Aromatics have long been added to pump-grade gasoline to increase fuel octane number by increasing autoignition resistance. As octane number is expensive and impractical to determine, ignition delay time measurements are a promising way to understand autoignition resistance under modern engine operating conditions across equivalence ratios, with and without exhaust gas recirculation dilution. Therefore, ignition delay time measurements were used in Chapter 4 of this dissertation to understand the effect of six different aromatic additives on the autoignition resistance of a gasoline surrogate fuel between 700 K and 950 K at equivalence ratios relevant to current and next generation engines (φ = 0.6, 0.8, 1.0) and with exhaust gas recirculation dilution (0%, 15%, and 30%). The substituted phenol additives tested were p-cresol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol, which all varied in methyl group quantity and location. From the results presented, it was found that the para-substituted methyl group was most important for increasing the ignition delay time of the base fuel, and that nearby methyl groups are also beneficial. In order of the greatest to least overall lengthening effect on the gasoline surrogate’s ignition delay time, the additives are: 3,4-xylenol, 2,4-xylenol, p-cresol, 3,5-xylenol, 2,5-xylenol, 2,6-xylenol.As autoignition resistance is important for appropriate combustion timing to prevent misfires and extreme pressure rise rates, the next chapters of this dissertation aimed to characterize a turbulent jet ignition system to accommodate fuels with variable autoignition resistance. Turbulent jet ignition has long been studied with high octane number fuels to reduce engine emissions and extend the lean operating limit from spark ignition operation. This is possible because turbulent jet ignition works by increasing the rate of flame propagation through the main chamber by multiple ignition points, reducing the dependence on the mixture’s laminar flame speed during main chamber charge consumption. By increasing the burning rate in the main chamber, the amount of time the end gas region is held at elevated temperatures and pressures is reduced, as is the quantity of unburned fuel and oxidizer. This, in turn, delays the occurrence and severity of the peak pressure rise rate due to autoignition of the unburned reactants. To test the promise of turbulent jet ignition with high cetane number fuels, Chapter 5 and Chapter 6 present simulations and experiments in a rapid compression machine to quantify the events during successful turbulent jet ignition and identify performance metrics. F-24 jet fuel/air mixtures were studied at low-temperature intake conditions, and three distinct events during each case of turbulent jet ignition were identified: peak pre-chamber ignition pressure, main chamber jet ignition, and autoignition. The amount of fuel burned before autoignition was also determined and the peak pressure rise rate from the turbulent jet ignition system was reduced by up to 41% from cases where combustion was initiated by autoignition.
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