Always fancied building myself a custom series-like hybrid with a turbodiesel, variable speed generator/direct drive in place of the battery pack and regenerative breaks that dump energy back into the diesel engine using an electronically assisted turbocharger like those occasionally used in F1 (seen below).
My thought behind this is purely from a power: weight ratio perspective, due to substantial weight reduction from a lack of battery pack
OR drivetrain. In theory, extra power should also be gained due to fewer drivetrain losses, and the recycling of regenerative braking system energy to increase power output, rather than extend range. Also, currently few things exceed the energy density of Diesel, at least in terms of automobiles.
Not entirely sure about the engineering aspect,
truly just a dream at this point. Would be interesting to see though...
Ok, so to bring this out of the realm of fantasy for a moment; diesel electric series hybrid drive is not new; it's what is pulling nearly every train in America.
You will need a battery or capacitor (or Porsche flywheel, aka 'kinetic storage') to store power, otherwise there's no place to store energy recaptured from regenerative braking or from excess power developed from the engine while under light load- and no place to get it back from when heavy acceleration or towing demands it.
This battery/energy storage device needn't be very large in capacity, depending on the expected duration of the high load condition; think small for 1/4 mile drag racing, larger for towing.
Series hybrid eliminates transmission, direct drive in favor of generator set and electric traction motors. Think Chevy Volt.
Small turbodiesel would be an excellent choice for generating power due to small size, light weight and the freedom to run at peak efficiency or not at all, no idling or part load conditions to sap efficiency.
Power controller would shift power between genset, battery and traction motors depending on load and state of battery charge.
If high acceleration is desired, then larger capacity power controller is needed, plus fast discharge battery, plus turbodiesel genset running to maximize available power, plus traction motors sized to receive maximum output.
Towing would need larger storage, slow discharge/deep cycle battery pack and the rest would be the same, designed with additional cooling to handle longer duration loads.
Such a setup could deliver both high efficiency and the ability to completely embarrass a big bully truck in a towing match- or, set up differently, 9 sec quarter miles from a small engine and small battery.
PS; electric turbo assistance is completely unnecessary in any of the envisioned scenarios, since the battery would buffer turbo lag.