Effects and Models of Water Injection in an SI Engine

Abstract: Downsizing and turbocharging is a popular combination nowadays in cars inorder to decrease the fuel consumption. However, the boost pressure increasesthe risk of engine knock, limiting the engine in high-load operating points. Inthe current engines, fuel is used to cool the engine in these operating points,leading to a higher fuel consumption. Water injection is an effective method tomitigate knock and enable a more aggressive ignition. It enables the engine toproduce more power and cools the exhaust, thereby protecting the turbochargerand the catalyst from wear. In this thesis, the effects of injecting water in anengine is investigated and a further development of a cylinder pressure model,with a model that takes the water into account, is presented and validated. Themodel can be used to estimate the cylinder pressure in several operating points.