Why two spark plugs for each rotor?
Why, to sell you more spark plugs and spark plug wires at each tune-up, of course! Actually the upper pair of plugs, called the “trailing”, reduce emissions considerably, and improve power by a small amount as well, compared to using only the leading plugs. This happens because of the polymorphic nature of the rotary combustion chamber, which changes both in shape and position as the combustion process takes place.
