I do plan on Engines similar to Car Engines, which output Rotational Energy at a higher Efficiency but only for selected Fuels, similar to how Fluid Bed Burning Boxes only accept certain Types of Dust Fuels.
They would definitely have a dedicated exhaust for the Gasses that get created, similar to the Steam Engine exhaust of distilled Water, though I might make the output direction less “Stiff” than with that Engine (as in configurable).
And I do have “NO2 injections” on the same point in my TODO List, so unsure if I gonna add that too or not.
As for the Redstone Part, there is a Mode Selector Cover for such things, I do not want to rely on non-cover based Redstone Inputs, which just could pop up randomly from any other Mods Block.
Though the Engine would be a Single-Block thing, that I will say right away.
And things can accept and emit power at the same time no problem, what do you think Battery Boxes do? 