Abstract: An exhaust-gas after-treatment device having an oxygen storage capacitor substance which releases oxygen when the exhaust-gas is rich in air-fuel ratio and stores oxygen and heats up by itself when the exhaust-gas is lean in air-fuel ratio. The air-fuel ratio for the exhaust-gas flowing into the device is regulated so as to alternately come into the rich condition and the lean condition when the temperature of the exhaust-gas is not higher than a given temperature and when the device is not in a regeneration condition. Thus, when the device having a deNOx catalyst and a diesel particulate filter is not in a regeneration condition, the temperature of the device is raised by utilizing the self-heating function of the oxygen storage capacitor substance during oxygen absorption. As a result, the purification rate for NOx and particulate matter at the time when the temperature of the exhaust-gas is low is improved.

Abstract: In an exhaust-gas after-treatment device (10,10A) having an oxygen storage capacitor substance which releases oxygen when the exhaust-gas is rich in air-fuel ratio and storages oxygen and heats up by itself when the exhaust-gas is lean in air-fuel ratio, the air-fuel ratio for the exhaust-gas flowing into the exhaust-gas after-treatment device (10,10A) is regulated so as to alternately come into a rich condition (R) and a lean condition (L) when the temperature (Tg) of the exhaust-gas is not higher than a given temperature (Tc) and when the exhaust-gas after-treatment device (10,10A) is not in the condition of being regenerated. Thus, when an exhaust-gas after-treatment device (10,10A) having a deNOx catalyst and a DPF is not in the condition of the regeneration of deNOx catalyst, DPF regeneration, or the like, the temperature of the exhaust-gas after-treatment device (10,10A) is raised by utilizing the self-heating function of the oxygen storage capacitor substance during oxygen absorption.

Abstract: To provide an exhaust gas purifying system and a control method therefor, capable of burning and removing PM collected at the downstream side of a DPF by utilizing HC and CO generated when performing the operation for recovering the NOx direct reduction type catalyst from a catalyst deterioration due to poisoning with sulfur.

Abstract: A NOx purging system using a direct reduction type NOx catalyst, wherein sulfur is purged while avoiding the occurrence of secondary sulfur poisoning, taking advantage of capability of recovery from deterioration caused by sulfur poisoning at exhaust gas temperature exhibited at normal operating zone, so that the influence of sulfur poisoning can be eliminated and NOx is efficiently purged; and a method of reactivating deteriorated catalyst therein. In particular, a NOx purging system (10) comprising exhaust gas passage (2) and, arranged therein, direct reduction type NOx catalyst (3), which NOx purging system (10) is fitted with first sulfur purge control means (222) for performing such first sulfur purge operation that when exhaust gas temperature (Tg) becomes higher than given set temperature (T1) during normal operation, not only is the oxygen concentration of exhaust gas decreased but also the exhaust temperature (Tg) is raised to not below sulfur purge temperature (Tr).

Abstract: The present invention provides a method of deciding on catalyst deterioration in an exhaust gas decontamination system, which method enables making an accurate decision on the state of deterioration of catalyst caused by sulfur poisoning in a NOx purging system using a direct reduction type NOx catalyst in the purging of NOx from exhaust gas. In particular, a method of deciding on catalyst deterioration in a NOx purging system (10) comprising exhaust gas passage (2) and, arranged therein, direct reduction type NOx catalyst (3), wherein when the operating condition of engine (1) is within a deterioration decision zone and is of stationary operation, an exhaust gas for decision is generated and wherein when the concentration of NOx in exhaust gas (Cnox) resulting from pass of the exhaust gas for decision through the direct reduction type NOx catalyst (3) is not below prescribed decision level (Cnoxlim), the direct reduction type NOx catalyst (3) is judged as being deteriorated.