Table 2.10: Fuel Standards and Test methods for Pure Biodiesel
Property ASTM Method EN Method ASTM Limits EN Limits
Water and sediment ASTM D2709 EN ISO 12937 0.05 max 500 max
(% vol.) (mg/kg)
Total glycerol ASTM EN 14105 0.24 0.25 max (% mass) (% mol) Methanol - EN 14110 0.2 max 0.2 max
(% vol.) (% mol) Ash content ASTM D874 ISO 3987 0.02 max 0.02 max
(% mass) (% mol) Sulfur ASTM D5453 EN ISO 20846 10 max
S15 grade EN ISO 20884 0.0015 max (mg/kg)
(% mass)
S500 grade 0.05 max
(% mass)
Cetane number ASTM D613 EN ISO 5165 47.0 min 51.0 min Carbon residue ASTM D4530 EN ISO 10370 0.05 max 0.3 max
(% mass) (% mol)
Flash point ASTM D93 EN ISO 3679 130 min 120 min (°C) (°C)
Density, 15°C EN ISO 3675 860 – 900
EN ISO 12185 (kg/m3)
Kin. Viscosity 40°C ASTM D445 EN ISO 3104 1.9 – 6.0 3.5 – 5.0
ISO 3105 (mm2/s) (mm2/s)
The use of low quality biodiesel (due to incomplete reaction or contaminants) in a diesel engine could result in several engine problems, such as coking (Ma et. al., 1999). In order to prevent such problems, several fuel standards have been adopted for quality control. Among these standards are ASTM method (American Society for Testing and Materials) and EN method (European Committee for Standardisation) (AOCS, 1998). Some of these standards and methods are listed in Table 2.10. These standards serve as guide in determining the properties of biodiesel.
2.5.1 Kinematic Viscosity
Viscosity is a measure of the resistance of a fluid to flow (measure of fluid friction). In the case of liquid fuels, the less viscous the fluid is, the greater its ease of movement (fluidity) (Evangelos, 2013). This is a critical property in diesel engine because it affects the behaviour of fuel injection.
Viscosity is temperature-dependent, the higher the temperature the lower the viscosity. High viscosity can cause larger droplet sizes on injection, poorer vapourisation and narrower injection spray angle (Parag et. al., 2013). This can lead to overall poorer combustion, higher emissions and increased oil dilution. The reduced fuel leakage losses in the (mechanical) fuel pump due to higher kinematic viscosity lead also to higher injection pressures and, also higher mass of injected fuel (Evangelos, 2013).
Fuels with high viscosity may not provide sufficient lubrication for the precision fit of fuel injection pumps, resulting in leakage or increased wear. Higher viscosity value of vegetable oil
injection engine. Trans-esterification of vegetable oil produces biodiesel of very small viscosity value suitable for good diesel engine performance. According to ASTM standard, viscosity of biodiesel of good quality at 400C is 1.9 – 6.0 mm2/s.
2.5.2 Density
Density of a substance is the measure of the weight per unit volume of that substance. The air- fuel ratio and energy content within the combustion chamber are influenced by fuel density. The denser the oil the higher the energy content per liter. In general, densities of biodiesel are slightly higher than that of petroleum diesel, and increasing the level of biodiesel blends increases the
blend’s density (Evangelos, 2013).
FAME density is strongly affected by the degree of unsaturation, with higher unsaturation leading to increased density. It has been reported that biodiesel density is also affected by chain length, that is, the higher the chain length the higher the density (Parag et. al., 2013).
2.5.3 Flash Point
Flash point temperature of a fuel is the minimum temperature at which the fuel will ignite (flash)
on application of an ignition source. Flash point varies inversely with the fuel’s volatility.
Minimum flash point temperatures are required for proper safety and handling of fuel (Tan et.
al., 2011).
2.5.4 Pour Point
Pour point is the lowest temperature at which a material will flow due to crystal agglomeration. It is one main cold flow property and it is useful for characterizing the suitability of a fuel for large storage and pipeline distribution (Zlatica and Biljana, 2009; Chiu et. al., 2004). The ASTM
specifies standard of -15°C to 10 °C as the pour point of biodiesel, below the specified temperature the fuel loses it flow characteristics and becomes solid, clogging the engine (Kulkarni and Dalai, 2006).
2.5.5 Heating Value
Heating value (Heat of Combustion) of fuel is the amount of heat energy released by the combustion of a unit value of such a fuel. One of the most important determinants of heating value is moisture content. Air-dried biomass typically has about 15-20% moisture, whereas the moisture content for oven-dried biomass is negligible (Gerhard, 2005)
2.5.6 Ash Content
Ash is a measure of the amount of metals or waste materials present in the fuel. High concentration of these materials leads to injector tip plugging, combustion deposits and injection system wear. It lowers the heating value of biodiesel (Nada, 2011).
2.5.7 Sulphur Content
One important factor that should be considered is biodiesel sulphur content. This is because its release into the environment has negative effects, such as acid rain. Petroleum diesel has higher sulphur content when compare to biodiesel (William, 2006).
Therefore, of particular concern are the requirements to reduce the sulphur contents of diesel fuel. Ultra-low sulphur diesel has less than 50 ppm sulphur and new diesel regulations in most countries is sulphur content of less than 10 ppm (Miguel, 2006).
2.5.8 Cetane Number
Cetane Number (CN) is a measure of auto ignition quality of a fuel. It is a relative measure of the interval between the beginning of injection and auto ignition of the fuel. The higher the cetane number, the shorter the delay interval and the greater is its combustibility. Lower CN causes higher exhaust gas emissions and particulate matter. The CN of diesel fuel in European Union (EU) is regulated at ≥51, specified at ≥42 in Brazil and ≥40 in USA (Güzel, 2012). Since biodiesel is largely composed of long-chain hydrocarbon groups (with virtually no branching or aromatic structures), it typically has a higher CN than petroleum diesel (a good advantage over petroleum diesel). The CN of pure FAME molecules increases with chain length, but this effect is masked when considering complex mixtures of FAME fuels. On the other hand, the CN of FAME fuels clearly vary with average degree of unsaturation, the higher the degree of unsaturation the lower the CN (Parag et.al., 2013).
In general, diesel engines will perform efficiently well with fuels of ≥ 50 cetane numbers. While fuels with low cetane numbers (of say 35) will cause difficulty in starting the engine, generate noise and thick exhaust smoke (Sivaramakrishnan and Ravikumar, 2012).