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Control of mobile sources

Topic 9

Ms Sherina Kamal

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Mobile sources

On-road mobile

Trucks

Buses

Passenger cars

Motorcycles

Off-road mobile

Construction equipment

Lawn, garden equipment

locomotives,

Marine vessels

Personal recreation equipment

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Why do mobile sources matter?

Accounts for approximately 70-75% of all

man-made pollution emitted

Affects human and the environment

The emission contribute to the formation of

ground level zero ozone, smog

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Pollutant formation

Principal pollutants emitted from simple gasoline-powered IC

engines

CO

Present in the combustion products from any carbon-

bearing fuel, gasoline, natural gas, coal, wood,

charcoal, forest fires, garbage

Depend strongly on the A/F ratio

Excess air, little CO

Less air, more CO

HC

NOX

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Pollutant formation Auto engines produced these gases more per unit of fuel burned

principally because:

Auto engines

are often O2 deficient, which most other combustion systems are not

preheat their air-fuels mixtures, which most combustion systems do not

have unsteady combustion, in which each flame lasts about 0.0025s. Almost other combustion systems have steady flames that standstill while the materials burned pass through them

have flames that directly contact cooled surfaces which is not common in other combustion systems

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Factors influencing motor vehicle

emissions

Vehicle and fuel characteristics

Fleet characteristics

Operating characteristics

Vehicle and fuel characteristics

Engine type and technology

Two stroke

Four stroke

Exhaust, crankcase and evaporative emission control system

in place

Catalytic convertors

Exhaust gas recirculation

Air injection

Engine mechanical condition & adequacy of maintenance

Air conditioning

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Internal combustion engine

Four stroke IC gasoline engine

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Four stroke IC gasoline engine

The power source for 99% of the autos and small trucks

Relatively light and small

Durable

Moderately easy

Relatively inexpensive to manufacture

Has fairly good fuel efficiency

Responds quickly and smoothly to changes in throthle setting

Requires very little

Fleet characteristics

Vehicle mix (number and types of vehicles in

use) and utilization (km per vehicle per year)

Age profile or vehicle fleet

Traffic mix and choice of mode for passenger

and goods movements

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Operating characteristics

Altitude, temperature, humidity (for NOX)

emissions

Vehicle use patterns

Number and length of trips

Number of cold starts, speed, loading

Aggressive driving behaviour

Degree of traffic congestion, capacity and

quality of road infrastructure & traffic control

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Vehicle technology for controlling

emissions

Petrol-fuelled vehicles

Air-fuel ratio

Electronic control systems

Catalytic converters

Evaporative emissions and control

Diesel-fuelled vehicles

In-use vehicles

Fuel modifications12

Petrol-fuelled vehicles: Air-fuel

ratio

A/F ratio is the key design parameter for

spark-ignition engine

An air-fuel mixture that has exactly enough

air to burn the fuel, no air or fuel left

(stoichiometry)

If mixtures with more air than fuel-lean

If mixtures with more fuel than air-rich

Engines use lean mixtures are more efficient

that those stoichiometry mixture 13

Petrol-fuelled vehicles: Electronic

control systems

stoichiometric engines using three-way

catalysts has been extensively developed.

systems measure the air fuel ratio in the

exhaust and adjust the air-fuel mixture going

into the engine to maintain stoichiometry

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Petrol-fuelled vehicles: Catalytic

converters most effective emission control devices

available

comprises a ceramic support, a washcoat

(usually aluminum oxide) to provide a very

large surface area and a surface layer of

precious metals (platinum, rhodium, and

palladium are most commonly used) to

perform the catalyst function

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Petrol-fuelled vehicles: Catalytic

converters

Two types of catalytic converters

oxidation (two-way) catalysts control

hydrocarbon and carbon monoxide emissions

oxidation–reduction (three-way) catalysts control

hydrocarbons, carbon monoxide and nitrogen

oxides

New type - converter is the lean nitrogen-

oxide catalyst

which reduces NOx emissions in lean conditions,

where a three-way catalyst is ineffective16

Petrol-fuelled vehicles: Evaporative

emissions and control

Controlled by venting the fuel tank (and, in

carbureted vehicles, the carburetor bowl) to

the atmosphere through a canister of activated

charcoal

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Diesel-fuelled vehicles

The engine variables with the greatest effect

on diesel emission rates are the:

combustion chamber design

air-fuel ratio

rate of air-fuel mixing

fuel injection timing

compression ratio

the temperature and composition of the charge in

the cylinder18

Diesel-fuelled vehicles

typical approach to reducing diesel emissions:

