This paper deals with numerical and experimental analysis of the influence of fuel temperature on the injection process. The tested injection system is the mechanically controlled diesel fuel injection M system of a bus diesel engine. The considered fuels are neat biodiesel from rapeseed oil and neat mineral diesel. All injection parameters, obtained with biodiesel, are compared to those of mineral diesel. At first, attention is focused on a single injection assembly (plunger-in-barrel assembly, high pressure tube, and injector). The flow through a single assembly to one cylinder is investigated numerically by using an one-dimensional mathematical model. The injection process is simulated at different operating regimes. On the basis of the numerical results, the influence of fuel temperatures on the injection characteristics, especially on fuelling at some stage of injection, mean injection rate, mean injection pressure, injection delay, and injection timing is investigated in view of harmful emissions reduction. Furthermore, the fuel flow through the whole injection system (all six injection assemblies) to all six cylinders is investigated experimentally with respect to fuel temperature. The pressure drop through the fuel filter and fuelling through each of six injection assemblies are analyzed. (c) 2007 Elsevier Ltd. All rights reserved.