Impact of Aromatics on Engine Performance

Aromatics constitute a significant portion of refinery fuels. Characterizing the impact of various aromatic components on combustion and emissions facilitates formulation of surrogate fuels for engine simulations. The impact of blending aromatics in fuel surrogates is usually nonlinear for ignition characteristics responsible for knocking in spark engines and for combustion phasing in diesel engines. In this work, we have characterized the behavior of nine aromatics components under engine-relevant conditions. A self-consistent and validated detailed kinetics mechanism has been developed for gasoline and diesel surrogates that contains toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, isomers of xylene, 1,2,4-trimethylbenzene, and 1-methylnaphthalene. Numerical experiments using 0-D and 1-D models have been performed to study the relative behavior of these aromatics for different reacting conditions. Autoignition times and flame speeds of pure components as well as of gasoline and diesel surrogates have been studied. The impact of aromatic structures in gasoline was characterized using a PFI engine. CFD simulations of two different diesel engines were used to study the impact of aromatic structures in diesel. Trends in combustion and emissions based on the aromatic molecular structure under various engine operating conditions were observed.