# Effect of Performance by Excessive Advanced Fuel Injection Timing on Marine Diesel Engine
## 3 Results
### Diagnostics and Solutions with Engine Combustion Analysis
#### 3.1.2 Solutions  
The interpretations of the engine's condition based on Figures 3-5 are as follows:  
* The flywheel TDC mark was positioned 4.5 \({}^{\circ}\)CA ahead of the actual TDC. * The fuel injection timing was more advanced than that of a typical 4-stroke medium-speed diesel engine. * Due to excessively advanced fuel injection timing, ignition and P\({}_{\text{max}}\) occurred BTDC. This resulted in increased compression work and the occurrence of reverse torque. The dull noise and vibration observed in the engine are believed to have been caused by these combustion phenomena. Through the Figure 6 analysis, it can be observed that the portion of combustion occurring before TDC in the engine was significantly reduced. In actual engine observations, it was noted that the engine's dull noise and starting failure issues were also eliminated. Based on these findings, it can be concluded that all the anomalies observed in the engine were caused by excessive advancement of fuel injection timing, leading to negative torque. However, there is still room for improvement, in terms of output uniformity between cylinders. Figure 7 represents the pressure and ROHR waveforms after adjusting the fuel injection timing. Despite the experimental conditions on an actual operating ship engine, where the engine operated at the same speed (511 rpm), a slight load difference of approximately 3% occurred due to the cargo-loading condition (ballast vs. laden). However, it was deemed acceptable for comparison purposes. Comparing the fuel injection timing and ignition timing between Figures 5 and 7, it can be observed that the fuel injection timing shifted from 339 \({}^{\circ}\)CA to 343 \({}^{\circ}\)CA to 352 \({}^{\circ}\)CA to 354 \({}^{\circ}\)CA, and the ignition timing shifted from 349 \({}^{\circ}\)CA to 351 \({}^{\circ}\)CA to 356.5 \({}^{\circ}\)CA to 357.5 \({}^{\circ}\)CA after adjusting the fuel injection timing. The ignition timing of the fuel was delayed by approximately 6.5 \({}^{\circ}\)CA via the adjustment of fuel injection timing, and the ignition timing of each cylinder converged within a range of 1 \({}^{\circ}\)CA. P\({}_{\rm max}\) decreased by approximately 15 bar, and the \(\Delta\)P\({}_{\rm max}\) between cylinders also decreased by approximately 2.5 bar. Figure 8 illustrates the pressure-volume (P-V) diagrams before and after the adjustment of fuel injection timing. In this graph, although P\({}_{\rm max}\) decreased due to the reduction in ignition delay period, the P-V area increased due to the prolonged diffusive combustion phase, which is a characteristic of diesel engines. This indicates an increase in the indicated work, as shown in the graph. Table 2 compares the compression, expansion, and indicated work during one cycle in the P-V diagram before and after adjusting the fuel injection timing. The compression work before the fuel injection timing adjustment appeared to be larger than the compression work after the adjustment in all cylinders. A larger compression work resulted in greater losses during the cycle. The expansion work after the fuel injection timing adjustment was larger than the expansion work before the adjustment, indicating an increase in indicated work throughout the overall cycle in all cylinders. In the P-theta diagram, it is observed that the position of P\({}_{\rm max}\) before the fuel injection timing adjustment was located before TDC in all cylinders. P\({}_{\rm max}\) before TDC exerted a force in the opposite direction to the piston's movement during the compression process. As a result, the compression work increased while the expansion work decreased. Figure 6: (a) Cylinder pressure-crank angle diagram at 46% load after injection timing adjustment; (b) ROHR diagram at 46% after injection timing adjustment. Figure 9 represents the explosive force of all cylinders as the turning force of the crankshaft.