Answer: Three sources of pollutant from gasoline engine:-
1) Carburettor losses
2) Crankcase blow-by
3) Engine exhaust emission
Evaporative losses:-
1. Carburettor losses: occur due to air vent at float chamber. It also occurs due to hot soak losses which occur after the engine has been stopped, as a result of evaporation of petrol stored in the (float chamber) bowl, loss being through vent pipe or through air cleaner.
2. Crankcase blow-by: the blow-by is a phenomenon of leakage past the piston and piston rings from the cylinder to the crankcase. The blow-by HC emissions are about 20 % of the total HC emission from the engine. This is increased to about 30 % if the rings are worn.
3. Engine exhaust emission: complete combustion results carbon dioxide and water vapours. But due to incomplete combustion, the exhaust gas also contains carbon monoxide, unburnt hydrocarbons (UBHC).