CEE 452/652

Week 6, Lecture 2Mobile Sources

Dr. Dave DuBoisDivision of Atmospheric Sciences,

Desert Research Institute

2

Today’s topics

• Read chapter 18• Dr. Kavouras will lecture next 2 weeks• Fuel controls• Add-on controls• Evaporative controls• Emissions testing• MOBILE model• Quiz

3

Reid Vapor Pressure-Review

• RVP is measured in pounds per square inch (psi)

• The lower the psi in gasoline, the less evaporative emissions that generally will occur

4

California Reformulated Gas-RVP

• In California, the RVP standards were 9.0 psi until the CaRFG1 regulations were implemented in 1992, which lowered the RVP standard to 7.8 psi

• In 1996, with the implementation of the CaRFG2 regulations, the RVP standard was reduced to a flat limit of 7.0 psi– At a cost of $4 billion on capital equipment at refineries– Emissions benefits equivalent to removing 3.5 million

vehicles from California’s roads• In 2004, the CaRFG3 regulations are

implemented with a RVP flat limit of 6.9 psi– Remove MTBE as oxygenate

5

California Reformulated Gas-RVP

From CARB CaRFG2 staff report 1991http://www.arb.ca.gov/fuels/gasoline/carfg2/carfg2.htm

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Controls: Fuel Composition

• Reformulated gas: Phase II RFGPrevents fuel from evaporating as quickly as conventional gasolineContains oxygenate to improve combustion

Clean Air Act requires those metropolitan areas with worst ozone to participate in program

Map from US EPA

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California Reformulated Gas-RVP

Map from California Air Resources Board

April to end of Oct

May to end of Sept

June to end of Oct

May to end of Oct

Regulated according to warm season

8

Controls: Oxygenated Fuels• The Clean Air Act Amendments (CAAA) of 1990 requires

the Federal Wintertime Oxygenates Program• Section 211(m) of CAAA requires states to implement an

oxygenated gasoline program in those areas designated nonattainment for the Federal carbon monoxide (CO) standards, which began in the winter of 1992

• These requirements are in effect during the portion of the year in which an area is subject to high ambient concentrations of CO

• Regulatory control period of no less than four months (usually November, December, January, and February)

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Controls: Fuel Composition

• Oxygenated fuels– The Clean Air Act requires RFG to contain 2

percent oxygen by weight• CA tried unsuccessfully from EPA to allow percent

oxygen to be less than 2% in the warm months since it interferes with ability to reduce NOx and O3formation

– Reduces CO and VOC– The CAA does not specifically require MTBE– Refiners may choose to use other oxygenates,

such as ethanol or methanol

10

Controls: Add-on Controls

Catalytic converter• Oxidation of CO and VOC to end products CO2

and H2O• Chemical reduction of NOx to N2 and O2

• Uses 3-way catalyst: Oxidation-reduction (three-way) catalyst (TWC) for HC, CO, and NOxaccording to:

NO + CO + HC Pt - Rh

N + CO + H O2 2 2→

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Add-on Controls: Catalytic Converter

A three-way catalytic converter has three simultaneous tasks:

1. Reduction of nitrogen oxides to nitrogen and oxygen: – 2NOx → xO2 + N2

2. Oxidation of carbon monoxide to carbon dioxide: – 2CO + O2 → 2CO2

3. Oxidation of unburned hydrocarbons (HC) to carbon dioxide and water: – 2CxHy + (2x+y/2)O2 → 2xCO2 + yH2O

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Add-on Controls: Catalytic Converter

• Platinum (Pt) and rhodium (Rh) are used as a reduction catalyst

• Platinum and palladium (Pd) are used as an oxidization catalyst

• Cerium, iron, manganese and nickel are also used, though each has its own limitations

• Can be used on gasoline, diesel, liquifiedpetroleum gas (LPG), compressed natural gas (CNG)

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Add-on Controls: Catalytic Converter

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Add-on Controls: Catalytic Converter

Figure from International Catalyst Technology,http://www.ictcatalyst.com/indexMirrored.html

3-Way Catalyst

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Controls: Add-on Controls

• Positive Crankcase Ventilation (PVC) Valve– Works in conjunction with carbon canister

(small carbon bed adsorber) that collects evaporative emissions from hot engine when off

– When car started, carbon desorbed by mixing in intake air through carbon bed and vented back into cylinders

– PVC valve is to route air from crankcase to cylinders

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Controls: Add-on Controls

• Trap-Oxydizer on diesels– Combination catalytic converter and

particulate filter– Soot and diesel emissions are caught on the

trap and later oxidized– NOx is trapped on alkali or alkaline earth

materials (the “sorber” catalyst component)

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Other Effects on Emissions• Environmental factors such as elevation,

temperature– Air density decreases as height increases– Cold starts– Manufacturer optimization at 75°F

