Turbocharger Technical Facts and Anatomy
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Maxima Newb
Joined: Oct 2007
Posts: 26
From: Rockledge, FL
Turbocharger Technical Facts and Anatomy
Hey guys, I just wanted to share this info for anyone interested. It's taken from my website roastedpavement.com which focuses on FWD SR20DET projects. Lots of useful info and terminology about turbochargers. Enjoy!
Basic Turbocharger Anatomy:
Turbine Housing- Commonly referred to as the "exhaust housing" or "exhaust side" of the turbocharger. It is the part of the turbocharger that bolts to the exhaust manifold.
Turbine Wheel- This is the wheel located inside the turbine housing which spins as a result of concentrated exhaust pressure passing over it.
Turbine Inlet- This is the opening by which engine exhaust gases enter the turbine housing.
Turbine Discharge- This is the opening by which engine exhaust gases exit the turbine housing. This is where the downpipe connects.
Wastegate- The wastegate regulates the boost pressure that a turbocharger generates. It is essentially a valve which opens to prematurely release exhaust pressure from the turbine wheel whenever desired boost pressure is achieved. Internal wastegates are located in the turbine housing.
Compressor Housing- Commonly referred to as the "intake housing" or "intake side" of the turbocharger. It is the part of the turbocharger that connects to the intake of the engine (generally via an intercooler).
Compressor Wheel- This is the wheel located inside the compressor housing which spins to pressurize the intake air for the engine.
Compressor Inlet- This is the opening by which filtered air is drawn into the compressor housing.
Compressor Discharge- This is the opening by which charged air exits the compressor housing into the intake tract.
Center Shaft- This shaft connects the turbine wheel to the compressor wheel and runs through the center housing of the turbocharger.
Center Housing- The heart of the turbocharger, housing the center shaft and the turbine and compressor housings on either side. This is also where oil and water lines/drains are connected.
Bearings- Bearings both support and control the rotating center shaft in the turbocharger. Located in the center housing, they are of either the journal or ball bearing variety.
CHRA- The center housing and rotating assembly is basically a turbocharger without the compressor and turbine housings.
What a Turbocharger Does:
As we all know (hopefully), the internal combustion engine takes in air and fuel to be used as energy. The energy is realized when the air/fuel mixture is ignited. This occurs after the piston has compressed the air in the combustion chamber, and after ignition, the waste (exhaust gas) is expelled from the engine. Engine power is directly proportional to the amount of air that can get into the combustion chambers. It is commonly known that denser air makes more power since more air molecules are grouped together in this instance. Turbochargers compress and condense air into the combustion chambers, thereby making the air more dense and creating more power as a result.
The way a turbocharger does this is quite simple, however, turbochargers themselves are quite complex due to their many parts and tight tolerances. In the most basic sense, exhaust gases expelled from the engine are routed into the turbine housing of the turbocharger via the exhaust manifold. The turbine wheel, connected to the center shaft, spins inside the turbine housing from the concentrated exhaust pressure. On the other side of the center shaft, the compressor wheel is spinning inside of the compressor housing (due to the turbine wheel spinning) and as a result it draws in ambient air and forces it out of the compressor housing and into the engine.
Turbocharger Terminology
Inducer- This is a word used to describe the diameter of a wheel. Specifically, it is the diameter of the wheel at the point where air enters the wheel. For the compressor wheel, this is the diameter of the outermost side of the wheel (furthest from the center housing). For the turbine wheel, this is the diameter of the innermost side of the wheel (closest to center housing).
Exducer- This is a word used to describe the diameter of a wheel as well. Specifically, it is the diameter of the wheel at the point which air exits the wheel. For the compressor wheel, this is the diameter of the innermost side of the wheel (closest to center housing). For the turbine wheel, this is the diameter of the outermost side of the wheel (furthest from center housing.
Trim- This is a word used to express the relationship between the inducer and exducer of both turbine and compressor wheels. It is an area ratio defined by an actual formula. Generally (but not always), larger trim values denote more airflow capabilities. To find trim, square the inducer value and divide it by the squared exducer value. Multiply the quotient by 100. The result is the trim of the wheel.
A/R- This is an acronym used to describe housing size. Commonly, a misnomer is to refer to this as "aspect ratio." However, the acronym actually stands for area over radius. To the geometrically challenged, the concept of A/R can be difficult to understand, but for the tech-heads out there I'll explain anyway. A/R is defined as the cross-sectional area of the turbine inlet or the compressor discharge (depending on which housing A/R you are trying to figure) divided by the radius from the turbocharger centerline to the centroid of that area. Don't worry if you're confused, just pay attention to the following rules of thumb: 1) For compressor housings, larger A/R's are more for optimizing low-boost applications whereas smaller A/R's are more for optimizing high-boost applications. 2) For turbine housings, smaller A/R's create more engine backpressure but allow turbochargers to spool more quickly whereas larger A/R's create less engine backpressure but can be conducive to turbo lag.
Turbo Lag- This is the amount of delay from the time the throttle is opened to the time that the turbocharger produces boost.
Boost Threshold- This is the engine speed at which there is sufficient exhaust pressure to produce boost.
Boost Spike- This is a brief and uncontrollable "spike" in boost level which goes beyond desired regulatory settings.
Boost Creep- This is an occurance when boost rises above the desired regulatory setting. It generally occurs when the wastegate is not large enough to release the necessary exhaust gas pressure to maintain boost level.
Compressor Surge- This is undue pressure/stress put on the compressor wheel which can cause bearing failure and turbocharger damage. Typically, it happens when a blow-off valve is either not used, or not working properly. Basically, when the throttle plate closes, exhaust gases are still being produced which further spin the turbine wheel thereby creating boost which has no where to go. Blow-off valves release this pressure, but in the event where they don't, the back pressure is forced onto the compressor wheel.
