Sulfur concentration determination system for an internal combustion engine

A sulfur concentration determination system for an internal combustion engine which is provided with an exhaust gas purification device that is disposed in an exhaust passage and includes an oxidation catalyst, and a supply device that supplies fuel to an exhaust gas flowing into the exhaust gas purification device,

• the sulfur concentration determination system comprising:
• a controller comprising at least one processor configured to:
• carry out poisoning elimination processing which is to eliminate sulfur poisoning of the oxidation catalyst by raising the temperature of the oxidation catalyst;
• carry out fuel supply processing which is to supply fuel from the supply device to the exhaust gas purification device so as to make an amount of fuel supplied to the exhaust gas purification device per unit time constant, when the temperature of the oxidation catalyst is equal to or higher than a predetermined reference temperature which is equal to or higher than an activation temperature, after the end of the poisoning elimination processing;
• measure a physical quantity which is correlated with a period of time required from a starting point in time of the fuel supply processing until the temperature of the oxidation catalyst drops to a predetermined temperature or below which is equal to or higher than a temperature at the starting point in time of the fuel supply processing, under the condition that the fuel supply processing is continuously carried out, the physical quantity becoming larger as the period of time becomes longer;
• and
• make a determination that the concentration of sulfur components contained in the fuel is higher when the physical quantity is small, in comparison with when it is large.