Investigating the effect of increasing specific heat and the influence of charge cooling of water injection in a TGDI engine

Adding water to the intake air of gasoline engines efficiently improves operations and is highly influential to knock occurrence and NOx emissions. These factors largely benefit from the high latent heat of vaporization as well as the high specific heat of water. In this paper, based on a 1.5 L turbocharged gasoline direct injection engine, those impacts were deeply studied by separating the effect of charge cooling from the influence of increasing specific heat. An experimental test was undertaken to validate the effect of water introduction on the basic engine as well as to confirm boundary conditions and basic parameters for numerical analysis which was based on Ricardo WAVE code. Results indicate that the water introduction technique did improve engine output and thermal efficiency. Engine operations however, were primarily influenced by the impact of increasing specific heat. The charge cooling effect merely reduced the intake air temperature and had a minor impact on in-cylinder thermodynamics. Findings show the impact of water introduction on knock occurrence, engine output, thermal efficiency, and reduction in NOx emissions were mainly boosted by enhancing the specific heat of the operating medium and the effect of charge cooling was found to be insignificant