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Discussion Starter #1
The goal of a blowdown turbo is to capture the extra force of the charge blowing out of the piston without creating back pressure on the other cylinders. This is essentially free energy that could be recovered and used in an electric turbo compounding scenario where extra energy is set to the power pack.
 

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Any turbo will increase back-pressure somewhat. Nonetheless, I believe there are efficiency gains to be had. Basically what you are describing is a turbo that is hooked up to an electric generator instead of compressing the intake charge. I think it can be done, there are design challenges mostly relating to heat and electronics.
 

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Discussion Starter #4
Not a regular turbo, a blowdown turbo is a little bit like a twin scroll but better. Basically you feed turbofan from three different sides so that you capture energy from the pressure wave without increasing back pressure. It's one of the things they are doing with formula 1 to increase the thermal efficiency.
 

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Interesting concept, but the Insight has just 3 cylinders so the exhaust valve openings don't overlap at all. No benefit to feed from different sides.
 

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Discussion Starter #6
So the pressure waves would be naturally separated and wouldn't cause any back pressure on the other cylinders? The idea is to absorb as much energy as possible from the pressure wave without adding back pressure to the other cylinders.

Again this is something that they've been doing in formula 1 and apparently Mercedes is getting better thermal efficiency then we are with our insights.
 

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A formula 1 car has 6 cylinders, and the turbo has two inlets, one for each bank of 3 cylinders. With 6 cylinders you get some valve overlap where two exhaust valves are open at the same time. With only 3, there is no overlap.
 

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Discussion Starter #8
Thank you for explaining this to me.

So it sounds like the best way to capture the pressure wave energy without increasing back pressure would be to use a very very small turbo and a wastegate up closer the engine.

Using the hybrid battery and a generator to create a turbo compounding engine would be cool. You would be able to capture smaller amounts of energy that in instances where a normal turbo cannot. For example you can gain energy during a throttled scenario such as a lean burn where you would not want to turbo counteract the throttle and be a waste of energy. Electro turbo compounding could increase the efficiency and window of lean burn. Anyone who's used a mima similar system would understand how a little bit up electro boost really makes a big difference. This can be combined with throttle displacement energy recovery elctrocompounding which is also able to increase efficiency and lean burn. Then add a rankine cycle waste heat to energy system and 55 to 60% thermal efficiency should be possible.

It should be possible to out perform modern power plants in theory because the energy of motion can allow for more effective cooling. Especially if one radiates extra heat through the skin of the body panels in the back of vehicle... So some of the low grade heat could be used to reduce drag.
 
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