CHAPTER 5 FUEL CHARACTERISTICS

Transcription

1 66 CHAPTER 5 FUEL CHARACTERISTICS 5.1 EVALUATION OF PROPERTIES OF FUELS TESTED The important properties of biodiesel, biodiesel-diesel blends, biodiesel-ethanol blends, biodiesel-methanol blends and biodiesel-ethanoldiesel tri-compound fuel blends were experimentally determined. The biodiesel used for the research work was produced by transesterification from jatropha curcas oil and palm oil. The analytical grade ethanol and methanol (99.5% purity) was purchased in the market. Laboratory tests were carried out to determine the properties like specific gravity, kinematic viscosity, cloud point, pour point, flash point, fire point and calorific value of the blends using IS test methods shown in Table 4.1. The properties of jatropha curcas tested are shown in Table 5.1, JME in Table 5.2, and ethanol, methanol in Table 5.3, and J20, E15J20D65 and M15J20D65 fuels in Table 5.4. Table 5.1 Properties of jatropha curcas oil tested Sl. No. Properties Units Jatropha curcas oil 1 Density@ 15 C g/cm Flash point C Pour point C <-5 <-5 4 Kinematic 40 C cst Diesel 5 Calorific value MJ/kg

2 67 Table 5.2 Properties of JME tested Sl.No. Parameters Results 1 Kinematic viscosity at 40ºC 4.48 cst 2 Flash point 168ºC 3 Fire point 175ºC 4 Cloud point 8ºC 5 Pour point 6ºC 6 Sulphated ash % mass 7 Conradson Carbon Residue (CCR) 0.01 % mass 8 Saponification value Iodine number Density at 15ºC 0.86 g/cm 3 11 Copper strip corrosion Not worse than 2 12 Water content 0.43 % vol. 13 Sediment Nil 14 Acid number 0.46 mgkoh/g 15 Gross calorific value MJ/kg 16 Net calorific value MJ/kg 17 Hydrogen 13.0 % 18 Oxygen (by difference) 10.6 % 19 Carbon 76.4 % 20 Sulfur % mass Table 5.3 Comparison of properties of JME and Alcohols with Diesel Sl.No. Properties Units JME PME Diesel Ethanol Methanol 1 Density g/cm o C cst Flash point o C Heat value MJ/kg Cloud point o C 8 12 < -5 < -5 < -5 6 Fire point o C Molecular wt g/mol O 2 content wt %

3 68 Table 5.4 Comparative properties of fuels tested Properties, Units Diesel J20 JME E15J20D65 M15J20D65 Diesel % vol Ethanol % vol Methanol % vol JME % vol Density g/cm o C cst Flash point o C Heat value MJ/kg Cloud point o C < <-5 <-5 Fire point o C Oxygen content wt % Phase Stability Test Stability tests conducted show that biodiesel can be blended in any proportions with diesel fuel. Even at higher proportion of biodiesel in the blend, no physical separation was observed. The same trend was observed for biodiesel-ethanol blends and biodiesel-methanol blends. In the case of 99.5% ethanol, the intersolubility of the three-components was not limited. They could be mixed into a homogeneous solution at any ratio. Because 99.5% ethanol has lower water content than that of hydrous ethanol, it is more soluble in diesel fuel than hydrous ethanol. Since the mixtures are having biodiesel as an additive, they are having single liquid phase. This homogeneity was due to the fact that biodiesel can act as an amphiphile (a surface-active agent) and form micelles that have non polar tails and polar heads (Kwanchareon et al 2007). These molecules are attracted to liquid/liquid interfacial films and to each other. These micelles acted as polar or non-polar solutes, depending on the orientation of the biodiesel molecules. When the diesel fuel was in the continuous phase, the polar heads in a biodiesel molecule oriented itself to the ethanol, and the non-polar tail oriented to diesel. This phenomenon held the micelles in a thermodynamically

