An internal combustion engine has a secondary air supply system and a fuel injection system including a two-fluid injection nozzle operative to inject air and fuel both under pressure into engine intake system. The secondary air supply system includes an air pump and a secondary air supply line extending between the pump and the engine exhaust system. The two-fluid injection nozzle is pneumatically connected to an air distributor provided on the secondary air supply line whereby pressurized air from the air pump is also supplied to the two-fluid injection nozzle and injected thereby together with the fuel to facilitate atomization of the injected fuel as well as to supercharge the engine.