| abstract |
An exhaust gas emission-control system isndisclosed, wherein exhaust gases are alternately passednthrough either one of a pair of first filters(1,2),nwhich comes selectively in fluid communication with annexhaust pipe with operation of a change-over valve(21).nParticulate emissions in the exhaust gases areneffectively trapped in the first filters(1,2) andnburned away. Then, the exhaust gases are passednthrough a downstream second filter(3), where nitrogennoxides (NOx) in the exhaust gases are decomposed.nBy-pass valves(19,23) downstream of the first filtersn(1,2) are actuated to discharge a gas evolved bynburning the trapped particulate emissions onnregeneration of the first filters(1,2) into the air.nThus, no gas caused by burning the trapped particulatenemissions in the first filters(1,2) may pass throughnthe second filter(3). The second filter(3) isnenveloped with a warm-up gas jacket(16,33) throughnwhich the exhaust gases flow to keep the second filtern(3) at a temperature that is optimal to render ancatalytic compound of brownmillerite-like structureneffective in decomposition of nitrogen oxides (NOx)ncontained in the exhaust gases. |