Journal of Scientilic & Industri al Research

Vo l. 62, Janu ary-February 2003, pp 20-24

Application of CNG in Transportation Sector - A Review of the Current Status of Technology and Future Projections

B B Ghos h"', P K Bose, Ranajit Kumar Chakrabarti and Kalyan Kumar Das

Department of Mechani cal Engineering, Jadavpur Universi ty, Kolkata 700032, Indi a

The rapid depletion of petrol eum fu el, and ever ri sing costs have forced engineers to search for alternative fuels for the use in IC engines, With an abundant supply and cleaner ex haust, CNG has great potential as a subst itute of petrolt:u m fu els. CNG can also play vit al ro le in reli eving the fu el crisis worldover as a future source of energy a,; well as cleaner fuel. Full replacement of petrol in J::etrol engine with CNG is not a problem but in the case of diesel engine it gives various problems in operat ion and hence ex tens ive research work is necessary in this lield for full replacement of di esel with CNG. Ir. thi s paper, SOllle research work on the use of CNG in C I and S I engines at national and internat ional scenarios have been reported.

Introduction

GlobJI petroleum depos its will get depleted with in the nex t 100 and research on alternati ve fu el powered car is on, in earnest. Experts have been predicting the use of alternative fuel for vehic les for decades. With detori orating o il pollution and ri sing oil pr ices , it is natural th at there wou ld be focused th inking on producing cheap environmental-friend ly alternati ve fuel. There are plenty of alternative sourccs of energy to foss il fuels. Hydrogen, compressed natural gas (CNG), alcohol, bi ogas, produce r gas, liq ue fied petro leu m gas (LPG) and a host of vegetable oils are being tried allover the world as substitutes to conventi onal pet r01eum based ruc \ ~ . The biogas and producer gas are low energy content per uni t mass. Moreover, storage probl em is there wit h these fuels. Alcohol has poor energy contcnt per unit mass. These fuels have also low cetane numbers. As alcohol fue ls do not read il y combust in C I engines, thi s limits the substitutes fo r hi gh compress ion ignttt on engines l

. The mall1 co nstraint of using vegetable oil s as fu el is their hi gh cost. CNG occupies a very prominent place, primaril y because of its techn o economtc evaluation characteri sti cs and environmental benefits (Table I).

The use of CNG as an engine fuel, fortun ately, does not ca ll for radi ca l changes in engine des ign.

;, Emeritus Professor. AICTE, Jadavpur University, Ko lk ata, and Indi ,1Il Insti tu te ofTechnoiogy, Kharagpur, India

The properties of natural gas, which make it a better alternative fuel for IC engines are;

(i) Because of its gaseous state it defuses rap idly in air fu el mixing at lower inl et temperature than is poss ible with eith r gasoline or diese l. This leads to easi er starting, more rel iable idling, smoother accelerati on and more complete and e ffi c ient burning with less unburned hydrocarbons present In the exhaust.

(ii) The higher igniti on tempera ture of gas compared with petroleum based fuels leads to reduced au to igniti on delay. Due to thi s higher ignition temperature, CNG is less hazardous than any petroleum based fue ls .

(ii i) The hi gher octane rating of 120 for natural gas (NG) compared with 87 for gaso line allows a hi gher compressi on rati o (CR) or 15:6: I and , consequentl y, more effici ent fu el consumption . Due to its higher CR, CI engines can also use CNG a~ a fu el. But since cetane rati ng of CNG is poor it cann ot replace diese l totally like gaso line.

(iv) Maintenance costs for gas are lower th an that of gasoline or diesel engines, because gaseous fue ls burn c lea n without carbon depos its. Furthermore, in gas engines the fuel

j ,

GHOSH el al.: APPLICATION OF CNG IN TRAN SPORTATION SECTOR 2 1

T able 1- Physico - chemical properti es of CNG and gasoline

Properties

Composition

2 Stoichiometri c AJF rati o

3 Lower calorifi c value MJ/kg

4 Ign iti on temperature

) Ouane no.

6 Adiabati c Il ame temperature

7 Minimum energy required for ignition

g Volumetri c efficiency

<) HUCR

10 Storage and handling

II Availabi lit y

NG

M eth ane 82.2 per cent Eth ane 6. 1 Propane 2.4

Isobutane 1.0 N-butane, Isopcn tane 0.4

Nitrogen 7.7 Carbondi oxide and oxygen 0.2

17

44.24

649-72I"C

120

2 148 K

0.29 MJ

Les~

12.2

Dirtl cull

Abundanl

Gasolinc

14.6

43

n i 'c 87

2470 K

0.24 MJ

M ore

s .)

Ea~ i c r

Limil cd

12 Rcncwabilil y Rcnewab le and can be obtained from ~elVage and biomass. shale oil and olher sou rce

N OI

rcnewahle

does not mix up with the lubri cant s to dilute it or reduce its viscos ity so that lubricant consumpti on is lower in gas engine than that in gasoline/di ese l engines.

(v) Opt imised natural gas vehic les are expected to produce much less carbon monox ide near­zero reac ti vity of methane, natural gas vehicles may cause less ozone formati on than gaso line/d iese l vehi cles.

