The interest in energy from biomass, in particular for transportation, is related to the need to differentiate the energy sources to improve environment and protect human health. Objective of this study is a comparative evaluation of performance and exhaust emissions of an automotive diesel engine fuelled by mixtures of rapeseed and soybean methyl ester with reference to mineral diesel fuel. The spatial and temporal jet evolutions have been characterized injecting the fuel in a quiescent vessel by a standing alone common rail apparatus at diesel-like gas density conditions. The injection strategies have been chosen as representative of different engine working conditions for several speeds and loads, injecting the fuel in a non-evaporating high-density vessel. Fuel injection rate measurements, spatial and temporal fuel distribution have been carried out processing jet images captured by a CCD camera. Engine tests have been performed on a 4-cylinder DI Diesel engine for automotive applications equipped with a common rail 7-hole nozzle electro-injector system. Engine performance, gas emissions and smoke have been measured at the engine speeds of 1500 and 2500 RPM for different loads. Two different fuel blends, RME50 and SME50, have been tested comparing their performance and emissions with the diesel ones. (C) 2010 Elsevier Ltd. All rights reserved.