Thermal Runaway in Diesel Generators and How to Prevent It

Diesel generators are widely used in modern industries and for emergency power supply. Their efficiency and reliability make them a vital power source in many places. However, over time, diesel generators can sometimes experience a problem known as thermal runaway. This can damage the equipment and even cause it to shut down. Thermal runaway is often linked to the interaction between the battery's float charge current and its temperature. This can have serious consequences for the generator's stability and safety. In this article, we'll take a closer look at what causes thermal runaway in diesel generators and explore ways to prevent it.

What is Thermal Runaway?

Thermal runaway happens when the float charge current and temperature interact during constant-voltage charging, causing the battery to overheat and get damaged. Essentially, as the battery's temperature goes up, the float charge current increases. The higher current then raises the temperature even more, creating a vicious cycle. This is a common issue in Valve-Regulated Lead-Acid (VRLA) batteries, especially in hot environments, poor ventilation, or when the battery is installed incorrectly.

What Causes Thermal Runaway in Diesel Generators?

Thermal runaway in diesel generators usually happens during long periods of operation, leading to equipment damage or reduced efficiency. There are several reasons why this could happen.

1. High Load Operation and Heat Buildup

When the generator runs under heavy load, it produces a lot of heat. If the heat can't be released in time, and the generator's cooling system can't handle it, the temperature will keep rising. This can lower the generator's efficiency and trigger thermal runaway.

2. Cooling System Failure or Low Efficiency

The cooling system is designed to carry heat away and keep the generator at a safe temperature. But if something goes wrong with the cooling system, like a broken fan, radiator, or pump, heat can't be effectively dissipated. This causes the temperature inside the generator to rise, leading to thermal runaway.

3. Fuel Supply System Problems

The fuel supply system feeds the generator's engine with the necessary fuel for combustion. If there's a blockage or poor fuel delivery, the combustion process can't complete properly. This means heat builds up without being dissipated, leading to overheating. Incomplete combustion can also create harmful gases, which could affect the environment.

4. Lubrication System Failure

The lubrication system is essential for reducing friction, cooling, and cleaning inside the engine. If there's not enough lubricant or if the system fails, friction inside the engine increases. This leads to overheating of engine parts and raises the overall temperature of the generator. When the lubrication system doesn't work properly, the generator struggles to manage its temperature, increasing the chances of thermal runaway.

5. Poor Airflow

Diesel generators need good airflow to maintain proper combustion and heat dissipation. If airflow is restricted, especially if the air filter is clogged, combustion becomes inefficient. This creates more unburned heat, which can cause thermal runaway.

How Thermal Runaway Affects VRLA Batteries

Diesel generators often use Valve-Regulated Lead-Acid (VRLA) batteries, which are prone to thermal runaway due to their design. VRLA batteries have a sealed structure, thin electrolyte, and tightly packed glass fiber membranes. These features improve battery safety and lifespan, but they also make it harder for the battery to release heat. This is particularly problematic in high-load or high-temperature situations where the battery temperature can rise quickly.

Inside the battery, oxygen produced at the positive electrode reacts with the negative electrode, generating heat. If this heat isn't released quickly, the temperature continues to rise. As the temperature increases, it affects the battery's performance and can lead to an imbalance in the chemical reactions inside the battery, which can further increase the risk of thermal runaway.

How Temperature and Float Charge Current Are Connected

Temperature has a direct effect on the battery's charging current. When the temperature goes up, the float charge current also increases. There's a direct link between temperature and float charge current: higher temperatures lead to more current, which in turn raises the temperature further. This creates a feedback loop, making thermal runaway more likely.

How to Prevent Thermal Runaway

To prevent thermal runaway and keep the diesel generator running smoothly, a few key measures can be taken. These actions help ensure that the generator stays within a safe temperature range.

1. Set the Float Charge Voltage Correctly

If the float charge voltage is too high, the float charge current will increase, which raises the battery temperature. To prevent thermal runaway, it's important to set the float charge voltage within the recommended range. This keeps the charging current in check, preventing overheating.

2. Regularly Inspect and Maintain the Cooling System

To make sure the generator can effectively dissipate heat, especially during high-load operation, you should inspect the cooling system regularly. The radiator, fans, coolant flow, and pump should all be in good working order. If any part of the cooling system fails, it should be repaired quickly to avoid overheating.

3. Keep the Fuel Supply System Unclogged

Check the fuel supply system regularly to ensure that the fuel lines are clear. The system should be free of leaks and blockages, allowing for complete combustion. This helps prevent excess heat buildup.

4. Maintain the Lubrication System

Make sure the lubrication system is working properly. Change the oil regularly, check the oil level and quality, and ensure the system is free of issues. Proper lubrication helps reduce internal friction, which in turn controls the generator's temperature and prevents overheating.

5. Ensure Good Airflow

Regularly clean the air filters and ensure that the generator has good airflow. Proper airflow is essential for efficient combustion and effective heat removal. This helps prevent the buildup of excess heat and reduces the risk of thermal runaway.

6. Control the Ambient Temperature

For generators that use VRLA batteries, it's important to control the surrounding temperature. High ambient temperatures make it harder for the battery to dissipate heat, increasing the likelihood of thermal runaway. The generator should be installed in an environment with stable temperatures and good ventilation.

Conclusion

Thermal runaway in diesel generators is a complex issue caused by multiple factors, including the cooling system, fuel supply, lubrication, airflow, and battery management. By setting the right float charge voltage, regularly inspecting and maintaining the cooling and lubrication systems, ensuring proper fuel supply, and improving airflow, you can effectively prevent thermal runaway. Taking these precautions will improve the stability and safety of the generator, extend the equipment's lifespan, and ensure a reliable power supply.