Turbocharger Durability and Materials
Hannu Jääskeläinen
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Abstract: The life of a turbocharger can be affected by such factors as thermal cracking, fatigue and/or creep. The most common material for turbocharger compressor wheels has been aluminum alloys. Other materials, introduced since the 1990s, include titanium alloys, as well as magnesium and stainless steel alloys. Turbocharger turbine wheels must withstand high temperatures, especially in gasoline applications. Common turbine wheel materials include nickel-based superalloys and titanium alloys.
Turbocharger Durability
Design Factors
The expected life of a turbocharger can be influenced by a number of factors. One categorization of turbocharger failures is as follows [2588]:
- Thermal cracking, creep or oxidation of parts
- Cracked turbine housing.
- Rubbing or distortion of turbine housings due to over-heating.
- Compressor housing distortion due to over-heating.
- Compressor wheel failure due to creep.
- Fatigue of rotating parts
- Cracked compressor wheel.
- Cracked turbine wheel.
- Turbine wheel blade loss.
- Structural failure of the turbocharger or attached parts
- Loose bolts.
- Cracked flanges.
- Failure due to out of specification engine conditions
- High exhaust back pressure under engine braking.
- High or variable exhaust back pressure due to aftertreatment.
- Problems in the engine causing turbocharger failure
- Dirty oil.
- Broken engine parts going through the turbocharger.
While many of the above failures are outside the control of the turbocharger designer, others can be avoided or minimized through the turbocharger design process or by observing application limits. Some parameters that can be limited to avoid the failures mentioned above include:
- Turbocharger speed
- Temperature
- Turbine inlet temperature.
- Compressor outlet temperature.
- Structural loads
- External load limitations.
- Weight and torque reaction of external parts.
- Maximum vibration levels.
- Built in stresses due to assembly.
- General ‘not to exceed limits’
- Exhaust braking back pressure.
- Oil pressure.
- Under hood ambient temperature.
- Oil delivery delay after start up.
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