The speed of sound and isentropic bulk modulus of biodiesel at 21°C from atmospheric pressure to 35 MPa

Abstract

Biodiesel, an alternative diesel fuel consisting of the alkyl monoesters of fatty acids from vegetable oils and animal fats, can be used in existing diesel engines without modification. However, property changes associated with the differences in chemical structure between biodiesel and petroleumbased diesel fuel may change the engine's injection timing. These injection timing changes can change the exhaust emissions and performance from the optimized settings chosen by the engine manufacturer. This study presents the results of measurements of the speed of sound and the isentropic bulk modulus for methyl and ethyl esters of fatty acids from soybean oil and compares them with No. 1 and No. 2 diesel fuel. Data are presented at 21 ± 1°C and for pressures from atmospheric to 34.74 MPa. The results indicate that the speed of sound and bulk modulus of the monoesters of soybean oil are higher than those for diesel fuel and these can cause changes in the fuel injection timing of diesel engines. Linear equations were used to fit the data as a function of pressure, and the correlation constants are given.Biodiesel has come to be defined as the alkyl monoesters of fatty acids from vegetable oils or animal fats. It can be used as an alternative fuel for diesel engines. Many researchers have reported that oxides of nitrogen (NOx) increase, and particulate matter, carbon monoxide, and unburned hydrocarbons decrease when biodiesel is used in heavy-duty diesel engines (1,2). The reason for the higher NOx emissions is not currently understood but could be due to changes in the chemical composition and the physical properties of the fuel. A major difference between petroleum-based diesel fuel and biodiesel is the 10-11% oxygen content of the biodiesel. The oxygen could change the stoichiometry of the combustion process in a way that produces more NOx. Biodiesel also generally has a higher cetane number than petroleum-based diesel fuel. The cetane number is a diesel fuel property that quantifies the fuel's readiness to autoignite. Higher cetane number corresponds to a shorter ignition delay after the fuel is injected into the cylinder. This results in earlier combustion timing, which tends to increase NOx, and less of the fuel participating in the rapid combustion of the fuel that has premixed during the ignition delay period, which will reduce NOx. These two effects partially offset each other, but higher cetane number in petroleum-based diesel fuels is generally observed to reduce NOx (3). The contribution of biodiesel's higher cetane number to NOx production is still not understood. Changes in physical properties such as viscosity, speed of sound, and bulk modulus also may contribute to higher NOx levels. Injection system anomalies, such as longer injection duration, higher injection pressure, and early injection have been reported by other researchers (4-6).Diesel engines operate by compressing fuel to a high pressure and injecting it into the cylinder where the fuel spontaneously ignites. The fuel is compressed with a piston ...

Correlation and prediction of biodiesel density for extended ranges of temperature and pressure

“…The equations of state used for density correlation by those authors are also mentioned in that table. Tat et al [22] presented density values at 294 K and up to 35 MPa for methyl soy biodiesel. However, access to the values is difficult and uncertain because they are presented in graphic form.…”

“…Literature usually reports biodiesel density measurements made close to the ambient temperature (285-295) K and atmospheric pressure [8][9][10][11][12][13][14] and few measurements of this property have been reported in wider temperature ranges [15][16][17][18][19][20]. The inclusion of pressure has been made in the works by Pratas et al [1], Tat and Van Gerpen [2,21,22], Nikolic et al [23], Aparício et al [24], Dzida and Prusakiewicz [25], and recently by Chhetri and Watts [26] and Schedemann et al [27]. Since density depends on the used raw material from which biodiesel was produced, FAMEs profile is crucial for applying the correlation and prediction models to that property, which also has not been provided by authors [23][24][25].…”

“…Aiming to gather a sufficiently large amount of data, and for the sake of statistical significance for biodiesel density correlation and prediction, the measured densities for cottonseed made in this study were combined with biodiesel data provided by Pratas et al [1], Tat and Van Gerpen [1,22], and Schedemann et al [27].…”

Function K - As a Link Between Fuel Flow Velocity and Fuel Pressure, Depending on the Type of Fuel

“…Huber et al [19] determine by measurement the speed of sound and density of examined fuels at the atmospheric pressure, for the temperature range of 278-333 K, and starting from the Molar Helmholtz Free Energy equation, they form a model for calculating fuel characteristics for pressures of up to 500 bar and temperatures of up to 700 K. Tat et al [20,21] present the dependence of these characteristics on the pressure of up to 350 bar at 293-313 K. Ott et al [22] determine the density and speed of sound at 0.83 bar and temperatures of 278 to 338 K. Kegl [23] experimentally determines the speed of sound and density for pressures of up to 400 bar as well as the influence of a temperature change on density (from 273 to 313 K). The author also determines the bulk modulus for pressures of up to 400 bar and provides a comparative overview of results obtained by simulation.…”

Physiochemical and Phase Behaviour Study of Jatropha curcus Oil - Ethanol Microemulsion Fuels Using Sorbitane Fatty Esters

“…Mixing oil with alcohols is one of the approaches to achieve standard biodiesel viscosity alongside other physicochemical properties (PCP): density and surface tension are essential indicators for proper analysis of biodiesel. For instance, the cetane number and gross heating values are directly related to density and affect fuel efficiency [26][27][28]. Similarly, viscosity is an important parameter for development of fuels that governs the engine operation [29][30].…”