Exhaust Emission Measurement and Control

transcript

1Preet Ferozepuria

Content1. Exhaust Smoke, Measurement, Regulations & Control

General Considerations, Smoke Types Smoke Measuring Instrumentation

◦ Filter Soiling Spot Meters◦ Opacimeters, Light Absorption Coeff., Hartridge No.

Transient Smoke as per EPA Free Acceleration Smoke Smoke limit for off-highway & commercial Vehicles & Genset Engines

2. Pollution test procedures – ECE R49, ESC, ETC, ELR. 3. Emission Standards for HD vehicles in USA, European Union & India4. Emission Standards for off-highway vehicles in USA, European Union & India5. Emission Standards for Power Generation engines in India6. Certification & Self Audit7. Deterioration factors8. On Board Diagnostics for diesel engines

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Content9. Exhaust Pollutants and their formation

Formation in diesel engine of:◦ NOx◦ HC◦ CO◦ PM◦ Effect of Sulfur on pollutant Formation

Control of pollutants in diesel engine: ◦ NOx◦ HC◦ CO◦ PM

10. Exhaust Gas After treatments Three- Way Catalytic Converters for spark ignition engines Diesel Oxidation Catalysts DeNOx Diesel Particulate Filters Selective Catalyst Reduction

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Training Content11. EGR (Exhaust Gas Re-circulation)

Internal EGR External EGR On/Off vs. Proportionate EGR ECU and sensors for EGR

12. CO2 emission from diesel engines13. Diesel vs. CNG engines14. Analyzers for Measurement of NOx, HC, CO, CO2, PM etc.15. Wet and Dry measurement of emission contents16. Units of emission measurement – Emission Index and Specific Emission17. Equivalence Ratio determination from Exhaust Gas constituents18. Combustion Inefficiency

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EXHAUST SMOKE, MEASUREMENT, REGULATIONS & CONTROL

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GENERAL CONSIDERATIONS

The presence of smoke in the diesel engine exhaust is anindication of poor combustion resulting from some malfunctionor maladjustment.

Most industrialized countries have therefore introducedregulations of varying degrees of complexity to control smokeemission from road vehicles.

The regulations have been in addition to the relatively simpleexisting regulations covering industrial plant and have involvedmuch development both of test methods and instrumentation.

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SMOKE TYPES

Smoke may be defined as particles, either solid or liquid(aerosols), suspended in the exhaust gases, which obstruct, reflect,or refract light. Diesel engine exhaust smoke can be categorized under twoheadings:

1. Blue/white in appearance under direct illumination, and consisting of a mixtureof fuel and lubricating oil particles in an unburnt, partly burnt, or cracked state.

2. Grey/black in appearance, and consisting of solid particles of carbon fromotherwise complete combustion of fuel.

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BLUE/WHITE

The blue component derivesmainly from an excess oflubricating oil in the combustionchamber, resulting fromdeterioration of piston ring sealing,or value guide wear, and is thusan indication of a need formechanical overhaul.

Unburnt fuel can also appear asblue smoke if the droplet size iscirca 0.5 µm.

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BLUE/WHITE The white component is mainly a result of

too low a temperature in the combustionchamber during the fuel injection period.

It has a droplet size of circa 1.3 µm. This can occur as a transient condition

during the starting period, in low ambienttemperatures or at high altitude,disappearing as the engine warms up.

It can result from too late fuel injection ormay even be an indication of a designfault, in the sense that the compressionratio is too low, or has been optimized foran inappropriate combination of operatingconditions.

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Grey/black smoke is produced at or near full load if fuel in excess ofthe maximum designed value is injected, or if the air intake isrestricted.

In normal operation its onset is associated with reduced thermalefficiency and sets a limit to power output before any seriousproportion of toxic component such as carbon monoxide isdischarged.

The main causes of excessive black smoke emission in service areeither poor maintenance of air filters and/or fuel injectors, orincorrect setting of the fuel injection pump.

GREY/BLACK

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Such smoke consists essentially of carbon particles or coagulatesof a wide range of sizes, ranging from 0.02 µm upwards to over0.12 µm mean diameter.

This size distribution depends to some extent on the type ofcombustion system, which also affects the onset of smoke emissionas fuel input quantity is increased.

GREY/BLACK

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1. Filter-soiling 'spot' meters2. Opacimeters

1. Sampling opacimeters2. Full-flow opacimeters

SMOKE MEASURING INSTRUMENTATION

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If exhaust gas is passed through awhite filter paper, the carbonparticles are deposited, and thedarkening of the paper can betaken as a measure of the smokedensity.

For consistency of measurement itis essential that a fixed volume ofgas is passed through a definedarea of filter paper, and the paperitself needs to be closely specified.

FILTER-SOILING 'SPOT' METERS

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The gas sample should be passed through the paper at aconstant rate, and excessive pressure fluctuations at thepoint in the exhaust system from which the gas sample isextracted will produce erroneous results, as willcondensation of moisture on the filter paper.

A high proportion of aerosols in the exhaust gives areduced value of smoke density, since the paper isrendered transparent, to some extent.

Such smoke meters are therefore of no use in caseswhere blue/white smoke is present.

FILTER-SOILING 'SPOT' METERS

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The visibility of smoke is by definitionan optical phenomenon, and its densitymost easily measured in terms of lightabsorption.

