The characteristics of ethanol autoignition and the associated HCCI performance are examined in this work. The experiments were conducted over wide ranges of engine speed, load and intake boost pressure (Piⁿ) in a single-cylinder HCCI research engine (0.98 liters) with a CR = 14 piston.The data show that pure ethanol is a true single-stage ignition fuel. It does not exhibit low-temperature heat release (LTHR), not even for boosted operation. This makes ethanol uniquely different from conventional distillate fuels and offers several benefits: a) The intake temperature (Tiⁿ) does not have to be adjusted much with changes of engine speed, load and intake boost pressure. b) High Piⁿ can be tolerated without running out of control authority because of an excessively low Tiⁿ requirement.However, by maintaining true single-stage ignition characteristics, ethanol also shows a relatively low temperature-rise rate just prior to its hot ignition point. Therefore, ethanol does not tolerate as much combustion-phasing retard as fuels that exhibit LTHR and/or pronounced intermediate-temperature heat release. Since combustion retard is important for avoiding excessive pressure-rise rates, the distinct single-stage ignition characteristic of ethanol can be considered a drawback when reaching for higher loads. Nonetheless, an IMEPg of 11.3 bar was demonstrated for Piⁿ = 247 kPa.Finally, the latest ethanol chemical-kinetics mechanism from the National University of Ireland - Galway was evaluated against the experimental engine data using a multi-zone model. Overall, the mechanism performs very well over wide ranges of operating conditions.