Research into technologies directed towards the improvement in the efficiency of the internal combustion engine has been motivated over the past several years by the regulation of the United States automotive market to more stringent standards for fuel economy and emissions. Lean burn operation of spark-ignited (SI) internal combustion engines may have the potential to help meet the high fuel economy goals of the future decade by improving the efficiency of SI engines at partial loads. Although gains in efficiency are found for engines operating with diluted mixtures, these mixtures present difficulties that manifest themselves through the slow flame speeds and poor ignitability associated with lean or diluted air-fuel mixtures. Two types of ignition systems are examined here that attempt to mitigate these negative effects. They are a radio-frequency plasma-enhanced ignition system and a pre-chamber-initiated ignition system called Turbulent Jet Ignition.First, the effects of a plasma-enhanced ignition system on the performance of a small, single-cylinder, four-stroke gasoline engine are examined. Dynamometer testing of the 33.5 cm3 engine at various operating speeds was performed with both the engine’s stock coil ignition system and a radio frequency plasma ignition system. The radio frequency system is designed to provide a quasi-non-equilibrium plasma discharge that features a high-voltage pulsar that provides 400 mJ of energy for each discharge and voltages of up to 30 kV. Tests show improvement in the engine’s combustion stability at all operating conditions and the extension of the engine’s lean flammability limit with the radio frequency system. Particular attention is given to the improvements that the radio frequency system provides while burning lean air-fuel mixtures. Additionally, analysis of the 33.5 cm3 engine’s exhaust and high-speed images of the radio frequency system taken in a separate 0.4-liter optical engine are also presented. Second, fully three-dimensional computational fluid dynamic simulations with detailed chemistry of a single-orifice turbulent jet ignition device installed in a rapid compression machine are presented. The simulations were performed using the computational fluid dynamics software CONVERGE and its RANS turbulence models. Simulations of propane fueled combustion are compared to data collected in the optically accessible rapid compression machine that the model’s geometry is based on to establish the validity and limitations of the simulations and to compare the behavior of the different air-fuel ratios that are used in the simulations. In addition to being compared to a companion experimental study, investigations into the effect of TJI orifice size and pre-chamber spark location are performed. The data generated in the simulations is analyzed and insights into the processes that make up the operation of the TJI are given. Finally, CFD analysis tools are applied to the early development and design of a TJI system intended for a heavy-duty diesel engine being converted to run on natural gas.
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