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Mukesh - A Comparative Study of Diesel and CNG
1. A Comparative Study of Diesel and CNG Driven Mid-size
Vehicles for Particulate Emission Characterization, EC/OC,
and NOx at Idling Condition
Manish K. Jha, Umesh Vitthalrao
Mukesh Sharma & Tarun Gupta
Environmental Engineering and Management Program
Indian Institute of Technology Kanpur
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2. In Kanpur โฆโฆ
These three-wheelers were the main mode of public transport.
About 7000 of them, mostly run on diesel, were on road in
2004 (EPCA).
All diesel vehicles have now been converted to CNG vehicles
like this one.
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3. Objectives
Establish how good is CNG
Establish source emission profile of CNG
๏ Design an in-house portable exhaust sampler;
๏ Characterize particulate emission (size and composition) from
diesel and CNG vehicles.
๏ Study elemental and organic carbon signatures of diesel and
CNG three wheeler exhaust.
๏ Compare the NOx and metal emission from CNG and diesel
three-wheeler exhausts.
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4. Diesel Vs. CNG
1. Diesel comes from the middle
distillate fraction of a crude
oil
2. 75% saturated HC, 25%
aromatic HC.
3. Average chemical formula of
Diesel oil is C12H26
4. Often contains higher conc. of
Sulfur, metals present.
5. High CO2 production due to
longer carbon chain.
1. CNG is found in oil and natural
gas fields;
2. 85% or more methane and
some heavier gaseous HC such
as ethane, propane and butane
3. Average Chemical Formula is
CH4
4. Metals, Sulfur absent
5. Highest energy/carbon ratio
(70MJ/KgC); produces less
CO2 per unit of energy.
Diesel CNG
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5. Diesel Engine vs CNG Engine
1. Diesel engine operates at
700-9000C.
2. NOx formation is more
3. Soot particles in exhaust are
more
4. Toxic PAH and metals
present in exhaust
5. Higher health risk
6. Exhaust contains mutagens
and carcinogens in vapor
and solid form.
1. Bi-fuel CNG engine operates
at 400-6000C;
2. Lesser NOx formation
3. Lesser soot particles in
exhaust
4. Lesser amounts of metals and
toxic HC in exhaust?.
5. Health risk just 55% of diesel
exhaust (Cohen, 2003 )
6. Lesser carcinogens and
mutagens present ?
Diesel Engine CNG Engine
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6. Materials and Methods
Vikram 1500CG and Tiger by JS Auto vehicles were used for CNG
and 750D for diesel emission studies
The CNG powered vehicle had a bi-fuel engine that runs both on
gasoline and CNG
CNG kit manufactured by Landi Renzo SPA, Italy.
Catalytic converter as an integral part of the O.E in CNG vehicles.
Particulate trap was present in diesel vehicle.
CNG vehicles used were 4 months and Diesel vehicle 3.5 years old
Samples taken at idling conditions.
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8. Why a special Sampler?
Residence time and Dilution Ratio main design criteria
Particle formation in diesel exhaust, Kittleson (1997)
Most of the
Volatile nano-
particles formed
at this stage
Particle
formation is
almost complete
at this stage
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9. Sampler Design
Lipsky and Robinson used a RT of 2.5 sec. No change in
particulate with an additional 40 sec. RT.
2.5-3.0 Sec was used in this design.
DR= Total volumetric flow rate
Pure vehicle exhaust rate
Hildemann et al. (1989) used a DR of 25-100. Lipsky and Robinson
(2005) used a dilution ratio 6-64.
Graze (1993)used a DR between 6-12. Chosen DR brings exhaust
to ambient temperature.
We used a DR of 8-10 as this brought down the temp. of exhaust to
ambient temp.
Stainless Steel is used for fabricating the sampling system.
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15. Measurement of NOx Emissions
Thermo Electron Corporationโs model 42C NO-NO2-
NOx analyzer is used.
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16. Measurement of EC and OC in exhaust particulate
DRI Model 2001 Thermal/Optical Carbon Analyzer for the
measurement of elemental and organic carbon in exhaust samples
collected on quartz filters.
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18. Gravimetric Results
Particulate Concentration in Vehicle Exhaust
Particulate Concentration in Vehicle exhaust
0
1000
2000
3000
4000
5000
6000
CNG Diesel
Dilution Condition
ParticulateConcentration
(ยตg/m3
ofpureexhaust)
Diluted Undiluted
Diluted
condition has
10 times more
particulate
Diluted
condition has
2.8 times more
particulate
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19. Particle Size Distribution
All the scans for diluted condition are shown here
High particle
concentration at
engine startup
Low particle
concentration for
ambient air in
blank tunnel
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20. Average Particle Size Distribution in Diluted
CNG exhaust
Number
Distribution Peaks
at 30 nm.
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21. Comparison of particle number distribution for experiment
Diluted and Undiluted Condition in CNG
Higher number of
finer particles in
diluted condition
Higher number of
coarse particles in
diluted condition
It is important that sampling of automobile exhaust must be carried
out after providing dilution air and adequate residence time for
complete particle formation.
