There is an increasing concern about the air pollution due to SOx [3][4], NOx [2], and CO₂ emissions [5]. The International Maritime Organization (IMO) has been aggressively legislating and managing these concerns, as detailed in many research pa-pers [1][6]. Specifically, for marine diesel engines, methods to minimize the emission of these air pollutants include applying an Exhaust Gas Cleaning System (EGCS) or using low-sulfur fuel to reduce SOx emissions [9], using Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR) to reduce NOx and CO2 emissions, and maximize performance efficiency through Energy Saving Devices (ESD), Engine Power Limitation (EPL), and alternative fuel usage to comply with the Carbon Intensity Index (CII). Several studies are actively investigating these topics [7][8][10].

Although there is significant interest in the development of ma-rine diesel engines to minimize air pollution, there is a lack of case studies related to accidents in this context. Most accident prevention diagnostics and operational performance analyses have been conducted through land-based test beds or simulations [13][14][16][17].

This study aims to provide a detailed analysis of an actual inci-dent of incomplete combustion that led to a blackout on a Very Large Crude Carrier (VLCC). This analysis aims to identify the root causes of this incident, evaluate the effectiveness of existing maintenance practices, and propose specific recommendations for preventing similar occurrences in the future. The importance of stable power supply for ships, which is a crucial factor, has been studied in many papers [11][12][15].

This thesis is organized into five main chapters. Chapter 1 in-troduces the background and motivation for this study, outlining the regulatory context and the need for more case studies on ma-rine diesel engine failures. Chapter 2 provides a detailed descrip-tion of the case study, including the specifics of the vessel, black-out incidents, and immediate actions taken by the crew. Chapter 3 delves into the analysis of accident causes, focusing on the lubri-cating oil (LO) system and evidence of incomplete combustion. Chapter 4 presents an experimental analysis conducted to validate the findings and better understand the dynamics of the incident. Finally, Chapter 5 concludes the study with key findings, rec-ommendations for engine designers and operators, and sugges-tions for future research.

This case study focuses on a VLCC constructed in a promi-nent domestic shipyard. This vessel, with the capacity to transport millions of barrels of crude oil, was designed to operate on long-haul routes between the Far East and Middle East. The ship was ten years old at the time of the incident, a period during which many of its critical systems, including the propulsion and power generation systems, began to show signs of wear and aging.

The vessel was equipped with three diesel generator sets, each rated at 1, 277 kW. These generators provide essential electrical power for ship operations such as navigation and communication as well as for cargo handling systems. Given the size and com-plexity of the vessel, the reliability of these generators is of para-mount importance, particularly during critical phases of naviga-tion, such as transiting narrow straits or operating in congested waters.

The blackout incident occurred when the VLCC was near the entrance of the Singapore Strait, which is one of the busiest and most strategically important maritime chokepoints in the world. The vessel was then operating with only one of its three online generators, Generator No. 2. This operational configuration, while not unusual, placed significant demands on the active gen-erator, particularly in terms of maintaining stable power output under fluctuating loads. The circumstances surrounding the blackout incident on this vessel are listed in Table 1.

At approximately 01:52 AM, a sudden steering maneuver was executed to avoid a potential collision with another vessel. This maneuver, combined with the operation of the air compressor, introduced significant load fluctuations in Generator No. 2. Sub-sequently, Generator No.2 tripped, resulting in a complete black-out onboard. The loss of electrical power led to the immediate shutdown of the main engine, causing the vessel to lose its ma-neuverability. In the congested waters of the Singapore Strait, this poses a serious risk of grounding or collision.

Fortunately, within approximately 10 s, Generator No. 1, which had been on standby, automatically started and was recon-nected to the main power supply. This swift response restored power to the ship and prevented a major maritime disaster.

In the immediate aftermath of the incident, the ship crew con-ducted a rapid assessment to determine the cause of blackouts. The initial findings suggested that the trip of Generator No. 2 was due to a sudden drop in the LO pressure. The Alarm Moni-toring System (AMS) data indicated that the LO pressure had begun to decrease approximately 25 s before the generator tripped, eventually falling to a critical threshold of 3.0 bar, at which point the generator safety systems automatically shut down to prevent damage.

The crew's initial actions focused on restoring the normal op-erating conditions and ensuring the continued safety of the ves-sel. Generator No. 2 was shut down for further inspection, and the ship continued its voyage using the two remaining generators. However, the incident raised significant concerns about the relia-bility of the ship's power generation system, particularly in light of similar incidents involving Generator No. 2.

