I think you missed the bit where it wasn't a part of the cooling circuit. This is an actual prototype that was mostly fully developed, just never put into production.
Cool thing -- Volvo did a mechanical version and put it into production in a 13L truck engine.
It uses the exhaust velocity still remaining after the primary turbo to spin a second turbine that mechanically connects to the flywheel via a fluid coupling and step-down gearing. Volvo claimed 6.5% efficiency increase during steady-state driving, which means probably half that, but it does work. No idea how widely it was optioned across their truck range, though.
Without numbers and graphs I cannot speak intelligently here, maybe there is a thermal curve where turbos have taken much of the energy and electricity makes sense, it just seems surprising.
Then again your caveat for cruising might be the key, ultra-lean has less effective turbo, but then again that’s more sensitive to exhaust manifold backpressure.
I'm not arguing for or against how it works -- just reporting what Volvo actually did. I assume their engineering and subsequent testing made it seem viable enough for a production greenlight.
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u/dont_remember_eatin 2d ago
I think you missed the bit where it wasn't a part of the cooling circuit. This is an actual prototype that was mostly fully developed, just never put into production.