Investigations on Gasoline Spray Propagation Behaviour Characteristic for Multihole Injectors 2014-01-2732
Modern concepts of downsized DI gasoline engines set up high requirements on the injection system to meet the emission targets. The fundamental knowledge and understanding of spray propagation physics are essential for the development of nozzles and injection strategies, due to reduced displacements in combination with the continuing trend of elevated fuel pressures.
A detailed analysis of micro- and macroscopic spray parameters was carried out using a multihole solenoid driven DI injector. The measurements were performed in a continuously scavenged pressure chamber with full optical access. Fuel pressure up to 38MPa and backpressures in a range from 0.03 - 0.2 MPa were varied. Optical investigations were done by Shadowgraphy imaging and Phase Doppler Anemometry.
The combination of micro- and macroscopic spray results are used to discuss the propagation behaviour of gasoline spray. Against conventional opinions it could be demonstrated that gasoline spray is decelerated at the spray front due to air interactions, even under low gas density conditions. Temporal velocity gradients between the spray front and the following main spray cause droplet overtaking processes. These affect shear zone driven recirculation areas located at the spray front.
Reduced penetration values can be achieved by shortening the injection duration. Due to the stopped mass flow and momentum, overtaking processes will stop and penetration stagnates in a constant dimension.