Ignition Delay Time Measurements of Substituted Phenol Additives in a Toluene Reference Fuel

Using a rapid compression machine, fuel autoignition resistance can be quantified by the ignition delay time measurements of homogeneous mixtures. As the occurrence and intensity of knock in spark ignition engines are related to autoignition resistance, ignition delay time measurements give valuable insight into fundamental fuel combustion properties that can be used to predict undesirable combustion behavior. Therefore, the work presented in this paper aims to understand the autoignition resistance of a gasoline surrogate fuel and how it is affected by the addition of substituted phenol additives from ignition delay time measurements in a rapid compression machine. Six substituted phenols were tested: p-cresol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol. Lean and stoichiometric mixtures, as well as stoichiometric mixtures with N₂ dilution, were studied at engine-relevant conditions of 20 bar between 700 and 950 K. It was found that most additives were able to lengthen the base fuel ignition delay time at high and low temperatures, but that the most effective had two methyl groups located adjacent to each other.