Reliability study of glow plug fixation of heated plastic fuel rail

Cold start systems used on flex fuel engines to assist engine start are equipped with heated plastic fuel rails, which contain glow plugs to heat up injected fuel. The rail assembled on the engine is under cyclic and constant pressure caused by injectors activation and fuel feeding and is considered safety relevant due to risk of fuel leakage. This paper describes application of one comprehensive design for reliability (DfR) method called physics of failure (PoF) to predict product life. The method was applied on a plastic fuel rail design to understand failure mechanism, critical points and to model the stress-strength relationship. As outcome, it was possible to quantitatively determine the cause-effect relationship between design parameters and failure probability and to gain insights into design margins and limits. The predicted model was validated with actual stress tests.