## 4 Case Study: Reliability Analysis of a Diesel Engine
### FMECA-FHA Analysis Results  
Once all system functions were determined, the functional failure of each subsystem could be judged. Firstly, a system-level FMECA was executed to identify the functional failure modes, which could be defined as the failures of main system functions, and to estimate their impacts, causes, and risks. Then, a system-level FHA was performed to identify the impacts of the functional failure modes on safety. Table 7 reports the quantitative evaluation of the FMECA of each subsystem in the diesel engine, which was analyzed by experts as being responsible for diesel engine maintenance. In particular, the input data collection stage was judged in a meeting with relevant experts. The expert group conducted a quantitative evaluation of the FMECA factors of each subsystem. Three experts who had been working in this field for 15, 10, and 5 years were invited and the scoring weights of the  
Figure 11: The corresponding relationships between the product function level and the structure level of diesel engines. three experts were 0.4, 0.3, and 0.3, respectively. The expert group scored the system-level failure modes to determine their priority. As shown in Table 7, the subsystem with the most serious functional failure at the system level was the pressurization and intake and exhaust system. Thus, the failure impacts of the components in that subsystem were further investigated. In the next step, a system-level safety analysis was carried out. The combination of the FHA and RSR in Section 3 was used to score the degree of injury \(v_{1}\) that would be caused to personnel by each failure mode, the economic loss \(v_{2}\) that would be caused by each failure, the maintenance cost \(v_{3}\) that would be caused by failure, and the frequency \(v_{4}\) of the failure according to the expert group. As shown in Table 8, the expert group evaluated the impacts of the system-level failure modes on safety and the ranking results of the risk assessment of each failure mode was obtained at the system level using the FHA evaluation method that was discussed in Section 3. By comparing the analysis results of the FMECA-FHA model in Tables 7 and 9, the severity of the failure modes of each subsystem could be determined. It can be seen that the comprehensive severity of the failure of the control system, as well as those of the supercharger and the intake and exhaust systems, of the diesel engine was the highest. In order to reduce the workload, the RDFTA model of the faults in the control system, as well as those of the pressurization and intake and exhaust systems, was established as the top event. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**System** & **Failure Mode** & **S** & **O** & **D** & **RPN** \\ \hline Pressurization and intake and exhaust system & Compressor failure & 4 & 6 & 3 & 108 \\ Control system & Sensor failure & 6 & 5 & 3 & 90 \\ Fasterner system & Cylinder head failure & 7 & 1 & 7 & 49 \\ Moving parts system & Linkage failure & 5 & 7 & 2 & 70 \\ Fuel supply system & Fuel injection pump failure & 4 & 3 & 6 & 72 \\ Cooling system & Water pump failure & 6 & 2 & 2 & 24 \\ Lubrication system & Filter failure & 4 & 5 & 2 & 40 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The FMECA system-level results. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Failure Mode** & **Personal Injury** & **Economic Loss** & **Maintenance Costs** & **Frequency of Occurrence** \\ \hline Supercharger system fault & 74 & 78 & 84 & 68 \\ Control system failure & 65 & 74 & 75 & 59 \\ Fastener system failure & 40 & 60 & 40 & 42 \\ Moving parts system fault & 42 & 57 & 34 & 44 \\ Fuel supply system failure & 44 & 20 & 57 & 32 \\ Cooling system failure & 47 & 27 & 42 & 36 \\ Lubrication system & 35 & 34 & 29 & 31 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The expert evaluation results of each failure mode.