Photocell output is related linearly tothe reduction in light intensity (opacity)resulting from the presence of smoke,and opacity is usually expressed as apercentage:

where I is the light intensity at the photocell with smoke present

in the light path; Io is the light intensity at the photocell with only clean air

present in the light path.

OPACIMETERS

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Opacimeters may be classified as: Sampling, or Full- flow,

• In-line and • End-of- line types.

TYPES OF OPACIMETERS

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SAMPLING OPACIMETERS In its simplest classical form, the

exhaust gas sample is extractedfrom the system by a probe, andpassed through a tube having aphotocell at one end and a filamentbulb at the other.

Zero is checked by passingscavenging air through the tube.

Not only is this scavenginguncertain in its efficiency, but zeroerrors occur from soiling of the lightsource and the photocell.

Diffusion of light from both smokeparticles and condensation dropletsalso forms a source of error.

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The full-flow end-of-line opacimeter designed by USPHS for the measurement of smoke emitted by heavy-duty vehicle engines is based logically on the premise that the appearance of the smoke plume discharged from the tail pipe is the essential quality to be assessed.

The sensor, as shown in Figure, consisting of the light source and photocell, is carried on a rigid ring which is mounted close above the vertical exhaust pipe, so that the collimated light beam is transmitted diametrically through the plume.

A supply of clean air under pressure to the optical system is required both to keep the system cool and avoid soiling by smoke.

FULL-FLOW OPACIMETERS

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LIGHT ABSORPTION COEFFICIENT

Smoke density is defined by naQ = k,where n is the concentration of smoke particles (for black smokegm/cu m carbon); a is the average particle projected area; Q is the average particle extinction coefficient; The parameter k being referred to as either the 'extinction coefficient', or the 'coefficient of lightabsorption‘.

This is related to the opacity and effective length of light path bythe equation:

where L is the effective light path length within the smoke (in meters)

k thus represents a smoke density parameter independent ofthe particular design configuration of the opacimeter.

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FREE ACCELERATION SMOKE

Free Acceleration Test: means the test conducted by abruptly but notviolently, accelerating the vehicle from idle to full speed with thevehicle stationary in neutral gear.

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FREE ACCELERATION SMOKE TEST - ISSUES Smoke readings differ with warming up of the vehicle. It is very

difficult to achieve the specified 10 km warming up in the field toget the consistent readings.

The free acceleration test is a transient test. (raising the speed fromidling to max rpm). The smoke readings may vary depending on theway the accelerator pedal is pressed by various operators.

There is a complaint in the field that the smoke readings at differentPUC centers do not match.

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SMOKE LIMIT FOR OFF-HIGHWAY & COMMERCIAL VEHICLES & GENSET ENGINES

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SMOKE LIMIT FOR OFF-HIGHWAY & COMMERCIAL VEHICLES & GENSET ENGINES

GENSET ENGINES

Power (kw) Smoke(1/m)

Kw<= 37 0.7

37<kw<=75 0.7

75<kw<=130 0.7

130<kw<800 0.7

1. Time – lines: April 2015/April 2014 Considering productdevelopment, Certification.

2. Fuel Specifications: Less than 50ppm sulfur Diesel fuel, acrossthe Country

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POLLUTION TEST PROCEDURES –ECE R49, ESC, ETC, ELR.

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The R49 is a 13-mode steady-state diesel engine test cycleintroduced by ECE Regulation No.49 .

It had been used for type approval emission testing of heavy-duty highway engines through the Euro II emission standard.Effective October 2000 (Euro III), the R49 cycle was replaced bythe ESC schedule.

The R49 test is performed on an engine dynamometer operatedthrough a sequence of 13 speed and load conditions.

Exhaust emissions measured at each mode are expressed ing/kWh.

The final test result is a weighted average of the 13 modes.

POLLUTION TEST PROCEDURES ECE R49

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ECE R49

ECE R49 and US 13-mode Cycles

Mode No. Speed Load, % Weighting Factors

R49 US

1 idle - 0.25/3 0.20/3

2 maximumtorquespeed

10 0.08 0.08

3 25 0.08 0.08

4 50 0.08 0.08

5 75 0.08 0.08

6 100 0.25 0.08

7 idle - 0.25/3 0.20/3

8 ratedpowerspeed

100 0.10 0.08

9 75 0.02 0.08

10 50 0.02 0.08

11 25 0.02 0.08

12 10 0.02 0.08

13 idle - 0.25/3 0.20/3

The test conditions of the R49 cycle are shown in Table

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The weighting factors of the R49 cycle areshown in Figure .

The areas of circles in the graph areproportional to the weighting factors forthe respective modes.

The running conditions of the R49 testcycle are identical to those of the US 13-mode cycle. The weighting factors,however, are different.

Due to high weighting factors for modes 6and 8 (high engine load), the Europeancycle is characterized by high averageexhaust gas temperatures.

ECE R49

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The ESC test cycle (also known as OICA/ACEA cycle) hasbeen introduced, together with the ETC (European TransientCycle) and the ELR (European Load Response) tests, foremission certification of heavy-duty diesel engines in Europestarting in the year 2000

The ESC is a 13-mode, steady-state procedure that replacesthe R-49 test.

