Emissions in engines

1. Emissions in engines
Rampal Singh
B.E. (Mechanical), M.Tech (Production Engineering),
Thrice GATE Qualified

2. Engine emission
Exhaust emission
Unburnt HC
Oxides of carbon
(CO,CO2)
Oxides of nitrogen
Oxides of sulpher
Particulate/sort/smoke
Non exhaust emission
Evaporative losses
Crankcase blowing

3. comnustion
• Ideal combustion – CO2 +H2O+N2+O2+SOX
• Ideal combustion – CO2 +H2O+N2+O2+SOX + UHC +CO+Csoot+NO+NO2

4. Emission from SI Engine
• Rich fuel air mixture would have HC and CO since there is insufficient
oxygen for complete oxidation
• NO and Nox produced at higher temperature
• Nox emission depends on combustion temperature and hence highest
near stoichiometric condition
• Typically max Nox emission happens at slightly lean mixture at this
condition cylinder temperature is sufficiently high and excess oxygen
also

5. What happens in two stroke engine
• Process of scavenging results in unburnt fuel escaping with exhaust
• Lubricant (higher molecular weight)with fuel will also undergo
incomplete combustion that further add to emission
HC
Unburnt fuel
Partially reacted
components

6. Limitation with HC
• Acts as irritant and oderants
• HC reacts with atmospheric gases to form photochemical smog (very
harmful)
• Higher content can be present in rich mixture, they have less oxygen
• Too lean mixture very less fuel to sustain combustion
• Process and causes of HC Emission in SI ENGINE

7. Incomplete
combustion
Due to improper
mixing
Flame
quenching(closer to
wall it may get
quench)
Contamination of
exhaust gases
During expansion of
burnt gases P,T
Decrease

8. 2. Fuel trapped in compression and oil rings
• During compression stroke, the fuel air mixture may be forced into
crevices, during expansion this may back into cylinder known as
reverse blow by effect

9. 3. Valve overlap
• Two thing fuel air mixture escape by simultaneous opening of inlet
and exhaust valve, fuel air mixture may directly flow into exhaust
• More severe at idling and low speed

10. • 4. leakage past exhaust valve
• 5. absorption by wall deposits and lubrication oil

11. CO Emission
• Incomplete combustion, not fully oxidized to CO2
• Colorless and odorless gas
• Formation happens with rich mixture
• CO Is detrimental to engine performance
• Lower in CI engine as operates on lean mixture
• Represents chemical energy could have been converted into thermal
energy

12. NOX Emissions
• NO and NO2
• At high temperature NOX production occurs, it reacts with 02 to form
o3 which harmful for environment
• Nox + sun NO +O +Smog and O2+O O3
• BY decreasing temperature NOX Decreases
• Trade off between reduced NOX and engine performance

13. Particulate
• Solid carbon soot particle contained predominantly in exhaust of CI
Engine
• Commonly seen as heavy exhaust smoke when vehicle accelerates at
higher load

14. sulpher
• Part of fuel
• Oxidise to form SO2 and SO3 Which will combine with water to form
sulphuric

15. Lead
• TEL to increase octane number to reduce knocking