Automobile Pollution Control Engineering�(Principle of production of exhaust gases.)

Automobile Engineering Department

(L.J.Polytechnic-Ahmedabad)

Content

• 2.1 Theoretical air-fuel ratio.
• 2.2 Carbon monoxide (CO) gas.
• 2.3 Hydro Carbon (HC) gas.
• 2.4 Oxides of Nitrogen (NOx).
• 2.5 Driving conditions and exhaust gases.

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Air –Fuel Ratio

• Air–fuel ratio (AFR) is the mass ratio of air to fuel present in a combustion process such as in an internal combustion engine .
• The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 15:1.
• Lean-burn refers to the burning of fuel with an excess of air in an internal combustion engine. 65:1
• Lean mixtures are more efficient but may cause engine damage or premature wear and produce higher levels of nitrogen oxides.

• Rich mixtures are caused by too much fuel or not enough air. Engines that run rich or lean will create excessive exhaust emissions. If the engine is starved for fuel (too lean), or getting flooded with fuel (too rich) it will fail to start and run.
• Complete Combustion: 4HC+5O2=4CO2+2H2
• Incomplete Combustion:3HC+2O2=H2O+CO2+HC+CO

• Petrol Engine Exhaust: CO ,HC, Nox.
• Diesel Engine Exhaust: Nox.
• Sources for Unburnt HC:
• Blow By
• Unburnt Fuel
• Carbon Deposit
• Engine Oil
• Improper Combustion.

Effect of Air Fuel Ratio Amount on Exhaust Gases Pollutant

• Less emission & Low consumption of fuel at correct air fuel ratio.
• Low temperature at correct air fuel ratio, Stop the production of Nox
• Less emission of HC and CO at correct air fuel ratio.
• Rich Mixture : Incomplete combustion occurs and it will raise the proportion of HC and CO
• Lean Mixture : Will produce NOx (More Oxygen)

Factor Affecting Production of Exhaust Gases

• Unburnt Fuel, Engine Warm Up Time, Load , Engine Idling, Presence of water in Combustion Chamber (White Smoke).
• Insufficient Air Fuel Mixture, Black smoke produce by Rich Mixture.
• Wearout of Cylinder Liner, Piston Ring, Lubricating oil blue smoke.

Smog

• Smog is a kind of air pollution, originally named for the mixture of smoke and fog in the air.
• NOx and HC react with air and produce smog.
• Factor for Production of smog.
• HC and NOx Pollutant
• Steady Air & Sunlight
• Effect of Smog: Reduce Visibility, Problem in respiration system, Head Ache

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HC GAS

• Sources & Causes for Production of HC.
• Unburnt Fuel because of unreachable flame.
• Unburnt fuel from Quenching Zone
• Lubrication oil layer absorb the fuel before burning and release it after burning.
• Rich Mixture cause Incomplete combustion.
• Evaporation of Fuel
• Blow By Gas
• Ill effect of HC.

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Quenching Zone

• those parts within the combustion chamber of an engine where the temperature of the A/F mixture is lower than necessary for optimum combustion, due to contact with the relatively cold metal surface; incomplete combustion in the quench zones is one of the two major factors contributing to HC and CO concentrations in the exhaust gas.
• It also depends on concentration Air Fuel Ratio.

• Complete combustion reduced amount of CO & HC , Followings are factor because of engine exhaust of HC.
• Incorrect Air-Fuel Ratio.
• Low Compression
• Valve Overlapping
• Quenching

Incorrect Air Fuel

• Rich Mixture Increase HC emission.
• More Lean Mixture also increase HC amount.

Low Compression

• Leads Incomplete Combustion.

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Valve Overlapping

Definition & Explanation Auto Engine.

Quenching

CO GAS

• Production and Ill effect of CO Gas.

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Remedies for Reducing CO Gas

• Use Three way Catalyst
• Gradually closing of throttle Valve by using throttle position sensor.
• Air Injection system to convert CO in CO2.
• Hot ideal compensating valve to stop rich air fuel mixture.
• By using catalyst convertor to convert CO in CO2
• Reducing overloading
• By Using MPFI system instead of Carburetor.

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• Minimizing Idling time
• By using lean Mixture.
• By using proper grade fuel.
• By stopping acceleration while vehicle is steady.
• By using supercharging and Turbocharging.

NOx-Nitrogen Oxide

• Temperature -1645 K

Remedies of Reduction of NOx Concentration

• Reducing temperature in Combustion chamber
• Spark Retard
• Reducing Speed
• Reducing Compression Ratio
• EGR
• Reducing NOx proportion in flame front
• By using rich mixture
• By reducing Homogeneity.

Driving Condition –Air Fuel Ratio

• Warm up
• Idling
• Steady Running
• Accelerating
• Decelerating
• Heavy Load

Warm Up

• Engine Cold Start-Coolant Warm Up to Normal Temp.
• Gasoline will not vaporize sufficiently.
• Rich-5:1 Gives CO and HC

Idling

• Temp falls due to fuel doesn’t vaporize sufficiently .
• Insufficient temperature will not vaporize completely.
• 11:1 CO & HC due to incomplete combustion
• NOx reduce because of lower temperature.

Steady Running

• Low and Medium Speed:
• Air Fuel Ratio is Leaner 16 to 18:1 more temp exhaust Nox.
• Rise in temperature.
• High Speed:
• Rich 13 to 14 : 1
• CO,HC,NOx

Acceleration

• Throttle Valves open wide increase amount of air sucked in manifold.
• 8:1
• CO,HC,NOx

Decelerating

• Close throttle
• Strong Vacuum in combustion chamber and intake manifold.
• Lower the speed of the flame propagation cause incomplete combustion.
• Unburned HC & CO.
• Vacuum cause the fuel adhering to manifold walls to evaporate extremely rapidly. Increase Concentration of CO and HC. Lower the combustion chamber temperature.

Heavy Load

• Throttle is fully open, Rich Air Fuel
• 11 to 13:1
• CO,HC,NOx

Air Injection System

• Air injection is a method of reducing exhaust emissions by injecting air into each of the exhaust ports of an engine so that air mixes with the hot exhaust and oxidises HC and CO.
• Basic System Components and Operation
• The basic air injection system constitutes the following components :�(i) Air supply pump with filter.�Hi) Air manifolds and nozzles.�iiii) Anti backfire valve.�(iv) Check valve.�(v) Connecting hoses.

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