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ENVE 4003

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DIESEL COMBUSTION CHARACTERISTICS ... DIESEL NOx FORMATION CHARACTERISTICS ... Sensing and monitoring devices to detect malfunctions. Light indicator ... – PowerPoint PPT presentation

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Title: ENVE 4003


1
ENVE 4003
  • MOBILE SOURCES
  • Types of emissions, control technologies and
    trends, inspection and maintenance programs.

2
Motor Vehicles
  • Internal combustion (IC) engines
  • Spark ignition (SI) - gasoline, propane, natural
    gas, ethanol
  • 4-stroke vs 2-stroke
  • Compression ignition (CI) - diesel, biodiesel

3
Figure 13.1 de Nevers
  • Schematic of piston and cylinder in IC engine

4
Figure 18.2 Cooper Alley
  • Schematic of four stroke IC engine

5
Figure A3.1.5 Faiz, Weaver Walsh
  • Two stroke motorcycle engine

6
Figure A3.2.1 Faiz, Weaver Walsh
  • Diesel combustion stages

7
MOTOR VEHICLE EMISSIONS
  • Regulated (criteria pollutants)
  • CO, NOx, NMHC, PM
  • Non-regulated
  • Individual (speciated) HCs
  • carbonyl compounds (alcohols, aldehydes, ketones)
  • Air toxics, e.g. benzene, toluene, ethylbenzene,
    1,3,butadiene, formaldehyde, acetaldehyde
  • CO2 (i.e. fuel economy)

8
Table 13.1 de Nevers
  • Contribution of motor vehicles to U.S. national
    emissions

9
MOTOR VEHICLE EMISSIONS
  • Exhaust (tailpipe) (CO, NOx, VOC, PM)
  • Evaporative (VOC)
  • Resting
  • Diurnal heat build
  • Hot soak
  • Running
  • Refuelling

10
COMBUSTION IN IC ENGINES
  • Air/Fuel ratio, mass of air per mass of fuel,
    15
  • Normalized A/F ratio,
  • ? (A/F) actual / (A/F) stoichiometric
  • Equivalence ratio
  • ? (A/F)stoichiometric / (A/F) actual
  • ? ? 1 for gasoline engines most of the time,
  • ? gt 1 (fuel rich) during high power demand and
    start
  • ? lt 1 (fuel lean) for diesel most of the time,
  • ignition - combustion - extinction
  • sequence repeated 102 103 times a minute
    unsteady combustion

11
Figure (13.2) de Nevers
  • Emissions and fuel consumption vs lambda

12
Figure 10.16 (7.5) de Nevers
  • Effect of air-fuel ratio and quality of mixing on
    composition of combustion gases

13
Table 13.3 de Nevers
  • Equivalence or A/F ratios

14
POLLUTANT FORMATION MECHANISMS - SI ENGINES
  • HC
  • Rich Fuel/Air mixture, oxygen deficit
  • Flame quenching at walls, crevices, quench
    zone
  • CO
  • Rich Fuel/Air mixture, oxygen deficit
  • incomplete reaction, even with sufficient
    oxygen
  • NO, Thermal
  • ?T compression 600 F
  • ?T combustion 3600 F
  • Short times but high peak temperatures

15
DIESEL COMBUSTION CHARACTERISTICS
  • Only air is compressed during compression stroke,
    reaching 700-900 C
  • Fuel is injected into hot air just before top
    of compression stroke
  • A fuel-air mixture forms around the periphery of
    the fuel jet and ignites after an ignition delay.
    This premixed combustion phase accounts for only
    a fraction of the fuel and causes a pressure peak
  • The remainder of the fuel burns under mixing
    controlled combustion causing a more gradual
    pressure increase, and then decline with expansion

16
DIESEL NOx FORMATION CHARACTERISTICS
  • Most NOx formed during the high T and P premixed
    combustion phase
  • NOx formation can be reduced effectively by
    reducing flame temperature
  • delay combustion into the expansion phase
  • cool the air charge going into the cylinder
  • exhaust gas recirculation (EGR)

17
PARAMETERS AFFECTING DIESEL PM AND HC EMISSIONS
  • Air/Fuel ratio, generally lean overall, to allow
    for complete combustion within limited time
    available for mixing
  • Minimum ?? 1.5 for smoke point, smoke
    increases dramatically below this limit
  • Rate of air-fuel mixing, can be enhanced by
    imparting a swirl to the injected fuel
  • fuel injection timing
  • compression ratio
  • temperature and composition of charge in the
    cylinder

18
DIESEL VISIBLE SMOKE
  • Black smoke from soot
  • White, blue or gray smoke condensed hydrocarbon
    droplets in the exhaust
  • Blue or gray generally due to vaporized lubricant
  • White due to cold start
  • Sulfur in the fuel forms sulfuric acid which is
    later sampled as PM

19
Table 13.5 de Nevers
  • Comparison of gasoline and diesel engines

20
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21
VEHICLE EMISSION CONTROL
  • Control technology is aimed at reducing the
    second term fuels, engines, vehicles etc.
  • Urban and transportation planning addresses the
    first term housing density, location,
    transportation infrastructure
  • the second term is relatively insensitive to the
    number of passengers in the vehicle
  • Increasing vehicle occupancy helps reduce
    emissions mass transit, car pooling etc.

