Structural design and CFD modelling of a new type of hydrogen fuel injector for internal combustion engine applications

• Main Author: Overend, Elizabeth
• Published: University of Edinburgh 2004
• Subjects: 629.2
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.660254

A new type of fuel injector, incorporating a steel, annular diaphragm as the open/close device has been designed. This design would avoid sliding contact between components and exhibit low wear when metering hydrogen fuel. Further, it has been shown by simulation that the injector can a designed to withstand cyclic stresses and deliver hydrogen fuel at a rate suitable for direct injection to the cylinder of an IC engine. Investigation of the possibility of incorporating a pump in the injector unit to provide elevated pressure shows that a minimum of 3.4% of the fuel energy supplied would be required to power hydrogen compression. Structural analysis of the clamped diaphragm component shows that bending stress would be at least 236 MPa when sufficient deflection is achieved. Material such as spring steel, with a high yield strength and fatigue endurance limit, would need to be used to avoid failure. CFD analysis of compressible flow models of two commercial injectors shows good agreement with published data, indicating the expected linear relationship of mass flow rate to supply pressure in the super-sonic range. A model of a commercial annular plate injector on which the new design is based indicates mass flow rate up to 50% lower than published data, and the model indicates a discharge coefficient of 22%. This is the result of key differences between actual and modelled injector geometries. Good agreement between results of a CFD model of the diaphragm injector geometry and compressible flow theory is obtained. These results show agreement of the relationship between back pressure and shock wave formation, and sub- and super-sonic mass flow rate-pressure relationship. The model suggests that 66 bar supply pressure would be required to achieve the highest design mass flow rate of 23 g/s, and that the discharge coefficient of the new injector design would be 90% under these conditions.