4 69 stable state, depending on the component concentrations and other physical parameters. Thus biodiesel is known to act as an emulsifier for ethanol (Rahimi et al 2009). Makareviciene et al (2005) characterized the solubility of biodiesel fuel components in fossil diesel-ethanol-ree systems and they proved that addition of ester to ethanol and diesel fuel mixture increases solubility of ethanol in diesel fuel. Solubility and stability of ethanol in biodiesel-diesel fuel blends will be greatly improved without other additives (Chotwichien et al 2009) Relative Density The specific gravity, also known as relative density refers to the density of the fuel to the density of water at the same temperature. The specific gravity of the fuel blends were measured by using a hydrometer. Specific gravity of JME-diesel blends and PME-diesel blends are shown in Figure 5.1. Relative density values obtained are 0.860, and for JME, PME and diesel fuel respectively. When referring to density, the international standards require values between 0.85 and 0.90 g/cm 3, the obtained value for both JME and PME are well within the accepted limits. The ASTM D6751 does not regulate the density of biodiesel fuels. It was observed from Figure 5.1 that relative density of the all the biodiesel-diesel blends were higher than that of diesel fuel, and increased with the increase of biodiesel content in the blends. The density of JME is higher than the diesel fuel density by 4.87% and for B20 blend (20% JME; 80% diesel) it is only 0.97%. Therefore one can expect that the fuel spray penetration might not be significantly affected due to this density difference. Figure 5.2 shows the variation of relative density of JME-alcohol blends. It can be observed that the density of the blends decreased with an increase of the percentage of ethanol or methanol in the blends. This is

5 Relative Density JME-D PME-D Biodiesel Content, vol.% Figure 5.1 Variation of relative density with biodiesel fraction Relative Density Alcohol Content, vol.% Figure 5.2 Variation of relative density with alcohol fraction in JMEalcohol blends attributed to the fact that ethanol/methanol has lower density and as such will lower the density of the mixture. But, when the percentage of biodiesel was

6 71 increased, the density increased, which is due to the fact that the jatropha oil biodiesel (JME) has a higher density than the ethanol/methanol. Normally, it is recognized that higher density leads to higher flow resistance of fuel oil, resulting in higher viscosity and can lead to inferior fuel injection. However, all the blends had density values that were acceptable for the standard limit for high-speed diesel Flash Point and Fire Point Flash point is the minimum temperature at which the vapor given off by a fuel when heated will flash with a test flame held above the surface without the fuel catching fire and it plays a vital role when determining the fire hazard of the fuel. Flash point gives an idea about the amount of low boiling fraction present in the liquid fuel, volatility of the liquid fuel and explosive hazards. The flash points of the diesel-biodiesel blends with increasing biodiesel concentration are shown in Figure 5.3. Most of the International standards impose a flash point higher than 120 o C; in consequence, the JME and PME, with a very high flash point of 168 o C and 183 o C respectively, are within the limits required by standards. It is observed that with increasing quantity of JME and PME in the diesel-biodiesel blends, due to higher value of flash point of PME and JME, flash point of the blend is found to increase. Fire point is the minimum temperature at which the flammable vapors will continue to form and steadily burn once ignited. Flash and fire points of the fuel blends were measured by Pensky-Martens flash point closed apparatus. In comparison to diesel fuel, the flash point and fire point of JME and PME are found to be around three times more as shown in Figure 5.3 and 5.4, facilitating safe transport and storage of biodiesel fuels.

7 72 Flash Point, o C JME-D PME-D ASTM limits 40 Biodiesel Content, vol.% Figure 5.3 Variation of flash point with biodiesel fraction Fire Point, o C JME-D PME-D 60 Biodiesel Content, vol.% Figure 5.4 Variation of fire point with biodiesel fraction The flash point of tri-compound fuel blends was substantially different from diesel and found to be extremely low, in the range of 13 to 17 o C. All of the blends containing ethanol were highly flammable with a flash point temperature that was below the ambient temperature. The flash point of the tri-compound fuel blend affects the shipping and storage classification of

