In order to examine in detail the effect of C = C bond on the combustion chemistry of biodiesel fuels, two C4 fatty acid methyl esters (FAMEs) were investigated, namely methyl butanoate (MB) and methyl crotonate (MC). Pyrolysis experiments of these two FAMEs at 30,150 and 780 Torr were conducted in a flow reactor over the temperature range of 773-1323 K, using gas chromatography-mass spectrometry. A number of pyrolysis species including C1 to C4 hydrocarbons, oxygenated products, esters and aromatics were observed and identified. A comprehensive kinetic model for MB and MC combustion was developed, and applied to validate against the new experimental data. In this work, peak mole fraction of benzene, as well as other unsaturated hydrocarbons in MC pyrolysis, was found to be in slightly higher amounts in comparison with that of MB. Kinetic modeling analysis revealed that the dominant formation pathway of benzene was the self-combination reaction of propargyl radical. Furthermore, the model was also validated against the previous experimental data on MB and MC combustion, including oxidation in jet stirred reactor, pyrolysis in shock tube and laminar premixed flame. This study suggests that the effect of C = C double bond in FAMES might give rise to a growing tendency of initial PAH and soot precursors in the whole thermal decomposition process. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.