A practical approach for rapid catalyst light-off by means of strategic engine control

Cold-start emissions pollution from gasoline engines has always been an iss ue in the urban driving cycle as it contributes a significant share of the overall engine emissions in a typical car journey. Rapid engine warm-up and catalyst light-off are two important factors deciding the overall exhaust emissions in a gasoline-powered electronic fuel injection (EFI) engine. Thi s paper presents a practical approach for rapid catalyst light-off by means of strategic engine control. An existing engine control unit (ECU) was rep laced by a programmable engine management system (EMS) so that idling speed , excess-air factor and spark timing can be optimized for improved catalyst light-off at the engine cold-start phase. Results show that with a proper high value of ignition retard (HVIR) control strategy the catalyst light-of f time can be shortened to about 40 s with idle speed set at 1750 r/min. Co mpared with the normal spark timing setting, the cumulative tailpipe emissi ons during the cold-start phase have been decreased by 90 per cent for CO, 80 per cent for hydrocarbons and 65 per cent for NOx with HVIR implementati on. A further increase in the idle speed to 2000 r/min, if allowable, could reduce the catalyst light-off time to less than 30 s from engine cold-star t.