The specific gravity of biodiesel and its blends with diesel fuel

Abstract

The specific gravities of biodiesel and 75, 50, and 20% blends with No. 1 and No. 2 diesel fuels were measured as a function of temperature from the onset of crystallization to 100°C. The results indicate that biodiesel and its blends demonstrate temperature-dependent behavior that is qualitatively similar to the diesel fuels. The temperature dependence of the specific gravity for biodiesel and its blends was compared with the ASTM D 1250-80 procedure for the temperature correction of hydrocarbon fuels, and the procedure was found to provide accurate corrections. A blending equation was developed that allows the specific gravity of blends to be calculated from the specific gravities of the biodiesel and diesel fuels.A large amount of research has been conducted in recent years to investigate alternative fuels for transportation. Renewable biomass resources such as plant seed oils and animal fats could play a role in meeting our society's future energy needs in an environmentally sound way. While the high viscosity of vegetable oils and animal fats tends to cause problems when used directly in diesel engines (1-4), if the oils and fats are transesterified using short-chain alcohols, the resulting monoesters have viscosities that are closer to petroleum-based diesel fuel (5-7). These monoesters have come to be known as biodiesel.The specific gravity of biodiesel will depend on the fatty acid composition of the mixed esters and their purity. In a similar manner, the specific gravity of petroleum-based diesel fuel varies depending on the refinery feedstock and day-today variability of the blending streams in the diesel fuel boiling range. The specific gravity of diesel fuel is constantly monitored and many performance indicators, such as cetane number and heating value, are correlated against it. However, the specific gravities of hydrocarbons are strongly affected by temperature. Since specific gravity measurements made outside the laboratory are usually at nonstandard temperatures, ASTM standard D 1250 (8) was developed to correct measured specific gravities back to a reference temperature. The standard consists of a series of tables relating specific gravity and temperature.As biodiesel moves closer to commercialization, a similar procedure for correcting measured specific gravity data will be needed. The specific objective of the research described in this paper was to measure the specific gravity of biodiesel and its blends with diesel fuel as a function of temperature, to compare the temperature-dependent behavior with that predicted by ASTM D 1250, and, if necessary, to develop a new correction table.Equipment and procedure. In this study, commercially available soybean oil-based biodiesel (NOPEC Corporation, Lakeland, FL) was used and its properties are shown in Table 1. Commercial grades of No. 1 and No. 2 diesel fuel were obtained from local fuel suppliers and their properties are given in Table 2. Blends of 20, 50, and 75% biodiesel with No. 1 and No. 2 diesel fuels were prepared by weight. Owing to the d...

Prediction models for density and viscosity of biodiesel and their effects on fuel supply system in CI engines

“…Specific gravity is defined as a ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4°C and 1atm. Tat and Garpen [10] measured experimentally the specific gravity of 20%, 50%, 75%, and 100% soyabean biodiesel as a function of temperature in the temperature range of crystallization temperature to 100 o C using the standard hydrometer method. The results indicate that the biodiesel and its blends demonstrate temperature dependent behaviour.…”

“…Tat et al [4] also reported similar linear equation for three different biodiesels namely, canola-oil biodiesel, soyabean-oil biodiesel and fish-oil biodiesel. These equations were developed based on the data obtained from a capacitance type liquid level meter within temperature range of 20 o C to 300 o C. Clements (referenced in [10]) suggested that equation (2) can be used to determine the specific gravity of different biodiesel blends at a standard temperature. In this equation the specific gravity of the blend has been considerd to be proportional to mass fractions of the constituents.…”

“…By considering the carbon number, Krisnangkura et al [18] proposed different equations [equation (9) and equation (10)] to determine viscosity of biodiesels with long and short carbon structure at different temperatures. In Krisnangkura's equations, number of the carbon atoms is required a-priori which limits the use of equation (9) and equation (10).…”

“…The higher viscosity causes mixture to burn lean in the engine as fuel moves slowly through the fuel filter and fuel lines. In addition, the higher viscosity of biodiesel fuel affects the start of injection, injection pressure and the fuel spray characteristics, which are the main parameters that affect engine performance and exhaust emission [7,8,9].The density of the diesel fuel is also very important parameter, since other crucial performance parameters of engine such as cetane number and heating value have been correlated against it [10]. In addition, the density values have also been used to measure the amount fuel in fuel system by volumetric method [5].…”

“…The effect of mixing on density and viscosity variation of biodiesel with respect to temperature, percentage of blend, and the chemical structure (fatty acid, position and number of double bond) have been well reported. Different empirical correlations have been developed, which relate various performance parameters with density and viscosity of biodiesel [5][6][7][8][9][10][11]. The works of previous researchers on biodiesel density and viscosity have been summarized below.…”