| Summary: | A fuel injector utilising High Pressure Direct injection technology is being developed by Westport
Innovations Ltd. It is designed to allow heavy-duty diesel engines to run primarily on natural gas
and yet still retain the inherent advantages of diesel engines. The operation of the injector is fairly
complex and the cost of prototyping is high. Fatigue cracks were detected in injector components
subjected to engine cycle testing.
To better understand the stresses in the injector and decrease the stress levels, several finite
element models of the different components are created for analysis. Using submodelling
techniques, the fine details of the design are examined at important sections of the injector.
Alternative design choices are examined by creating alternative submodels with different hole
intersection configurations and comparing the results to the original submodel. The results of this
analysis indicate that more significant changes than altering the hole configuration are necessary
if the stress levels are to be decreased.
The diesel and gas needle components are studied in a separate analysis in which contact
elements are utilised to model the interaction with each other and the injector tip. The sealing
surface at the contact between the components is predicted to be smaller than was previously
assumed. Decreasing the relative angle between the contact surfaces results in an increase in
the sealing surface.
The significance of thermal stresses as a cause of the fatigue failures is shown to be minor. A
transient heat transfer analysis of the injector tip is performed. This predicts very small thermal
variations once steady state had been reached.
The end of the tip is a critical area as the injection holes act as a stress concentration and the
repercussions of failure of this section are great as this section of the injector is exposed to the
engine cylinder. Different design alternatives for this particular section are modelled and
compared to assess the relative merits of each configuration.
Finally, an investigation is conducted into the effect of pressurising the spring bore of the injector.
Under the current conditions of the model, the deformation caused by this pressurisation will be
unacceptable as there will no longer be sufficient clearance for the plungers in the cage and
check block components of the injector. === Applied Science, Faculty of === Mechanical Engineering, Department of === Graduate
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