Dimethyl ether (DME) and methanol are thought to be one of the most promising alternative fuels for IC engines. Meanwhile, previous investigations also have pointed out the good prospects for adopting DME and methanol in IC engines. The experiments in this paper were carried out at idle condition to investigate the effect of applying the methanol/DME blended fuel in a SI engine. The engine was modified to be fueled with the mixture of methanol and DME which were injected into the engine intake ports simultaneously. Various DME fractions were selected to investigate the effect of DME addition on engine performance. The experimental results showed that indicated thermal efficiency was increased by 25% and coefficient of cyclic variation in engine speed was decreased by 29.2% at the DME energy fraction of 85.2% in the total fuel. In addition, both flame development and propagation durations were shortened with the increase of DME enrichment level at idle condition. Meanwhile, the largest drop of HC emissions was nearly 50% compared with the original methanol engine at stoichiometric condition. However, CO and NO(x) emissions increase with the addition of DME. (C) 2011 Elsevier Ltd. All rights reserved.