Experimental and numerical study of the water injection to improve the fuel economy of a small size turbocharged SI engine

In this work, a promising technique, consisting of a liquid Water Injection (WI) at the intake ports, is investigated to overcome over-fueling and delayed combustions typical of downsized boosted engines. In a first stage, experimental tests are carried out in a spark-ignition twin-cylinder turbocharged engine at a fixed rotational speed and medium-high loads. A spark timing and a water-to-fuel ratio sweep are both specified, to analyze the WI capability in increasing the knock-limited spark advance. In a second stage, the considered engine is schematized in a 1D framework. The model, developed in the GT-Power (TM) environment, includes user defined procedures for the description of combustion and knock phenomena. The validated model is applied to investigate the full potential of water injection in reducing the knock tendency and improving the fuel economy in a wide load range. The numerical results highlight that WI technique involves significant fuel consumption advantages, especially at the medium-high loads. These benefits are limited by the maximum allowable levels for the in-cylinder pressure, while additional advantages are obtained in terms of reduced turbine inlet temperature, turbocharger speed, and boost pressure.