Fault Analysis and Maintenance of Diesel Engine Smoke Phenomenon—Blue Smoke

Diesel engines have come a long way in terms of improvement and performance. However, certain issues such as blue smoke, white smoke, and black smoke continue to persist, especially in construction machinery operating in challenging environments. In this blog post, we will focus on the phenomenon of blue smoke emitted by diesel engines, its causes, common fault locations, and troubleshooting and maintenance solutions.

Blue smoke is typically observed as light blue emissions coming out of the exhaust pipe during engine operation. It occurs when oil enters the engine cylinder and gets burned. This condition is often referred to as "up and down leakage," which describes the oil leakage into the cylinder from various engine parts.

Allowing the engine to emit blue smoke unchecked can have serious consequences. Initially, the engine oil level will decrease, triggering an oil level alarm. As the problem persists, inadequate lubrication can lead to cylinder and bearing damage, resulting in significant losses.

There are two main reasons why engines burn oil:

1. Normal wear and tear: Over the service life of an engine, increased wear between working parts leads to larger clearances or gaps. This reduces the seal's ability to prevent engine oil from leaking into the cylinder, resulting in oil entering the combustion chamber, burning, and producing blue smoke.

2. Abnormal wear: When an engine is not adequately lubricated, such as running without oil or with old oil, or if the engine oil and filter are not regularly replaced, abnormal wear occurs. This can cause oil leakage and burning, resulting in blue smoke.

Let's explore some common fault locations related to blue smoke:

1. Between the valve and the valve oil seal: As the engine operates over time, the gap between the valve and the valve oil seal increases due to friction. This gap allows oil to seep directly into the cylinder, participate in combustion, and produce blue smoke.

2. Between the pistonand the cylinder: The proper functioning of the engine relies on a sufficient compression ratio and effective lubrication between the piston and the cylinder. The piston rings spread oil, forming an oil film. Neglecting engine maintenance can result in an increased gap (end gap) between the piston ring and the cylinder. A larger gap reduces the sealing performance of the piston ring, allowing engine oil to enter the cylinder, burn, and produce blue smoke. Piston ring alignment issues can also lead to oil leakage, burning, and blue smoke.

3. Turbochargerturbine shaft seal damage: The turbocharger operates at high speeds and requires sufficient and stable oil for lubrication, cooling, and overall performance. If the turbocharger turbine shaft seal fails, it can cause oil to leak into the turbocharger air passage.

• If the engine oil enters the turbine side, it burns under high-temperature exhaust, resulting in blue smoke emissions. This condition leads to carbon deposits in the air passage, increasing the workload and temperature of the turbocharger. Severe cases can cause the turbocharger to overheat and fail.

• If the engine oil enters the compressor wheel side, it enters the intake port, reaches the cylinder, burns, and produces blue smoke. Combustion of engine oil in the cylinder increases carbon deposits on the pistons, leading to engine shaking and increased risk of knocking.

To address turbocharger-related oil leaks and blue smoke, it is essential to promptly replace the turbocharger seal. This preventive action ensures proper lubrication and heat dissipation, preventing damage to the turbocharger and minimizing economic losses.

1. Excessive oil addition: Adding too much engine oil raises the oil level, increasing the likelihood of engine oil entering the cylinder for combustion. This excess oil can cause the engine to emit significant amounts of blue smoke. In such cases, removing the excess oil resolves the blue smoke issue.

Now, let's discuss troubleshooting and solutions for blue smoke emissions:

Start the engine in a cold state and emit blue smoke: If blue smoke is observed when starting the engine from a cold state but gradually disappears as the engine warms up, it indicates that the engine is burning oil during cold operation. This condition is typically caused by aging valve oil seals that compromise the sealing effect. Engine oil leaks into the cylinder through the valve oil seals, resulting in blue smoke. As the engine temperature rises, the expansion of the valves closes the gaps, reducing blue smoke emissions.

Solution: This situation is common in older equipment. To resolve the issue, the engine needs to be disassembled, and the valve oil seals should be replaced. It is recommended to replace the entire set of valve oil seals.

2. Blue smoke emission during acceleration: If the engine emits a significant amount of blue smoke when the load increases suddenly, and the throttle is raised, it indicates a large gap between the piston and the cylinder barrel.

Under high throttle conditions, engine oil passes through the oil pan, flows through the larger gap between the cylinder and the piston or piston rings, enters the cylinder, and burns, resulting in blue smoke. In this case, the engine needs to be disassembled to determine if the issue stems from excessive gaps between the piston and the cylinder or if it is related to piston ring misalignment causing oil leakage.

Solution: Disassemble the engine piston and check the alignment of the piston rings. If misaligned, adjust the opening position of the piston rings. If misalignment is not the issue, measure the gap between the piston and the cylinder, as well as the end gap of the piston rings. Compare the measurements with the values provided by the engine manufacturer to determine if replacement parts are necessary. This scenario is often referred to as "upswing."

3. Continuous emission of blue smoke at all times: If the engine emits significant amounts of blue smoke regardless of the working conditions, it indicates severe engine wear requiring an overhaul. Failure to address this issue promptly can lead to scuffing, bearing damage, or even complete engine failure, resulting in substantial losses.

Because engine oil is vital for engine performance and longevity, abnormal oil loss can directly impact the engine's functionality. Therefore, when blue smoke emissions or low engine oil pressure alarms occur, it is crucial to promptly inspect and repair the engine lubrication system to prevent unnecessary losses.

In conclusion, blue smoke emissions from diesel engines are typically caused by oil entering the combustion chamber and burning. Addressing the underlying issues related to valve oil seals, piston-cylinder gaps, turbocharger seal damage, and oil level management is crucial to prevent engine damage and ensure optimal performance. Regular maintenance, timely repairs, and adherence to manufacturer guidelines for lubrication system maintenance are key to minimizing blue smoke emissions and extending the engine's lifespan.

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