Exhaust gas emission-control system

摘要

An exhaust gas emission-control system is disclosed, wherein exhaust gases are alternately passed through either one of a pair of first filters(1,2), which comes selectively in fluid communication with an exhaust pipe with operation of a change-over valve(21). Particulate emissions in the exhaust gases are effectively trapped in the first filters(1,2) and burned away. Then, the exhaust gases are passed through a downstream second filter(3), where nitrogen oxides (NOx) in the exhaust gases are decomposed. By-pass valves(19,23) downstream of the first filters (1,2) are actuated to discharge a gas evolved by burning the trapped particulate emissions on regeneration of the first filters(1,2) into the air. Thus, no gas caused by burning the trapped particulate emissions in the first filters(1,2) may pass through the second filter(3). The second filter(3) is enveloped with a warm-up gas jacket(16,33) through which the exhaust gases flow to keep the second filter (3) at a temperature that is optimal to render a catalytic compound of brownmillerite-like structure effective in decomposition of nitrogen oxides (NOx) contained in the exhaust gases.