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ESC Test Modes

Mode Engine Speed % Load Weight factor, %

Duration

1 Low idle 0 15 4 minutes

2 A 100 8 2 minutes

3 B 50 10 2 minutes

4 B 75 10 2 minutes

5 A 50 5 2 minutes

6 A 75 5 2 minutes

7 A 25 5 2 minutes

8 B 100 9 2 minutes

9 B 25 10 2 minutes

10 C 100 8 2 minutes

11 C 25 5 2 minutes

12 C 75 5 2 minutes

13 C 50 5 2 minutes

The engine is tested on an engine dynamometer over a sequence of steady-state modes (Table )

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The engine is tested on an enginedynamometer over a sequence ofsteady-state modes (Figure)

The engine must be operated for theprescribed time in each mode,completing engine speed and loadchanges in the first 20 seconds.

The specified speed shall be held towithin 50 rpm and the specified torqueshall be held to within 2% of themaximum torque at the test speed.

Emissions are measured during eachmode and averaged over the cycleusing a set of weighting factors.Particulate matter emissions aresampled on one filter over the 13modes.

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Maximum emission at these extra modes are determined byinterpolation between results from the neighboring regular test modes.

The engine speeds are defined as follows:1. The high speed nhi is determined by calculating 70% of the

declared maximum net power.2. The low speed nlo is determined by calculating 50% of the declared

maximum net power.3. The engine speeds A, B, and C to be used during the test are then

calculated from the following formulas:A = nlo + 0.25(nhi - nlo)B = nlo + 0.50(nhi - nlo)C = nlo + 0.75(nhi - nlo)

The ESC test is characterized by high average load factors and very highexhaust gas temperatures.

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The ETC test cycle (also known as FIGE transient cycle) has beenintroduced, together with the ESC (European Stationary Cycle),for emission certification of heavy-duty diesel engines in Europestarting in the year 2000The ESC and ETC cycles replace theearlier R-49 test.

The ETC cycle has been developed by the FIGE Institute,Aachen, Germany, based on real road cycle measurements ofheavy duty vehicles.

The final ETC cycle is a shortened and slightly modified version ofthe original FIGE proposal.

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Different driving conditions are represented by three parts of the ETC cycle, including urban, rural and motorway driving.

The duration of the entire cycle is 1800s. The duration of each part is 600s.◦ Part one represents city driving with a maximum speed of 50 km/h, frequent

starts, stops, and idling.◦ Part two is rural driving starting with a steep acceleration segment. The

average speed is about 72 km/h◦ Part three is motorway driving with average speed of about 88 km/h.

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Vehicle speed vs time over the duration of the cycle

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ETC Transient Cycle - Engine Speed

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ETC Transient Cycle - Engine Torque

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The ELR engine test has been introduced by the Euro IIIemission regulation, effective year 2000, for the purpose ofsmoke opacity measurement from heavy-duty diesel engines.

The test consists of a sequence of three load steps at each ofthe three engine speeds A (cycle 1), B (cycle 2) and C (cycle 3),followed by cycle 4 at a speed between speed A and speed Cand a load between 10% and 100%, selected by the certificationpersonnel.

Speeds A, B, and C are defined in the ESC cycle.

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The sequence of dynamometer operation on the test engine

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Smoke measurement values are continuously sampled during the ELRtest with a frequency of at least 20 Hz. The smoke traces are then analyzed to determine the final smoke

values by calculation. First, smoke values are averaged over 1 second time intervals using

a special averaging algorithm. Second, load step smoke values are determined as the highest 1s

average value at each of the three load steps for each of the testspeeds.

Third, mean smoke values for each cycle (test speed) are calculatedas arithmetic averages from the cycle's three load step smoke values.

The final smoke value is determined as a weighted average from themean values at speeds A (weighting factor 0.43) , B (0.56), and C(0.01).

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EMISSION STANDARDS FOR HD VEHICLES IN USA, EUROPEAN UNION &

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EPA EMISSION STANDARDS FOR HEAVY-DUTY DIESEL ENGINES

PM(g/ bhp-hr)

NOx(g/ bhp-hr)

NMHC(g/ bhp-hr)

0.01 0.20 0.14

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EU EMISSION STANDARDS FOR HD DIESEL ENGINES, G/KWH (SMOKE IN M-1)

Tier Date CO HC NOx PM Smoke

Euro IV 2005.10 1.5 0.46 3.5 0.02 0.5

Euro V 2008.10 1.5 0.46 2.0 0.02 0.5

Euro VI†

2013.01 1.5 0.13 0.4 0.01

† Proposal (2008.12.16)

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Year Reference CO HC NOx PM

2005† Euro II 4.0 1.1 7.0 0.15

2010† Euro III 2.1 0.66 5.0 0.10

† earlier introduction in selected regions,

INDIAN EMISSION STANDARDS FOR HD DIESEL ENGINES, G/KWH (SMOKE IN M-1)

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EMISSION STANDARDS FOR OFF-HIGHWAY VEHICLES IN USA, EUROPEAN

UNION & INDIA

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TIER IV EMISSION STANDARD (g/kWh)Enginepower

