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This paper aims to investigate the effects of HE20 hydrous ethanol gasoline (20% hydrous ethanol v/v) on the cycle-to-cycle variation in a spark ignition engine. Comparative experiments were carried out on a port fuel injection engine fueled with HE20, anhydrous ethanol gasoline (E20) and pure gasoline (E0). The engine was run at speeds of 1200 rpm, 1600 rpm, and 2000 rpm and the engine loads were varied from 10 Nm to 50 Nm for each speed, because higher cyclic variation occurs at relatively low engine load. Our experimental results show that the influence of HE20 on cyclic variation depends on the engine working conditions. At low speeds and low loads, the combustion variation of both E20 andHE20 is reduced in contrast to the results with gasoline. However, utilization of HE20 still has higher cycle-to-cycle variation than E20. At 1600 rpm, HE20 performs poorer and its cyclic variation is higher than the other fuels. At 2000 rpm, the addition of hydrous ethanol promotes the combustion process and the cycle-to-cycle variation of HE20 is lower than that of E20 and E0. From the correlation coefficient of combustion phase related parameters conclusions are gained that the variation of first half stage of combustion is affected by the flame development period whereas the after burning also plays an important role in increasing the cyclic variation. [ABSTRACT FROM AUTHOR]