A detailed review of the ship’s Planned Maintenance System (PMS) revealed a troubling pattern of incidents involving Gener-ator No. 2 over the past year, all of which were associated with a decrease in the LO pressure. Notably, these incidents occurred three times within one year, each time resulting in a blackout similar to that investigated in this study, as shown in Table 2.

Each of these incidents was addressed by the ship's engineer-ing team through various maintenance activities such as replacing pressure sensors and flushing LO lines. After these interventions, the LO pressure was consistently recorded at 4.5 bar, which is considered satisfactory. However, this pressure level represents a 0.5 bar discrepancy from the manufacturer’s recommended standard (5.0 bar), a critical detail that has not been fully ad-dressed or understood in previous incident reports.

The analysis of the AMS data, illustrated in Figure 1: AMS Trend of No.1 & No.2 G/E LO Pressure, provides critical in-sights into the events leading up to the blackout incident. This section discusses the specific factors that contributed to the pres-sure decline and subsequent generator shutdown.

Figure 1: 
AMS Trend of Generator No. 1 & 2 Engine Lubricating oil (G/E LO) Pressure

Figure 1 displays the time-series data of the LO pressure for Generator No. 1 and 2. At the outset, the LO pressure for Gener-ator No. 2 was maintained at 4.5 bar, which was slightly below the manufacturer’s recommended pressure of 5.0 bar, and was considered stable by the crew based on historical operational data.

The LO system in a marine diesel engine is essential for ensur-ing the proper operation and longevity of the engine moving parts. The system provides continuous lubrication, reduces fric-tion, cools the engine components, and removes contaminants that can cause wear or damage. Maintaining an appropriate LO pressure is crucial for engine performance and safety.

Figure 2 illustrates the components and flow of the LO system within the generator engine. The LO pump, relief valve, pressure-regulating valve, and various filters are the key components that are critical for maintaining the correct pressure and ensuring that the engine operates smoothly.

Figure 2: 
G/E LO System P&I Diagram

A comprehensive inspection of the system was conducted to understand the root cause of the pressure drop in the LO that led to the blackout. This inspection involved disassembling and ex-amining each component of the LO system as outlined in Table 3.

3.2.1. LO Pump Relief Valve

The "LO Pump Relief Valve" is designed to maintain the dis-charge pressure from the LO pump at a constant level, typically set to 5 bar as per the manufacturer’s specifications. However, during inspection, it was discovered that this valve had accumu-lated a significant amount of carbon sludge. Figure 3 provides a visual evidence of the condition of the relief valve before and after maintenance.

Figure 3: 
G/E LO Pump Relief Valve

In the "Before Maintenance" state, the valve showed heavy carbon deposits that had hardened over time, leading to the loss of elasticity in the internal spring. This buildup compromised the valve’s ability to maintain the correct pressure, contributing di-rectly to the pressure drop observed in Generator No. 2.

Ship engineers had already recognized chronic issues related to incomplete combustion in the vessel generators (No. 1–3) based on their operational characteristics and the findings from a piston overhaul conducted on Generator No. 2 six months before the blackout incident. The observations are detailed below.

1. Operational Characteristics of the Generators

• • Abnormal Exhaust Gas Temperatures: Under normal oper-ating conditions, the exhaust gas temperature at the inlet of the turbocharger should be within the range of 450–550 °C. However, it was frequently observed that this tem-perature exceeded the acceptable limit, often rising above 580 °C. This abnormal increase in temperature was occa-sionally accompanied by a surging phenomenon, indicating instability in the combustion process.
• • Carbon Deposition on Turbocharger Components: To ad-dress these issues, engineers routinely disassembled the turbocharger to clean significant carbon deposits found on the exhaust side of the turbine rotor and nozzle ring. After reassembling the cleaned components, the exhaust gas tem-perature temporarily returned to normal. However, this is a short-lived solution, as an abnormal temperature increase would reoccur after approximately 1, 000–1, 500 h of opera-tion.
• • Visual Evidence: Figure 4 illustrates the condition of the turbine rotor and nozzle ring before and after maintenance, highlighting the extent of carbon deposition due to incom-plete combustion.

