In-Cylinder Fuel-Air Mixture Investigation by Particle Image Velocimetry in a GDI Engine

Abstract

The present paper aims at providing experimental results on the spray structure and its interaction with the air flow generated by the intake ducts of a commercial light duty gasoline direct injection (GDI) engine head. The investigation was carried out by the Particle Image Velocimetry (PIV) technique to investigate the air flow and fuel droplets velocity evolution within a prototype cylinder with optical accesses. Experiments were carried out at various operating conditions reproducing the mixture preparation for an early injection strategy. The PIV technique was applied in a flow test rig assembled with a blower, which supplied the intake flow rate, connected to the intake manifold of a commercial 4-valve direct injection gasoline engine head modified to lay down an external driving control system for the valves motion. Experiments were taken equipping the engine head with a common rail injection system able to work up to 10 MPa, and a swirled type injector having a nozzle diameter of 0.50 mm and a nominal cone angle of 60°. Tests were taken, on a plane crossing the cylinder and the injector axes, supplying to the prototype cylinder an intake flow rate of 29 m3/h and spraying the gasoline at two injection timings in a range of injection pressure of 6, 8, and 10 MPa. The results provided detailed information on the intake flow field behavior and the evolution of fuel jet within the air flow. The intake flow velocity distribution, acquired at different cam angle during the induction, showed the development of an initial clockwise tumble flow with a tendency to produce two large flow structures: a main counter clockwise vortex and a clockwise ones located at the opposite side of the field of view. Images of the interaction of the fuel with the tumble motion displayed, firstly, a fuel jet shape that traveled not affected by the tumble motion because of its high momentum. Later during the intake, the fuel was strongly distorted by the air motion with the formation of clusters detached from the main jet and spread within the cylinder so allowing to hypothesize that the intake bulk flow may be a crucial parameter to control the fuel penetration and the droplets distribution within the cylinder.