Optimization of Injector Performance on the Combustion Process in the Generator Engine to Support Operational Continuity on Board MT. Semar 77

Abstract

The fuel injector is a critical component of the diesel generator engine, responsible for atomizing fuel into the combustion chamber to achieve complete and efficient combustion. This study investigates the causes of injector performance degradation on the Anqing Daihatsu 6DL-20 diesel generator engines on board MT. Semar 77, an oil tanker, and proposes optimized maintenance strategies to restore and sustain optimal injector function. During the author's sea practice period, two significant incidents were recorded: on February 22, 2022, the exhaust gas temperature of cylinder no. 3 on generator no. 3 rose from the normal range of 350–450°C to 495°C, and the injector fuel pressure had dropped from the specified 300 kg/cm² to 190 kg/cm²; on April 22, 2022, cylinder no. 2 on generator no. 2 exhibited an abnormal exhaust gas temperature of 490°C despite normal fuel pressure readings, indicating a different failure mode. Investigation using a descriptive qualitative approach identified two principal causes. First, the injector failed to atomize fuel uniformly due to spring fatigue causing loss of nozzle needle seating pressure, compounded by inaccurate adjusting screw settings during pressure testing that resulted in improper needle valve lift timing. Second, the nozzle orifices became clogged by carbon deposits from combustion residues and contaminant particles in the fuel that bypassed the filtration system, obstructing fuel passage and converting the intended atomized spray pattern into irregular droplets. The recommended corrective measures include periodic injector pressure testing at 1,500 running-hour intervals with target atomization pressure of 300 kg/cm², systematic spring inspection and replacement, precise adjusting screw calibration procedures, routine nozzle cleaning and replacement according to the Planned Maintenance System (PMS) schedule, and improvement of fuel quality management from bunker reception through purifier and filter maintenance.