Combustion Noise Investigation on a Turbocharged Spray Guided Gasoline Direct Injection I4-Engine 2005-01-2527
Downsizing of Gasoline Direct Injection engines is a way to reduce greenhouse emissions. A downsized engine will have a much higher specific power density, caused by a significant higher brake mean effective pressure (BMEP). This higher BMEP can be enabled by a turbocharger in combination with gasoline direct injection. In addition, good efficiency is accompanied by fast combustion, i.e. a fast heat release rate. All these factors can lead to an increased level of combustion noise excitation, which means in turn a higher level of radiated noise. Thus a study on impact factors on the combustion noise excitation was carried out on a small I4-gasoline engine, having spray-guided direct injection, combined with a turbocharger. It was found that high intake tumble levels, which e.g. are caused by the intake port geometry or different actuation strategies of the swirl control device, can lead to an increased level of noise and roughness. The level of noise can be controlled by varying the spark angle. In addition, the impact of different fuel qualities were taken into account when comparing 95RON versus 98RON. When using the necessary different turbo charging control strategies for the different fuel qualities, a trade off in NVH, not only for the combustion excitation, can be observed, too.