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This topic is the follow-up to the original topic:

Why are turbo compound engines not more widely used? Why are turbo compound engines not more widely used?

Please, do understand that I am a pure dilettante, and I ask these questions to understand more about modern trends with Internal Combustion Engines (ICEs). I upfront apologize for my ignorance, and maybe mechanical conceptual errors.

According to what was said and written there, I tried to find answers to the following questions.

The original lines which initiated these questions:

So when you design an engine you have a few choices. For instance, you can either increase engine efficiency, or sap energy from the exhaust line. If you employ variable valve timing, for instance, you can extract much more of that exhaust energy and put it into the crankshaft without a turbo. If you instead add a turbo, you've added another set of gears, more moving parts, taken up more space, and added more weight.

Now the turbo might be slightly better at extracting energy than the variable valve timing, but does it offset the additional cost, weight, and reliability?

[1] Why not employ a variable valve timing engine with the addition of the turbocharger?

The rationale behind this will be that the combustion is almost ideal, so even more exhaust gas energy will be deployed to the turbocharger Exhaust Gas Turbine (EGT)?

[2] What about variable valve timing engine with EGT addition which directly applies additional momentum to the crankshaft (probably with the additional CVT gear mechanism in between a ICE and EGT, to synchronize the effort of the ICE engine + EGT)?

This is the one with EGT without turbo charger, rather to use all the EGT energy as mechanical energy (I could not find this patent, and it should be somewhere)?

Furthermore, no (google search) evidence that this one was ever used in the automotive and truck industry?!

[3] Seems that [2] is somehow cheaper than [1], but with a few percentage less efficiency... Is this a known fact (pointing to some papers proving such a hypothesis)?

Thank you all very much in advance, Zoran

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  • $\begingroup$ please define what you mean by GT & SUS. These are not engine terms I am familiar with. I suggest the main problem with your idea is that the energy one can gain from an exhaust-driven turbine will be both extremely small compared to output from the engine's piston-driven power and also at a speed that requires significant gearing to get it to a drive shaft.. $\endgroup$ – Tiger Guy Aug 5 '20 at 20:26
  • $\begingroup$ My bad... SUS supposed to be: Internal Combustion Engine (ICE). GT -> Exhaust Gas Turbine (EGT). Let me fix this in the initial text. Apologies for such catastrophic error/misplacement (SUS on my native language is ICE, I somehow slipped meaning thru my brain). $\endgroup$ – Zoran Stojsavljevic Aug 6 '20 at 17:30
  • $\begingroup$ VVT isn't one thing, it's about twenty different things. And there are about 200,000 different models of engines out there doing literally millions of different jobs. Pick one - then we know what we are working with. $\endgroup$ – Phil Sweet Aug 7 '20 at 0:28
  • $\begingroup$ Thank you for pointing to me strict requirements. Let me try to narrow down [2]. So, let assume that ICE is just basic ICE with EGT added to the crankshaft WITHOUT Turbo Charger added. I hope this one use case, [2], now becomes enough simplistic to be answered upon. $\endgroup$ – Zoran Stojsavljevic Aug 7 '20 at 13:54

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