Analysis and Solutions for Carbon Buildup in Diesel Generators

Diesel generators play an essential role in various fields such as industrial production, construction, marine power, and backup power supply. However, carbon buildup in diesel generators during long-term operation acts like an invisible "killer," silently eroding the performance and lifespan of the equipment and causing numerous problems for users. This article will delve into the causes, hazards, and effective removal methods of carbon buildup in diesel generators to help relevant professionals better address this challenging issue.

The formation of carbon buildup in diesel generators is a multi-factorial process involving equipment structure, fuel and lubricant properties, operating conditions, and working conditions.

Firstly, from the perspective of equipment structure, the design of the combustion chamber, the atomization effect of the fuel injector, and the sealing of the valves all directly affect combustion efficiency. If the combustion chamber design is not rational, it may lead to local oxygen deficiency, resulting in incomplete combustion of fuel and lubricant and the subsequent formation of carbon buildup. For example, in some older models, the combustion chamber design is not optimized, and fuel cannot mix and burn fully inside the chamber. This often leaves unburned residues in corners, which then form carbon deposits.

Secondly, the types of fuel and lubricants are also key factors. The quality of diesel varies, and some inferior diesel contains more impurities and unsaturated hydrocarbons, which are more likely to produce soot and tar particles during combustion. If the lubricant is not chosen properly, with high volatility or poor high-temperature oxidation resistance, it can decompose and form carbon deposits in high-temperature environments. For instance, some small diesel generator users, in an attempt to save costs, use low-quality lubricants. After running at high temperatures for a while, significant carbon deposits can form on the cylinder walls and piston ring grooves.

Furthermore, operating conditions and working conditions exacerbate the formation of carbon buildup. When diesel generators operate at high loads and for extended periods continuously, the temperature in the combustion chamber rises continuously, and lubricant is more likely to enter the combustion chamber and participate in combustion, producing a large amount of carbon. In addition, if the working environment has poor ventilation and poor heat dissipation, it will also accelerate the formation of carbon. For example, diesel generators used in underground mines or enclosed machine rooms often suffer from high carbon buildup due to the limited space and poor air circulation, which prevents the heat generated during operation from dissipating in time and leads to excessively high combustion chamber temperatures.

Currently, research on the mechanism of carbon formation has not yet formed a complete system theory. However, the widely accepted view is that carbon is a product of fuel and lubricant under high-temperature oxidation. During combustion, when oxygen supply is insufficient, fuel and lubricant that enters the combustion chamber cannot burn completely, producing soot and tar particles. These particles mix with lubricant and further oxidize in high-temperature environments to form a viscous colloidal liquid—hydroxy acid. Hydroxy acid continues to oxidize into semi-fluid resinous colloid, which firmly adheres to parts and polymerizes into more complex polymer hard carbon deposits under high temperature, forming carbon buildup. The composition of carbon buildup is complex and diverse, including lubricant, hydroxy acid, asphaltene, oil resin, carbon black, sulfates, and silicon compounds. The higher the temperature, the harder and more tightly the carbon buildup forms, and the more firmly it adheres to metal.

Once carbon buildup forms on key components of diesel generators, it triggers a series of chain reactions that severely harm the normal operation of the equipment.

After using diesel generators for a while, key parts such as fuel injectors, throttle valves, exhaust valves, and combustion chambers often have a layer of firmly adhered carbon buildup on their surfaces. Carbon has poor thermal conductivity, and a large amount of carbon accumulation on the surface of parts can cause local overheating, reducing the stiffness and strength of the parts. In severe cases, fuel injectors may sinter and fail to spray fuel normally; valves may burn and leak; piston rings may seize, causing serious accidents such as cylinder pulling. For example, in a ship's diesel generator, excessive carbon buildup at the fuel injector nozzle blocked the spray holes, leading to poor fuel atomization and deteriorated combustion. This ultimately reduced engine power, slowed the ship's speed, and significantly increased maintenance costs.