Figure 4: 
G/E Turbocharger

2. Generator No. 2 Overhaul Report

• • Carbon Clogging in Piston Components: During overhaul of Generator No. 2, it was discovered that the grooves of the piston and oil scraper rings were clogged with carbon deposits. These deposits blocked the drain holes, signifi-cantly impairing the functionality of these components.
• • Replacement of Components: As a corrective measure, all affected piston rings and oil scraper rings were replaced. In addition, the upper section of the cylinder liner, particularly the explosion area, exhibited a high wear rate.
• • Improvement in Operational Performance: Following the overhaul, a significant improvement in generator perfor-mance was observed. Daily sump oil consumption de-creased from approximately 60 L to a normal level of ap-proximately 10 L.
• • Visual Evidence: Figure 5 shows the condition of the pis-ton ring grooves before and after the overhaul, emphasizing the effect of carbon buildup on engine performance.

Figure 5: 
G/E Piston

Despite these maintenance efforts, the issue of incomplete combustion persisted, leading to repeated carbon deposition and associated mechanical problems. Ship engineers have been work-ing closely with engine manufacturers to find a definitive solu-tion; however, a clear resolution has yet to be achieved. The chronic nature of these combustion issues suggests that there may be underlying design or operational factors contributing to the persistent incomplete combustion and its resulting effects on engine performance.

The presence of carbon sludge in the LO pump relief valve and other system components has raised serious concerns regarding the source and impact of these contaminants. The carbon deposits were traced back to the incomplete combustion within the engine cylinders, where soot and other carbonaceous materials were produced. These materials entered the L.O. system and gradually accumulated in areas with slower oil flow, such as within the relief valve.

Incomplete combustion contributes significantly to the me-chanical wear of critical engine components, particularly cylindri-cal liners and piston rings. The following details elucidate the process that leads to the degradation of these components and their subsequent consequences.

Incomplete combustion was identified as the root cause of car-bon build-up in the LO system and increased mechanical wear on the cylinder liner and piston rings. Several factors contribute to this issue.

• • Aging Engine Components: The engine piston and scraper rings, which were designed to seal the combustion chamber and prevent blow-by, were worn out. This allowed the com-bustion gases to enter the LO system, leading to contamina-tion.
• • Suboptimal Fuel–Air Mixture: Variations in the fuel–air mixture, possibly owing to inconsistencies in the fuel injec-tion system or changes in the engine load, contributed to the incomplete combustion, resulting in the production of soot and other carbonaceous materials.

The resulting blow-by not only contaminated the LO system but also increased the mechanical wear on the engine compo-nents, setting off a vicious cycle of degradation that ultimately led to the failure of the generator.

The inspection and analysis of the LO system components, as demonstrated in Figures 3, 4, and 5, clearly indicate that the pri-mary cause of the blackout incident was the failure of the LO system to maintain adequate pressure owing to carbon sludge accumulation. This failure was exacerbated by the incomplete combustion within the engine, which introduced contaminants into the LO system, increased the mechanical wear on the cylin-der liner and piston rings, and led to exhaust gas blowing into the sump oil tank.

The analysis highlights the importance of maintaining the LO system according to the manufacturer’s specifications, and the need for more frequent and thorough inspection of key compo-nents, particularly in older engines that are more susceptible to such issues. Regular maintenance is crucial to prevent the buildup of carbon deposits and ensure the long-term reliability and safety of marine diesel engines.

To validate the findings from the inspection and better under-stand the dynamics of the incident, a series of controlled experi-ments were conducted using Generator No. 2. The experiments were designed to replicate the conditions leading up to a blackout and to measure key parameters such as the LO pressure, cylinder explosion pressure, and sump-tank pressure under varying loads.

The generator was operated at three load levels: 25, 50, and 75% of its rated capacity. These load levels were selected to simulate the typical operating conditions of a generator during normal shipboard operation. Each load level was maintained for a specific period, allowing sufficient time for the system to stabilize and facilitate accurate measurements.

Figure 6 shows the experimental setup and load conditions used during the tests. The generator load was increased incre-mentally, as detailed in Table 4 (No. 2 G/E load test phase).

