1997-10-01

Interaction of Airflow and Injected Fuel Spray Inside the Intake Port of a Six Cylinder Four Valve SI Engine 972984

Measurements of crank angle resolved air velocity and fuel droplet velocity inside the intake port of a six cylinder four valve production engine were performed using two component Laser Doppler Velocimetry (LDV). Prior to the engine measurements the fuel injector was characterized by determining time resolved droplet sizes and velocities with Phase Doppler Velocimetry (PDV) at an injector test rig with complete optical access.
PDV results indicate that during spray penetration into quiescent air at atmospheric pressure (test rig conditions) large droplets move at the tip of the spray while small droplets due to their low force of inertia are slowed down by aerodynamic pressure and pile up at the end of the spray. Mean values of the droplet diameter rise with the distance from the injector because the smallest droplets do not reach the downstream measurement locations.
Engine measurements show the behaviour of the injected fuel spray in a highly transient airflow inside the intake port. Under part load conditions the spray is affected by velocity waves running through intake port and manifold. Fuel droplets remaining in the air are accelerated and slowed down through the wave motion which is induced by the pressure differential between cylinder and intake port at intake valve opening. Finally, an estimation of the maximum relative velocity between droplets and air shows that secondary atomization of droplets due to aerodynamic pressure inside the intake port can support mixture formation at high engine speed, high engine load and open valve injection into maximum air velocity.

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