Emission Done by S.I Engine

There are three main sources of air pollution due to petrol engine.

1. Exhaust emissions through tail pipe,

2. Evaporative losses through carburetor, and

3. Crankcase blow by.

I) EXHAUST EMISSIONS THROUGH TAIL PIPE :

The Exhaust Emission contains HC, CC and NO2 ( Oxides Of Nitrogen). HC Occurs in exhaust gases due to incomplete combustion. The emission of HC is closely related to many designing and operating factors like induction system , combustion chamber design, air fuel ratio, speed, load and mode of operation. Lean mixture gives lower HC emission.

CO Occurs due to insufficient amount of air in the air fuel mixture or insufficient time for complete combustion. The combustion of nitric oxide (NO) and Nitrogen Dioxide (NO2) ( Called Oxides of Nitrogen No2) occurs only in the engine exhaust. High Temperatures and availability of oxygen are the two main reasons for the formation of No2. The Spark advance and air-fuel ratio are the two important factors which affect the formation of NO2.

II) EVAPORATIVE EMISSIONS :

Evaporative emission takes place from the fuel supply system. The main reason Of Hydrocarbon evaporation is high Temperature. Fuel Volatility , locations of tank, layer of fuel line and mode of operation also affect the evaporation. About 30% of the total hydrocarbon emission is occurring from the fuel tank, Fuel line and carburetor.

III) CRANK CASE BLOW BY :

Crankcases blow by means of the leakage past the piston and piston rings from the cylinder to the crankcase. In blow by gases, there are about 85% of raw HC and rest 15% of the other gases. It is about 20% of the total HC Emission from the engine and may be 30% of the rings are worn out. The blow by the gases are controlled by the crankcase ventilation system.

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