Impact of Aromatics on Engine Performance 2019-01-0948
To formulate more accurate surrogate fuels for engine applications, we have focused on characterizing the impact of aromatic structures on combustion and emissions. The impact of blending aromatics in fuel surrogates can be non-linear for ignition characteristics that govern knocking in spark engines and combustion phasing in diesel engines. Aromatics are also primarily responsible for engine emissions, especially soot. The structure of aromatics has a great impact on both combustion and emissions characteristics of a fuel. We systematically investigated the impact of nine different aromatics under various engine conditions. We have developed a detailed, self-consistent, reaction mechanism for gasoline and diesel surrogates that contain toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, isomers of xylene, 1,2,4-trimethylbenzene, and 1-methylnaphthalene. The mechanism has been validated extensively using data from publications covering various types of experiments and a broad range of conditions. Numerical experiments using 0-D and 1-D models have been performed to study the relative behavior of these aromatics for different reacting conditions. For conditions pertaining to low-temperature heat release in diesel engines as well as knocking in spark engines, the reactivity was found to increase with an increase in the length of the side chain attached to the benzene ring. The exception was for o-xylene, which showed the highest reactivity of the aromatic fuels at low-temperatures. On the other hand, p-xylene exhibited the highest anti-knocking behavior. Laminar flame speeds were found to decrease with an increase in the number of methyl sidechains and to increase slightly with an increase in the length of the sidechain. This may impact combustion phasing in spark engines. Based on CFD simulations of two diesel engines under different fuel load and engine speed conditions, aromatics were found to affect soot emissions as well as combustion under certain conditions.
Chitralkumar Naik, Karthik Puduppakkam, Ellen Meeks