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Old 10th May 2013, 15:44   #1
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Default Effective utilization of wasted boost pressure (Turbo)

In many modern cars, esp the cutting edge hybrid ones, the goal is not to let go of any energy. Every waste energy source is tapped, and then that is fed back. For example, regenerative braking.
I was wondering, why do we ignore a waste energy source, the turbo charger.

Now a turbo is a turbine. This turbine rotates at high speed under the power of hot gases, and then this turbine powers an air compressor which forces air into the engine. Often Intercoolers are employed to cool this compressed hot air.

The higher the engine RPM, the more speed of the turbine. But too much turbine speed, and your boost pressure can damage stuff.
So you have the wastegate. Above a certain rpm, this wastegate opens, and some gas is expelled as "waste".

Now I am wondering, can a smaller lighter turbo be attached to the waste, and this can power a small air conditioning mechanism, which can cool the intercooler further.
Infact, this waste exhaust gas can also be used to augment the AC compressor, reducing load on the engine esp when the engine is most strained.
When you are doing high RPMs, this waste energy could entirely power your AC.

In theory my idea sounds good to me atleast. Requesting inputs from Automobile engineers and designers on this.
I know its a cost, but in vehicles where we squeeze out everything using stuff like regenerative braking, it seems we are ignoring an abundant source of energy which goes waste through the wastegate.
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Old 11th May 2013, 00:39   #2
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Default re: Effective utilization of wasted boost pressure (Turbo)

Okay I realized this has been already done.
Twin turbo does this. Not Bi-Turbo engines which use two turbo chargers in parallel, but a sequential dual turbo. I think the Quanto uses a two stage turbo charger setup.
The smaller turbo spools at low speeds, and then engine rpm rises and the smaller turbo cannot provide enough boost, the second stage turbo uses the extra waste exhaust to create additional boost.
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Old 11th May 2013, 09:51   #3
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Default re: Effective utilization of wasted boost pressure (Turbo)

Another take; why not use the waste exhaust to power the alternator instead of using engine power directly. That should take the load off the engine and increase efficiency.

Quote:
Originally Posted by tsk1979 View Post
Okay I realized this has been already done.
Twin turbo does this. Not Bi-Turbo engines which use two turbo chargers in parallel, but a sequential dual turbo. I think the Quanto uses a two stage turbo charger setup.
The smaller turbo spools at low speeds, and then engine rpm rises and the smaller turbo cannot provide enough boost, the second stage turbo uses the extra waste exhaust to create additional boost.
Quanto has a twinscroll turbo charger, it doesn't use two turbo chargers.
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Old 11th May 2013, 10:27   #4
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Default re: Effective utilization of wasted boost pressure (Turbo)

1. What is the ratio of used compressed air vs that let out thru waste gate ?
2. Is the wasted air significant enough to be used to continually support a/c ?
3. If yes, what is the break-even of development + manufacturing costs - and what gets passed on to the customer vs cost saved by customer / user during actual usage ?
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Old 11th May 2013, 11:22   #5
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Default re: Effective utilization of wasted boost pressure (Turbo)

Considering a large amount of waste heat available in the engine compartment, wouldn't an absorption refrigeration system be more beneficial in getting something cooled ?

Low efficiency will probably not make it useful for cooling the cabin but intercooler or even other parts can be taken a look at. The system is not complex and the plumbing should be relatively easy.
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Old 11th May 2013, 11:52   #6
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Default re: Effective utilization of wasted boost pressure (Turbo)

At the end of the day, lots of energy produced in a car by burning fuel is wasted - some estimate it to be as high as 75%. Harnessing that wasted energy to improve efficiency adds to the cost and increases complexity. Actually, where exactly the energy is wasted is known to all the car companies. So when Governments introduce new higher fuel efficiency norms every X years, the automobile companies are ready with their new technology.


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Further Reading:

http://www.consumerenergycenter.org/...gy_losses.html

http://www.fueleconomy.gov/feg/atv.shtml
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Old 11th May 2013, 11:56   #7
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Default re: Effective utilization of wasted boost pressure (Turbo)

The problem would be consistent power availability. Then it would require a controller to choose between sources for uninterrupted working which is added cost. Honda had demonstrated a steam generator based one in the engine bay. So you need multiple methods to harness the wasted energy

Last edited by srishiva : 11th May 2013 at 11:59.
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Old 11th May 2013, 12:55   #8
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Default re: Effective utilization of wasted boost pressure (Turbo)

The first obstacle is that the wastegate really wont be open 95+% of the time. Especially in cases where you'd need the A/C most = in traffic etc.

Something you could explore is the Peltier Generator. From what little i know, it uses a temperature difference to generate an electric current.

Car exhaust = very hot (wasted energy). This can be harnessed. I think BMW is working on some concepts where they've lined the exhaust pipes with peltier generators, which then drives some of the cars electricals.



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Old 11th May 2013, 14:30   #9
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Default re: Effective utilization of wasted boost pressure (Turbo)

Quote:
Originally Posted by Rehaan View Post
Something you could explore is the Peltier Generator. From what little i know, it uses a temperature difference to generate an electric current.
The only problem being that Peltiers are horribly inefficient- see this:
http://en.wikipedia.org/wiki/Thermoe...ng#Performance

It will work... just not efficiently. Which is why they are used more often for heat transfer than power generation.
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