Figure 6: 
No. 2 G/E Load Test

The experimental procedure involved the following steps:

• 1. Preparation: Before starting the experiments, the generator was thoroughly inspected and any remaining carbon deposits were removed from the LO system. Fresh LO was added, and all sensors and measurement devices were calibrated.
• 2. Load Testing: The generator was initially started at no load and then gradually increased to 25% of its rated capacity. The generator was operated at this load for 60 min, during which the LO, cylinder explosion, and sump tank pressures were continuously monitored and recorded.
• 3. Incremental Load Increase: After the initial load test, the generator load was increased to 50% and then to 75%, with similar monitoring and recording at each load level.
• 4. Data Collection and Analysis: The data collected during the load tests were analyzed to identify any trends or anomalies in the system performance. Particular attention was paid to changes in the LO and cylinder explosion pressures, which are key indicators of incomplete combustion and potential mechanical failure.

The results of the experiments confirmed the findings of the initial inspection. At all load levels, the LO pressure stabilized at 5.0 bar, indicating that the cleaning and maintenance procedures restored the system to its proper operating conditions. However, the cylinder explosion pressure was consistently lower than the manufacturer's design specification by approximately 3–5%, suggesting that incomplete combustion still occurred to some extent.

Table 5 summarizes the key parameters measured during the load tests.

The sump tank pressure remains positive throughout the tests, further indicating the presence of blow-by gases in the crankcase. This finding is consistent with earlier observations of worn pis-ton and scraper rings, which allowed combustion gases to escape into the LO system.

The experimental findings reinforced the conclusion that in-complete combustion was the primary cause of blackouts. The persistent presence of blow-by gases in the LO system, even after maintenance, suggests that the engine components were significantly worn and required extensive repairs or replace-ments.

Figure 6 illustrates the process by which incomplete combus-tion leads to carbon build-up within the engine. This carbon dep-osition accelerates the wear of critical components, such as piston rings and cylinder liners, leading to blow-by and subsequent contamination of LO.

Figure 6: 
Illustration of the mechanical failure due to incomplete combustion

The lower-than-expected cylinder explosion pressure indicated that the engine did not operate at peak efficiency, likely owing to a suboptimal fuel-air mixture or other factors affecting the com-bustion process. This reduced efficiency not only increases the risk of mechanical failure but also contributes to higher fuel con-sumption and emissions, further underscoring the importance of addressing incomplete combustion in marine diesel engines.

The positive sump pressure trend observed during the tests al-so suggests that the blow-by gases contributed to the contamina-tion of the LO, which in turn affected the viscosity of the oil and its ability to maintain proper lubrication and cooling of the engine components.

This study conducted an in-depth analysis of a blackout inci-dent on a VLCC caused by a mechanical failure in one of its generator engines. Their investigation revealed that the root cause was incomplete combustion, which led to carbon deposition in the engine. These carbon deposits significantly accelerate the wear of critical components such as piston rings and cylinder liners, resulting in blow-by gases contaminating the LO system.

The experimental analysis confirmed that despite maintenance efforts, the generator continued to exhibit lower-than-expected cylinder explosion pressures and positive sump-tank pressures, indicating ongoing incomplete combustion and mechanical wear. The following key findings were identified:

• 1. Incomplete Combustion: The primary cause of mechanical failure is incomplete combustion, which results in the for-mation of carbon deposits in the engine. These deposits con-tribute to the accelerated wear of critical engine components, reduced engine efficiency, and increased likelihood of me-chanical failure.
• 2. Mechanical Wear: Significant wear on the piston rings and cylinder liners compromised the sealing of the combustion chamber, allowing exhaust gases (blow-by) to enter the crankcase. This blow-by-contaminated LO degrades the qual-ity and exacerbates engine wear.
• 3. Lubricating Oil Contamination: The presence of blow-by gases and combustion residues in the LO reduces its viscosi-ty and ability to lubricate effectively, creating a cycle of in-creasing mechanical wear and declining engine performance.
• 4. Impact on Engine Performance: The experimental tests showed that, while the LO pressure was maintained, the gen-erator engine suffered from reduced cylinder explosion pres-sure and increased sump pressure, indicating suboptimal op-erating conditions that increased the risk of further mechani-cal failure.

Based on the findings, several recommendations are proposed for engine designers:

• 1. Enhanced Combustion Efficiency: Engine designs should incorporate advanced technologies that optimize fuel–air mix-tures and ensure complete combustion. This may include pre-cision fuel injectors, variable timing mechanisms, and real-time monitoring systems that adjust the combustion parame-ters based on the operating conditions.
• 2. Improved Material Durability: Considering the observed wear on piston rings and cylinder liners, it is recommended that these components be made from more wear-resistant ma-terials or coatings to extend their operational life and reduce maintenance frequency.
• 3. Advanced Lubrication Systems: The development of ad-vanced lubricating systems with enhanced filtration capabili-ties and the use of synthetic or specialized lubricants that re-sist contamination and degradation from blow-by gases are recommended to maintain oil quality over extended periods.