8 73 fuels and the precautions that should be used in handling and transporting the fuel. In general, flash point measurements are typically dominated by the fuel component in the blend with the lowest flash point. The flash point of a tricompound mixture is mainly dominated by ethanol. As a result, the storage, handling and transportation of blended fuel must be managed in a special and proper way, in order to avoid explosion Cloud Point and Pour Point The cloud point of any petroleum fuel oil is defined as the temperature at which a cloud of wax crystals first appear in the oil when it is cooled at a specific rate. Figure 5.5 shows the effect of biodiesel content on cloud point of the blend. As biodiesel content is increased in the blend, its cloud point increased. Neat JME has the cloud point as 6 o C, while neat PME has it as 12 o C. The pour point of any oil is defined as the lowest temperature at which the oil will flow, or pour, when cooled without agitation under standard conditions. Both cloud point and pour point are often used to specify cold temperature usability of fuel oils (Bhale et al 2009). The variation of pour point of biodiesel-diesel blends are shown in Figure 5.6. All of the JMEdiesel blends were found to have pour point less than 5 o C, while the PMEdiesel blends have slightly higher pour point up to 8 o C. Tri-compound fuel blends have very low pour point compared to biodiesel-diesel fuel blends. The reason is that ethanol has a very low pour point and biodiesel normally has a pour point higher than conventional diesel. But E15J20D65 blend has diesel as a major component, and, therefore, the pour point of the fuel blend was found to be not much different from conventional diesel. Blending alcohol with biodiesel, the cold flow properties of the biodiesel were improved.

9 Cloud Point, o C JME-D PME-D Biodiesel Content, vol.% Figure 5.5 Variation of cloud point with biodiesel fraction 10 5 Pour Point, o C Biodiesel Content, vol.% JME-D PME-D Figure 5.6 Variation of pour point with biodiesel fraction Kinematic Viscosity The viscosity of a liquid is a measure of its resistance to flow. It is an important property of all liquid fuels since it affects the atomization of fuel oils and the performance and wear of diesel pumps. The kinematic viscosity ( ) is defined as the ratio of absolute or dynamic viscosity to the density of oil. The experiments were carried out at 40 o C for neat JME, neat PME,

10 75 various JME-diesel blends and ethanol-jme blends using the Redwood viscometer. The apparatus was based on the principle of measuring the time of gravity flow in seconds of the fuel sample through a specified hole. Dynamic viscosity measured by this method is expressed in centistokes or mm 2 /s. Dynamic viscosity of liquid fuels is given by, µ = t (1.78/t) for t < 100 seconds (5.1) µ = t (0.50/t) for t > 100 seconds (5.2) where µ = dynamic viscosity in centistokes, t = time of flow of a fixed amount of oil in seconds. The measured values of kinematic viscosity at 40 o C are 4.48 cst, 5.21 cst for JME and PME respectively, which are higher than the diesel fuel (3.61 cst). Since the maximum limit for kinematic viscosity of biodiesel as per ASTM 6751(Biodiesel standard 2002) and IS is 6 cst, the obtained values of both biodiesel fuels are well within the international standards. The kinematic viscosity at 40 o C for raw jatropha oil is 35.6 cst. It is important to notice that transesterification process has significantly decreased the viscosity of JME to 4.48 cst. The kinematic viscosity values of different JME-diesel blends with increasing concentration of JME (0 to 100%) are shown in Figure 5.7. It is observed that increasing the content of biodiesel in the blend resulted in the corresponding remarkable increase in the kinematic viscosity. The higher viscosity of biodiesel fuel compared to diesel fuel makes it an excellent lubricating additive (Graboski et al 1996). Fatty acid composition has a significant effect on the viscosity of biodiesel fuels. The fatty acid compositions of fats and oils are feedstock dependent and are also affected by factors such as climate conditions, soil type, plant health, and plant maturity upon harvest.

11 Kinematic viscosity, cst JME-D PME-D ASTM limit Biodiesel Content, vol.% Figure 5.7 Variation of viscosity of biodiesel-diesel blends with biodiesel content Kinematic Viscosity, cst E-JME M-JME 0 Alcohol Content, vol.% Figure 5.8 Variation of viscosity of alcohol-biodiesel blends with biodiesel content The kinematic viscosity values of different blends with increasing concentration of ethanol in ethanol-jme blends are shown in Figure 5.8. Since the kinematic viscosity of neat JME is higher than that of diesel fuel, it

