Enabling Ethanol Use as a Renewable Transportation Fuel: A Micro- and Macro-scale Perspective

Abstract

The transportation sector remains the most challenging area to reduce greenhouse gas emissions from the combustion of fossil fuels. A successful transition away from fossil fuels is possible through the use of ethanol as an alternative fuel. Ethanol has considerable promise to reduce the carbon intensity of passenger vehicles, but a better understanding of the promise and limitations of ethanol as a renewable energy carrier is required, particularly using non-food feedstocks. Blending ethanol with gasoline has been demonstrated at a significant scale in the United States and Brazil. Currently, ethanol is blended with gasoline in the U.S. as an octane booster to a maximum blend level (E10 – 10% by volume); which is indistinguishable from gasoline to the engine application and the fueling infrastructure. However, optimum blend levels have not been determined from an engine application perspective. Also, current production of ethanol from primary food crops presents challenges like competition with food sources; thus, alternative feedstocks for ethanol production are required. This dissertation takes a novel approach which presents micro and macro-scale perspectives to enable ethanol as a transportation fuel. First at the micro or device scale, physical experiments were used to determine the optimum blend level of ethanol and gasoline for production spark ignition engines. Engine operating strategies which provide the most benefit, in terms of improving efficiency and lowering emissions, with the use of these blends were identified. Mid-level blends (30%) of ethanol by volume with gasoline show the most benefit in terms of several engine performance metrics. An improvement of 2% in thermodynamic efficiency on an absolute basis, and more than 90% reduction in particulate emissions was observed by combining use of such a blend with a triple-injection per cycle fueling strategy. Second at the macro scale of the transportation fuel production and distribution level, analytical methods were applied to determine the feasibility of producing cellulosic ethanol based on high-fidelity geographically-resolved data on agricultural waste for the regional districts of Ghana. Biorefinery locations and fuel blending infrastructure recommendations are made, by minimizing transportation costs involved in the biomass residue feedstock collection and distribution of the ethanol produced by the biorefinery. Previous studies have shown significant potential of biofuel production in Ghana, but there were no previous studies that focused on development of geographic infrastructure for 2nd generation transportation biofuels (i.e. based on non-food feedstocks). This study was the first attempt in this direction. Both the process used and the outcomes of this study provide valuable input for the development of sustainable biofuels infrastructure in Ghana. This work demonstrates considerable benefit of ethanol blending for modern engine architecture, with identification of strategies which leverage the thermo-physical fuel properties of ethanol and translate across engine hardware architectures. The thesis outcomes also offer an unprecedented attempt towards development of a geographic infrastructure for producing and distributing 2nd generation transportation biofuels in Ghana based on minimizing the costs of collecting crop residue and distributing ethanol from biorefineries. The application-scale and system scale perspectives enable transitions to lower carbon emissions from the transportation sector using sound engineering principles and provide foundations for future work at both the micro- and macro-scale and for integration of the methods.