Alcohols fuels, principally methanol and ethanol, have the potential to displace a substantial portion of the domestic petroleum consumption in the U. S., used either neat or in blends with petroleum fuels. In order to develop effective policies that encourage economical and environmentally-sustainable use of such fuels, engine technology options must be made available that can achieve these ends. One promising option, being developed by the U.S. EPA's National Vehicle and Fuel Emissions Laboratory, uses low-cost port-fuel-injection, spark-ignition technology with neat alcohol fuels to reach peak brake thermal efficiency levels of over 40%, comparable to state-of-the-art diesel engines. This research has more recently been extended to a full range of blends with gasoline, demonstrating significant efficiency gains using fuel containing as little as 30- 50% alcohol by volume. The engine research program described in this work examines the efficiency benefits of higher compression ratio and reduced intake air throttling, enabled by the high octane rating and high dilution tolerance of alcohol fuels. The research centers on a turbocharged, diesel engine.