12 77 can be reduced by blending it with ethanol. Ethanol and methanol are having kinematic viscosity of 1.41 cst and 0.59 cst respectively at 40 o C Net Calorific Value Heat of combustion is one of the most important fuel properties. Gross calorific value of petroleum fuels are in the range of 42 to 47.5 MJ/kg, the higher value being for gasoline and lower for heavy fuel oils. Petroleum products are high in hydrogen content (11.8% to 14.5%) and hence their net calorific value is less than the gross calorific value by 2.6 to 3.2 MJ/kg. Calorific value of fuel is determined by using a bomb calorimeter. The net calorific value of JME, PME and diesel fuel is MJ/kg, MJ/kg and 42.5 MJ/kg respectively. The net calorific value of JME is only 6.17% less than that of diesel fuel. A similar result was obtained for JME by many researchers (Sundaresan et al 2007, Achten et al 2008, Banapurmath et al 2008 a). The net calorific value of JME-diesel blends and PME-diesel blends are shown in Figure 5.9. The net calorific values of all biodiesel-diesel blends tested were lower than that of diesel fuel. Since the net calorific values of both JME and PME fuels are lower than that of diesel fuel, as the biodiesel content in the blend increases, the net calorific value of the blend reduces. When 20% substitution (B20) is made by JME and PME, the reduction in net calorific value of the fuel blend is only 1.34% and 2.45% respectively. It is seen from the Fig. 5.9 that the calorific values of B20 blend of JME and PME are in close agreement with the base diesel fuel. Figure 5.10 shows the net calorific values of ethanol-jme blends and methanol-jme blends. The net calorific value of ethanol is only MJ/kg. Hence the net calorific values of ethanol-jme blends reduce as the content of ethanol in the blend increases. For E50J50 and M50J50 blends

13 78 Calorific Value, MJ/kg JME-D PME-D 36 Biodiesel Content, vol.% Figure 5.9 Variation of calorific value with biodiesel fraction Calorific Value, MJ/kg E-JME M-JME 15 Alcohol Content, vol.% Figure 5.10 Variation of calorific value with alcohol fraction the net calorific values are MJ/kg and MJ/kg which are nearly 22% and 30% lower than that of base diesel fuel. For E15J20D65 and M15J20D65 fuels the net calorific values are MJ/kg and MJ/kg which are nearly 6.7% and 9.3% lower compared to diesel fuel. The heat of combustion of tri-compound fuel blends decreased, when greater amounts of ethanol or methanol and biodiesel were added, which is due to the their lower heating value. These results have the same trend as those reported earlier by Ajav and Akingbehin (2002), Fernando and Hanna (2004), and Cheenkachorn

14 79 et al (2004). Lower heating value of a fuel has a direct influence on the power output of an engine. This suggests that in order to produce the same power in diesel engines, more quantities of alcohol-biodiesel fuel blend should be injected depending on their calorific values. However, it seems that the heating value of the tri-compound blends containing alcohol lower than 15% were not much different from conventional diesel Acidity The maximum value of the acidity of biodiesel as per the ASTM 6751 is 0.80 mgkoh/g and IS limits it to only 0.50 mgkoh/g. The acidity value for the JME produced by the transesterification process was found to be 0.48 mgkoh/g, which was well within the limit imposed by most of the international standards for biodiesel fuel Sulfur Content Sulfur content in the fuel was determined by bomb calorimeter. Sulfur is largely present in the fuel in the form of corrosive organic compounds. On combustion, it gives off foul gases. The maximum value of sulfur content on mass basis for biodiesel as per the ASTM 6751 is 0.05% and it is only 0.005% for IS Sulfur content increases with increase in boiling range of products (Gupta 2004). Since the boiling range of the biodiesel fuel is low, the sulfur content of the biodiesel fuel is usually very low. JME produced by the transesterification process possesses only 0.004% on mass basis, which is within the limit imposed by most of the international standards. Only traces of sulfur were found in ethanol and methanol Ash Content The ash content of a fuel or oil is given as the percentage by weight of the organic residue left after ignition of the fuel. Ash in the fuel is determined by gradually burning a weighed quantity of fuel in a silica

