Experiments were conducted on a 6-cylinder turbocharged intercooled heavy duty (HD) diesel engine with diesel/methanol compound combustion (DMCC) mode. The baseline engine was equipped with a common rail fuel injection system and had been modified to run under DMCC mode. In DMCC mode, methanol is fumigated into the intake manifold to form lean air/methanol homogeneous mixture, and then ignited by the direct-injected diesel fuel in cylinder. This study is aimed to investigate the effects of injection timing on performance and exhaust emissions of the engine with DMCC mode. Experimental results showed that under DMCC mode both increasing methanol substitution ratio and advancing injection timing could increase the peak cylinder pressure and the maximum heat release rate. The brake specific energy consumption (BSEC) and exhaust temperature of DMCC engine decreased with advancing injection timing. NOX was increased and soot was decreased as the diesel injection timing was advanced. Compared with the diesel fuel mode, the DMCC mode had benefits in reduction of intake air temperature, NOX and soot emissions, while there was an obvious increase in NO2, HC and CO emissions. In addition, the HC and CO emissions of DMCC mode exhibited a decreasing trend according to an advance in the injection timing. (C) 2014 Elsevier Ltd. All rights reserved.