Module 2:Genesis and Mechanism of Formation of Engine Emissions
  Lecture 7:Mechanisms of CO and HC Formation  in SI Engines
 


HC EMISSIONS FROM SI ENGINES

Main sources of hydrocarbon emissions in the four-stroke, homogeneous charge spark ignition engines are:

(i)
    Flame quenching on the cylinder walls
(ii)
    Flame quenching in crevices
(iii)
    Absorption and desorption in oil film on cylinder walls
(iv)
    Absorption and desorption  in carbon deposits in the chamber
(v)
    Misfired combustion or bulk gas quenching
(vi)
    Liquid fuel in the cylinder
(vii)
    Exhaust valveleakage,and
(viii)
    Crankcase blow by gases

In the vehicles, fuel evaporation from fuel tank and fuel system is another source of unburned HC emissions.