The presented paper introduces a performed study into the possibility of replacing mineral diesel fuel with pure biodiesel fuel or their blends with diesel fuel. The presented work was carried out experimentally and numerically on a heavy-duty bus diesel engine using mineral diesel fuel, neat biodiesel fuel made from rapeseed oil and their 25% (B25), 50% (B50) and 75% (B75) blends. The influence of biodiesel fuel and blends on engine combustion, performance and emission characteristics was studied experimentally on an engine test-bed and numerically using an AVL BOOST simulation program. A new empirical sub-model for determining a combustion model parameters was proposed within a BOOST program. All the model's parameters were determined regarding the properties of the tested fuel and engine speed. The obtained results show a reduction in engine power and torque when increasing the percentage of biodiesel fuel in the fuel blends due to lower calorific value of biodiesel fuel. Higher oxygen content in the biodiesel and blends contributed to a better oxidation process within the combustion chamber, which resulted in a reduction of carbon oxides (CO) and nitrogen oxides (NOx) at three different engine speeds (1360, 1700 and 2000 min(-1)) and full throttle position. Both the experimental and numerical results indicated that neat biodiesel or biodiesel-diesel blends can be used within a heavy-duty diesel engine with modified static fuel delivery angle (injection pump timing) of the mechanically-controlled injection system. (C) 2014 Elsevier Ltd. All rights reserved.