Ammonia burning internal combustion engine

An ammonia burning internal combustion engine using ammonia as fuel, comprising a reformer reforming ammonia and producing a reformed gas containing hydrogen, the reformed gas is fed into a combustion chamber in addition to the ammonia, an exhaust purification catalyst is arranged in an engine exhaust passage, a secondary air feeding device is arranged in the engine exhaust passage upstream of the exhaust purification catalyst, an ammonia ratio indicating a ratio of an amount of ammonia fed to a total amount of fuel fed after completion of engine warmup is set in advance in accordance with an operation state of the engine and, when a reforming ability of the reformer is less than a predetermined reforming ability, the ammonia ratio is increased over the ammonia ratio after completion of engine warmup set in advance in accordance with the operation state of the engine and a secondary air is fed from the secondary air feeding device into the engine exhaust passage upstream of the exhaust purification catalyst.