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Old 07-08-2020, 04:39 PM   #11 (permalink)
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Originally Posted by cRiPpLe_rOoStEr View Post
Stopping the compressor and decoupling it from the turbine doesn't seem to be any beneficial.
If that were true, then electronic wastegates wouldn't be useful.

Spinning the compressor at part throttle is wasted energy because the precise opposite of what you need is more airflow and more pressure. Converting that turbine shaft power to electricity is harvesting wasted energy.

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Old 07-08-2020, 10:38 PM   #12 (permalink)
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Originally Posted by serialk11r View Post
If that were true, then electronic wastegates wouldn't be useful.
But they don't decouple anything. Their purpose is to better direct the exhaust flow and to provide some eventual restriction as some sort of exhaust-brake.


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Spinning the compressor at part throttle is wasted energy because the precise opposite of what you need is more airflow and more pressure.
It used to be more critical for older vehicles with either a carburettor or port-injection than with the newer direct-injection gassers, not to mention the downsizing trend.


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Converting that turbine shaft power to electricity is harvesting wasted energy.
Just like some engines have an intercooler bypass for cold start maybe a compressor bypass could be tried, as long as some coupling from the center shaft of the turbo to a motor-generator is provided.
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Old 07-09-2020, 12:43 AM   #13 (permalink)
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An electronic wastegate reduces the amount of engine power being sent to the turbine which will just be wasted on spinning a compressor at part throttle.

If you have a turbine that minimizes backpressure and use an electric motor to give the compressor a boost, then if you decouple the compressor you can extract a small amount of free electrical power even at part throttle.

The principle is the same: Don't send power to the compressor if you don't need it. You can think of the power in the second case as power from the battery. In the first case, it's power supplied via backpressure.

In practice, an engine isn't producing much blowdown energy at part throttle, so there's not much to collect, but hypothetically, a hypermiler would be better off deleting the compressor for efficiency.
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Old 07-09-2020, 06:19 PM   #14 (permalink)
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Quote:
Originally Posted by serialk11r View Post
If you have a turbine that minimizes backpressure and use an electric motor to give the compressor a boost, then if you decouple the compressor you can extract a small amount of free electrical power even at part throttle.
Finding a safe way to decouple the compressor is the most challenging. Maybe instead of decoupling the compressor, it's still easier to divert the exhaust flow to another turbine connected to a generator, in a way somewhat similar to those twin-stage turbocharging setups.


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In practice, an engine isn't producing much blowdown energy at part throttle, so there's not much to collect, but hypothetically, a hypermiler would be better off deleting the compressor for efficiency.
To some extent it could help while cruising, but not all the time. At least not for most engines developed around the downsizing trend.
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Old 07-09-2020, 08:28 PM   #15 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Finding a safe way to decouple the compressor is the most challenging. Maybe instead of decoupling the compressor, it's still easier to divert the exhaust flow to another turbine connected to a generator, in a way somewhat similar to those twin-stage turbocharging setups.

To some extent it could help while cruising, but not all the time. At least not for most engines developed around the downsizing trend.
Yea I think the easier way is to have the turbine spinning a generator, and then the compressor separately powered. Of course, that means more parts and more money.

I apologize, you're right, on throttle-less engines and high-volume EGR engines operating at medium load, light boost can possibly be beneficial for efficiency, but the compressor itself would probably be operating inefficiently at part throttle.
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Old 07-11-2020, 05:40 PM   #16 (permalink)
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Originally Posted by serialk11r View Post
Yea I think the easier way is to have the turbine spinning a generator, and then the compressor separately powered. Of course, that means more parts and more money.
Something like this, being assisted by a turbine-powered generator, might be the easiest way to perform what you were considering, but it's also far from being so cheap.



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