Water injection in highly boosted gasoline direct injection (GDI) engines has become an attractive area over the last few years as a way of increasing efficiency, enhancing performance and reducing emissions. The technology and its effects are not new, but current gasoline engine trends for passenger vehicles have several motivations for adopting this technology today. Water injection enables higher compression ratios, optimal spark timing and elimination of fuel enrichment at high load, and possibly replacement of EGR. Physically, water reduces charge temperature by evaporation, dilutes combustion, and varies the specific heat ratio of the working fluid, with complex effects.Several of these mutually intertwined aspects are investigated in this paper through computational fluid dynamics (CFD) simulations, focusing on a turbo-charged GDI engine with port water injection (PWI). Different strategies for water injection timing, pressure and spray targeting are investigated. Two combustion modeling approaches are used and compared, the perfectly stirred reactor model with reduced chemical kinetics for a TPRF surrogate, and the G-equation turbulent combustion model. Combustion rate results are validated against available experimental engine data, in regular and knocking conditions. Multi-cycle simulations are required because of the wall film dynamics, and therefore have been performed to assess the effect of water injection strategies. The results of the study are an assessment of the optimal injection parameters, in terms of injector location, injection timing and primary atomization quality, for achieving the maximum effectiveness of water injection. Knock occurrences are in very good agreement with the experimental data and its suppression is demonstrated through the injection of water at a ratio of 30% to the fuel mass.

In the present study, a commercial high pressure, common rail injection system for automotive DI diesel engines was fed with a conventional diesel fuel, a bio-derived fuel and a blend of them. The comparison of spray characteristics was carried out in terms of tip penetration and cone angles; the fuel spray, generated by rail pressures ranging from 60 MPa to 120 MPa, developed in an atmospheric chamber. The experimental set-up is based on a laser sheet technique. The radiation scattered by the spray, generated by a Nd-Yag pulsed laser, is collected by a CCD camera and fed to a frame grabber. A suitably set-up automatic image analysis process allows not only to determine the spray average development in terms of its geometric characteristics, but also to analyse in detail its internal structure. In particular, a suitable elaboration allowed the evaluation of the probability of presence in space of spray liquid fractions.

In the present paper, an analysis of non-evaporating, transient Diesel sprays generated by an automotive common-rail, electronic controlled injection system is described. A standard Diesel fuel and a pure Biodiesel were used for the tests, with sprays evolving in a pressurized test chamber and generated by both cylindrical and conical hole nozzles. The spray analysis is performed mainly by means of a laser sheet technique in order to obtain global spray data suitable for tuning direct injection systems to such fuels and for numerical codes validation. A dispersion analysis among different jets was also performed, along with the injection rate measurement. A PDA system was also used to characterize the behavior of the two fuels with the prototype injector nozzles at ambient conditions.

In order to evaluate the potentialities of bioderived diesel fuels, the effect of fueling a 1.9 l displacement HSDI automotive Diesel engine with biodiesel and fossil/biodiesel blend on its emission and combustion characteristics has been investigated. The fuels tested were a typical European diesel, a 50% biodiesel blend in the reference diesel, and a 100% biodiesel, obtained by mixing rape seed methyl ester (RME) and recycled cooking oil (CME). Steady state tests were performed at two different engine speeds (2500 and 4000 rpm), and for a wide range of loads, in order to evaluate the behavior of the fuels under a large number of operating conditions. Engine performance and exhaust emissions were analyzed, along with the combustion process in terms of heat release analysis. Experimental evidences showed appreciably lower CO and HC specific emissions and a substantial increase in NOx levels. A significant reduction of smoke emissions was also obtained.