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

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journal contribution
posted on 09.04.2019, 00:00 by Ang Li, Liang Yu, Xingcai Lu, Zhen Huang, Lei Zhu
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-to-intermediate 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.

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