Year CO NMHC NMHC+ NOx

NOx PM

kW<8 2008 8.0 - 7.5 - 0.4

8≤ kW<19 2008 6.6 - 7.5 - 0.4

19≤ kW<37 2008 5.5 - 7.5 - 0.3

2013 5.5 - 4.7 - 0.03

37≤ kW<56 2008 5.0 - 4.7 - 0.3a

2013 5.0 - 4.7 - 0.03

56≤ kW<130 2012-

5.0 0.19 - 0.40 0.02

a - 0.4 gm/kWh(Tier 2) manufacturer complies with the 0.03 gm/kWh standard from 2012

c- 25% engines must comply in 2012-2014, with full compliance from 31st

December 2014500ppm diesel available from June 2007. 50ppm (ULSD) availability from June 2010

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EU-OFF HIGHWAY EMISSION NORMSSTAGE IIIA

Category Applicable

CO(g/kwh)

NMHC + NOx

(g/ kwh)

PM(g/ kwh)

19≤P<37 2007-01 5.5 7.5 0.6

37≤P<75 2008-01 5.0 4.7 0.4

75≤P<130 2007-01 5.0 4.0 0.3

Test cycle NRTC(Non road transient cycle) : (with 10% weightage of cold start, 90%

for hot start run) Diesel fuel : Maximum sulphur limit of 350 ppm and cetane No. of 51.(presently )

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STAGE IIIB (G / KWH)Categor

yApplicab

leFrom

CO(g/kw

NMHC(g/ kwh)

NMHC + NOx

(g/ kwh)

NOx(g/

37≤P<56

2013-01 5.0 - 4.7 - 0.025

56≤P<75

2012-01 5.0 0.19 - 3.3 0.025

75≤P<130

2012-01 5.0 0.19 - 3.3 0.025

Engine torque is expressed in present of maximum available torque at a given Engine speed. Rated speed is the speed at which the manufactures specifies the rated engine speed. Intermediate speed lies between 60% to 75% of rated speed.

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CURRENT BHARAT (TREM) STAGE-III NORMS FOR AGRICULTURAL TRACTOR ENGINES (w.e.f Year 2005)

CO(g/ kWh)

HC + NOx(g/ kWh)

PM(g/ kWh)

5.5 9.5 0.8

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PROPOSED BHARAT (TREM) STAGE-III A NORMS FOR AGRICULTURAL TRACTOR ENGINES

Category Applicable

CO(g/kWh)

HC + NOx(g/ kWh)

PM(g/ kWh)

kW < 19 1.4.2010 5.5 8.5 0.8

19 ≤ kW < 37

1.4.2010 5.5 7.5 0.6

37 ≤kW < 75

1.4.2011 5.0 4.7 0.4

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EMISSION STANDARDS FOR POWER GENERATION ENGINES IN INDIA

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CURRENT EMISSION NORMS FOR DIESEL ENGINE FOR GENERATOR SETS

Engine power (P)

Date CO(g/

Nox(g/

Smoke(1/m)

P≤800KW 2004.7 3.5 1.3 9.2 0.3 0.7

Test cycle : ISO 8178- 5 mode –D2

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NEXT LEVEL(PROPOSED) GENERATOR ENGINE EMISSION NORMS:CPCB STAGE-II

2. Fuel Specifications: Less than 350ppm sulfur Diesel fuel,across the Country

Power (kw) NOx(g/ kwh)

HC(g/ kwh)

CO(g/ kwh)

PM(g/ kwh)

Smoke(1/m)

Kw<= 37 8 1.3 3.5 0.3 0.7

37<kw<=75 7 1.3 3.5 0.3 0.7

75<kw<=130

6 1 3.5 0.3 0.7

130<kw<800

6 1 3.5 0.2 0.7

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Power (kw) NOx + HC(g/ kwh)

CO(g/ kwh)

PM(g/ kwh)

Kw<= 37 7.5 3.5 0.3

37<kw<=75 4.7 3.5 0.3

75<kw<=130 4 3.5 0.3

130<kw<800 4 3.5 0.2

FURTHER NEXT LEVEL PURPOSED GENSETS ENGINE EMISSION NORMS:CPCB STAGE-II

2. Fuel Specifications: Less than 50ppm sulfur Diesel fuel, acrossthe Country

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CERTIFICATION & SELF AUDIT

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BIS APPROVAL STEPS

1) For new manufacturer, manufacturer has to get approval of plant facilities from BIS. (ISO:9001/2 desirable for the plant).

2) Application for first engine model to be sent to BIS on prescribed format declaring power, SFC, governing class etc.

3) As listed in BIS:10000,all major components drawings to be submitted4) Before assembly of engine, dimensional inspection of components to be

done &submitted.5) Engine to run 500hrs endurance

-BIS may insist for submission of the engine at their lab for endurance.-Mainly engine power , SFC ,governing, overload 10% for one how to be checked by BIS.

• Power should not to be less than 97% declared• Tolerance on SFC 5%

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CPCB DIRECTIVE:

- Declaration to be made to CPCB that the manufacture hasn’t produced any un-canopised genset engine in last 3 yrs.

- As per CPCB directive, Genset engine below 19 KW should be BIS approved.

NOISE TEST OF CANOPISED GENSETS

- Noise at a distance of 1m from canopy surface to be less than 75 dB(A)

- During canopy noise test, intake temperature at 50mm from air filter or air intake point shall not exceed 7˚C above ambient.