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22. Number and Volume distribution of Diluted
Diesel Exhaust
Ambient
air
profile
Peak at
50 nm
Volume
distribution
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23. Number and Volume distribution of Undiluted
Diesel Exhaust
Peak at
50 nm
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24. Comparison of Particle Size Distribution for
Diluted and Undiluted Diesel Exhaust
Diluted condition
has more particles,
gap larger over
finer diameter
Difference
narrows down
at larger
diameters.
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25. Particle number concentration as a function of particle size is
always higher for diesel exhaust.
Peak particle number concentration for CNG at 30nm; peak in diesel
exhaust at 50nm
Comparison of CNG and Diesel Exhaust
Under Diluted Conditions
Difference in particle number concentration between CNG and diesel
exhaust widens for larger particle sizes
Diesel exhaust has larger particles (>450 nm);,number conc. Over
larger diameters reduces to ambient air profile in CNG
Higher volume Concentration in Diesel exhaust
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26. Comparison of Present Study with
that of Holmen and Ayala (2002)
Diesel has higher particle number concentration than CNG
Peaks matches with Holmen and Ayala
Partile Size Distribution for different
vehicles (Holmann and Ayala; 2002 )
Particle Size Distribution for CNG and
Diesel vehicles found in this study.
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27. CNG Exhaust Vs Lubricating Oil
Metals in CNG Exhaust and Lubricating Oil
0
10
20
30
40
50
60
70
Zn Pb Cd Fe Al Mg Na
Metals
Metal(ยตg/g)
0
5
10
15
20
25
30
Metal(ยตg/m3)
Lubricating Oil CNG Exhaust
Metals emission in CNG exhaust pattern matches with the
metal content in lubricating oil
Metal emissions in CNG exhaust are from lubricating oil
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28. Metal mass ratio CNG to Diesel
Metal Mass Ratio CNG to Diesel Exhaust
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
MassRatio(CNG/Diesel)
Pb
Cd
Al
Mg
Na
Metal Mass Ratio CNG to Diesel Exhaust
0
0.5
1
1.5
2
2.5
3
3.5
4
Massratio(CNG/Diesel)
Zn
Fe
Metals except, iron and zinc in CNG exhaust are much lower
than in diesel exhaust
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29. NOx
NO2, NO and NOx Emission
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Ratio(CNG/Diesel)
NO2 NO NOx
It is found that in diesel NO2 is 7.47, NO is 16.6 and NOx is
14.7 times higher than that of CNG
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30. EC and OC in CNG Exhaust
95% of the total carbon is in the form of Organic carbon.
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31. EC and OC in Diesel Exhaust
15% of the total carbon as EC and about 85% of total
carbon is represented by organic carbon in diesel exhaust.
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32. Ratio of EC/OC Components in CNG Exhaust
to that in Diesel Exhaust
Ratio of EC/OC Components in CNG Exhaust to
that in Diesel Exhaust
0
0.1
0.2
0.3
0.4
0.5
0.6
OC1 OC2 OC3 OC4 EC1 EC2
EC/OC Fractions
Ratio(CNG/Diesel)
All the fractions of EC and OC are less in CNG exhaust.
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33. Explanation of Results?
Lack of EC core in CNG exhaust is responsible for lesser
particles in CNG.
46% and 40% of the PM are represented by TC in diesel and
CNG exhaust respectively.
High percentage of carbon in diesel engine implies that particle
formation is mostly influenced by elemental and organic carbon
fractions.
EC fraction is about 8 times less than that in diesel exhaust, but
particles less than 30nm in diesel exhaust is just about 2.5-5
times that in CNG exhaust.
It can be concluded that EC is not the main source of finer
particle (less than 30 nm) in CNG exhaust. Metals may be more
important in particle formation in CNG exhaust.
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35. Impact on Air Quality โ Elemental Carbon
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
January
February
March
April
May
June
January
February
March
April
May
June
January
February
March
April
May
June
Regular
E C
2005
Pre-CNG
2006
Pre-CNG
2007
Post CNG
People are breathing cleaner air
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36. Conclusions
Sampling should be done under diluted conditions only.
CNG vehicle has lower number distribution than diesel
Peak particle number concentration for CNG at 30nm; peak in
diesel exhaust at 50nm
Pb, Cd, Mg , Na, and Al emission in diesel exhaust is much
higher compared to CNG exhaust.
CNG vehicle has 16-20 ppm NOx; diesel vehicle has about 290-
310 ppm.
40% of PM in CNG exhaust and 46% in Diesel exhaust was EC
or OC.
OC accounted for 85 % of TC in diesel exhaust and 95% of TC
in CNG exhaust.
Organic carbon in both the vehicles was dominated mainly by
VOC fraction.
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37. The main conclusion of this research is that CNG
fuel compared to diesel is a cleaner and superior
fuel in terms of (i) particle size and mass emissions
(ii) EC (black carbon) and OC (iii) Metal
concentration and (iv) NOx
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