In the present work the benefit of a 50 MPa gasoline direct injection system (GDI) in terms of particle number (PN) emissions as well as fuel consumption is shown on a 0.5 l single cylinder research engine in different engine operating conditions.
The investigations show a strong effect of injection timing on combustion duration. As fast combustion can be helpful to reduce fuel consumption, this effect should be investigated more in detail. Subsequent analysis with the method of particle image velocimetry (PIV) at the optical configuration of this engine and three dimensional (3D) computational fluid dynamics (CFD) calculations reveal the influence of injection timing on large scale charge motion (tumble) and the level of turbulent kinetic energy. Especially with delayed injection timing, high combustion velocities can be achieved.
At current series injection pressures, the particle number emissions increase at late injection timing. With up to 50 MPa it is possible to overcome this trade off. Higher injection pressures allow faster combustion by delaying injection timing without rising particle number emissions. Especially at high engine loads the enhanced combustion speed enables an extension of knock limit and the use of optimized spark timing. This results in higher thermal efficiency and reduced fuel consumption.
