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Module 7Module 7
Mobile Sources
MCEN 4131/5131
2
PreliminariesPreliminaries• Design night Thursday 7:30? How many will come?• Pizza party at the Sink, Tues May 2 6pm• Conference on World Affairs - 5 HW pts per session, can go to 2 sessions (turn in write ups)• Seminar Thursday 3:30 DLC - 5 HW pts (turn in write ups)
MCEN 4131/5131
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LearningObjectivesfor Today Module 7 Educational Module 7 Educational
ObjectivesObjectives• Impact of mobile sources• Equivalence ratio ER• pollutant emissions under different
combustion conditions – Fuel rich and fuel lean– ER – crank angle
• The IC engine • Add-on technologies that control
emissions – catalytic converter – carbon canister
• Non-combustion related emissions
MCEN 4131/5131
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Clicker Question?Clicker Question?
The rise of mobile sources has altered the field of air pollution control around the world. There are several reasons for this change. Which of the following is NOT a reason discussed in the text?
a. Millions of small sources that move around are more difficult to control than fewer stationary sources
b. The sources of the pollutants are very close to people living and working in urban areas
c. Many vehicles are equipped with 2-stroke engines and these engines are a necessity and difficult to control
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
5
Equivalence RatioEquivalence Ratio
The equivalence ratio, , is defined as:
• A = mass rate of air, F = mass rate of fuel
The Air equivalence ratio, ER, is defined as:
(F/A)actual
(F/A)stoichiometric
(A/F)actual
(A/F)stoichiometric
ER
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
6
ER ExampleER Example
CH2 + (1.5) O2 + (1.5)(3.76)N2 CO2 + H2O + (1.5)(3.76)N2
What is (A/F)stoichiometric?
(1.5 moles O2 x 32 g/mole) + (5.64 moles N2 x 28 g/mole)
(1 mole CH2 x 14 g/mole)
= 14.7 g air / g CH2
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
7
Group Clicker Group Clicker Question?Question?
Will the AFR for a gasoline-burning engine decrease or increase if it is driven in Mexico City and what pollutant emissions will be increased?
a. decrease, NOxb. increase, NOxc. decrease, COd. increase, CO
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
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Fuel Lean vs. Fuel Fuel Lean vs. Fuel RichRich
• What if the system is fuel rich (ER < 1)?– Not all of the fuel is combusted completely– There will probably be some CO, H2, and other
products of incomplete combustion in the exhaust– Not all of the chemical energy has been released as
heat– The final adiabatic temperature will be lower than if
ER=1
• What if the system is fuel lean (ER > 1)? – There will be extra oxygen left over after the
combustion – All of the chemical energy available in the fuel is
definitely released– However, that energy has to heat up more mass in
the form of the extra O2 and N2 – Thus, the temperature is also lower
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
9
Effects of AFR on HC, Effects of AFR on HC, CO, and NOx exhaust CO, and NOx exhaust
emissionsemissions
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
10
Crank Angle Crank Angle influences emissions!influences emissions!
is the angleBefore top dead center
For the purposes ofcontrolling emissions,Some engines are Operated so thatIgnition takes placeSlightly after TDC
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
11
Clicker question?Clicker question?
Why is the combustion in an IC gasoline-burning engine not 100% complete?
a. spark ignition timing is offb. cylinder walls cool
combustion reactionsc. gasoline is contaminated
with sulfur
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
12
Add-On TechnologiesAdd-On Technologies
• Catalytic converter• Carbon canister
– Carbon bed adsorber that collects evaporative emissions of VOCs from hot engine. If carbon is spent, breakthrough will occur and VOCs are not collected (happens if you let your car sit for a long time)
• Positive crankcase ventilation valve
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
13
1st Catalytic 1st Catalytic converterconverter
• Original catalyst fully oxidized CO and HCs left over from incomplete combustion in the cylinders
• The reactions taking place in the catalyst are (where CH2 represents some generic hydrocarbon)– CO + 1/2 O2 CO2
– CH2 + 3/2 O2 CO2 + H2O
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
14
2nd Catalytic 2nd Catalytic ConverterConverter
• Realized this didn’t remove NOx• New 2-stage system used HC, H2,
and CO to reduce NOx to N2
– Reduction by CONO + CO 1/2N2 + CO2
2NO + CO N2O + CO2
– Reduction by H2
NO + H2 1/2 N2 + H2O
2NO + H2 N2O + H2O
2NO + 5H2 2NH3 + 2H2O
– Reduction by hydrocarbons3 NO + CH2 3/2 N2 + CO2 + H2O
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
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3-Way Catalyst3-Way Catalyst
• Introduced in 1979• Combines chemistry of the 2
stage system into a single catalyst
• Requires very tight control over the A/F mixture, must be very near stoichiometric
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
16
Single bed oxidation catalyst
Dual bed catalyst
Single bed 3 way catalyst
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
17
Non-combustion related Non-combustion related emissions from mobile emissions from mobile
sourcessources
• Breathing emissions• Refueling emissions• Running losses• Hot soak losses
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
MCEN 4131/5131
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Clicker question?Clicker question?
Why are oxygenated fuels of high interest?
a. NOx emissions are reducedb. CO emissions are reduced
LearningObjectivesImpact of mobile sourcesEquivalence ratioCombustion conditionsIC engineAdd-onsNon-combustion emissions
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