Download - Exhaust Emission Measurement and Control
Exhaust Emission Measurement and Control
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
2Preet Ferozepuria
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
3Preet Ferozepuria
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
4Preet Ferozepuria
EXHAUST SMOKE, MEASUREMENT, REGULATIONS & CONTROL
5Preet Ferozepuria
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.
6Preet Ferozepuria
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.
7Preet Ferozepuria
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.
8Preet Ferozepuria
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.
9Preet Ferozepuria
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
10Preet Ferozepuria
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
11Preet Ferozepuria
1. Filter-soiling 'spot' meters2. Opacimeters
1. Sampling opacimeters2. Full-flow opacimeters
SMOKE MEASURING INSTRUMENTATION
12Preet Ferozepuria
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
13Preet Ferozepuria
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
14Preet Ferozepuria
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
15Preet Ferozepuria
Opacimeters may be classified as: Sampling, or Full- flow,
• In-line and • End-of- line types.
TYPES OF OPACIMETERS
16Preet Ferozepuria
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.
17Preet Ferozepuria
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
18Preet Ferozepuria
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.
19Preet Ferozepuria
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.
20Preet Ferozepuria
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.
21Preet Ferozepuria
SMOKE LIMIT FOR OFF-HIGHWAY & COMMERCIAL VEHICLES & GENSET ENGINES
22Preet Ferozepuria
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
23Preet Ferozepuria
POLLUTION TEST PROCEDURES –ECE R49, ESC, ETC, ELR.
24Preet Ferozepuria
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
25Preet Ferozepuria
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
26Preet Ferozepuria
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
27Preet Ferozepuria
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.
ESC
28Preet Ferozepuria
ESC
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 )
29Preet Ferozepuria
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.
ESC
30Preet Ferozepuria
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.
ESC
31Preet Ferozepuria
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.
ETC
32Preet Ferozepuria
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.
ETC
33Preet Ferozepuria
ETC
Vehicle speed vs time over the duration of the cycle
34Preet Ferozepuria
ETC
ETC Transient Cycle - Engine Speed
35Preet Ferozepuria
ETC
ETC Transient Cycle - Engine Torque
36Preet Ferozepuria
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.
ELR
37Preet Ferozepuria
The sequence of dynamometer operation on the test engine
ELR
38Preet Ferozepuria
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).
ELR
39Preet Ferozepuria
EMISSION STANDARDS FOR HD VEHICLES IN USA, EUROPEAN UNION &
INDIA
40Preet Ferozepuria
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
41Preet Ferozepuria
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)
42Preet Ferozepuria
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)
43Preet Ferozepuria
EMISSION STANDARDS FOR OFF-HIGHWAY VEHICLES IN USA, EUROPEAN
UNION & INDIA
44Preet Ferozepuria
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-
2014c
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
45Preet Ferozepuria
EU-OFF HIGHWAY EMISSION NORMSSTAGE IIIA
Category Applicable
From
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 )
46Preet Ferozepuria
STAGE IIIB (G / KWH)Categor
yApplicab
leFrom
CO(g/kw
h)
NMHC(g/ kwh)
NMHC + NOx
(g/ kwh)
NOx(g/
kwh)
PM(g/
kwh)
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.
47Preet Ferozepuria
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
48Preet Ferozepuria
PROPOSED BHARAT (TREM) STAGE-III A NORMS FOR AGRICULTURAL TRACTOR ENGINES
Category Applicable
From
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
49Preet Ferozepuria
EMISSION STANDARDS FOR POWER GENERATION ENGINES IN INDIA
50Preet Ferozepuria
CURRENT EMISSION NORMS FOR DIESEL ENGINE FOR GENERATOR SETS
Engine power (P)
Date CO(g/
kwh)
HC(g/
kwh)
Nox(g/
kwh)
PM(g/
kwh)
Smoke(1/m)
P≤800KW 2004.7 3.5 1.3 9.2 0.3 0.7
Test cycle : ISO 8178- 5 mode –D2
51Preet Ferozepuria
NEXT LEVEL(PROPOSED) GENERATOR ENGINE EMISSION NORMS:CPCB STAGE-II
1. Time – lines: April 2011/April 2010 Considering productdevelopment, Certification.
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
52Preet Ferozepuria
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
1. Time – lines: April 2015/April 2014 Considering productdevelopment, Certification.
2. Fuel Specifications: Less than 50ppm sulfur Diesel fuel, acrossthe Country
53Preet Ferozepuria
CERTIFICATION & SELF AUDIT
54Preet Ferozepuria
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%
55Preet Ferozepuria
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.
56Preet Ferozepuria
DETERIORATION FACTORS
57Preet Ferozepuria
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
58Preet Ferozepuria
ON BOARD DIAGNOSTICS FOR DIESEL ENGINES
59Preet Ferozepuria
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.
60Preet Ferozepuria
MALFUNCTION INDICATOR LIGHT (MIL)
Should a malfunction bedetected, a warning light willappear on the vehicle'sinstrument panel to alert thedriver.
61Preet Ferozepuria
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.
62Preet Ferozepuria
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
63Preet Ferozepuria
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.
64Preet Ferozepuria
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.
65Preet Ferozepuria
EXHAUST POLLUTANTS AND THEIR FORMATIONFORMATION IN DIESEL ENGINE
66Preet Ferozepuria
EXHAUST POLLUTANTS AND THEIR FORMATION
EMISSION FROM DI DIESEL ENGINE
67Preet Ferozepuria
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
68Preet Ferozepuria
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
69Preet Ferozepuria
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
70Preet Ferozepuria
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
71Preet Ferozepuria
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.
