Exhaust gas purification system and exhaust gas purification method

摘要

An exhaust gas purification system which, in a wider temperature range, can reduce and remove nitrogen oxides in an exhaust gas by a reduction catalyst with the use of hydrogen as a reducing agent is provided. The exhaust gas purification system has an electronic control device (41) which controls an EGR valve (4) and an EGR pipe (5) so that the concentration of oxygen in the exhaust gas obtained from a data map based on the state of an engine (10) becomes less than a predetermined value, and which controls a microreactor (19) so that hydrogen is added to the exhaust gas when the concentration of oxygen in the exhaust gas is less than the predetermined value.