Nowadays, in order to meet the various emission regulations and improve the atmospheric environment, methanol has been used as a clean fuel to replace conventional fuels for engines. In this study, original emissions under various engine operating conditions are simulated, and the effects of different spark timings, engine speeds, mixture concentrations and combustion chamber shapes for emissions in a SI methanol engine are studied based on LES (large eddy simulation) with detailed chemical kinetics. A methanol reaction mechanism including 84-reactions, 21-species is used to simulate the methanol combustion. The results showed that carbon monoxide (CO) emission could be decreased by retarding ignition timing or increasing engine compression ratio. The formaldehyde (CH2O) had two effects, which were production and consumption. The produced formaldehyde was consumed quickly in the later stages of the combustion process, so the residual formaldehyde was very little after combustion. With the increase of equivalence ratio, the carbon monoxide emission was gradually increased, when the equivalence ratio was less than 0.9, the produced carbon monoxide was gradually decreased, and almost approached zero in lean conditions. It was difficult to improve the carbon monoxide emission for the present SI (spark ignition) methanol engine by optimizing the combustion chamber shape. (C) 2015 Elsevier Ltd. All rights reserved.