The invention relates to an internal combustion engine (10) which comprises a cylinder (14, 54) provided with a piston (16, 56) and a combustion chamber (18, 58) supplied with an air-fuel mixture. The inventive internal combustion engine is characterised in that a cool-flame reactor (26, 66) constructed in such a way that it pretreats said air-fuel mixture. It is possible to control the quantity of air-fuel mixture to be injected. Said internal combustion engine can also comprise an inlet pipe (22) which can be supplied with the pre-treated air-fuel mixture and with air and fuel, an igniting device (46) and a thermal catalyst (40) connected downstream. Said internal combusting engine can operate according to HCCI techniques within a large power and mode range or as a classic internal combustion engine supplied with a cool flame product in order to reduce a pollutant substances emission.