CAMARO6 - View Single Post

toohighpsi · 02-24-2017, 04:07 PM

OEM's look at the following items when making a decision for their FI needs (super or turbo):

1. Quality (reliability)
2. Efficiency (performance)
3. Cost

First off is the durability of the device, it needs to be as maintenance free as possible and capable of surviving the OEM's testing requirements with no degradation of performance over that test period. Testing in this area consists of hundreds of hours of operation at or near the peak requirements of the boosting device. While this is the entry condition to even be considered for these applications, efficiency plays into this role also when controlling thermal conditions for long life.

Next is efficiency - specifically "Compressor Efficiency" which is all encompassing of the boosting device and is the measurement that is used when making comparisons between options. This should NOT be confused with "Adiabatic" or Thermal" efficiency - which is the information that you will normally find posted for SC and TC devices out there.

So what is the difference?

Adiabatic or Thermal Efficiency (%) is the comparison between the IDEAL air temperature rise during the compression process and the ACTUAL air temperature rise during the compression process. It provides information on the compressor only related to the compression process - no information relating the mechanical efficiency of the compressor is included.

Compressor Efficiency (%) is the comparison between the IDEAL power required for a specific mass flow and pressure ratio and the ACTUAL power required for a specific mass flow and pressure ratio. It encompasses all aspects of the compressor - thermal and mechanical efficiency.

When you start looking at mechanical efficiency, speed is not your friend, we all know the equation right? HP = Torque * RPM / 5252. All of the friction mechanical losses in any SC are pretty much the same amount of torque, we have bearings, gears, windage from oil, and seals. While lots of advancements exist and are applied to these components whenever possible, we can see one impact from the equation that could separate very similar components is the speed. As SC impeller speed increases, the HP requirements for frictional losses increase - which in turn decreases your Compressor Efficiency.

In the OEM world, most companies use an Eaton (or Eaton based) device. On these SC's, Adiabatic Efficiency and Compressor Efficiency are very close to each other indicating a very high mechanical efficiency (along with good thermal efficiency).

For example, the TVS R1900 used on the CTSV has a peak adiabatic (thermal) efficiency of about 72% and peak Compressor Efficiency of about 69% - essentially losing only a small percent of its drive power to mechanical losses.

On the other hand, if we want to look at a worse case scenario, we'd consider a "friction drive" centrifugal supercharger. In this case we're relying on the friction (bad word already) of rollers or balls to provide the step-up ratio from our input pulley to drive our centrifugal impeller wheel to speed of 60,000 RPM - 80,000 RPM - along with seals and bearings (at least 1 seal and 2 bearings) at that same high speed. This type of device will have an adiabatic efficiency of about 72% and a Compressor Efficiency of about 31%. So, at least half of the input power put into the belt for this device is consumed by the drive system to get the compressor wheel up to the speed and compress the air.

Just because a device has low Compressor Efficiency dosen't mean that it can't make a lot of power, it just means that it will consume more power when doing it. Top Fuelers are a great example of this, while they have a SC that probably has less than 45%-50% Compressor Efficiency, they still make thousands of HP because they have the capability of moving huge amounts of air. You need to move enough air to make the power you are desiring, but the SC with the highest Compressor Efficiency will make the most power (with all else - intercooler, throttlebody, etc being the same).

Now I've pretty much provided you with the best and worst examples that exist in the SC market today, everything else out there falls somewhere between these two examples. If you're an OEM, you have access to this data - most OEMs have test stands to acquire this data themselves or have contracted test facilities that can perform the tests for comparison purposes.

Finally there is cost which is a tough one, but you have to hit the other hurdles to get to this point. Turbochargers are the big competition in this area, turbocharger device cost is cheap, but installation cost is not.

02-24-2017, 04:07 PM	#8
toohighpsi Drives: 2015 C7 Z06 M7 Join Date: Dec 2012 Location: So-Cal Posts: 665	OEM's look at the following items when making a decision for their FI needs (super or turbo): 1. Quality (reliability) 2. Efficiency (performance) 3. Cost First off is the durability of the device, it needs to be as maintenance free as possible and capable of surviving the OEM's testing requirements with no degradation of performance over that test period. Testing in this area consists of hundreds of hours of operation at or near the peak requirements of the boosting device. While this is the entry condition to even be considered for these applications, efficiency plays into this role also when controlling thermal conditions for long life. Next is efficiency - specifically "Compressor Efficiency" which is all encompassing of the boosting device and is the measurement that is used when making comparisons between options. This should NOT be confused with "Adiabatic" or Thermal" efficiency - which is the information that you will normally find posted for SC and TC devices out there. So what is the difference? Adiabatic or Thermal Efficiency (%) is the comparison between the IDEAL air temperature rise during the compression process and the ACTUAL air temperature rise during the compression process. It provides information on the compressor only related to the compression process - no information relating the mechanical efficiency of the compressor is included. Compressor Efficiency (%) is the comparison between the IDEAL power required for a specific mass flow and pressure ratio and the ACTUAL power required for a specific mass flow and pressure ratio. It encompasses all aspects of the compressor - thermal and mechanical efficiency. When you start looking at mechanical efficiency, speed is not your friend, we all know the equation right? HP = Torque * RPM / 5252. All of the friction mechanical losses in any SC are pretty much the same amount of torque, we have bearings, gears, windage from oil, and seals. While lots of advancements exist and are applied to these components whenever possible, we can see one impact from the equation that could separate very similar components is the speed. As SC impeller speed increases, the HP requirements for frictional losses increase - which in turn decreases your Compressor Efficiency. In the OEM world, most companies use an Eaton (or Eaton based) device. On these SC's, Adiabatic Efficiency and Compressor Efficiency are very close to each other indicating a very high mechanical efficiency (along with good thermal efficiency). For example, the TVS R1900 used on the CTSV has a peak adiabatic (thermal) efficiency of about 72% and peak Compressor Efficiency of about 69% - essentially losing only a small percent of its drive power to mechanical losses. On the other hand, if we want to look at a worse case scenario, we'd consider a "friction drive" centrifugal supercharger. In this case we're relying on the friction (bad word already) of rollers or balls to provide the step-up ratio from our input pulley to drive our centrifugal impeller wheel to speed of 60,000 RPM - 80,000 RPM - along with seals and bearings (at least 1 seal and 2 bearings) at that same high speed. This type of device will have an adiabatic efficiency of about 72% and a Compressor Efficiency of about 31%. So, at least half of the input power put into the belt for this device is consumed by the drive system to get the compressor wheel up to the speed and compress the air. Just because a device has low Compressor Efficiency dosen't mean that it can't make a lot of power, it just means that it will consume more power when doing it. Top Fuelers are a great example of this, while they have a SC that probably has less than 45%-50% Compressor Efficiency, they still make thousands of HP because they have the capability of moving huge amounts of air. You need to move enough air to make the power you are desiring, but the SC with the highest Compressor Efficiency will make the most power (with all else - intercooler, throttlebody, etc being the same). Now I've pretty much provided you with the best and worst examples that exist in the SC market today, everything else out there falls somewhere between these two examples. If you're an OEM, you have access to this data - most OEMs have test stands to acquire this data themselves or have contracted test facilities that can perform the tests for comparison purposes. Finally there is cost which is a tough one, but you have to hit the other hurdles to get to this point. Turbochargers are the big competition in this area, turbocharger device cost is cheap, but installation cost is not.