22
CONTROL TECHNOLOGY - SI
  • Air/Fuel ratio. CO and HC emissions increase as
    mixture gets richer in fuel (start and high power
    conditions), NOx emissions peak near
    stoichiometric ratio
  • Fuel metering systems carburetors and fuel
    injectors (throttle body TBI, multi-port PFI,
    simultaneous or sequential)
  • Electronic Control Systems adjust the air/fuel
    ratio based on the signal from an oxygen sensor
    in the exhaust

23
EXHAUST GAS RECIRCULATION (EGR) - SI AND CI
ENGINES
  • Dilutes Air/Fuel mixture with exhaust gases
    thereby reducing peak combustion temperatures and
    NOx formation
  • There are limits to how lean an air-fuel-exhaust
    gas mixture can be for ignition
  • Ignition systems (spark plugs etc.) and
    combustion chambers can be designed to improve
    performance with these lean mixtures

24
EXHAUST AFTERTREATMENT SI ENGINES
  • Air injection - thermal oxidation of residual CO
    and HC with excess air introduced after the
    engine into the exhaust system, very temperature
    sensitive Minumum 600 C for HC, 700 C for CO
  • Catalytic convertors can achieve conversion at
    lower temperatures 350 C
  • Oxidation (two-way) catalyst - for HC and CO
  • Oxidation-reduction (three-way) catalyst (TWC)
    for HC, CO, and NOx according to

25
CATALYTIC CONVERTORS SI ENGINES
  • Pellet and monolith types
  • Require near stoichiometric combustion for
    effective conversion of all three pollutants, CO
    and HC conversion efficieny drop for rich
    mixtures, NOx conversion efficiency drops for
    lean mixtures
  • Exhaust gas oxygen sensor (Zirconia, ZrO2 based)
    essential to keeping the Air/fuel ratio in window
    of optimum conversion efficiency for all three

26
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27
TWC picture from ICT-Umicore CD
28
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29
EVAPORATIVE EMISSION CONTROL SI ENGINES
  • Blowby and Crankcase emissions - fuel and partial
    combustion product molecules pass by the piston
    into the crankcase - recycled back to air intake
    manifold by Positive Crankcase Ventilation (PCV)
  • Charcoal canister for capturing fuel tank,
    carburetor and miscellanous evaporative
    emissions. Adsorption during hot-soak, diurnal
    heat build (breathing), refuelling periods,
    desorption into the air intake during engine
    operation (regeneration)

30
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31
CONTROL TECHNOLOGY - CI
  • PM and NOx more important in diesel exhaust than
    CO and HC, relative to gasoline exhaust
  • A general trade-off between PM and NOx exists
    although reductions in absolute levels of both
    emissions have been achieved
  • Emissions more strongly dependent on engine
    design - most emission reductions so far have
    been achieved through combustion modifications
    rather than exhaust aftertreatment in contrast
    to gasoline engine emissions

32
DIESEL PM FORMATION CHARACTERISTICS
  • Particulate Matter forms in fuel rich zones
    primarily during the mixing controlled combustion
    phase
  • mostly an aggregate chain carbon core (soot)
  • adsorbed hydrocarbons (aliphatic and
    polyaromatic) soluble organic fraction (SOF)
  • significant fraction of SOF may come from
    lubricating oil
  • Most of the PM formed during combustion is
    subsequently burned during the expansion stroke,
    the unburned part forms the emissions
  • Sulfur in the fuel forms sulfuric acid which is
    later sampled as PM

33
DIESEL EXHAUST AFTERTREATMENT
  • Flow through oxidation catalyst (two-way
    catalytic convertor) for reduction of CO and VOC
    (80), and PM SOF (20-30), does not retain PM
  • Trap oxidizer (Diesel particulate filter), reduce
    PM by 95, filter oxidation (regeneration)
    functions
  • active and passive regeneration types
  • Passive regeneration catalyst coated onto trap
    or added to fuel bring regeneration temperature
    down to 400-450 C which can be achieved in diesel
    exhaust
  • Active regeneration monitors PM build-up on the
    trap and triggers regeneration by diesel fuel
    burning, electric heating, catalyst injection

34
DPF from ICT-Umicore CD
35
DPF detail from M.Walsh
36
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37
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38
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39
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40
EXHAUST EMISSION MEASUREMENT
  • Simulated driving conditions
  • Mass Emission rates in g/km for light duty
    vehicles (LDV) on a chassis dynamometer
  • Mass Emission rates in g/kWh for heavy duty (HD,
    diesel) engines on an engine dynamometer
  • Actual driving conditions
  • On-board measurement systems
  • Tunnel studies
  • Remote sensing, g/L of fuel burned

