In engine combustion studies of bioethanol blended diesel fuels, biodiesel is a very important blending fuel for preventing phase separation between diesel and bioethanol. The purpose of this study is to investigate the impact of biodiesel in bioethanol blended diesel fuel on ignition delay, premixed combustion phasing, engine performance and exhaust emissions characteristics. In this work, the fuel properties of diesel-bioethanol blends were measured and engine tests were conducted using a single cylinder diesel engine. Based on the experimental results, we found that increasing the biodiesel blending ratio recovered the reduced fuel density and cetane number of bioethanol blended diesel fuel, while the kinematic viscosity and surface tension both increased. In addition, the lower heating value (LHV) slightly decreased when biodiesel fuel was added. By increasing the blending ratio of biodiesel fuel, the ignition delay and the premixed combustion phasing advanced, and the IMEP decreased. However, the premixed combustion duration in all tested blended fuels showed almost similar values, regardless of the biodiesel contents. Biodiesel blending decreased the EI-HC emission in wide engine operating regions. In addition, for the premixed combustion phasing and ignition delay, the increase of biodiesel fuel influenced the decrease of EI-HC emission. In the case of EI-CO and EI-soot emissions at advanced injection timings (around 30 degrees BTDC), when the combustion occurred in the squish area of the combustion chamber, the biodiesel blending impact was clear. The increase of biodiesel fuel reduced EI-CO and EI-soot emissions. In addition, the increase of biodiesel fuel slightly reduced the EI-NOx emission. (C) 2012 Elsevier Ltd. All rights reserved.