,
 |
| I ran the same calculations for the turbine side. As you can see from this chart, it appears the turbine side is not quite as sensitive to error as the compressor side; but the turbine side poses a greater challenge to measurements in the form of heat. |
The turbine side of the turbocharger deals with a lot of heat. Electronics and heat typically don’t get along well together, go figure. Remember the pressure example of trying to measure a larger range (0-20 PSIA vs. 0-100 PSIA) creating a greater error? Well, instead of only having to measure 385 K temperature on the compressor side, we now have to deal with 1250 K on the turbine side (or hotter) making for a much larger range of operation. The high temperatures pose an even greater problem for pressure transducers… as in I don’t think there are any that can handle the temperature directly. Even the compressor outlet temperatures are too hot I think. So that means some type of thermal isolator needs to go between the compressor and turbine flows and the pressure transducers which probably means another potential source of measurement error. Hey, no one said getting the data for calculating turbo efficiencies was easy!
Now you know the basics of what goes into creating compressor and turbine maps. It involves a test cell to house all the equipment and create an environment for controlled and repeatable tests. A gas stand within the cell is needed to generate the exhaust gases to spin up the turbo. Finally, you need a lot of highly accurate temperature, pressure, and mass flow rate sensors along with the associated datalogging equipment; the very high accuracy is required to minimize the error in the efficiency calculations which would otherwise become worthless with too much error. As you can see, creating the maps is difficult which is why only the major turbo suppliers have the ability to do it. In the words of Biggie Smalls, “pimpin’ ain’t easy.”
2 comments
Really nice article for someone to start understanding efficiencies! The turbine side is not too hard to measure the pressure, but you do need to consider the flow conditions and take the average pressure measurement from a few points around the exhaust pipe and not a single one. The bigger problem with the turbine side is that you need to consider heat losses as the delta T to the environment is much larger compared to the compressor side and heat losses will glorify the turbines performance.
Pre turbine pressure is the only relevant one. A few locations around the exhaust manifold is not useful