Experimental and Modeling Study on Autoignition of a Biodiesel/n-Heptane Mixture and Related Surrogate in a Heated Rapid Compression Machine

Abstract

In this paper, ignition delay time of two kinds of biodiesel, soybean oil methyl ester (SME) and waste cooking oil methyl ester (WCOME) blended with n-heptane, were measured in a heated rapid compression machine (RCM). To meet the requirement of measuring high boiling fuels like biodiesel, several modifications were applied in RCM platform, which embodied in global preheating, reactant preparation, and gas dilution. Along with these methodologies, ignition delay times of SME30 and WCOME30 (30% biodiesel and 70% n-heptane in volume fraction) were measured at 15 bar, within temperature range of 641−772 K. Both biodiesels exhibited typical two-stage ignition characteristics and pronounced negative temperature coefficient behaviors. To better investigate the ignition process of biodiesel, novel surrogate fuels have been formulated including methyl decanoate, n-hexadecane, methyl trans-3-hexenoate, and 1,4-hexadiene, according to Chemical Deconstruction Methodology. Autoignition properties of surrogate and target biodiesel were investigated under the same conditions in RCM and good agreements have been found in point-to-point validation experiments, which verified good performance of quaternary surrogate fuels for biodiesel. Furthermore, kinetic models of biodiesel were proposed on the basis of surrogate fuels, which consisted of 4901 species and 18 669 reactions. The novel model has good predictions in ignition delay times in low-tointermediate temperature regions measured in RCM, and the kinetic model has great potentials in revelation of autoignition mechanisms and in development of CFD applications in internal combustion engines.

Biodiesels Manufactured from Different Feedstock: From Fuel Properties to Fuel Atomization and Evaporation

“…A number of studies on biodiesels and excellent reviews on this topic (both fundamental studies and biodiesel utilization) can be found in the literature. ,,− The common findings noted in the current literature include the following: (i) biodiesels can be made from different feedstock and could be a potential candidate to partly replace fossil diesel used in compression ignition engines , and these biofuels could be blended with fossil diesel with or without additives, − (ii) biodiesels have a higher cetane number but a lower calorific value and higher viscosity compared to fossil diesel, , and (iii) fueling engines with biodiesels can help to decrease specific particulate matter in mass basic, while the effect of biodiesels on NO x formation and particle number and size distribution is not fully understood. , Further investigations of physical and chemical properties of biodiesels made from different feedstock are essential to have a comprehensive understanding of the engine performance when operating with biodiesels. The impact of FAME profiles, especially oxygen content, on the properties of biodiesels made from different feedstock, and the influence of fuel properties on fuel atomization and evaporation, according to the authors’ knowledge, is not quite clear in the literature.…”