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DETERIORATION FACTORS

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AGING TEST FOR EVALUATING DETERIORATION FACTORS (D.F)Category Useful life (hours)

(Emission Durability Period)

≤19 kw 3, 000

19 < kw ≤ 37 5, 000

> 37 kw 8, 000

FIXED DETERIORATION FACTORS FOR BHARAT(TREM) STAGE-III A NORMS

CO HC NOx PM

1.1 1.05 1.05 1.1

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ON BOARD DIAGNOSTICS FOR DIESEL ENGINES

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ON BOARD DIAGNOSTICS• A system in the engine’s on-board computer that monitors the

performance of emission-related components for malfunctions.• Uses information from sensors.• Mostly software that runs diagnostics in the background.

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MALFUNCTION INDICATOR LIGHT (MIL)

Should a malfunction bedetected, a warning light willappear on the vehicle'sinstrument panel to alert thedriver.

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STANDARDIZED INFORMATION When a malfunction is detected, information about the malfunctioning

component is stored. Technicians can download the information with a “scan tool”. Information is communicated in a standardized format so one tool

works with all vehicles.

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WORKING OF OBD• Uses information from sensors to judge the performance of the

emission controls• These sensors do not directly measure emissions

EXAMPLE OF HOW OBD WORKS

• Fuel system pressure control• Fuel pressure sensor measures how well pressure is controlled• Manufacturer correlates pressure control error to correspondingemission increase• OBD system is calibrated to turn on MIL when pressure is outsidelimits

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BENEFITS OF OBD

• Encourages design of durable emission control systems.• Aids diagnosis and repair of complex electronic engine controls.• Helps keep emissions low by identifying emission controls in

need of repair.• Works for life of the vehicle.

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APPLICATION

• All passenger cars, SUVs, and small trucks Started in 1996 for gasoline and 1997 for diesel

• Over 120 million OBD II-equipped vehicles operating in the UnitedStates today.

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EXHAUST POLLUTANTS AND THEIR FORMATIONFORMATION IN DIESEL ENGINE

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EXHAUST POLLUTANTS AND THEIR FORMATION

EMISSION FROM DI DIESEL ENGINE

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NOx FORMATION IN DI DIESEL ENGINE

NOx consisting of NO(nitric oxide) & NO2(nitrogen dioxide) NO is predominant component being generated from atmospheric

nitrogenRate of NOx formation:

There is strong dependence of NOx generation on resident temperatureas it comes in exponential terms

Higher oxygen concentration also results in higher NO formation rates The NO formation rate peaks at the mixtures leaner than Stoichiometric

composition (A/F ratios 22 to 25) and decreases rapidly as the mixturebecomes richer

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HC EMISSION MECHANISM IN DIESEL ENGINES

OVERLEANING UNDERMIXING(Fuel escaping burning due tooverleaning appears inexhaust as HC emission)(depends on ignition delay)

Factors effecting overleaning condition-Low ambient temperature-Poor air fuel mixing due to low injectionpressure-Load on engine

Over leaning results into white smokeand misfiring in extreme conditions

- Fuel evaporating from thenozzle sac late intocombustion at the time orafter needle has taken backits seat after injection

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CARBON MONOXIDE

Depends upon fuel/air equivalence ratio

As diesels operate on the lean side of Stoichiometric, CO emissions from diesels are low enough

But for high speed engines greater than 3000rpm,CO generation also become critical for diesel engines due to less time available for mixing and combustion

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It is composed of soot (carbonaceous solid matter similar to carbonblack), an extractable fraction (hydrocarbons extractable with a strongsolvent) adsorbed onto the soot, and other contained inorganiccompounds (largely sulphates, water and ash).

Particulate concentrations are measured by drawing exhaust gasthrough a filter maintained at 52º C, and computing the change in filterweight.

The soot component of the Pm corresponds to the smokemeasurement, while the extractable fraction corresponds to a portion(ranging from about 25-50%) of the gaseous HC emissions.

The exact fraction depends on the engine type and operatingconditions, as these affect the distribution of the boiling range of thegaseous HCs emissions.

PARTICULATES

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EFFECT OF SULFUR ON POLLUTANT FORMATION

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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EXHAUST POLLUTANTS AND THEIR FORMATIONCONTROL OF POLLUTANTS IN DIESEL ENGINE

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EFFECT OF INJECTION TIMING RETARD ON NOX FORMATION

The easiest way-out for NOx reduction in an existing engine is toretard the fuel-injection timing. This also reduces combustionnoise and cylinder pressures.

The engine cycle efficiency decreases at later injection timings asthe heat release shifts away from TDC in this situation. Thisexplains the fuel-consumption and smoke/particulate increase atretarded injection.

The effect of retard on smoke level, particulate matter andincreased fuel consumption can be overcome by using higher fuelinjection rates.

CONTROL OF POLLUTANTS IN DIESEL ENGINENOx

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NOxDIRECTION TOWARDS CLEAN & EFFICIENT COMBUSTION

1. LOWER INITIAL HEAT RELEASE RATE, LOWER INITIAL COMBUSTIONTEMPERATURE AND LESS NOx. ACHIEVED THROUGH LATE FUELINJECTION.