41
EVAPORATIVE EMISSION MEASUREMENT
  • SHED Test, Sealed Housing Evaporative
    Determination
  • Carbon canisters attached to various points on
    vehicle to adsorb HC vapors

42
DRIVING OR OPERATING CYCLES
  • Actual vs Synthesized
  • Transient, steady state, multi-mode
  • Modal analysis
  • Acceleration
  • Cruise
  • Deceleration
  • Idle

43
EMISSION FACTORS
  • Amount of pollutant emitted per unit activity
  • g/km, (distance travelled)
  • g/kWh, (mechanical energy delivered)
  • g/L, (quantity of fuel burned)
  • For a single vehicle with given engine and
    emission control technology, the factors that
    influence the emission factor are speed,
    acceleration/deceleration, trip length, ambient
    temperature
  • Vehicles with similar size, engine, and emission
    technology may be expected to show similar
    emission behaviour

44
EMISSION FACTORS AND EMISSION MODELLING
  • Regulated emissions from new vehicles vs
    emissions from in-use vehicles
  • Emissions surveillance program to test emissions
    from thousands of in-use vehicles at different
    ages in the U.S.
  • Emission modelling from motor vehicles involves
    the consideration of different types of vehicles
    and their driving conditions to arrive at a grand
    total

45
INSPECTION AND MAINTENANCE PROGRAMS
  • Field studies suggest that more than 50 of motor
    vehicle pollution may come from less than 10 of
    vehicles which have poorly maintained or
    malfunctioning emission control devices
  • Inspection and maintenance (I/M) programs aimed
    at identifying such gross-emitter vehicles and
    ensuring the repair of their emission control
    systems are becoming more important in the face
    of reduced emission regulations for new vehicles
  • Remote sensing of CO, HC, and NOx, along with CO2
    offers both I/M and fuel-based emission inventory
    advantages

46
I/M PROGRAMS
  • Emission control technology for LDGV very
    effective 90--95 reduction compared with no
    controls
  • Emission control system performance deteriorates
    with vehicle age but only gradually
  • Emissions from a small fraction of vehicles with
    malfunctioning control systems erode the benefits
    of emission reductions from a large number of
    vehicles
  • I/M programs aim to maintain control system
    efficiency for the entire fleet, over the useful
    life of vehicles

47
I/M PROGRAMS
  • Objectives
  • Identify and repair vehicles with maladjustments
    or control system malfunctions
  • Discourage willful tampering with control systems
  • Modes
  • Periodic checks of all vehicles
  • Identification and repair of high emitting
    vehicles,
  • Identification and exemption of low emitting
    vehicles,
  • clean screening

48
I/M PROCEDURES
  • SI Engines
  • Exhaust concentrations measurement CO, HC, NOx
  • No load, idle/2500 rpm
  • Loaded dynamometer tests
  • ASM, Acceleration simulation mode
  • (AMS2525, 25 mph, 25 maximum FTP acceleration)
  • IM240, first 240 seconds of FTP (Federal Test
    Procedure)
  • Visual inspection of control system components
  • Pressure/purge tests for evaporative emission
    control systems
  • CI Engines
  • Bosch method for smoke pull measured amount of
    exhaust through filter paper, check light
    transmission of filter
  • Opacity meter check light attenuation directly
    across exhaust path under snap acceleration
    conditions

49
I/M PROGRAMS
  • Institutional setting
  • Centralized - inspection
  • Decentralized - test and repair
  • Frequency
  • Vehicle age at first test, 1-4 years
  • Subsequent tests every 1-2 years
  • Costs
  • Program operating costs
  • Repair costs
  • Cost/benefit ratio
  • Improvement in ambient air quality vs I/M costs

50
I/M PROGRAMS - COMPLEMENTS
  • Remote sensing
  • Clean screening, high emitter profiling
  • On-board diagnostics (OBD)
  • Sensing and monitoring devices to detect
    malfunctions
  • Light indicator
  • Stored computer codes for malfunctioning
    components
  • catalyst
  • oxygen sensor
  • engine misfire
  • evaporative system integrity

51
Pb, S, and Transportation fuels
  • Pb used to be added to gasoline (tetra-ethyl lead
    TEL) as an octane enhancer.
  • Phased out in most countries and being phased out
    in others
  • permanent poisoning of TWC using leaded
    gasoline in a vehicle with TWC once is sufficient
    to make the TWC useless
  • Neuro-toxic health effects on children

52
Pb, S, and Transportation fuels
  • S is a natural component of crude oil. Can be
    removed effectively by hydrodesulfurization.
  • Adverse (though reversible) effect on efficiency
    of TWC and DPF. Low sulfur fuel increases
    efficiency of modern TWC and makes it possible to
    use advanced diesel exhaust after-treatment like
    DPF
  • contribution to PM emissions as sulfate
  • contribution to gaseous Sox emissions
  • Current trends coming down to 15 ppm (ULSD
    ultra low sulfur diesel), from 300-500 ppm.
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