he's asking if the 3rd (middle cylinder) has its own spark plug.
i would assume it might, to attempt to get a bit more combustion out of the unburnt fuel.
but, being based off of diesel, it might just combust on its own due to temp/force. im no diesel expert having never owned rarely driven anything with one in it, but i remember them not actually having a fire source except for start up. even then its more of a heater than a fire.