The possibility of using, in Diesel engines, a liquid fuel derived from waste synthetic polymeric matrices, such as scrap tyres, was evaluated in this paper. The liquid fuel was obtained by a combined thermo-mechanical cracking process carried out at moderate temperatures (300-500 degrees C). Fuel properties of the pyrolytic oil were analyzed with standard methods, showing density, viscosity, calorific value and flash point comparable to those of a commercial automotive Diesel fuel (DF), but with significantly higher sulphur content and a lower cetane number. Also the other pyrolysis products (gas and solid) were analysed in terms of yield and composition in order to individuate their potential re-uses. A preliminary engine investigation was carried out on a 440 cm(3) single-cylinder Diesel engine using two tyre pyrolysis oil (TPO)-Diesel blends: TPO20 (containing 20% TPO and 80% of DF in volume basis) and TPO40. The cytotoxicity and genotoxiticy of the particulate from engine exhaust emissions were evaluated on D7 strain of Saccharomyces cerevisiae yeast cells by in vitro short-term tests. Results were compared with those obtained using the DF only. Engine performance, evaluated at different engine speed and loads, showed that the use of TPO20 not involve significative differences in terms of torque, power, specific fuel consumption and exhaust emissions in respect to those obtained using the DF, while the use of TPO40 leads to a general worsening in engine combustion characteristics. Lubricant oil analysis, made at the end of the tests, showed a certain level of contamination. No meaningful mechanical inconvenience occurred during the engine experimental activity. In vitro assays on particulates showed similar cytotoxic potency and no genotoxic effect for Diesel and TPO/Diesel blend emissions. (C) 2013 Elsevier Ltd. All rights reserved.