Engine operators should adopt the following maintenance practices to ensure optimal performance and mitigate the risk of incidents:

• 1. Lubricating Oil Renewal Cycle: While manufacturer’s manual recommends a LO renewal cycle of 2, 000 h, it is ad-visable to adjust this interval based on regular laboratory oil analyses conducted every 3–6 months. This approach allows operators to extend or shorten the renewal cycle based on the oil conditions and contamination levels.
• 2. Piston Overhaul Interval: The recommended overhaul interval of 16, 000 h should be initially reduced to 8, 000 h based on the observed wear. Further extensions may be con-sidered based on engine performance and condition assess-ments during shortened intervals.
• 3. Air Supply System Maintenance: To ensure stable scav-enging of air pressure according to the engine load, it is rec-ommended that scavenging air filters be replaced weekly, air coolers undergo annual chemical cleaning, and turbochargers be cleaned with water during operation, according to the manufacturer’s guidelines.
• 4. Performance Monitoring and Diagnostics: Although retro-fitting existing engines with advanced sensors for real-time monitoring may be impractical, operators should prioritize these features when acquiring new engines. For existing en-gines, regular manual inspections and performance tests should be conducted to detect the early signs of wear and de-terioration.

The shift towards using liquefied natural gas (LNG) and lique-fied petroleum gas (LPG) as alternative fuels in marine diesel engines is driven by the need to comply with stringent NOx, SOx, and CO₂ emission regulations [19]. However, this transi-tion introduces new challenges in achieving complete combus-tion, particularly in engines that were not originally designed for dual-fuel operation.

Incomplete combustion in dual-fuel engines can lead to un-burnt gases entering the crankcase, thereby increasing the risk of explosions [21]. Therefore, the development of advanced com-bustion control systems is essential to ensure safe and efficient operation of these engines. In addition, the variability in retrofit-ting costs based on engine type, output, and ship design high-lights the complexity and financial implications of such modifica-tions.

The integration of systems such as the EGCS, SCR, and EGR in response to emission regulations has brought about various mechanical challenges. Examples include the backflow of wash-water in the EGCS, which leads to pipe corrosion, and the mal-function of exhaust valves in SCR systems, which causes engine shutdowns. Additionally, the adoption of low-sulfur fuels in non-EGCS-equipped vessels lead to mechanical issues such as fuel pump sticking owing to reduced lubricity [18][20][22][23].

With the increasing use of gas fuels, such as LNG and LPG, achieving complete combustion has become even more critical. The ongoing shift towards cleaner emissions and alternative fuels necessitates further research to mitigate these mechanical chal-lenges and ensure the safety and reliability of marine diesel en-gines.

To address the identified mechanical challenges, future re-search should focus on the following areas:

• 1. Mechanical Impact of Emission Control Systems: It is crucial to investigate the long-term mechanical effects of inte-grating EGCS, SCR, and EGR systems, particularly on en-gines not originally designed to accommodate these technol-ogies. Strategies to mitigate the mechanical stresses intro-duced by these systems must be developed.
• 2. Optimization of Lubricating Management: Further re-search on the best practices for lubrication management, es-pecially in engines operating with low-sulfur fuels and emis-sion control systems, is necessary. This includes the devel-opment of advanced lubricants and additives that can better withstand the challenges posed by the operating conditions.
• 3. Compatibility of Alternative Fuels with Engine Designs: Studies should assess the compatibility of LNG, LPG, and other alternative fuels with various engine designs, particular-ly in terms of combustion efficiency and mechanical wear. Such studies will help guide future engine designs and retro-fitting decisions.
• 4. Development of Advanced Combustion Technologies: Continued innovation in combustion technology is essential to meet the challenges posed by new fuel types and strict emission regulations. Research should focus on developing systems that can achieve higher efficiency and lower emis-sions, while maintaining engine reliability and safety.

In conclusion, while the adoption of cleaner fuels and stricter emission controls is necessary, it introduces significant mechani-cal challenges that require ongoing research and innovation. En-suring the reliability and safety of marine diesel engines in this new regulatory landscape depends on developing solutions that can effectively manage these emerging risks.