Development of a Compact Intake Porting Design for a 2-Stroke DI Outboard Engine 2012-32-0116
Early implementations of direct injection technology were primarily adaptations of fuel systems to existing loop scavenge carbureted engines that did not leverage the strong interaction between the scavenge flow and fuel distribution in the cylinder. Emissions reduction techniques have been limited to engine calibration strategies using injection timing to minimize lost fuel at the expense of mixture preparation and power. This work focuses on manipulating the scavenging pattern to reduce lost fuel while improving mixture preparation and trapped oxygen.
The project goals were to design an intake porting specifically for a 3.4 liter V6 2-stroke DI outboard engine that meets EPA 3 star NTE emissions regulations while increasing power by 10 percent and increasing fuel economy 10 percent over production baseline. Project constraints on the radial space available for the intake ports limited traditional guidance provided by the port walls and required alternative methods to target the scavenge flow.
The multi-dimensional CFD code KIVA-3V2 was used to simulate and design the intake ports. The model setup is a single cylinder with pressure boundary conditions incorporating an outwardly opening hollow cone fuel injector. CFD results, both integrated and spatially resolved, are evaluated on the basis of scavenging, mixture preparation and lost fuel out the exhaust port.
Correlation of scavenging performance was achieved by comparing delivered oxygen levels calculated from emissions data to simulation results. For mixture preparation, a qualitative correlation was achieved by using experimental metrics including specific fuel consumption and power output sensitivity to injection timing.
Simulation and experimental results are presented for two compact porting designs that strike different balances between lost fuel and mixture preparation. One of these new configurations had a unique scavenge pattern that allowed for substantially increased fuel penetration while maintaining good fuel trapping. This penetration allowed for improved interaction with exhaust plug induced flow and an associated improvement in mixture preparation.