Ethanol has the potential to improve engine efficiency and reduce harmful emissions when used as fuel in a spark-ignited engine. Ethanol is mostly supplied in a splash-blended form with gasoline or in a pure form; however, this is not an optimal way of using ethanol because the use of ethanol leads to increased brake specific fuel consumption. To fully utilize the merits of ethanol, on-demand control of ethanol and gasoline is required so that the fuel-blending ratio can be altered according to the engine operating conditions. This study investigated the effect of ethanol port fuel injection and gasoline direct injection systems on engine combustion and emission characteristics under full load conditions. The experiment was conducted using two different compression ratios and various ethanol injection timings. Knock occurrence decreased as the ethanol injection timing was held while intake valves were open. Minor reductions in carbon monoxide, total hydrocarbon, and particulate emissions were observed under a compression ratio of 9.5, while the reduction in emissions became significant under a compression ratio of 13.3 as the amount of ethanol injection increased. (C) 2015 Elsevier Ltd. All rights reserved.