2. SHORTEN DIFFUSION COMBUSTION FOR IMPOROVED FUELECONOMY AND LESS PM. ACHIEVED THROUGH HIGHER INJECTIONPRESSURES AND RE-ENTRANT COMBUSTION BOWLS.

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NOxFollowing figure shows the effect of retard on NOx emission of a turbo-charged inter-cooled engine running with rotary pump with injectionpressure in the range of 1200 bar.

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HCThe overall reduction in HC emission due to reduction in sac hole volume is shown below in fig. below as weighted mass emission for 8 mode emission cycle applicable for off-road vehicles.

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The effect of nozzle sac volume on HC emission of a one-litre per cylinder displacement engine is shown below:

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- Lower crevice volumes in the combustion chamber- – 80% - Good C.R of the order of minimum 18:1- - sacless nozzles with hydro – emission of the holes for

- Optimizing coefficient of discharge - Tighten flow – rate tolerances- Allows use of smaller holes

-Smoke reduction advantage

.)- For taking care of nozzle choking , mini – sac design available from BOSCH

- Has less choking tendency- But HC ,CO & PM increases

- Not recommended for tractor and Genset engines at the moment

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CREVICE HC MECHANISM

CREVICE VOLUME SOURCES

- TOP LAND VOLUME- CREVICE AROUND INTAKE AND EXHAUST VALUE HEAD

- CYLINDER HEAD GASKET CREVICE ZONES

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CARBON MONOXIDE

As diesel engines operate with an overall lean mixture, their COemissions are normally well below legislated limits and not ofmuch concern.

Any CO from a diesel engine is due to incomplete mixing:combustion taking place in locally rich conditions.

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SMOKE/PM REDUCTION TECHNIQUES ON DI DIESEL ENGINE 1. Advance fuel injection timing: For early start of combustion so as to give more

time for fuel to burn, before the exhaust valve is opened.

2. Higher fuel injection pressure: For better and faster mixing of fuel and air, theinjection pressure shall be as high as possible. This is achieved by largerdiameter fuel injection pump plungers, higher injection velocity fuel cams, highpre-stroke of pumps etc.

3. Better air swirl: The intake air port is so designed that intake air has betterswirling properties so as to cause faster air & fuel mixing.

4. More air mass induction: To burn fuel in an efficient way, more mass of air tobe inducted into the cylinder using turbocharger, intake air cooling or by tuningintake manifolds to desired speeds.

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APPLICATION OF SMOKE REDUCTION TECHNIQUES

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EXHAUST GAS AFTER TREATMENTS

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Conversion of harmful ofproducts combustion into lesstoxic products.

Catalytic convertors canachieve conversion at lowertemperatures ~ 350 C

Simple device fitted in theexhaust system of allmodern Automobile.

Catalyst: Pt/Pd/Rh

THREE- WAY CATALYTIC CONVERTERS FOR SPARK IGNITION ENGINES

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Three-way catalytic convertor .Ceramic honeycomb structures:

Reduction catalyst (Pt/Rh).- Reduction of nitrogen oxides

Oxidation catalyst (Pt/Pd).- Oxidising unburnt hydrocarbons

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Require near stoichiometriccombustion for effectiveconversion of all three pollutants,CO and HC conversion efficiencydrop for rich mixtures, NOxconversion efficiency drops forlean mixtures

Exhaust gas oxygen sensor(Zirconia, ZrO2 based) essentialto keeping the Air/fuel ratio inwindow of optimum conversionefficiency for all three

EFFICIENCY

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DIESEL OXIDATION CATALYSTS

Flow through oxidation catalyst (two-way catalytic convertor) forreduction of CO and VOC (80%), and PM SOF (20-30%), doesnot retain PM.

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Trap oxidizer (Diesel particulate filter), reduce PM by 95%, filter + oxidation (regeneration) functions

The performance of the engine, as well as the consumption of fuel and the Co2 emissions similar levels to the ones of the functioning without filter are remained it.

The escape system, that includes a pre catalysis next to the engine and a catalysis of oxidation, was conceived to reduce all the emissions of gases, in special of hydro-carbons (HC) and carbon monoxide (CO).

DIESEL PARTICULATE FILTER (DPF)

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DIESEL PARTICULATE FILTER (DPF)

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Conversion of NOx into N2 and H2O. Gaseous reductant: Ammonia/Urea

Scheme of reactions:

Reaction temperature: 450 – 800 F

SELECTIVE CATALYTIC REDUCTION [SCR]

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Ceramic materials used as a carrier (Titanium oxide)

Active catalytic components:: oxides of base metals, zeolites &precious metals

Base metal catalysts – lack thermal stability but inexpensive

Zeolite catalysts – high thermal stability.

SELECTIVE CATALYTIC REDUCTION [SCR]

CATALYST

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Commonly used today are honeycomb and plate type

Honeycomb type - smaller, - higher pressure drops, - plugging

Plate type – larger, less susceptible to plugging, expensive.

SELECTIVE CATALYTIC REDUCTION [SCR] CATALYST GEOMETRY

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EGR (EXHAUST GAS RE-CIRCULATION)

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EGR (EXHAUST GAS RE-CIRCULATION)

Concept : exhaust –gas recirculation (EGR) is highly effective measure for NOx emissions on diesel engines.

