Substantial use of alternative fuels with Diesel and gasoline engines will be in effect in the foreseen regulations both in the US and European markets. Moreover, Diesel engines are under continuous development targeting emissions reduction and increased efficiency. Technological advances applied on internal combustion engines include increased fuel injection pressures, multiple fuel injections strategy and exhaust gas recirculation. However, undesirable effects such as coking, corrosion and fouling of the fuel system are enhanced with increased injection pressures, multiple injections and the use of blends of Diesel/gasoline and alternative fuels. Therefore, quality of Diesel fuel has been brought into debate and, subsequently, increased the demand for fuel additive packages. Diesel fuel additives play a valuable role in reducing potential adverse effects in fuel of lower natural quality or fuel blends. Additionally, it constitutes a method for overcoming the aforementioned difficulties without redesigning of the complete fuel system. At the same time claims for improved combustion efficiency and emissions reduction have been made.The present proposal aims to characterise in a systematic way the effects of selected marketed additives on the operation of Diesel and gasoline engines. Using a combination of experiments and simulations, we propose to identify the following:a. The effect of fuel additive on the internal nozzle flow (characterisation of cavitation), nozzle discharge coefficient and nozzle thermal behaviour due to excess fuel pressurisationb. The effect of fuel additive on spray developmentc. The effect on engine combustion and exhaust emissionsd. The effect on overall thermodynamic efficiency of the engine