrocarbons. It helps in the determination of various aromatic compounds and harmful corrosive substances present in fuels.

The test was done using a copper corrosion apparatus as the per ASTM D130-12 standard, the instrument is used for determination of corrosiveness to copper for fuel samples. A test tube of 25 mm in diameter and 150 mm in length was taken and the test tube was filled with 30 mL of fuel sample. A polished copper strip of 12.5 mm in width, 1.5 to 3.5 mm in thickness, and 75 mm in length was made to slide inside the sample test tube. The glass tube was closed with a vented stopper and it was placed inside a bath which is maintained at 50°C. After 2 h, the test tubes are withdrawn from the bath and the strips examined as per chart of the ASTM copper strip corrosion standards (ASTM method D 130 / IP 154).

Meenakshi et al. studied Karanja biodiesel and found that the degree of tarnish at the corroded strip corresponds with the fuel sample’s overall corrosiveness. ASTM certifies a maximum corrosion value of 3 on copper strips for biodiesel. The corrosion property of the copper strip of the investigated biodiesel was found to be 2, well within ASTM D6751 requirements (Parameswaran, Anand, and Krishnamurthy 2013). The Jatropha biodiesel was found to be within the limits, having less corrosive effect on the engine components (Kywe and Oo 2009).

Flash and Fire Point

As per the standard ASTM D93, the flash and fire point of fuel samples are measured by the Open Cup Cleveland apparatus. The fuel sample was taken in the test cup and filled up to a particular limit. Heat is supplied to the cup electrically and the rise in temperature was measured with the help of a thermometer. For every 1°C temperature rise, a flame was introduced above the surface of the fuel sample using a match stick. The temperature at which flash is observed over the fuel surface when the flame is introduced is recorded as the flash point. If the fire caught over the surface of the fuel sample when the flame source was introduced and the fire continued for a minimum of 5 min even after removal of the flame source, the temperature was recorded as the fire point temperature.

The flash point is defined as the lowest temperature at which a liquid generates sufficient vapors to ignite in the presence of an ignition source and is a major property used in industrial processes for flammable liquids while assessing process safety (Laz/.iis 2010). Likewise, the fire point is described as the lowest temperature at which the material’s vapors can easily be attracted to fire and proceed to burn also after removal of the source of ignition. The flash point is lower than the fire point, as the creation of the vapors at the flash point is not sufficient for the ignition of the fuel. The volatility of the biodiesel highly affects the flash and fire points. Volatility is the material’s tendency to vaporize, and is directly related to the pressure of the vapor of the respective biodiesel at that specific temperature. The higher the vapor pressure exhibited by a biodiesel at a specified temperature, the more volatile it is compared to those which exhibit low vapor pressure at the same temperature. The flash point and fire point of the biodiesel derived from palm oil were found to be 180°C and 194°C, respectively (Gorey et al. 2017). AMC biodiesel was found to have flash and fire points of 164°C and 175°C, respectively. The Karanja biodiesel flash point was found to be at 97.8°C. The Jatropha biodiesel flash point was found to be at 192°C.

 
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