module 7 mobile sources. mcen 4131/5131 2 preliminaries design night thursday 7:30? how many will...

Module 7Module 7

Mobile Sources

MCEN 4131/5131

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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)

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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

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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

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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


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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


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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


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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


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Effects of AFR on HC, Effects of AFR on HC, CO, and NOx exhaust CO, and NOx exhaust

emissionsemissions


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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


MCEN 4131/5131

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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


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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


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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


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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


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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


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Single bed oxidation catalyst

Dual bed catalyst

Single bed 3 way catalyst


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Non-combustion related Non-combustion related emissions from mobile emissions from mobile

sourcessources

• Breathing emissions• Refueling emissions• Running losses• Hot soak losses


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Clicker question?Clicker question?

Why are oxygenated fuels of high interest?

a. NOx emissions are reducedb. CO emissions are reduced


module 7 mobile sources. mcen 4131/5131 2 preliminaries design night thursday 7:30? how many will...

Documents

air equivalence ratio

rise of mobile sources

fuel rich

rich er

ups slide

fuel lean er crank

engine decrease

mass rate of fuel