Dimethyl ether (DME) is thought to be one of the most favorable alternative fuels or additives for internal combustion (IC) engines in the future. Because spark-ignited (SI) ethanol engines have the poor performance at cold start and low operating conditions caused by negative properties of ethanol such as the high latent heat, DME is introduced aiming at improving the engine economical and emissions performance. The experiments were carried out on a modified 4-cylinder gasoline engine under a typical city driving speed of 1400 rpm and an intake manifold absolute pressure (MAP) of 61.5 kPa. In this paper, the effect of DME blending on the engine performance at different excess air ratios and two DME volume fractions of 1% and 2% was experimentally investigated. The engine manifold was modified so that ethanol and DME can be injected and mixed with air simultaneously in the intake ports. A hybrid electronic control unit (HECU) was specially developed to control the injection timings and durations of ethanol and DME, accomplishing specified excess air ratios and DME volume fractions in the intake. The experimental results indicated that, DME addition benefits enhancing the indicated thermal efficiency, which is increased by about 10% at) lambda = 1.25 compared with the original ethanol engine. And the maximum reduction of COVimep is about 50% after DME addition. Besides, the HC emissions from the DME-enriched ethanol engine at the DME volume fraction of 2% are averagely reduced by 45% compared with those from the original ethanol engine. But the NOx emissions slightly increase with the increase of DME volume fraction in the intake. Consequently, DME addition can be considered as a potentially applicable approach for improving the overall performance of SI ethanol engines. (C) 2012 Elsevier Ltd. All rights reserved.