Exhaust gas control system for internal combustion engine

An exhaust gas control system for an internal combustion engine, the internal combustion engine being a compression ignition-type internal combustion engine operated to perform lean combustion,

• the exhaust gas control system comprising:
• an upstream purification device disposed in an exhaust passage of the internal combustion engine, the upstream purification device including an oxidation catalyst;
• a downstream purification device disposed in a portion of the exhaust passage downstream from the upstream purification device, the downstream purification device including a selective catalytic reduction catalyst;
• a fuel addition valve disposed in a portion of the exhaust passage upstream from the upstream purification device, the fuel addition valve being configured to add fuel into exhaust gas of the internal combustion engine;
• a urea addition valve disposed in a portion of the exhaust passage between the upstream purification device and the downstream purification device, the urea addition valve being configured to add urea aqueous solution into the exhaust gas;
• and
• a cooling device having a cooling passage configured to carry refrigerant flowing through the cooling passage, the cooling passage being configured such that the refrigerant cools the fuel addition valve first and then cools the urea addition valve subsequent to the fuel addition valve.