Vehicle Emission Measurement

10-06-2019

Andriannah Mbandi, PhD

Stockholm Environment Institute, Africa Centre

Combustion Process

Ideal Combustion λ = 1

Fuel

Fuel

Fuel

CO2

CO2

CO2

O2

O2

O2

Combustion processLean Mixture λ > 1

Rich Mixture λ < 1

Fuel

Fuel

Fuel

CO2

CO2

CO2

O2

O2

O2

O2

O2 O2

O2

Fuel

Fuel

Fuel

CO2

CO2

O2

O2

Unburnt

Fuel

CO

O

Combustion gas: oxygen (O2)• O2 levels inverse of CO levels-

without air injection system

• Lean Mixture: O2

• Rich Mixture: O2

• O2 content increases sharply as λ>1

© http://www.youtube.com/watch?v=nIhDLnTGMAE

Combustion gas: carbon dioxide (CO2)

• Result of complete combustion

• Overall combustion and catalytic converter efficiency

• Not a pass or fail gas

• CO2: 12-16%

Combustion gas: carbon monoxide (CO)

• Incomplete combustion

• Excess fuel = rich mixture

• Partially burnt fuel

• Catalytic converter requires air/fuel ratio to vary lean to rich➢ Pre-catalytic converter: CO<1.5%

➢ After catalytic converter: CO~0%

• Feedback carburetted engine ran rich at idle: CO~9%

Combustion gas: hydrocarbons (HC)

• Unburned fuel due to incomplete combustion

• All engines produce HC:➢ Pre-catalytic converter: 150-300 ppm

➢ After catalytic converter: ~0 ppm

• Wasted fuel ➢ 1% partially burnt fuel produce 200 ppm HC

Combustion gas: oxides of nitrogen (NOX)

• Primary contributor of ozone

• Formed under high T & P: not formed at idle or light loads

• Lean mixture at high T: excess O2 molecules combine to form NOX

• Exhaust gas recirculation(EGR): O2 and T

Combustion gas: oxides of sulphur (SOX)

• High sulphur (S) content in fuel

➢ Reduction in S content reduces emissions in exhaust

➢ Marine engineshave higher contribution

© Bilfinger, 2014

Combustion particles-particulate matter (PM)

• Formed in combustion cylinder and in the exhaust system of the vehicle.

• Mostly attributable to heavy duty diesel vehicles

Mix (condensed) liquid & solid-Organic or Inorganic

• Sulphates• Nitrates• Ammonia• Sodium chloride• Black Carbon• Mineral dust• Water

©ARB, 2009

Source apportionment: what are the sources of urban air pollution?

Source: Karagulian, F. et al. (2015) ‘Contributions to cities’ ambient particulate matter (PM): A systematic review of local source contributions at

global level’, Atmospheric Environment. doi: 10.1016/j.atmosenv.2015.08.087.

Impact of air pollution in Africa?

GBD (2016) Global burden of Disease Study 2015-Results by risk factor-country level (online data base-Viz Hub-GBD Compare). Seattle.

Available at: https://vizhub.healthdata.org/gbd-compare/.

Petrol and Diesel Engines

Petrol Engine Diesel Engine

Spark Ignition Compression Ignition

Fuel/Air premixed before compression

Fuel/Air not premixed

Lower efficiency & Lighter Higher efficiency-High compression ratio & Heavier

AFR:14.7 (predetermined) AFR: 20-100/1 (air injected not controlled)

Emissions: More fuel, >CO2, less NOX and low PM

Emissions: less fuel, <CO2, >NOX

Higher PM

Pollutants: CO, HC, NOX Pollutants: NOX, PM, Smoke

Units of measurementGasesO2: % CO2: %CO: %HC: ppmNOX: ppm

PMParticulate Mass (µg/m3)Particulate Number (#/km)

Smoke:Opacity: % Smoke density: m-1

Engine: λ, RPM, T, P

Vehicle Emission Legislation

Emission limits

Test cycles

Test and Measurement Specifications

Result Calculation and reporting specifications

Standards

Regulations

© AVL, 2014

Use of PEMS to measure gases & PM

Exhaust sample

Heated sample line

GPS & weather probe

power supply 110 VAC, 220VAC or 12 VDC

Exhaust Flow Meter (EFM)

Weighing

Flow tube

Gas bench: CO/CO2 (NDIR) NOx(NDUV), THC (FID)

EU Emission legislation

© AVL, 2014

Light Duty Heavy Duty

Vehicle technology and fuel quality

ECUSCR

EGR

DOC

DPF

Adopted ICCT, 2012

TWC

©factsaboutscr, 2014

Selective Catalytic Reduction (SCR)Diesel engine control emissions technology

• Reduces NOx (~90%) using urea as a reductant within a catalyst system

• End product: N2, H2O and small CO2

3 Way Catalytic converter (TWC)Petrol engine control emissions technology• Most vehicles sold have TWC• use of TWCs with an oxygen sensor-based

closed-loop fuel delivery system• Simultaneous conversion of the three

criteria pollutants-HC, CO, and NOx

© clickcarparts, 2014

Inspection & Maintenance

Test CO HC NOX PM Smoke Cost Time Where?

