# Effect of Performance by Excessive Advanced Fuel Injection Timing on Marine Diesel Engine
## 4 Discussion  
This study analyzed the combustion pressure measured during the diagnosis and recovery process of abnormal operating conditions in a ship's engine during actual navigation. The abnormal phenomena observed included engine startup failure, dull noise from the combustion chamber during operation, and engine vibration. Ship engines are classified into air running and fuel running, with the latter using compressed air for ignition instead of battery startup. In the measured engine, which experienced a failure during fuel running, it was determined that there was an issue with the fuel injection timing. The analysis of the measured data revealed that the injection timing was excessively advanced, as indicated by the position of P\({}_{\text{max}}\). The difficulty in achieving the designed fuel injection timing for the measured engine posed a limitation in establishing criteria for engine recovery. Additionally, the fuel pump lead value was adjusted as a method of adjusting the injection timing. This method involved adjusting the height of the thrust piece of the roller  
Figure 9: (**a**) Positive and negative turning force during one cycle; (**b** –**i**) individual cylinder turning force curves before and after fuel injection timing adjustment. guide between the fuel pump and camshaft. Therefore, there was a limitation in accurately determining the exact degree of change in crank angle [25]. Thus, in this study, confirmation was made using the pressure-theta diagram and a ROHR diagram. To analyze the engine cycle, a data acquisition device with a very high sampling rate is required. In this study, the cylinder pressure was measured at a crank angle interval of 0.5 degrees, necessitating data collection at a sampling rate of at least 6000 Hz. Despite applying filters to remove noise from data, there were difficulties in accurately determining the fuel injection timing from the ROHR curve, due to a significant amount of noise. Via the physical adjustment of injection timing delay and the ROHR diagram, it was confirmed that the engine's injection timing was excessively advanced prior to adjustment. The start failure was resolved by adjusting the injection timing, but the study had limitations in providing conclusive data to support this. The engine equipped with turbocharging demonstrates proper performance of the turbocharger under the NCR load, as it operates at its full potential. However, at low loads, the diesel engine suffers from insufficient airflow [26]. Typically, the NCR load is set at around 85-90% of the MCR, while the 43% and 46% loads measured in this study represented the low-load range [27]. Since the focus of this study was not on performance improvement at low loads but rather on the impact of excessive fuel injection timing, the data collected at low loads were considered valid. However, to ensure greater confidence in the study results, data from the commercially operating NCR range would be valuable. Due to limitations in applying desired experimental scenarios in actual commercially operated vessels, the inability to collect data at NCR loads was a limitation of this study. Considering the abnormal symptoms of noise and vibration in the engine, presenting the results of noise and vibration measurements would have led to a higher level of research outcomes. While there is disappointment about not having measured data on noise and vibration, the improvement level of vibration can be inferred through the variation of angular velocity data of the crankshaft [28]. Figure 10 presents the angular velocity variation data of the crankshaft before and after the adjustment of fuel injection timing, along with the corresponding fast Fourier transform (FFT) results. Figure 10a shows the angular velocity variation before and after the adjustment within one cycle, while Figure 10b presents the normalized angular velocity variation. Figure 10c represents the FFT result of the angular velocity variation data from Figure 10a.