A method and an arrangement for purifying exhaust gas in an internal combustion engine

摘要

The invention relates to a method for purifying exhaust gas in an internal combustion engine (1) provided with a NO x trap catalyst (11) and a particulate matter filter (12) arranged in an exhaust gas conduit (10, 13, 14) of said engine (1), comprising de-sulfurisation of said NO x trap catalyst (11) and regeneration of said particulate matter filter (12). The invention comprises the following steps: initiating a heating phase wherein the engine (1) is set to generate heat sufficient for said de-sulfurisation and said regeneration; initiating a de-sulfurisation phase (22) during a first time period (t 1 ), in which the engine (1) is set to generate a rich exhaust gas in said exhaust gas conduit (10, 13, 14); keeping said first time period (t 1 ) below a maximum value (t 1max ) so as to avoid release of emissions of H 2 S from said engine (1); initiating a regeneration phase (23) during a second time period (t 2 ), in which the engine (1) is set to generate a lean exhaust gas in said exhaust gas conduit (10, 13, 14); keeping said second time period (t 2 ) below a further maximum value (t 2max ) corresponding to a risk for uncontrolled combustion in said particulate matter filter (12); and repeating said de-sulfurisation phase (22) and said regeneration phase (23) in a periodical manner.