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- Reduction in fresh intake air mass going into cylinder as it isreplaced with inert exhaust gases.

-This results in drop in rate of combustion and thus leads intoreduction of peak temperature.

Reduction in local excess – air factor.

- At part load with higher EGR rates, almost homogeneous mixtureconditions are achieved resulting into extremely low – NOx and low –particulate combustion.

EGR IS EFFECTIVE MAINLY DUE TO :

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WORKING OF EGR

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Internal EGR occurs when the valve timing isarranged so that there is some back-flow intothe combustion chamber from the exhaust, orall exhaust gases are not pushed out of thecombustion chamber on the exhaust stroke.

Such engines normally have variable valvetiming so that internal EGR occurs only whendictated by the ECU; when internal EGR isrequired, this is achieved by increasing valveoverlap.

Internal EGR appears to be a better approach(at least on engines with variable valve timing)as it avoids the need for external pipes andvalves, reducing cost and improvingpackaging.

INTERNAL EGR

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External EGR is achieved bymeans of a pipe that connectsthe exhaust to the inlet manifold,with a control valve interposed inthis line to regulate EGR flow.

For exhaust gas to flow in thispipe, the pressure in the exhaustmust be higher than the pressurein the intake.

EXTERNAL EGR

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ON/OFF EGR USING VALVE :-Solenoid operated on/off EGRvalue

-Value put on intake side for longerlife

-On/off status to be decided by-Position of accelerator lever of fuelinjection pump

-Usually valve is switched at 80 -90 % offull travel of accelerator

-A micro – switch or a throttleposition sensor (TPS) used tosignal On/ Off position

-Around 10-20 % NOx reductionpossible under steady statetesting.

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MAPPED / PROPORTIONATE EGR:

- Very high rates of EGR flows possible (upto 30% at part loadconditions).

- Possible reduction of NOx by 50%.

- Exhaust flow still driven by differential pressure between exhaustand intake.

- Requires higher exhaust back pressures .This drawback can beovercome by having an intake throttle.

- Costlier equipment .

TYPICAL EGR MAP(% OF VALVE OPENING)

ADDITIONAL MAPS FOR EGR OPERATION

The EGR system is having a control valve which is controlled by theelectronic control unit (ECU).The ECU output to control EGR valvedepends on the three inputs:1. Throttle Position: Throttle position is sensed by the throttle

position sensor(TPS), which is mounted on the accelerator leverof on FI pump or throttle paddle in the cabin.

2. Water Temperature: Water temperature sensor is mounted onthe water out let of the engine.

3. R.P.M: R.P.M is sensed by the magnetic r.p.m sensor which ismounted on the bell housing of the flywheel.

ECU AND SENSORS FOR EGR

EGR OPERATION

CO2 EMISSION FROM DIESEL ENGINES

Combustion of a hydrocarbon fuel should produce only carbondioxide and water (H2O).

The relative proportion of these two depends on the carbon-to-hydrogen ratio in the fuel, about 1 : 1.75 for ordinary dieselfuel.

Thus, an engine's CO2 emissions can be reduced by reducingthe fuel's carbon content per unit energy, or by improving thefuel efficiency of the engine.

The high fuel efficiency of diesel engines gives them anenvironmental advantage over some fossil fuels, though theprocessing of crude oil into diesel fuel has fairly high COemissions.

CO2 EMISSION FROM DIESEL ENGINES

DIESEL VS. CNG ENGINES

CNG vehicles emit 60 to 95% less PM and 0 to 30% less NOx than equivalent diesel vehicles.

Relative emissions depend on driving behavior.

With non-aggressive driving in CBD cycle,CNG NMHC emissions are double, NOx is50% less, and PM is 97% less than diesel

With aggressive driving in CBD cycle, CNG NMHC emissions are 10X, NOx is 30% less, and PM is 97% less than diesel

CNG with catalysts have reduced emissions vs. diesel, butadvanced after treatment can make them similar.

CNG vs. diesel Diesel aftertreatment

NMHC +2X to +10X+2X typ.

-60 to -95%catalysts and filters

NOx -10 to –75%-10 to –40% typ.

-20% catalysts-40% cooled EGR-70% SCR

PM -60 to –97%-85 to –97% typ.

-70 to –95% filters

In the critical sub-100 nm range, CNG particulate numbers maynot be much different from diesel

ELPI used for measurements

PM Particle Count by Size.

Emissions Summary

CNG Cost Factors.

Clean Diesel Cost Factors.

In comparison to CNG, diesel is inherently more fuel efficient

While CNG has historically had an inherent emissionsadvantage, new technologies applied to diesel havedramatically closed the gap

Even with the new technologies (which have added cost),diesel retains a significant cost advantage over CNG.

Chassis testing shows CNG NOx is much more variable thandiesel NOx.

COMPARISON

ANALYZERS FOR MEASUREMENT OF NOX, HC, CO, CO2, PM ETC.

Analyzers used for measuring diesel exhaust gases must besensitive enough to detect the sometimes low levels of gases inthe exhaust, especially in diluted exhaust streams, and bedevoid of any significant interference from other gases whichmight be present.

ANALYZERS

Nitric oxide can be measured using thenon-dispersive infra-red principle.