Reducing parasitic hydrocarbon & PM emissions

(those not directly related to the combustion

process) by minimizing injection nozzle sac

volume and oil consumption

Reducing PM emissions and improving fuel

efficiency and power output through

turbocharging and by refining the match between

the turbocharger and the engine

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In-use vehicles

Inspection and maintenance (I/M) measures to

control emissions from in-use vehicles are an

essential complement to emission standards

for new vehicles

I/M programmes ensure that the benefits of

new-vehicle control technologies are not lost

through poor maintenance and tampering with

emission controls

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Fuel modifications

major advantage

often take effect quickly and begin reducing

pollutant emissions immediately

can be targeted geographically or seasonally by

requiring the more expensive “clean” fuels only

in highly polluted areas or during seasons with a

high incidence of elevated pollution episodes

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Recommendations and suggestions for

mitigating vehicular pollution

Pollution control technology

Burning less fuel

Zero-emission vehicles

Cleaner fuels

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Pollution control technology For petrol vehicles (can reduce smog-forming

emissions by a factor of ten)

Three way catalyst

Precise engine and fuel controls

Evaporative emission control

Diesel vehicles

Two wav catalysts and engines controls

Able to reduce hydrocarbon and carbon monoxide

emissions

Nitrogen oxide and toxic particulate matter emissions

remain very high23

Burning less fuel Key is to make cars & trucks more efficient

and putting that efficiency to work in

improving fuel economy

more efficient engines and transmissions

Improve aerodynamics

Better tires and high strength steel and aluminum

More advanced technologies:

Hybrid-electric vehicles that use petrol engines and

electric motor, battery- can cut fuel use but with

additional cost24

Zero-emission vehicles

Eliminating emissions from tailpipe can cut

down on harmful air pollutants

Ex: hydrogen fuel cell

Ex: electric vehicles

Use electrochemical processes instead to

produce the energy needed to drive a car

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Fuel cell vehicle

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Fuel cell vehicle (Toyota)

powered by fuel cells

which generate electricity from hydrogen and

oxygen

The only byproduct is water – (reason for zero

emission vehicles)

which is not only environmentally friendly and

highly energy-efficient, but can also be produced

using a variety of readily available raw materials

fuel cell vehicles are ideal for achieving

sustainable mobility 27

Electric vehicle

Store energy in an onboard battery, emitting

nothing from the tailpipe

Cleaner fuels

Petrol and diesel fuels in use today contain

significant amounts of sulphur and other

compounds that make harder for existing

control technology to keep vehicles clean

Removing the sulphur the fuel and cutting

down on the amount light hydrocarbons helps

pollution-control technology to work better

and cuts down evaporative and refueling

emissions29

Cleaner fuels

Further large scale reductions of other tailpipe

pollution and CO2 can be accomplished with a

shift away from conventional fuels

Alternative fuels

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Alternatives and the future

Other options to reformulated gasoline and

diesel are the oxygenated fuels

Ethanol

Methanol

Lighter end components of crude oil

Liquid petroleum gas

Compressed natural gas

Liquefied natural gas

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Alternatives and the future

Pure methanol

Expected to have significantly lower evaporative emissions and running losses

Problem-difficulty in starting the engine

Study found out that

Methanol had a lower ozone-forming potential than gasoline

Methanol fuel engine had high emissions of formaldehyde

Both methanol & formaldehyde are listed hazardous air pollutants and represent increased risks to public health

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Alternatives and the future

Pure ethanol

Its vapor pressure at low temperatures and the formation of acetaldehyde during combustion

Ethanol & formaldehyde

adverse effects on public health because of the toxicological effects

Expensive fuel

made from fermentation processes and distilled into fuel

Major contribution

blending compound for lowering CO emission

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Liquefied petroleum gas

Non-methane tailpipe emissions can be

relatively high

Significant reduction in ozone-forming

potential

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Compressed natural gas

Comprised of methane

One of the cleanest burning alternative fuels

Among the best because of the combustion

kinetics which can be more easily optimized

Advantages:

Less expensive than gasoline

About 5%-9% less GHG emissions

Roughly 20%-45% less smog-producing pollutants

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Biodiesel clean burning alternative fuel

contains no petroleum, but it can be blended at any level with

petroleum diesel to create a biodiesel blend

Made from renewable resources

Vegetable oil

Animal fat

simple to use

Biodegradable

Nontoxic

essentially free of sulfur and aromatics

END OF LECTURE

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