Thermodynamic Analysis of Direct Water Injection on Engine Performance for Diesel Engine

Water injection is a effective technology to control combustion temperature and NOx emission, especially direct water injection into the cylinder. In this study, the effects of in-cylinder direct water injection on engine performance and in-cylinder state are investigated by an analysis of engine thermodynamic cycle. A new thermal cycle called two-phase working medium thermal cycle for diesel engine is proposed, which consists of the Mixed cycle and Rankin cycle. Water is used to replace phase-change working medium to study the influence rules between injection parameters and cycle performance. The results indicate that direct water injection reduces in-cylinder temperature, and leads to a decrease of in-cylinder pressure. It has also demonstrated that direct water injection decreases the cycle thermal efficiency. With a water-fuel ratio of 0.4:1 by mass, the cycle thermal efficiency is reduced by 0.42%, and the work output is reduced to 20.5kJ. In addition, compared to the temperature of injected water, the mass of injected water affects engine performance more.