15 80 crucible and its charred contents at 800 o C. Ash content determination was carried out by an extraction method. The ash content in the fuel is given by, % Ash = (w/w) 100 (5.3) where w is weight of ash in gram, and W is weight of sample fuel in gram. The amount of ash in the petroleum products is normally very low. It increases with the viscosity of the fuel, since most of the original inorganic impurities allowed to remain in the crude are concentrated in the primary residue. The ash content of the biodiesel-type fuels is regulated in some of the international standards and in these standards the upper limit is set at 0.01 to 0.02% (Rosca et al 2005). The ash content for the JME produced is 0.001%, which is within the requirements of the standards. The ash content for ethanol and methanol is negligible. Hence it is expected that use of the neat JME, JME-diesel blends and alcohol-jme blends will not cause any major problems concerning soot formation on the injector tip and inside the combustion chamber Water and Sediment Content The sediment and water content determination was carried out for JME and both are represented as percent of fuel sample using the following expressions: % sediment = (weight of sediment / weight of fuel sample) 100 (5.4) % water = (weight of water / weight of fuel sample) 100 (5.5)

16 81 The sediment content in JME was negligible, while the water content in it is 0.43%. The maximum limit of water content specified by both ASTM 6751 and IS is 0.05%. Thus, for the JME produced from jatropha curcas oil, water and sediment content is within the maximum limit prescribed by the international standards Conradson Carbon Residue (CCR) The carbon residue is the percentage of carbonaceous residue left after the distillation of crude or its products in the absence of air. The determination of CCR is important for any fuel, lubricant and cracking of feed stock etc. Carbon deposits foul the surface, result in wear and scoring of cylinder wall and affect the regeneration of cracking catalyst. It is determined by Conradson apparatus, which is normally used for fuel oil. In conradson method, a weighed quantity of fuel is taken in a crucible, which is placed in an iron crucible having a cover with a small opening. These are, then placed in a third crucible and covered with a hood and strongly heated at a specified rate and the residue is cooled and weighed. The result is expressed as percentage of the residue on the original weight taken. The CCR value obtained for JME produced is 0.01% and 0.159% for ethanol. Due to 10.6% fuel oxygen in JME, the measured carbon content in it is reduced to 77.4% compared to 87.3% in base diesel fuel (Hamasaki et al 2001). The reduced carbon content in JME may be the reason for the low level of CCR value in it. The maximum limit for the CCR level as per both ASTM 6751 standard and IS is 0.05% on mass basis. The obtained value for JME is well within the limits imposed by the international standards Iodine Value and Saponification Number Iodine value is a measure of the degree of saturation or number of double bonds per mass sample. If iodine value is less, saturation is more. The

17 82 measured iodine value of JME produced in this study is 99. High iodine value of JME indicates the more quantity of unsaturated compositions in JME. The measured saponification number of JME produced by transesterification process and used in this study is Cetane Number Estimation Since the necessary facility is not available, the cetane number of biodiesel was estimated by using measured saponification number and iodine value of JME. Cetane number of biodiesel is given by (Bekal and Babu 2008) CN = (5458/SN) (0.225 IV) (5.6) where CN is cetane number, SN is saponification number, and IV is iodine value. Thus for JME, the measured SN = 183, and IV = 99. CN = (5458/183) ( ) Hence for JME the estimated CN = The cetane number of ethanol was extremely low (5 to 7) compared to the diesel fuel cetane number (45 to 47). Using 12% ethanol with diesel fuel reduced the cetane number of the fuel blend to 40 (Rahimi et al 2009). But adding JME improved ethanol diesel cetane number due to higher cetane number (53.85) of JME in the present case. This cetane number could be regarded as a suitable one to be used in diesel engines Copper Strip Corrosion Test Several components of the engine, fuel delivery and fuel tank are made of copper and copper alloys. Copper strip corrosion test is used to detect