• Operation and maintenance– Engine maintenance – Driving sensibly– Not overloading vehicle– Using proper fuel– Proper air in tires

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Emissions Testing

• New vehicle performance standards base on Federal Test Procedure (FTP)– Approximates average urban driving:

numerous accelerations, deaccelerations, stop-and-go patterns

– Based on 1970s Los Angeles driving pattern– Uses chassis dynamometer– Results go into emissions model (MOBILE),

emission tables and used in air quality planning

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Emissions Testing: FTP

Figure taken from EPA, http://www.epa.gov/otaq/sftp.htm

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Emissions Testing0

30

60

90

120

L1 P

1

L1 P

2

L1 P

3

L1C

L2 P

1

L2 P

2

L2 P

3

L2C

L3 P

1

L3 P

2

L3 P

3

L3C

M1

P 1

M1

P 2

M1

P 3

M1C

M2

P 1

M2

P 2

M2

P 3

M2C

M3

P 1

M3

P 2

M3

P 3

M3C

Em

issi

ons

(mg/

mi)

0

170

340

510

680

H1

P 1

H1

P 2

H1

P 3

H1C

H2

P 1

H2

P 2

H2

P 3

H2C

H3

P 1

H3

P 2

H3

P 3

H3C

S1

P 1

S1

P 2

S1

P 3

S1C

S2

P 1

S2

P 2

S2

P 3

S2C

S3

P 1

S3

P 2

S3

P 3

S3C

Em

issi

ons

(mg/

mi)

0

1500

3000

4500

6000

D1

P 1

D1

P 2

D1

P 3

D1C

D2

P 1

D2

P 2

D2

P 3

D2C

D3

P 1

D3

P 2

D3

P 3

D3C

Em

issi

ons

(mg/

mi)

Elements NO3&SO4 Org (p) Org (g) EC OC

9209

Summer fleet emission rates by chemical group for the various vehicle categories and FTP phases.

Denver metropolitan area in 1997

Fujita et al. (1998) Northern Front Range Air Quality Study, Volume I

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Emission Testing

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.09019

97

1996

1995

1994

1993

1992

1991

1990

1989

1988

1987

1986

1985

1984

1983

1982

1981

1980

1979

1978

1977

1976

1975

1974

1973

Frac

tion

of V

ehic

les

model year distribution from study in 1997 in Metro Denver area

Fujita et al. (1998) Northern Front Range Air Quality Study, Volume I

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Heavy Duty Emissions Testing Inertial Engine Engine Odometer Sample PM HC CO NOx

Vehicle Use GVWR Weight Manufacturer Model Mileage Number (mg/mi) (g/mi) (g/mi) (g/mi)

Food Delivery 33000 23667 International DT466 142242 2 471.31 0.41 2.65 12.33

Lease 25500 18049 Navistar DT408 122406 5 668.37 1.31 16.19 16.95

RTD Bus 38000 34867 DDC Series 50 85200 6 457.19 0.10 18.51 43.09

Dump Truck 28000 23667 International DT466 89528 7 443.99 0.09 14.02 31.93

Lease 11050 9550 Isuzu 215c 4CU 82618 8 1633.85 1.79 13.93 10.02

School Bus 28000 22960 GMC 8.2 L 89054 10 1759.03 1.49 1.57 4.18

RTD Bus 38000 34867 DDC Series 50 85200 12 1026.68 0.58 6.09 17.57

Food Delivery 80000 48250 Cummins N14 47797 13 1256.88 1.00 11.4 23.83

Dump Truck 80000 55000 Cummins NIC 350 595606 14 309.96 0.13 12.44 34.54

School Bus 30000 23960 Cummins B5.9 62549 15 304.75 0.23 18.14 47.44

Furniture Delivery

22000 17120 Isuzu 6BG1XN 150788 16 516.64 1.41 8.17 16.32

Concrete Mixer 60000 42150 Cummins L10 96262 17 2123.45 3.76 11.42 17.52

Dump Truck/Plow

36220 29010 Navistar DT466 5320 18 1692.69 0.64 16.4 16.27

Garbage Hauler

50000 44237 Cummins LT A10 72251 24 741.02 2.12 9.33 23.15

Dump Truck/Plow

33000 24800 Navistar DT466 101925 32 4506.28 1.24 65.16 34.09

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Emission Model• MOBILE6 vehicle emission factor model from

EPA• which is a software tool for predicting gram per

mile emissions of:– Hydrocarbons (HC)– Carbon monoxide (CO)– Oxides of nitrogen (NOx)– Carbon dioxide (CO2)– Particulate matter (PM) and air toxics

• from cars, trucks, and motorcycles under various conditions

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Emissions Testing

• Inspection and Maintenance (I/M) or “smog testing”– Regular vehicle inspections to check vehicles

meet minimum emission standards– Only highly emitting vehicles fail– Reduces the “super emitters” from the fleet