You don’t need so big a change, there were startups making steam cars for pollution reasons until the invention of the catalytic convertor. (The steady continuous flame of a boiler generating far fewer harmful emissions than the pulsing flame of a diesel or petrol engine)

Sure they’re less efficient, but that’s compensated for somewhat by the lack of a gearbox, as well as the fact that modern steam engines are to 1911 steam engines what modern diesels are to this thing