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.Alcohol from a second tank is used to provide increased knock resistance at higher values of torque, enabling high compression ratio, turbocharged operation that provides comparable efficiency and torque to a diesel engine in a smaller size engine. The alcohol can be neat or a high concentration blend. It can also be a hydrous alcohol (alcohol and water). Hydrous alcohol use can reduce the fraction of fuel that must be provided by alcohol by knock suppression through evaporative cooling.We have used computational models to determine minimal alcohol requirements for knock-free operation and to provide illustrative engine parameters for various forms of alcohol and engine operation modes, including upspeeding to reduce alcohol required for knock suppression and use of open-valve port fuel injection to facilitate use of modified SI natural gas or diesel engines as gasoline/alcohol engines.