F01N 13/009

Exhaust or silencing apparatus characterised by constructional features {; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups [CPC: F01N1/00] - [CPC: F01N5/00], [CPC: F01N9/00], [CPC: F01N11/00] having two or more separate purifying devices arranged in series}