High-temperature carbon particles accumulated in the combustion chamber can cause surface ignition, resulting in power loss. According to relevant experimental data, the power loss can range from 2% to 15%. At the same time, the volume of the combustion chamber is reduced due to carbon accumulation, increasing the actual compression ratio and making pre-ignition and knocking more likely. These phenomena not only reduce engine power output but also cause shock and damage to internal engine components, shortening their lifespan.

A large amount of carbon buildup can also contaminate the lubrication system, blocking oil passages and filters. Lubricant, contaminated by carbon during circulation, will deteriorate faster and lose its lubricating, cooling, and cleaning functions. Carbon entering the lubricant can block oil passages and holes, disrupting the normal operation of the lubrication system. In severe cases, it can even cause bearing seizure accidents. For example, in some industrial enterprises' diesel generators, long-term neglect of carbon cleaning led to clogged oil filters, insufficient lubricant supply, and poor lubrication of internal engine components. This ultimately caused crankshaft bearing damage and significant economic losses.

Due to mechanical vibration and thermal stress during the operation of diesel generators, deposited carbon can fracture and flake off. The hard particles become foreign abrasives, causing friction and wear between internal friction pairs of diesel generators, shortening the service life of pistons, piston rings, cylinder liners, and crankshaft bearings. For example, carbon in the piston ring groove can cause the piston ring to lose elasticity and seize. On one hand, this reduces the sealing of the piston ring, causing oil burning and further increasing carbon formation; on the other hand, it weakens the cooling effect of the piston ring, and the piston may melt due to high temperature.

Given the significant harm of carbon buildup to diesel generators, timely removal of carbon is of great importance. Currently, there are several common methods for removing carbon buildup:

Using a fuel system cleaning agent to clean diesel generators is a relatively simple and commonly used method. This cleaning agent is drawn into the fuel supply line along with the fuel by the fuel pump when the diesel generator is operating. As the fuel flows, it can clean the gums and carbon deposits on the fuel tank, fuel pump filter, and fuel injectors. It can also automatically clean carbon deposits on the valves and inside the cylinders during normal engine operation. However, it should be noted that the gums cleaned from the fuel tank, fuel pump filter, and fuel lines will deposit in the fuel filter. Therefore, after the "no-disassembly" cleaning, the fuel filter must be replaced in time. In addition, since the chemical cleaning components in the cleaning agent have a certain corrosive effect on rubber fuel lines, it is essential to pay attention to the usage cycle and interval time to avoid accelerating the aging and corrosion of rubber fuel lines.

For diesel generators with severe carbon buildup, if the performance remains poor after "no-disassembly cleaning" and the problem is caused by excessive carbon deposits on the valves and inside the cylinder, the "disassembly" method must be used. Cleaning valve carbon is relatively simple. After removing the intake manifold, it can be removed manually or by soaking in cleaning agents. Cleaning cylinder carbon is much more complex because the power and sealing performance of the diesel generator often deteriorate after disassembly and reassembly. Therefore, cleaning cylinder carbon should not be done lightly and should only be performed in a professional repair shop when absolutely necessary; otherwise, the equipment performance will be greatly compromised.

The mechanical method uses tools such as wire brushes, scrapers, bamboo pieces, or sandpaper to remove carbon deposits. Special brushes and scrapers can be made according to the shape of the part to be cleaned. Taking the removal of carbon deposits from the top of the cylinder liner as an example, the specific steps are as follows: First, use a scraper or similar blunt-edged tool to loosen the carbon deposits; then, use a grinding nylon pad and solvent to remove the remaining carbon. It should be noted that the carbon deposits must be removed, but the surface does not need to look brand new. In addition, a high-quality wire wheel brush mounted on an electric drill can also be used to remove carbon deposits. However, do not use the wire wheel in the piston ring travel area and move the wire wheel in a circular direction for cleaning. At the same time, avoid using inferior wire wheel brushes because the wire may fall off during operation, causing additional contamination. This method is currently used by many large diesel generator maintenance shops.

