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Failure Mode and Effects Analysis of Engine Function and Component Design for Mercury Marine 15hp Outboard and Stihl FS45 Line-Trimmer Engines.
Orbital Engine Company
Report to Environment Australia, November 2002
The purpose of this report is to identify potential sources of system function failure of typical non-automotive engine applications, when used with ethanol-blended E20 fuel. The report also identifies possible sources of component failure, through the use of ethanol-blended E20 fuel, on two engine applications. The selected applications for investigation were a 15hp Outboard marine engine and a Line-trimmer engine.
A technique termed Failure Mode and Effect Analysis (FMEA) was used to perform the functional and design FMEAs detailed in this report. This technique is used throughout industry to enable objective assessment of designs, processes, systems and functions.
A functional FMEA was used to investigate the effect of ethanol-blended E20 fuel on various engine functions (eg. cold start, idle). The FMEA technique was repeated on four engine groups defined by typical applications. The groups were: Aircraft; Utility; Marine and Vehicle engines. The FMEA identified that investigation is required to determine the effects of E20 fuel on numerous engine functions.
The results of the functional FMEA tend to be biased as the data reflects test programs that are in place to evaluate engine operation on E10 and E20 fuels. This is illustrated in Figure 5, where aircraft and vehicle engine groups exhibit the highest risk priority number (RPN) since these engine groups show the highest detection rating (no control in place to detect failure). It must be noted that the RPN for the aircraft group is higher than the vehicle group due to the severity rating shown in Figure 1.
Of particular concern is the use of E10 and E20 fuel for aircraft applications. Due to associated risks of engine failure, the use of E10 and E20 fuel use for this application is not recommended without successful completion of a comprehensive testing program approved by the appropriate aviation authorities.
A design FMEA was used to investigate the effect of ethanol-blended E10 and E20 fuel on the components of a 15hp Outboard marine engine and a Line-trimmer engine. The design FMEA for both engines highlighted the possibility of engine failure through: material compatibility with E10 and E20 fuel; enleanment; and gumming. Material compatibility was found to potentially cause engine damage through corrosion of critical bearing surfaces and external fuel leaks. Enleanment occurs as a result of the E10 and E20 fuel properties and leads to knock and pre-ignition in engines intended for use with regular gasoline. This effect was found to be potentially the main source of base engine component failure. Gumming was highlighted as a potential failure mode, due to the potential risk of fuel residues depositing on critical surfaces or causing blockages within components.
The FMEAs performed have investigated the effect of the use of E10 and E20 fuel on engine function. The analyses have highlighted potential failure modes and mechanisms of failure.
The FMEA technique is a valuable tool to identify potential component/ system design or functional issues, however rigorous verification techniques are required to fully ascertain functionality compliance. The outcome of an FMEA is a list of functions and components with an assigned objective risk priority number (RPN). The RPN is typically used to identify and rank the priority of components and functions that require verification. In conjunction with other inputs such as: warranty data; design studies; competitive analysis; etc, the FMEA is used to generate a verification plan that details the necessary analysis and testing required for validating component and/ or system function.
The potential failure modes as identified by the FMEAs presented in this report, require appropriate testing to establish whether these are in fact issues affecting the function of non-automotive engine applications, when used with ethanol-blended E10 and E20 fuel.