18 83 the corrosiveness of automotive diesel and gasoline, kerosene, aviation gasoline and turbine fuel, lubricating oil and certain other petroleum products (Indian Standard methods of test for petroleum and its products 1976). In this test a polished copper strip was immersed in a given quantity of sample fuel and heated to certain temperature and the characteristics of copper strip were tested periodically. The copper strip was removed at the end of the test period, washed and compared with ASTM copper strip corrosion standards. Table 5.5 Copper strip classifications Classification Designation Description 1 Slight tarnish Light orange, almost the same as a freshly polished strip 2 Moderate tarnish Multicolored with lavender blue, over laid on claret red or brassy or gold 3 Dark tarnish Magenta overcast on brassy strip multicolored with red and green 4 Corrosion Transparent black, dark grey or brown with peacock green or jet black or graphite The CSN , ASTM 6751 and EN standards (Biodiesel standard 2003) refer to copper strip corrosion (Rosca et al 2005). The maximum limit for the copper strip corrosion level as per ASTM 6751 standard is dark tarnish (not worse than 3) and IS imposes a limit of slight tarnish (not worse than 1). Copper strip corrosion test conducted for JME and ethanol shows moderate tarnish, that is not worse than 2 as shown in Table 5.5. The copper strip corrosion test conducted on JME-diesel blends indicated slight tarnish (not worse than 1), while the ethanol-jme blends indicated moderate tarnish (not worse than 2). Since both ethanol and JME are slightly corrosive in nature, moderate tarnish was observed for ethanol- JME blends. The values obtained from the copper strip corrosion tests

19 84 conducted on neat JME, JME-diesel blends and ethanol-jme blends are within the indicated values by most of the international standards. The results obtained from copper strip corrosion test, water content test and acidity test on JME show that JME and its blends with diesel fuel can be used in diesel engines without corrosive problems of engine components Oxygen Content The oxygenated fuel is the most common additive that improves fuel combustion and reduces the engine emission level. Several oxygenated compounds were used for this purpose but the most common ones are biodiesel, alcohols, and ethers. Ethers that are octane enhancers increase fuel oxygen content but their use is limited because of the cancer risk probability and they are non-renewable. On the other hand, ethanol is an aliphatic alcohol which is produced from plants and agricultural wastes and is more suitable in comparison to other alcohols. Experimental results showed that oxygen content on mass basis of ethanol, methanol, JME, PME and diesel was 35%, 50%, 10.6%, 11% and 0% respectively. The oxygen content of ethanolbiodiesel-diesel blends and methanol-biodiesel-diesel blends was calculated from equation 5.7 and 5.8 respectively (Rahimi et al 2009). B o = 34.8 e V e b V b (5.7) B o = 50 m V m b V b (5.8) where B o is the mass of oxygen in blend (wt %), e, density of ethanol (g/cm 3 ), m, density of methanol (g/cm 3 ), b, density of biodiesel (g/cm 3 ), V e, volume of ethanol in blend (vol. %), V m, volume of methanol in blend (vol. %), and V b, volume of biodiesel in blend (vol. %).

20 85 12 Oxygen Content, Wt % JME-D PME-D Biodiesel Content, vol.% Figure 5.11 Variation of oxygen content with biodiesel fraction 60 Oxygen Content, Wt % E-JME M-JME Alcohol Content, vol. % Figure 5.12 Variation of oxygen content with alcohol fraction The variation of oxygen content of JME-diesel and PME-diesel blends are shown in Figure 5.11, while for ethanol-jme and methanol-jme blends are shown in Figure Adding the oxygenated fuels like biodiesel, ethanol or methanol with diesel fuel increases the oxygen content of the blend. On the other hand it reduces the heating value of the blend, which is depicted in Figures 5.9 and 5.10 respectively.

21 SUMMARY Laboratory tests were carried out to determine the properties like specific gravity, kinematic viscosity, cloud point, pour point, flash point, fire point and calorific value of the fuels used. The net calorific value of JME is only 6.17% less than that of diesel fuel. There was no much difference in the heating values of the conventional diesel and tri-compound blends containing alcohol lower than 15%. Addition of ethanol/methanol improves low temperature flow properties of biodiesel. Blending alcohol with biodiesel-diesel improves oxygen content, volatility, while it reduces density and viscosity compared to biodiesel-diesel blends. Biodiesel is known to act as an emulsifier or a co-solvent for ethanol/methanol that allows more alcohol in the blend fuel. Solubility and stability of alcohol in fuel blends, and blend tolerance for water will be greatly improved without other additives. Most of the measured properties of fuels tested are well within the limit imposed by National and International Standards for diesel engine fuels. Further experimental investigation is required to compare the performance and emissions of biodiesel and its blends with diesel fuel, an experimental setup was fabricated which is explained in the chapter 6.