Combustion Chemistry and Physics of Ethanol Blends to Inform Biofuel Policy

Abstract

This dissertation provides new fundamental and quantitative understanding of the combustion chemistry and physics of ethanol and ethanol blends. The results provide a means to inform strategic energy policy-making in the transportation sector. Scientifically informed vehicle regulation can drive the development of technologies that optimize fuel performance and minimize pollutant emissions when using ethanol to displace gasoline.

In this work, two experimental facilities were used to study the global reactivity and detailed ignition chemistry of ethanol, iso-octane and ethanol/iso-octane blends at conditions relevant to advanced engine strategies. Rapid compression facility (RCF) studies were used to quantify global reactivity in terms of ignition delay times and to provide new data on the reaction pathways of pollutant species like aldehydes and soot precursors. The RCF ignition study of ethanol/iso-octane blends demonstrated their reactivity tends to increase with the carbon content in the blend within the limits defined by pure ethanol and pure iso-octane across the range of temperatures studied. Furthermore, the reaction pathways of each fuel develop independently with no significant fuel-to-fuel interactions, but with a shared radical pool. At the same conditions of the RCF studies, ignition quality tester (IQT) studies of ethanol/iso-octane blends considered the effects of spray injection physics, stratification and mixing effects on the fuel blend reactivity. The results showed that although thermal-fluid effects reduced the overall reactivity for all the blends studied, the chemistry effects dominate the temperature dependence for all blends and conditions studied.

The results of these studies represent vital data for developing, validating and verifying the combustion chemistry of detailed and reduced chemical kinetic models for ethanol blends, which are used to predict global reactivity and pollutant formation in fundamental and applied combustion systems. The quantitative understanding of the chemistry behind the knock resistance attributes and pollutant formation pathways of ethanol and ethanol blends can allow regulatory agencies to set more ambitious and simultaneously more realistic efficiency and emission standards for integrating ethanol into the transportation infrastructure.