Method and apparatus for controlling harmful emissions from internal combustion engines

A method and an apparatus for controlling the emission of harmful gases from internal combustion engines (10) fitted with an afterburning catalytic system (24). Primary and secondary air for combustion are fed to the engine (10) by means of a main air-feeding circuit (11) comprising a carburettor (12), as well as by an auxiliary air-feeding circuit (15) in parallel to the carburettor (12). An air-flow control valve (16) in the auxiliary circuit (15), allows to change the air/fuel ratio fed to the engine (10) under the control of an electronic control unit (18). Process data detected by sensors (20-23) from operative parameters of the engine (10), are processed by the electronic control unit (18) which is programmed to actuate the air-flow control valve (16), to operate an automatic starter device (17) of the carburettor (12), and for conditioning the ignition timing. A metered quantity of secondary combustion air is fed into the fuel mixture by modulating the opening time of the control valve (16) by means of control signals provided by the electronic control unit (18), in relation to process data detected from the operative parameters of the engine (10).