Development of a reduced oxidation mechanism with low-temperature chemistry for real biodiesel methyl esters

Abstract

Accompanied with the development of advanced engine combustion modes, biodiesel as an important biorenewable fuel has the potential to be a regular engine fuel due to its advantages in carbon neutrality and reducing the emission of major pollutants. In the present study, a compact biodiesel oxidation mechanism for the numerical study of low-temperature biodiesel combustion is developed by reducing a comprehensive mechanism based on five major biodiesel methyl esters. For the mechanism reduction, a method based on direct and indirect species interactions is developed and proven to have improved effectiveness in reducing large complex mechanisms compared to existing methods. The method is preceded by reaction path analysis and followed by isomer lumping and sensitivity analysis, and the overall reduction process finally leads to a compact biodiesel mechanism with 187 species and 689 reactions. The fidelity of the reduced biodiesel mechanism is first demonstrated by simulating the auto-ignition of homogeneous biodiesel-air mixtures from various initial conditions. Predicted ignition delay data show discrepancies in the order of milliseconds, compared to those predicted using the original mechanism and experimental data. Agreement is also found in the instantaneous mole fraction of major species and mixture temperature, indicating that the reduced mechanism preserves the key reaction paths of the original mechanism. A further validation of the reduced mechanism is also accomplished by simulating the low-temperature oxidation of saturated and unsaturated biodiesel methyl esters in a jet-stirred reactor, and reasonable agreement is observed between predicted mole fraction of major product species and the corresponding experimental data at different temperatures.