F MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F01 MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
F01N GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
F01N3/00 Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
F01N3/08 for rendering innocuous
F01N3/10 by thermal or catalytic conversion of noxious components of exhaust
F01N3/18 characterised by methods of operation; Control
F01N3/22 Control of additional air supply only, e.g. using by-passes or variable air pump drives