Gasoline and diesel as fuels for internal combustion engines have been commonly available and used for decades. In this study, the performance and emission formation of a direct injection engine fueled with gasoline/diesel blend fuel are investigated numerically. Simulations are conducted on pure diesel and its blend fuels with 10%, 20%, 30% and 40% gasoline at an engine speed of 2800 rpm under 10%, 50% and 100% loads. A reduced PR? (primary reference fuel) mechanism which consists of 45 species and 142 reactions is used in coupled KIVA4-CHEMKIN code for detailed chemistry calculations. In this mechanism, gasoline and diesel are represented by iso-octane and n-heptane, respectively. Comparing the results among different blend conditions, it is found that the ignition delay time is extended by increasing the ratio of gasoline in blend fuels. However, this extended ignition delay has diverse effects on engine performance for different engine loads. At low load, pure diesel condition achieves a better performance; in contrast, a better performance could be realized by blend fuels at medium and high loads, though a slightly higher NOx emission level. (C) 2014 Elsevier Ltd. All rights reserved.