Shaft Play- This is a side-by-side play in the center shaft indicative of worn out bearings that need to be replaced.
Basic Turbocharger Anatomy:
Turbine Housing- Commonly referred to as the "exhaust housing" or "exhaust side" of the turbocharger. It is the part of the turbocharger that bolts to the exhaust manifold.
Turbine Wheel- This is the wheel located inside the turbine housing which spins as a result of concentrated exhaust pressure passing over it.
Turbine Inlet- This is the opening by which engine exhaust gases enter the turbine housing.
Turbine Discharge- This is the opening by which engine exhaust gases exit the turbine housing. This is where the downpipe connects.
Wastegate- The wastegate regulates the boost pressure that a turbocharger generates. It is essentially a valve which opens to prematurely release exhaust pressure from the turbine wheel whenever desired boost pressure is achieved. Internal wastegates are located in the turbine housing.
Compressor Housing- Commonly referred to as the "intake housing" or "intake side" of the turbocharger. It is the part of the turbocharger that connects to the intake of the engine (generally via an intercooler).
Compressor Wheel- This is the wheel located inside the compressor housing which spins to pressurize the intake air for the engine.
Compressor Inlet- This is the opening by which filtered air is drawn into the compressor housing.
Compressor Discharge- This is the opening by which charged air exits the compressor housing into the intake tract.
Center Shaft- This shaft connects the turbine wheel to the compressor wheel and runs through the center housing of the turbocharger.
Center Housing- The heart of the turbocharger, housing the center shaft and the turbine and compressor housings on either side. This is also where oil and water lines/drains are connected.
Bearings- Bearings both support and control the rotating center shaft in the turbocharger. Located in the center housing, they are of either the journal or ball bearing variety.
CHRA- The center housing and rotating assembly is basically a turbocharger without the compressor and turbine housings.
What a Turbocharger Does:
As we all know (hopefully), the internal combustion engine takes in air and fuel to be used as energy. The energy is realized when the air/fuel mixture is ignited. This occurs after the piston has compressed the air in the combustion chamber, and after ignition, the waste (exhaust gas) is expelled from the engine. Engine power is directly proportional to the amount of air that can get into the combustion chambers. It is commonly known that denser air makes more power since more air molecules are grouped together in this instance. Turbochargers compress and condense air into the combustion chambers, thereby making the air more dense and creating more power as a result.
The way a turbocharger does this is quite simple, however, turbochargers themselves are quite complex due to their many parts and tight tolerances. In the most basic sense, exhaust gases expelled from the engine are routed into the turbine housing of the turbocharger via the exhaust manifold. The turbine wheel, connected to the center shaft, spins inside the turbine housing from the concentrated exhaust pressure. On the other side of the center shaft, the compressor wheel is spinning inside of the compressor housing (due to the turbine wheel spinning) and as a result it draws in ambient air and forces it out of the compressor housing and into the engine.
Turbocharger Terminology
Inducer- This is a word used to describe the diameter of a wheel. Specifically, it is the diameter of the wheel at the point where air enters the wheel. For the compressor wheel, this is the diameter of the outermost side of the wheel (furthest from the center housing). For the turbine wheel, this is the diameter of the innermost side of the wheel (closest to center housing).
Exducer- This is a word used to describe the diameter of a wheel as well. Specifically, it is the diameter of the wheel at the point which air exits the wheel. For the compressor wheel, this is the diameter of the innermost side of the wheel (closest to center housing). For the turbine wheel, this is the diameter of the outermost side of the wheel (furthest from center housing.
Trim- This is a word used to express the relationship between the inducer and exducer of both turbine and compressor wheels. It is an area ratio defined by an actual formula. Generally (but not always), larger trim values denote more airflow capabilities. To find trim, square the inducer value and divide it by the squared exducer value. Multiply the quotient by 100. The result is the trim of the wheel.
A/R- This is an acronym used to describe housing size. Commonly, a misnomer is to refer to this as "aspect ratio." However, the acronym actually stands for area over radius. To the geometrically challenged, the concept of A/R can be difficult to understand, but for the tech-heads out there I'll explain anyway. A/R is defined as the cross-sectional area of the turbine inlet or the compressor discharge (depending on which housing A/R you are trying to figure) divided by the radius from the turbocharger centerline to the centroid of that area. Don't worry if you're confused, just pay attention to the following rules of thumb: 1) For compressor housings, larger A/R's are more for optimizing low-boost applications whereas smaller A/R's are more for optimizing high-boost applications. 2) For turbine housings, smaller A/R's create more engine backpressure but allow turbochargers to spool more quickly whereas larger A/R's create less engine backpressure but can be conducive to turbo lag.
Turbo Lag- This is the amount of delay from the time the throttle is opened to the time that the turbocharger produces boost.
Boost Threshold- This is the engine speed at which there is sufficient exhaust pressure to produce boost.
Boost Spike- This is a brief and uncontrollable "spike" in boost level which goes beyond desired regulatory settings.
Boost Creep- This is an occurance when boost rises above the desired regulatory setting. It generally occurs when the wastegate is not large enough to release the necessary exhaust gas pressure to maintain boost level.
Compressor Surge- This is undue pressure/stress put on the compressor wheel which can cause bearing failure and turbocharger damage. Typically, it happens when a blow-off valve is either not used, or not working properly. Basically, when the throttle plate closes, exhaust gases are still being produced which further spin the turbine wheel thereby creating boost which has no where to go. Blow-off valves release this pressure, but in the event where they don't, the back pressure is forced onto the compressor wheel.
Shaft Play- This is a side-by-side play in the center shaft indicative of worn out bearings that need to be replaced.
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