The purpose of this study is to investigate the effects of various engine conditions on the combustion, flame temperature and emission characteristics of dimethyl ether (DME) fuel compared with ultra-low sulfur diesel (ULSD) fuel through experimental and numerical analyzes. In order to analyze the temperature distribution, the KIVA-3V code and an optical HSDI diesel engine equipped with a visualization system were employed. The numerical validation was conducted with the experimental results from a DME-fueled compression ignition engine. In addition, measurement of the flame temperature from images captured during the combustion processes was performed using AVL-ThermoVision software. This investigation showed that the combustion pressure and heat release rate attained their peak value at the lowest engine speed condition for DME and ULSD fuels. The characteristics of the flame temperature value and distribution due to the differences in engine speed conditions and fuel properties were clearly revealed. When the engine speed increased, an inhomogeneous and low combustion temperature was observed. Furthermore, the nitrogen oxides (NOx) emissions, which are related to the combustion temperature, decreased as the engine speed increased. (C) 2013 Elsevier Ltd. All rights reserved.