Chemical carbon removal uses decarbonizing agents to soften the carbon deposits on parts. After the decarbonizing agent contacts the carbon, it forms an adsorption layer on the surface of the carbon layer. The interaction between the polar groups of the decarbonizing molecules and the carbon molecules allows the decarbonizing agent molecules to gradually diffuse into the interior of the carbon layer. It can also form polymers between the polar groups of the reticular molecules in the carbon layer, weaken the polar forces between the reticular molecules, disrupt the orderly arrangement of the reticular polymers, and gradually loosen the polymer arrangement. There are many common decarbonizing agent formulas, which can be selected according to different carbon conditions and part materials.

Nut shell blasting uses high-speed airflow to spray crushed nut shells (such as peach, plum, apricot, and walnut shells) onto the surface of parts to remove carbon deposits. This method is highly efficient and thorough in removing carbon, but it requires special equipment to generate high-speed airflow, and the cost is relatively high. Therefore, it is not suitable for widespread use. The specific steps are as follows: First, dry and crush the kernels of peaches, plums, apricots, and walnuts, and classify them by size as blasting materials. Then, use compressed air at 400–500 kPa to spray them onto the surface of the parts. Since the blasting material is softer than metal and easily crushed, it will not damage the surface of the parts. It only takes about 10 minutes to remove the carbon deposits from a cylinder head.

This method uses a mixture of liquid and quartz sand as the blasting material. The mixture is sent to the nozzle by compressed air and sprayed onto the parts. The content of quartz sand in the mixture varies depending on the material of the parts being sprayed: for soft non-ferrous metal parts, the sand content is 15%–18%; for hard non-ferrous metal parts, the sand content is 18%–20%; for steel parts, the sand content is 20%–30%; for cast iron parts, the sand content is 30‰–45%. The distance between the nozzle and the carbon deposits should be maintained at 80–100 mm, the spray angle should be 37°–40°, the mixture pressure should be 180–500 kPa, and the quartz sand particle size should not be less than 320 mesh. This method not only removes carbon deposits but also cleans and polishes the surface of the parts to some extent, improving the surface quality of the parts.

In addition to the above cleaning methods, preventing the formation of carbon buildup is equally important. The following are some effective measures to prevent carbon buildup.

Control the quality of fuel and lubricants from the source by choosing high-quality diesel that meets national standards and lubricants with good high-temperature oxidation resistance and low volatility. This can reduce the possibility of carbon formation during combustion and extend the maintenance cycle of the equipment.

Avoid long-term high-load operation of diesel generators as much as possible. Arrange working time and load reasonably to allow the engine sufficient time for heat dissipation. At the same time, maintain good ventilation conditions to ensure air circulation in the equipment operating environment, which helps reduce combustion chamber temperature and carbon formation.

Establish a comprehensive equipment maintenance system and regularly inspect and clean key components. For example, regularly clean carbon deposits from the combustion chamber, valves, and fuel injectors, and promptly replace aged lubricants and clogged filters to ensure the normal operation of the lubrication system. In addition, regularly perform engine performance tests to identify and resolve potential problems in a timely manner to prevent faults caused by carbon buildup from escalating.

In daily operation, it is appropriate to add some fuel additives. These additives can improve fuel combustion performance, promote complete fuel combustion, and reduce carbon formation. However, it is important to choose reliable quality additives suitable for diesel generators and use them correctly according to the instructions.

Carbon buildup in diesel generators is a complex and common problem that has a profound impact on the performance, lifespan, and operating costs of the equipment. Through in-depth analysis of the causes of carbon formation, we understand that it is closely related to equipment structure, fuel and lubricant properties, and operating conditions. The hazards of carbon buildup are multifaceted, affecting component performance, reducing combustion efficiency, contaminating the lubrication system, and causing mechanical wear. Fortunately, there are several effective methods for removing carbon buildup available, including fuel system cleaning agent method, disassembly cleaning method, mechanical method, chemical method, nut shell blasting method, and liquid and quartz sand blasting method. At the same time, by selecting high-quality fuel and lubricants, optimizing equipment operating conditions, regularly maintaining and inspecting the equipment, and using fuel additives, carbon formation can be effectively prevented. It is hoped that the introduction of this article will help relevant professionals better address the issue of carbon buildup in diesel generators, ensure the stable operation of equipment, improve production efficiency, reduce maintenance costs, and provide reliable power support for industrial production and social development.