Misfiring characteristics during cold-start in an EFI LPG engine

Experiments were conducted in a 125 cm3 single cylinder EFI SI engine fuelled with LPG. The complete misfiring of designed cycles was created by absence spark ignition. The effect of different cycles during cold-start on start-up speed and HC emissions with single-cycle misfiring, continuous two-cycle and three-cycle misfiring was studied. The HC emissions at different misfiring ratio during the first 120 cycles from cold-start were compared. The key cycle affecting cold-start speed and HC emissions were found experimentally, i.e. the ideal first firing cycle and the next cycle. Misfiring of the ideal first firing cycle has a strong effect on HC and start-up speed in cold start. Misfiring in the next cycle after the ideal first firing cycle affects the HC emissions secondarily. Misfiring of the other cycles have similar effect on HC emissions. Heightening the start-up speed was helpful for the stability of idle running. HC emissions are in a certain proportion to misfiring ratio. With one time increase of misfiring ratio, HC emissions increased by one time approximately. When the misfiring ratio was higher than 5%, the total HC emissions increased rapidly.