Application of commercial CFD to improve gasoline port fuel injector design and targeting

The need to meet ever more stringent emission regulations and the desire to improve fuel economy has led to the significant development of the gasoline spark ignition combustion engine in recent years. One area of development has been mixture preparation, and PH (Port Fuel Injection) has been introduced to increase engine responsiveness whilst meeting emission regulations. Successful PH designs however depend upon good targeting of the fuel spray onto the back of the intake valve. Geometric predictions based on injector axis and spray bone angles have been used in the past, but require development to account for the momentum exchange between the spray and the charge air. Alternatively CFD (Computational Fluid Dynamics) can be used. In this study a validated methodology has been successfully developed using the commercial CFD code Fluent5.5, to simulate the spray behaviour from a multi-hole port fuel injector. The approach taken ignored the primary and secondary atomisation phases, and instead droplets were injected at the injector tip position. The droplets velocity and size were then tuned until the predicted spray profile matched the measurement data at 60rnm and 90mm downstream of the injector tip. Having developed a tuned injector model, CFD simulations assessing the injector targeting performance of the Jaguar AJV8 engine were then undertaken. Based upon these assessments some suggestions to improve the engine's injector targeting performance were made. Before this methodology could be developed, a series' of experiments were necessary to characterise a state of the art port fuel injector. A combination of Planar Mie and PDA laser techniques, were used to measure how the spray behaved under different operating and atmospheric conditions. As well as providing spray boundary and validation data, an in depth understanding of the spray structure was gained for both pulsed and continuous injector operations.