Turbocharger Surging concept
When airflow collapse occurs in a turbocharger, back scavenging occurs through the diffuser and impeller blades inside the Blower, causing a surge, or a large oscillating airflow, to vibrate the turbocompressor impeller and its blades. Large oscillating airflow prevents the compressor from working correctly, and the reaction is high-pitched noise, also known as compressor surge.
Suppose the surge continues during regular engine operation and the frequency of the shock motor is high. In that case, it can lead to total bearing failure and possibly mechanical failure of the compressor rotor.
A turbocharger surge is therefore made up of various engine parts operating asynchronously. Also, remember that a worn engine cylinder or fuel system can cause severe problems with your engine and turbocharger. The turbocharger issue reduces the airflow out of the compressor against the increased back pressure and can cause a compressor surge.
Therefore, it is essential to properly match the turbocharger to the engine to balance air consumption rate and pressure over the operating engine range and not fall within the surge line.
Understanding the Surging Concept
For understanding the phenomenon of surging in Turbocharging Diesel Engines, let us consider the following conditions.
P1 Compressor outlet pressure.
P2 (Pressure 2) Pressure from Charge Air Cooler
M (mass Flow)
Case A: – P2/P1=1, and M is on the Higher side. In this case, it indicates no restriction to the flow of mass since boot the pressures are equal, and mass flow of air is also on the higher side.
Case B:- P2/P1 ≥1 and mass flow M offer is a little less
Case C:-P2/P1 ˂ one and Mass flow is wholly decreased.
Case C is when the Pressure ratio of P2 /P1 is less than one and mass flow is Negligible, and in this condition, surging occurs.
The Surge Line
Maintaining a sufficient amount of intake air pressure to maintain turbocharger balance and high efficiency is critical to the operating line of the engine.
For example, the pressure should drop to a constant velocity line if you draw more air. So to balance or be on the line of operation, you need to lower the volume.
Conversely, a slight decrease in volume can lead to a constant drop in pressure. Therefore, at this stage, the compressor cannot maintain the required pressure or capacity and may decrease further, resulting in a compressor surge.
Terminology for Turbocharger Surge
- Surge pressure dip in Turbocharger:- The pressure dip is the part of the compression cycle where the air enters the cylinder. The size of this dip will depend on a particular point in time, and if it’s not managed correctly, turbine blades can be damaged.
- Surge cycle time in Turbocharger:- We can understand the Turbocharger cycle time in terms of the time it takes to reach equilibrium again after the operation point has been changed. It is always desirable to reduce the surge cycle time in Turbochargers. Reducing the surge cycle will help increase their efficiency by reducing pumping losses.
- Surge temperature behaviour:- The surge temperature behavior is a phenomenon in which the temperature of the upstream increases as soon as the surge occurs. This phenomenon occurs due to a change in airflow that happens when there is a reverse flow of air after a surge. The sudden change in airflow causes an increase in heat and pressure, resulting in a rise in the upstream temperature.
- Surge shaft speed variations:-The turbocharger’s shaft experiences a speed change during the compressor surge, mainly containing the compressor and turbine. The shaft speed is increased because of the increase in pressure and temperature.
Classification of turbocharger surge
Mild Turbocharger Surging
A mild surging problem that is not significant will arise due to zero flow reversal. It will also happen when the load demands become substantial for the motor/system, initially operating at reduced capacity. In these cases, there will be no over-current protection on a power electronic converter to automatically switch off its attached loads to protect itself from damage
Classic Turbocharger Surging
Low-frequency oscillations are a common phenomenon in turbochargers. The pulsating combustion chamber causes these oscillations. The high-pressure oscillations are caused due to the fuel injecting directly into the exhaust pipe.
Classic surge is usually caused due to low-frequency oscillations and high-pressure oscillations, which result in a sharp increase in pressure. To avoid or minimize these oscillations, turbochargers need to have an efficient flow management system.
Deep Turbocharger Surging
Deep Turbocharger Surging is the most critical condition wherein the reversal of the mass flow occurs in the compressor due to which surging occurs.
Reversing of mass flow in a turbocharger occurs due to an increase or decrease in air pressure which causes temperature and density to increase or decrease, respectively. In such conditions, surge limiting becomes essential to reduce excessive vibrations and noise.
Reasons for Turbocharger Surging
Unbalanced Power In cylinders
Because when the power is unevenly distributed among the main engine cylinders, most often, one unit is used to produce power, and the other is used to produce less power. , the turbocharger may jerk. As a result, due to the surge, the air consumption required by the two turbochargers is different.
Badly Fouled Turbocharger Components
- A dirty turbine-side compressor inlet filter does not provide enough air for combustion and is a significant cause of surge.
- Likewise, if the nozzles and blades on the turbine side are dirty, they will not produce enough air for combustion.
- Damaged silencer
- Worn turbocharger bearings
- Excessive turbo outlet restriction
- Fouled Nozzle ring blades
- Fouled Compressor wheel Blades
- Damaged turbine and compressor blades on the turbo
Scavenge Air System Problem
- Chocked air cooler
- No water circulation in the cooler
- block cooling hose
- Carbon deposits on scavenge ports
- high receiver temperature
Exhaust system problem
- High exhaust backpressure
- Leaky Exhaust valves
- Turbo outlet pressure leak
- Fire in Scavenge space or Exhaust Trucking
Fuel system problem
- Faulty Fuel Valves
- Fuel injection pumps problem
- A badly worn fuel control linkage.
There may be other influencing factors
- Misfiring in one or more cylinders
- Erratic engine or engine control operation
- A muffler with a large amount of water in it.
- Sudden Load Change
- A collapsed air cleaner filter element.
- An improperly adjusted governor.
- A worn governor actuator.
- A voltage regulator with an intermittent output fault.
How can I prevent turbocharger surges?
To prevent turbocharger surge: However, please note that there are some differences depending on the design and construction of the turbocharger
Keep the turbocharger intake filter clean.
It is essential to keep the intake filter clean o prevent the turbocharger surge; when it gets clogged, it can cause a lot of damage to your engine.
Turbocharger surge is one of the most common problems that diesel engines face. A clogged intake filter can cause this problem. The intake filter should be cleaned regularly to prevent this problem from occurring.
Other Important factors to prevent turbocharger surges
- Wash the turbine and compressor sides of the turbocharger with water.
- Various parts of the turbocharger should be adequately maintained and inspected regularly. In case of a problem, turbocharger repair should be performed as soon as possible without straining the engine.
- For economizers or flue gas boilers, soot blowing should be performed occasionally.
Blog Conclusion
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