In this instance, if thin film interferencefilters were not used the filter cellswould be filled with a mixture of carbondioxide and carbon monoxide to avoidtheir interfering with the nitric oxidemeasurement.

The detector would of course containnitric oxide.

Water vapour absorbs infra-redradiation and since diesel exhaust,whether it be raw or diluted with air,contains water vapour the sample hasto be dried before it passes through thesample cell

NITRIC OXIDE

Rather displacing the non-dispersiveinfra-red detector is thechemiluminescence analyzer.

This has the advantage that it can beused to detect not just nitric oxide butalso nitrogen dioxide (or dinitrogentetroxide).

This is particularly important for themeasurement of the exhaust from thelarger medium speed engines.

Nitrogen oxide emissions from highspeed diesel engines tend to bemostly as nitric oxide, although up to30% dioxide can be detected undercertain operating conditions such asat low speed and high air-fuel ratios

NITRIC OXIDE

Hydrocarbons in diesel exhaust areuniversally measured using a heatedflame ionization detector (HFID).

A flame ionization detector cell, such asthat used on gas chromatographs,together with the necessary electronicsignal processing and readout equipment.

For diesel exhaust measurement wherethe hydrocarbons are of fairly highmolecular weight and consequently ofhigher boiling points, it is essential to avoidlosses due to condensation on anysurfaces in contact with the gas sample.

HYDROCARBONS

Carbon monoxide is alsomeasured using a non-dispersiveinfra-red detector.

This would be identical in principleto carbon dioxide except that, if athin film interference filter were notused, the filter cells would be filledwith pure carbon dioxide to avoidcarbon dioxide interference , andthe detector would contain carbonmonoxide.

CARBON MONOXIDE

Although not legislated for, the analysissystem for carbon dioxide is defined bya number of regulatory bodies.

Carbon dioxide is almost invariablymeasured using a non-dispersive infra-red (NDIR) analyzer.

This is possible because carbon dioxideabsorbs radiation in the infra-red region.

The degree of attenuation depends onthe amount of carbon dioxide present inthe path of the beam; the more carbondioxide the greater the attenuation.

CARBON DIOXIDE

WET AND DRY MEASUREMENT OF EMISSION CONTENTS

Transmissiometry – Dry gases – Accuracy: +/- 2%

• Scatter-light – Dry and wet gases – Accuracy: <+/- 2%

WET AND DRY MEASUREMENT OF EMISSION CONTENTS

Emission Concentration Monitors

When a light beam shines through a mixture of gas and particles,the particles weaken the beam by absorption and scattering. Themore particles in the light beam, the stronger the weakening of thebeam.

• The comparison of the intensities of initial light and received lightsupports a precise statement of the transmission.

• After conversion of the transmission in extinction and gravimetriccomparison measurement, the result is displayed in mg/m3.

TRANSMISSIOMETRY

A light sender radiates light that is scattered by the particles in thegas which is then detected by a sensitive detector. The dispersedlight principle is suited for small dust loads – also under 1 mg/m3.

• The correlation between measured value indication and dust loadis determined by means of gravimetric comparison measurements.

• Both backwards and forwards scattering are used for scatteredlight measurement applications.

SCATTER-LIGHT

SCATTER-LIGHT (DRY-GASES)

SCATTER-LIGHT (WET-GASES)

Emission measurement equipment – for passenger car engine without catalyst converter

Emission measurement equipment – for passenger car engine with catalyst converter

UNITS OF EMISSION MEASUREMENT – EMISSION INDEX AND SPECIFIC

EMISSION

The emission index for species i is the ratio of the mass of speciesi to the mass of fuel burned by the combustion process:

In principle, the emission index is a dimensionless quantity, The emission index is useful in that it unambiguously expresses the

amount of pollutant formed per mass of fuel, independent of anydilution of the product stream or efficiency of the combustionprocess. Thus, the emission index can be thought of as a measureof the efficiency of a combustion process in producing a particularpollutant, uncoupled from the specific application.

EMISSION INDEX

In the dynamometer testing of spark-ignition and diesel engines,emissions are frequently expressed as

where the units are typically g/kW-hr. or the mixed units of g/hp-hr.Mass specific emissions (MSE) are conveniently related to theemission index as

where mF is the fuel mass flow rate and is the power delivered.

SPECIFIC EMISSION

EQUIVALENCE RATIO DETERMINATION FROM EXHAUST GAS CONSTITUENTS

An accurate determination of fuel/air equivalence ratio canbe derived from measurements of exhaust gas constituents(CO , CO2, O2 , HC, and NOx ). This method is ideal for laboratoryengine testing and development, but is not practical for fieldengines and control due to the expensive and highmaintenance analyzers required.

Chemical equation for incomplete combustion utilizingequivalence ratio and exhaust constituents is :

nP = Total Moles of Exhaustxi = Mole Faction of ith Constituent

EQUIVALENCE RATIO FROM EMISSIONS

The HC measurement is typically from a fully wet sample with aflame ionization detector (FID). Given these types of wet/drymeasurements, the calculation for equivalence ratio is as follows:

EQUIVALENCE RATIO FROM EMISSIONS

COMBUSTION INEFFICIENCY

POTENTIAL TECHNOLOGIES FOR HD DIESEL ENGINES IN 2010

The End

Exhaust Emission Measurement and Control

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