Water Injection Applicability to Gasoline Engines: Thermodynamic Analysis 2019-01-0266

The WLTP and RDE emission cycles are pushing engine technology far forward toward different solutions aimed to reduce specific fuel, consumption and engine out emissions with emphasis on Carbon Dioxide. Among those solutions, the water injection is one of the candidate to accomplish with these emission targets for SI engines together with other technologies (Miller operation, Turbulent jet ignition, advanced turbo-charging solution, etc.). The potential benefit is to operate with stoichiometric mixture over the whole engine map increasing the efficiency. Despite the fact that the water injection has been exploited in the past, the renewal interest in it requires a deep investigation in order to outcome its potential as well as limits in its applications. A literature studied revealed many experimental campaigns have been performed while few researches have deeply investigated the effect of the water injection on air/fuel mixture under engine conditions. The latter are unavoidable in order to properly investigate the concept since experiments just operate like a black box and they might hide some important phenomena. First of all, however, a step backwards is necessary for analyzing in detail the fluid-dynamic characteristics of the water related to the real operating conditions typical of a GDI engine: this is an important step in order to understand the future results by CFD simulations carried on modern GDI engines and also to properly direct technical solutions. In the present paper, the authors highlighted by a thermodynamic point of view the effect of: - In-cylinder pressure and temperature; - Type of injection system (pressure, SMD, etc.) - Water injector location; - Injection timing on the final evaporated mass of water, considering the necessity of both limiting the water consumption and avoiding the dilution of the lubricant. The investigation has been carried out with aid of CFD simulation by using AVL FIRE v.2017 solver.