Internal combustion engines (ICE) emit significant pollutants, primarily due to the incomplete combustion of fossil fuels, which releases carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into the atmosphere. Key factors contributing to these emissions include non-stoichiometric combustion and impurities in fuel and air, leading to environmental issues such as global warming and smog. Additional emissions result from crankcase blow-by and evaporative losses from fuel tanks and carburetors during operation.

1. Subject: Internal Combustion Engines(2161902)
Topic: Pollutants from SI Engine

2. Pollutants from SI Engine
• An internal combustion engine operates by burning of
fossil fuels.
• Exhaust emission are major contribution to
environmental pollution.
• If combustion is incomplete, the only products being
produce from the exhaust would be water vapor and
carbon dioxide.
• The major pollutants emitted from the exhaust due to
incomplete combustion are: CO, HC, NOx.

3. Pollutants from SI Engine
• The main causes of emissions are non-stoichiometric
combustion of nitrogen and impurities in fuel and air.
• The emissions exhausted into the surroundings
pollute the atmosphere and causes the global
warming, acid rain, smog and other health hazards.
• IC engines are more responsible for too much
atmospheric pollution.

4. Pollutants from SI Engine

5. Pollutants from SI Engine
• Crankcase blow by fumes, it is due to leakage of
heating oil and burning fuel from combustion space
to the crankcase through piston rings.
• Due to wall quenching effect, air-fuel mixture is
trapped in the piston rings and not able to burn called
raw HC.
• Raw HC along with some burned gases and
lubricating oil is reached to crankcase .

6. Pollutants from SI Engine
• Evaporative losses:
– The fuel tank losses take place by vaporization of
petrol from tank, vapor escape the tank through a
breather vent to the atmosphere or vaporized
during filling the petrol into the tank.
– The carburetor losses take place during engine
idling operation and during parking the vehicle just
after the engine has been stopped.

7. Pollutants from SI Engine
• Exhaust emission, in SI engine exhaust gas
contains unburned HC, CO, NOx.
– Incomplete combustion
– Surface volume ratio
– Compression ratio
– Crevice volume and flow in crevice
– Valve overlap
– Leakage past the exhaust valve
– Deposits on walls
– Oil on combustion chamber walls

8. Pollutants from SI Engine
• Carbon monoxide emission, CO is intermediate
product of combustion remains in exhaust if there is
not enough Oxygen to convert to Carbon dioxide,
known as incomplete combustion.
• Maximum CO is generally formed when the mixture
is rich.
• Theoretically, petrol engine exhaust is free of CO if
the air fuel ratio is 16:1.

9. Pollutants from SI Engine
• Oxides of nitrogen emission, The main reason for
generation of NO and NO2 is high temperature and
availability of O2.
• The maximum NOx levels are observed with air fuel
ratios between 14:1 to 16:1.
• It is very undesirable, because it reacts to the
atmosphere in presence of sunlight to form ozone and
causes photochemical smog.

10. Pollutants from SI Engine

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