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Turbocharging, increasing the compression ratio, and downsizing a spark-ignition engine are well known strategies for improving vehicle fuel economy. However, such strategies increase the likelihood of engine knock due to higher in-cylinder pressures and temperatures. A high octane fuel, such as E85, effectively suppresses knock but is not necessary in most parts of the engine operating map. To better utilize a high octane fuel, dual fuel injection has been suggested where high octane fuel is injected only when the engine is about to knock. However, the effects of downsizing, retarding spark timing, and increasing compression ratio on dual fuel applications are not well understood. To investigate these questions, GT-power simulations along with engine experiments and engine-in-vehicle simulations for a passenger vehicle and a medium-duty truck were conducted.

The use of direct injection (DI) of a second fuel, ethanol or methanol (or their concentrated blends), is explored, via simulation, as a means of avoiding knock in turbocharged, high compression ratio spark-ignited engines that could replace diesels in certain vocational applications. The Ethanol Turbo Boost ™ concept uses the second fuel only under conditions of high torque to avoid knock, while using only conventional gasoline throughout the rest of the engine operating range. This approach is an attractive alternative for heavy duty vehicles that operate intermittently at high torque and within a confined locale, reducing the logistical issues of supplying the knock-suppressing fuel. The combination of GT-Power for engine calculations and a sophisticated chemical kinetics code for predicting knock were used in the study.

Non-petroleum based liquid fuels are essential for reducing oil dependence and greenhouse gas generation. Increased substitution of alcohol fuel for petroleum based fuels could be achieved by 1) use in high efficiency spark ignition engines that are employed for heavy duty as well as light duty operation and 2) use of methanol as well as ethanol. Methanol is the liquid fuel that is most efficiently produced from thermo-chemical gasification of coal, natural gas, waste or biomass. Ethanol can also be produced by this process but at lower efficiency and higher cost. Coal derived methanol is in limited initial use as a transportation fuel in China. Methanol could potentially be produced from natural gas at an economically competitive fuel costs, and with essentially the same greenhouse gas impact as gasoline. Waste derived methanol could also be an affordable low carbon fuel.

Long-haul and other heavy-duty trucks, presently almost entirely powered by diesel fuel, face challenges meeting worldwide needs for greatly reducing nitrogen oxide (NOx) emissions. Dual-fuel gasoline-alcohol engines could potentially provide a means to cost-effectively meet this need at large scale in the relatively near term. They could also provide reductions in greenhouse gas emissions. These spark ignition (SI) flexible fuel engines can provide operation over a wide fuel range from mainly gasoline use to 100% alcohol use. The alcohol can be ethanol or methanol. Use of stoichiometric operation and a three-way catalytic converter can reduce NOx by around 90% relative to emissions from diesel engines with state of the art exhaust treatment.

The Cu-zeolite (CuZ) SCR catalyst enables higher NOx conversion efficiency in part because it can store a significant amount of NH3. “NH3 storage control”, where diesel exhaust fluid (DEF) is dosed in accord with a target NH3 loading, is widely used with CuZ catalysts to achieve very high efficiency. The NH3 loading actually achieved on the catalyst is currently estimated through a stoichiometric calculation. With future high-capacity CuZ catalyst designs, it is likely that the accuracy of this NH3 loading estimate will become limiting for NOx conversion efficiency. Therefore, a direct measurement of NH3 loading is needed; RF sensing enables this. Relative to RF sensing of soot in a DPF (which is in commercial production), RF sensing of NH3 adsorbed on CuZ is more challenging. Therefore, more attention must be paid to the “microwave resonance cavity” created within the SCR assembly. The objective of this study was to develop design guidelines to enable and enhance RF sensing.

Direct Injection (DI) fueled gasoline engines provide higher efficiency than port fueled injected (PFI) engines. However, emission of small particulates is greatly increased when DI is used. Particulate mass emission is increased by more than a factor of 10 and particulate number is increased by a factor of 10-100 relative to PFI engines leading to health concerns and to implementation and consideration of new regulations. Optimized combinations of PFI and DI can greatly reduce DI-generated particulate emissions without compromising efficiency and performance. A DI enhanced PFI mode of engine operation is employed where PFI is the dominant means in dual-injection fueling over a drive cycle, and the fuel fraction that is directly injected is reduced/minimized while still preventing knock at high loads. Further reduction can be obtained by optimal use of spark retard.

1 Downsizing and turbocharging a spark-ignited engine is becoming an important strategy in the engine industry for improving the efficiency of gasoline engines. Through boosting the air flow, the torque is increased, the engine can thus be downsized, engine friction is reduced in both absolute and relative terms, and engine efficiency is increased. However knock onset with a given octane rating fuel limits both compression ratio and boost levels. This paper explores the operating limits of a turbocharged engine, with various gasoline-ethanol blends, and the interaction between compression ratio, boost levels, and spark retard, to achieve significant increases in maximum engine mean effective pressure and efficiency.