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A fuel matrix consisting of twelve gasolines was tested in presence of Exhaust Gas Recirculation (EGR). The fuels have different percentages of aromatics (20÷35% vol.), olefins (5÷15% vol.) and oxygen (0÷2% wgt). Four different oxygenated compounds (MTBE, ETBE, TAME, DIPE) were chosen as additives. Tests were carried out on a MPI premixed spark ignition engine at steady operating conditions (2000 rpm, 2 bar BMEP, 13.5% EGR) and stoichiometric air/fuel ratio. Regulated and unregulated pollutants were measured upstream the catalytic converter. Cyclic variation of Indicated Mean Effective Pressure (IMEP) in presence of EGR was also evaluated. The adoption of EGR increases PAH and aldehydes emissions, and decreases benzene emissions of unoxygenated fuels. Conversion efficiencies of CO and of total HC are lowered by EGR. An increase of aromatics content in an unoxygenated fuel leads to higher engine out NOx emission. This effect is reduced if MTBE is added.

Results of an experimental campaign conducted on a multi-hole gasoline injector are used to assess a numerical model for the spray dynamics suitable to be employed for the prediction of a GDI engine pressure cycle. The considered injector generates a spray with a hollow-ellipsoid footprint structure on a plane perpendicular to the spray axis. Spray penetration lengths and cone angles are measured at different injection pressures and total injected masses in an optically accessible vessel containing nitrogen at controlled conditions of temperature and pressure. Injected mass flow rate is measured on a Bosch tube. The numerical simulation is performed within the AVL Fire™ code environment. As a first step, the gasoline is considered as entering a constant volume environment containing nitrogen, in order to reproduce the effected experiments. Measured injection flow rates and cone angles are used as input variables for the model.

A number of Variable Valve Actuators (VVA) has been recently proposed to improve the performances and the part load efficiency of spark ignition engines. Due to their peculiarity, these systems work with different strategies (late or early inlet valve closing, reduced lift etc.). The shape and the timing of the valve lift affect not only the pumping losses, but also air motion inside the cylinder. That influences mixture formation and combustion evolution of Direct Injection Spark Ignition (DISI) engines. The present paper compares the performances of different VVA systems with the aid of a 1D code for the simulation of the inlet and of the exhaust phases, and of a fluid-dynamic 3D code to evaluate mixing phenomena inside the cylinder.

A commercial four stroke spark ignition engine has been tested at steady conditions, with three different compression ratios, namely: 10, 11.5 and 13. Exhaust Gas Recycle (EGR) has been varied in the range 0% - 20 %. Air/fuel ratio has been maintained at stoichiometric by a closed loop control with Exhaust Gas Oxygen sensor feedback. Significant gains on fuel economy and CO emission index have been achieved at medium and high loads by the simultaneous adoption of EGR and high compression ratios. In these conditions the sum of HC and NOx emission indices attains significant reductions at any load. The tests have shown that EGR allows to avoid knock even at wide open throttle and Maximum Brake Torque timing.