72Preet Ferozepuria
EXHAUST POLLUTANTS AND THEIR FORMATIONCONTROL OF POLLUTANTS IN DIESEL ENGINE
73Preet Ferozepuria
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
74Preet Ferozepuria
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.
75Preet Ferozepuria
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.
76Preet Ferozepuria
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.
77Preet Ferozepuria
HC
The effect of nozzle sac volume on HC emission of a one-litre per cylinder displacement engine is shown below:
78Preet Ferozepuria
- 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
HC
79Preet Ferozepuria
CREVICE HC MECHANISM
CREVICE VOLUME SOURCES
- TOP LAND VOLUME- CREVICE AROUND INTAKE AND EXHAUST VALUE HEAD
- CYLINDER HEAD GASKET CREVICE ZONES
80Preet Ferozepuria
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.
81Preet Ferozepuria
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.
82Preet Ferozepuria
APPLICATION OF SMOKE REDUCTION TECHNIQUES
83Preet Ferozepuria
EXHAUST GAS AFTER TREATMENTS
84Preet Ferozepuria
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
85Preet Ferozepuria
Three-way catalytic convertor .Ceramic honeycomb structures:
Reduction catalyst (Pt/Rh).- Reduction of nitrogen oxides
Oxidation catalyst (Pt/Pd).- Oxidising unburnt hydrocarbons
& CO
THREE- WAY CATALYTIC CONVERTERS FOR SPARK IGNITION ENGINES
86Preet Ferozepuria
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
THREE- WAY CATALYTIC CONVERTERS FOR SPARK IGNITION ENGINES
EFFICIENCY
87Preet Ferozepuria
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.
88Preet Ferozepuria
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)
89Preet Ferozepuria
DIESEL PARTICULATE FILTER (DPF)
90Preet Ferozepuria
Conversion of NOx into N2 and H2O. Gaseous reductant: Ammonia/Urea
Scheme of reactions:
Reaction temperature: 450 – 800 F
SELECTIVE CATALYTIC REDUCTION [SCR]
91Preet Ferozepuria
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
92Preet Ferozepuria
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
93Preet Ferozepuria
EGR (EXHAUST GAS RE-CIRCULATION)
94Preet Ferozepuria
EGR (EXHAUST GAS RE-CIRCULATION)
Concept : exhaust –gas recirculation (EGR) is highly effective measure for NOx emissions on diesel engines.
95Preet Ferozepuria
- 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 :
96Preet Ferozepuria
WORKING OF EGR
97Preet Ferozepuria
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
98Preet Ferozepuria
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
99Preet Ferozepuria
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.
100Preet Ferozepuria
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 .
101Preet Ferozepuria
TYPICAL EGR MAP(% OF VALVE OPENING)
102Preet Ferozepuria
ADDITIONAL MAPS FOR EGR OPERATION
103Preet Ferozepuria
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
104Preet Ferozepuria
EGR OPERATION
105Preet Ferozepuria
CO2 EMISSION FROM DIESEL ENGINES
106Preet Ferozepuria
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
107Preet Ferozepuria
DIESEL VS. CNG ENGINES
108Preet Ferozepuria
CNG vehicles emit 60 to 95% less PM and 0 to 30% less NOx than equivalent diesel vehicles.
109Preet Ferozepuria
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
110Preet Ferozepuria
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
111Preet Ferozepuria
In the critical sub-100 nm range, CNG particulate numbers maynot be much different from diesel
ELPI used for measurements
112Preet Ferozepuria
PM Particle Count by Size.
113Preet Ferozepuria
Emissions Summary
114Preet Ferozepuria
CNG Cost Factors.
115Preet Ferozepuria
Clean Diesel Cost Factors.
116Preet Ferozepuria
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
117Preet Ferozepuria
ANALYZERS FOR MEASUREMENT OF NOX, HC, CO, CO2, PM ETC.
118Preet Ferozepuria
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
119Preet Ferozepuria
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
120Preet Ferozepuria
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
121Preet Ferozepuria
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
122Preet Ferozepuria
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
123Preet Ferozepuria
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
124Preet Ferozepuria
WET AND DRY MEASUREMENT OF EMISSION CONTENTS
125Preet Ferozepuria
Transmissiometry – Dry gases – Accuracy: +/- 2%
• Scatter-light – Dry and wet gases – Accuracy: <+/- 2%
WET AND DRY MEASUREMENT OF EMISSION CONTENTS
Emission Concentration Monitors
126Preet Ferozepuria
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
127Preet Ferozepuria
TRANSMISSIOMETRY
128Preet Ferozepuria
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
129Preet Ferozepuria
SCATTER-LIGHT (DRY-GASES)
130Preet Ferozepuria
SCATTER-LIGHT (WET-GASES)
131Preet Ferozepuria
Emission measurement equipment – for passenger car engine without catalyst converter
132Preet Ferozepuria
Emission measurement equipment – for passenger car engine with catalyst converter
133Preet Ferozepuria
UNITS OF EMISSION MEASUREMENT – EMISSION INDEX AND SPECIFIC
EMISSION
134Preet Ferozepuria
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
135Preet Ferozepuria
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
136Preet Ferozepuria
EQUIVALENCE RATIO DETERMINATION FROM EXHAUST GAS CONSTITUENTS
137Preet Ferozepuria
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 :
Where
nP = Total Moles of Exhaustxi = Mole Faction of ith Constituent
EQUIVALENCE RATIO FROM EMISSIONS
138Preet Ferozepuria
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:
where
,
EQUIVALENCE RATIO FROM EMISSIONS
139Preet Ferozepuria
COMBUSTION INEFFICIENCY
140Preet Ferozepuria
POTENTIAL TECHNOLOGIES FOR HD DIESEL ENGINES IN 2010
141Preet Ferozepuria
The End
142Preet Ferozepuria