Idle Test χ χ low fast UK, EU

2-Speed idle Test χ χ low fast UK, EU

Snap or Free

acceleration Test

χ low fast California, SA

IM 240 χ χ χ High Medium USA

Full load χ χ χ χ χ High Medium EU, USA,

Japan

I/M Standards-based on distribution of emissions

levels

I/M requirement for operating vehicle + Linked to vehicle registration

Set Inspection fees to support I/M programs

Capacity building for all actors in I/M

Phased Approach: Learning Adaptation

Capacity building

EU Emission I/M Standards

Source: EU directives 96/96 EC and 2001/9/ECYear CO standard

(%)

Lambda

(λ)

Test (Petrol)

< 1986 4.5 - Idle

> 1986 3.5 - Idle

With Catalytic converter 0.5 - Idle

0.3 0.97< λ < 1.03 2 speed idle

Year Turbocharged Naturally aspirant Test (Diesel)

< 1980 - -

> 1980 3.0 m-1 2.5 m-1 Free acceleration

UK Emission MOT standards

Year Test Type (Petrol) Pass or Fail

All Visual Inspection Visual Black smoke/dense blue

>1975 Standard Emissions Gas Analyzer (non-

catalyst test)

CO :3.5%-4.5%

HC: 1200ppm

>1992 Basic Emissions Gas Analyzer & EC

Fast Idle

Normal Idle

CO<0.2% HC<200ppm

0.97 < λ <1.03

CO <0.3%

Year Turbocharged

Opacity (m-1)

Normal

Opacity(m-1)

Test (Diesel)

<1979 - - Visual

1979-2008 3 2.5 Diesel fast pass

> 2008 1.5 1.5 Diesel fast pass

©hicksmotandservice, 2014

• Decentralized: ~20 000 local car repair garages

• Test: ❑ Vehicle safety❑ Road worthiness❑ Exhaust emissions

Age: 3 years oldAnnual test Cost: £30-£130Failure: notice & repairRe-test: free or reduced fee(defect/time)Time: 45-60 min, 2 technicians

© www.gov.uk/government/publications/your-car-and-the-mot2014

California Air Resources Board (ARB)

• Heavy-duty trucks and buses: control excessive smoke emissions & prevent tampering (>6000lb)

• Test-Society of Automotive Engineers (SAE) J1667 snap acceleration procedure-opacity measurement

• Test using PEMS

❑ Periodic Smoke Inspection Program (PSIP)

❑ Heavy-Duty Vehicle Inspection Program (HDVIP)

Allowable levels of Smoke Opacity

All post 1991 or newer engines Must not exceed 40% opacity

All pre-1991 engines Must not exceed 55% opacity

South Africa-Cape Town Emission Legislation• Air Quality Management by-Law 2003, 2010

• Vehicles: Compression ignition (Diesel)

• Dark smoke (2010): Light absorption >=20%

• BP Hartridge smoke meter

2003 2010

Naturally aspirated 60 HSU2.125m-1

50HSU1.61m-1

18.57%

Turbocharged 66 HSU2.51m-1

56HSU1.191m-1

21.57%

©Oliver, 2014

Framework for Vehicle Emission

Measurement

1. Micro-scale per vehicle: real-world vehicle emission measurement

Mbandi, A. (2018) Assessing the contribution of road transport emission to air pollution and greenhouse gases in Africa: A disaggregate study in Kenya. University of York

1. Micro-scale per vehicle: real-world vehicle emission data

2. Meso-scale: urban vehicle fleet characteristics and activity

Mbandi, A.M.; Böhnke, J.R.; Schwela, D.; Vallack, H.; Ashmore, M.R.; Emberson, L. Estimating On-Road Vehicle Fuel Economy in Africa: A Case Study Based on an Urban Transport Survey in Nairobi, Kenya. Energies 2019, 12, 1177

2. Meso-scale: urban vehicle fleet characteristics and activity

Mbandi, A.M.; Böhnke, J.R.; Schwela, D.; Vallack, H.; Ashmore, M.R.; Emberson, L. Estimating On-Road Vehicle Fuel Economy in Africa: A Case Study Based on an Urban Transport Survey in Nairobi, Kenya. Energies 2019, 12, 1177

3. Macro-scale: Assessment of the impact of road transport policies on air pollution and

greenhouse gas emissions in Kenya

Mbandi, A. (2018) Assessing the contribution of road transport emission to air pollution and greenhouse gases in Africa: A disaggregate study in Kenya. University of York

3. Macro-scale: Air pollution, Greenhouse Gas emissions in

Kenya, 2010

Mbandi, A. (2018) Assessing the contribution of road transport emission to air pollution and greenhouse gases in Africa: A disaggregate

study in Kenya. University of York.