# Research on Data-Driven Performance Assessment and Fault Early Warning of Marine Diesel Engine
## 3 Performance Degradation Trend Analysis and Fault Early Warning of Marine Diesel Main Engines
### Data Processing
#### 3.1.3 Data Preprocessing  
Data preprocessing is one of the critical steps to ensure the accuracy of marine diesel main engine performance evaluation, aiming to eliminate abnormal performance samples. The primary causes of abnormal data include the following: First, sensor malfunctions during data acquisition lead to invalid values such as negative numbers, constant values, or abrupt fluctuations. Second, data packet loss occurs due to communication issues, resulting  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Performance Parameter** & **The Performance of a Marine Diesel Main Engine Reflects** & \\ \hline Speed, Power & & The power performance of the marine diesel main engine \\ Fuel Type, Fuel Flow Rate, SPOC & & The performance of the fuel system \\ Cylinder Exhausent Temperature (Six-cylinder) & & The performance of the combustion system \\ Lubricating Oil Inlet Temperature & & The performance of the lubrication system \\ Scavenge Air Temperature, Scavenge Air Pressure & & The performance of the turbocharging system \\ Jacket Cooling Water Inlet Temperature, Jacket Cooling Water Inlet & & The performance of the cooling system \\ Pressure Jacket Cooling Water Outlet Temperature (Six-cylinder) & & The performance of the cooling system \\ \hline \hline \end{tabular}
\end{table}
Table 2: Performance parameters information.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Performance Parameter** & **Data Type** & **Unit** & **Nullable** & **Lower Limit** & **Upper Limit** \\ \hline Speed & float (8, 3) & RPM & Yes & \(-200\) & \(200\) \\ Power & float (8, 1) & kW & Yes & \(-20,000\) & \(20,000\) \\ Fuel Type & int (11) & 1: HfO, 2: MGO, 3: & Yes & \(\backslash\) & \(\backslash\) \\ Fuel Flow Rate & float (12, 2) & kg/h & Yes & \(\backslash\) & \(\backslash\) \\ Cylinder Exhausent Temperature (Six-cylinder) & float (8, 3) & \({}^{\circ}\)C & Yes & \(0\) & \(600\) \\ Lubricating Oil Inlet Temperature & float (8, 3) & \({}^{\circ}\)C & Yes & \(0\) & \(200\) \\ Jacket Cooling Water Inlet Temperature & float (8, 3) & \({}^{\circ}\)C & Yes & \(0\) & \(200\) \\ Jacket Cooling Water Inlet Pressure & float (8, 3) & MPa & Yes & \(-0.1\) & \(0.6\) \\ Jacket Cooling Water Outlet Temperature & float (8, 3) & \({}^{\circ}\)C & Yes & \(0\) & \(200\) \\ (Six-cylinder) & & float (8, 3) & \({}^{\circ}\)C & Yes & \(0\) & \(200\) \\ Scavenge Air Temperature & float (8, 3) & \({}^{\circ}\)C & Yes & \(0\) & \(200\) \\ Scavenge Air Pressure & float (8, 3) & MPa & Yes & \(0\) & \(0.6\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance parameters store information.  
in parsing errors during data reception. Third, inconsistent sampling frequencies among sensors, causing missing parameters in monitoring data. The main categories of abnormal data are as follows:  
(1) Missing parameters: One or more performance parameters are absent in a sample, preventing the calculation of performance evaluation metrics;  
(2) Parameter anomalies: One or more parameters exhibit abrupt deviations or values far from the mean under current operating conditions (e.g., rotational speed below the minimum stable threshold, abnormally low shaft power, or fuel flow rate below operational limits). These anomalies are caused by sensor failures or data parsing errors and do not reflect the actual performance of the marine diesel main engine.  
Criteria for abnormal performance samples are as follows:  
Any performance parameter in the sample is null.  
Rotational speed falls below the minimum stable threshold (20 RPM).  
Power output is lower than 10 kW.  
Fuel flow rate is less than 0.0001 kg/h.  
Table 4 summarizes the statistical characteristics of the preprocessed dataset. As visualized in Figure 2, the postprocessed data (red curve) effectively eliminates subthreshold rotational speed anomalies (black raw data segments) through this protocol.