# Effect of Performance by Excessive Advanced Fuel Injection Timing on Marine Diesel Engine
## 3 Results  
### Diagnostics and Solutions with Engine Combustion Analysis  
#### 3.1.1 Diagnostics  
Figure 3a represents a compression-pressure diagram obtained by operating the engine at minimum load with the clutch disengaged and the fuel cut off, solely compressing air, to determine the position of TDC. Figure 3b shows the derivative diagram of the compression-pressure diagram in Figure 3a. In this case, the damping effect of the engine damper was negligible, allowing us to determine the position of TDC through this derivative diagram. From the diagram in Figure 3a, where all eight cylinders are overlapped, we could confirm that the target engine was an engine in which combustion occurred at equal intervals between cylinders. Additionally, since the P\({}_{\text{comp}}\) values were almost identical, we could determine that the sealing condition of the cylinders was the same for all cylinders. In Figure 3b, by observing the derivative diagram, we could see that the P\({}_{\text{comp}}\) was positioned 4.5 \({}^{\circ}\)CA after the TDC mark on the flywheel. Since all cylinders exhibited the same TDC error, the loss of angle could be considered as a possible cause. However, loss of angle typically occurs within a range of 1.0 \({}^{\circ}\)CA [5]. Therefore, the TDC error shown in Figure 3b was determined to be primarily caused by errors in the flywheel's TDC mark, rather than by loss-angle error. Figure 3: (**a**) Compression pressure–crank angle diagram at idle running; (**b**) \(dp/d\theta\) diagram of compression pressure at idling running. Figure 4 represents the cylinder pressure and ROHR graphs during fuel running at minimum load in the idling state. In Figure 4a, the cylinder pressure and the ROHR graphs are shown together. In all cylinders, after the common region of premixed combustion, fuel combustion did not occur continuously, and post-combustion caused two instances of P\({}_{\text{max}}\). It can be observed that incomplete combustion occurred due to insufficient air supply at low load conditions. There was a significant difference in P\({}_{\text{max}}\) among the cylinders, with a 10.4 bar difference between No. 2 cylinder and No. 8, with P\({}_{\text{max}}\) values of 42.5 bar and 52.9 bar, respectively. The cause of this difference could be identified from the magnified graph of the ignition timing in Figure 4b, which represents the ROHR graph. The variation in ignition timing among the cylinders resulted in differences in the ignition delay period, leading to variations in P\({}_{\text{max}}\). Furthermore, all cylinders had different positions of P\({}_{\text{max}}\), with a maximum difference of 1.5 \({}^{\circ}\)CA. Figure 5 shows the combustion pressure and ROHR curves for each cylinder at 43% load. Figure 5a illustrates that the ignition occurred before TDC and the P\({}_{\text{max}}\) happened after TDC for all cylinders. There was a difference of 10 bar in P\({}_{\text{max}}\) between the No. 1 cylinder and the No. 3 cylinder. The P\({}_{\text{max}}\) of the No. 1 cylinder was 110 bar, which matched the P\({}_{\text{max}}\) at 90% load that was observed in the sea trial report. Figure 5b presents the ROHR curve, indicating the ignition delay period for each cylinder. Although the design profile of the fuel injection timing for the engine under this study was unknown, considering that typical medium-speed 4-stroke marine engines have an injection timing of approximately BTDC 15 \({}^{\circ}\)CA, the fuel injection timing for the engine in question appeared to be excessively advanced, reaching a maximum of BTDC 21 \({}^{\circ}\)CA. Generally, an advanced injection timing can increase P\({}_{\text{max}}\) by prolonging the ignition delay period and improve engine performance [3,7,8]. However, excessively advanced injection timing can lead to abnormal combustion such as knocking, emphasizing the need for appropriate injection timing and ignition delay [9].