Surrogate formulation methodology for biodiesel based on chemical deconstruction in consideration of molecular structure and engine combustion factors

摘要

A novel methodology based on chemical deconstruction for the formulation of surrogate fuels for biodiesels was proposed, developed, and validated. Surrogates were formulated using sub-surrogates of methyl palmitate, stearate, oleate, linoleate, and linolenate, which are the major components of biodiesel. Each methyl ester sub-surrogate was constituted by a binary or ternary fuel mixture. To formulate the sub-surrogates, key physical and chemical parameters based on engine spray and combustion were considered with preferential weight functions. To calculate the optimal surrogates, novel weighted Euclidean distance and analytic hierarchy process algorithms were used to accurately determine the components and their proportions. Next, surrogates for biodiesels were assembled from the sub-surrogates according to the component ratios of the target fuels. Using this methodology, surrogates for biodiesels could be formulated regardless of feedstock origin and production region. For example, the surrogate fuel for soybean biodiesel consisted of 62.9% methyl decanoate, 15.0% n-hexadecane, 9.4% methyl trans-3-hexenoate, and 12.7% 1, 4-hexadiene in mole fractions. The process of experimental validation was divided into two steps: first, verifying the sub-surrogates for methyl palmitate, methyl oleate, and methyl linoleate; and second, comparing the quaternary surrogates with real soybean biodiesel. Point-to-point experiments were conducted on three platforms: a heated rapid compression machine, a laminar flow reactor, and an ignition quality tester. More specifically, the rapid compression machine experiments compared the autoignition characteristics, especially the low-temperature reactivity, of the surrogates and the target fuels under constant-volume adiabatic conditions. Laminar flow reactor was used to compare the low-to-intermediate oxidation properties of the surrogates with those of the target fuels, especially the early formation of olefins and carbon dioxide, which is a key characteristic of the combustion of biodiesel. Ignition quality tester was used to ensure that the surrogates had similar ignition and combustion delay times under engine-like conditions. The results of all of these experimental validations showed that the ignition and oxidation properties of the surrogates were consistent with those of their target fuels. In addition, a kinetic model of the quaternary surrogates was proposed and further validated in a laminar flow reactor. In sum, quaternary surrogate fuels were developed using a method based on chemical deconstruction, which was shown through validation experiments to be highly accurately and reliably reproduce the combustion properties of soybean biodiesel. Furthermore, chemical deconstruction method has great potential in surrogate modeling for various biodiesels.