Plasma fuel processing for NOx control of lean burn engines

A highly reactive reducing gas mixture is produced from vehicle fuel and introduced into the exhaust gas of an internal combustion engine (10) operated at lean burn conditions and passed over a reducing catalyst (15) to covert NOx emissions to benign emissions. The reducing means for producing from fuel used by said engine a reactive mixture substantially in gaseous form comprises a cracking unit (19) and an oxidation catalyst (22). Air (18,20) can be introduced to the cracked fuel prior to passage over the oxidation catalyst.