Review of Current Status of Technology

CO // l'eJ's i o // Kifs2 - The natural gas retrofit kits bas ica ll y consist of: ( i) On board storage tank, ( ii ) ri lling val ve, (iii ) Pressure regulator, (iv) Pressure gauge, (v) Load and speed dependent regul ators , (vi) Gas air mi xer, (vii ) Shut off and Cont ro l va lves, (viii ) Low and hi gh pressure tubing and fittin gs. Most kits arc mechanica l in operati on and are designed typica ll y for use as a 'Second-fuel System' . Kit s with electro ni c control, based on engine performance map systems have also been developed. Kits and engine deve lopments are also under way which can take care of va riati ons in gas co mpos itions and maintain engine performance c lose to gaso line or di ese l through

elect roni c control ,'.-l The choice between mec han ical and electroni c kit would depend upon the cost of kit , ease of conversi on, ease of maintenance and type of appli cati on.

Ex perimental in vesti gati ons, re lating to the utilisation of CNG in on automotive passenger ca r were carri ed out by Nagraj et (l1'- In vestigati ons "vere carri ed out for: (a) Gaso line operation , b) CNG with a standard kit , (c) CNG with the kit tu ned fo r max imum power, (d) CNG with the kit tu ned for lower emi ss ions. The studies indicated that the performance of the CNG kit with standard setting was fo und to be lower than gasoline operation . It was observed th at if this kit was tuned furth er, improvement in brake power could be achi eved. Under these co nditi ons the BSEC and emissi ons were noticed to be lower than gaso line versi on.

Ex periments were carri ed out by Das and Redd/' in the Engines and Unconventional Fuels Laboratory at liT, De lhi in developin g a CNG fuell ed spark Igniti on Engine . Res ults of th e work have shown that maximum level of ca rbon monoxide emissions was 0.325 per cent , NO, emiss ion concentrati ons achi eve the peak value around an­equi va lence rat io of 1.1 , whereas if it reduces the

22 J SCIINDRES VOL61 JANUARY-FEBRUARY 2003

leaner and ri cher mi xtures. Results of the work showed an improve ment in the performance and emi ss ion charac te ri sti cs of the CNG fue lled engine, using a spec ia lly des igned Electro Mechani cal Fuel (EMF,) sys tem.

F le ming and Allsup7 have carried out study of natural gas as low-po llution automotive fuel us ing a s ing le cy linder, a multi cy linder engine and six vehic les. Results showed that the light-l oad lean-limit mi sfire region o f natura l gas begins at an a ir fue l ratio be tween 140-150 per cent of sto ichiometric. Changes in igniti on timing, significantly influenced emi ss ion of nit rogen ox ides and hydroca rbon s but had little effect on CO emi ss ion. Lowe r emi ss ions can be achi eved (by adjustment) with current des ign engines, but with heavy pena lty to engine performance. Emi ss ions from vehic les fu e led with natural gas are virtuall y unaffec ted between 20-100°F. Natural gas ex hau st is estimated to be 22 per cent-2S per cent as reacti ve as gasoline ex haust.

x Paul et at. have conducted experiments on a commerc ial, four stroke, s ix-cy linders water-cooled , direct injection Tata diese l engine using thi s due l fu e l. The maximum percentage repl acement of diese l with CNG has been fo und to be 69.4 per cent at an optimum speed of 1900 rpm. The brake thermal e ffi c iency of thi s eng ine when run with dual fu e l is comparabl y at different speeds and loads with that if the eng ine when run with diesel only .

Das and Ghosh C) made comparati ve studi es of gaso line and CNG as fuel for spark ignition engine. In thi s paper, different pe rformance parameters, such as effic iency, spec ific fuel consumption. The presence of CO and NO, in the exhaust of SI engine run wit.h CNG as fuel have been measured and plotted as a function of air index at different running conditi ons. The CNG fue led engine showed improved effi c iency by 3-5 pe r cent depending on the compress ion ratio and air index, emits less CO but 51 ightl y higher amount of NO,.

Das and Ghosh' o have carried out ex periments on the diesel version of Richards va riable Commerc ial engine and a commercial Tata diesel engine to study the perfo rmance and e mi ss ion characte ri stics, percentage reduction o f diesel with CNG. It was observed that the dual fuel operation produced less amount of nitrogen oxides during AlF operation but slightly more CO than diese l fuel operati on.

At present, in India the c iti es like Delhi , Mumbai , Vadodara and Surat vehicl es are operat ing on CNG in a large sca le. Mo re than 30,000 vehi c les are running on CNG in New Delhi and ! 0,000 buses would be converted to CNG by October end . Most energy ex perts agree that it is not on l/ CNG but several other steps like phasing out of o ld vehicles and reducing sulphur content in the fuel can contribute to reducing a ir polluti on. A combinati on of CNG with other a lte rnative fuels could a lso be used to reduce air po llution.

On the g lobal scene, CNG is popular in pockets and that too onl y where e ithe r the government or the judiciary have pushed it. From the hea lth and safety point of view, C NG is as good as , or even be tte r than petro l and other alternative fuels. C hicago has about 30 pe r cent of its public tran sport be ing operated on CNG and it is as low as 5 percent in New York , and 2 per cent in Pari s.

In case of the Middle East countries, they prefer to flare up the gas instead of chang ing the ir entire fleet to CNG.

The fu e l is li ghter th an air hence in the event of a leak, it will ri se and di sperse in the atmosphere and neithe r form puddles (as in the case of petrol ) nor will it spread (as in LPG). The igniti on temperature of natural gas is much higher than pe tro l, making il more difficult to ignite.

Future Projections

CNG is going to playa vital role in re li eving the fue l c ri sis worldover as a future source o f energy as we ll as a cleaner fu e l. India has taken up the challenge and converting most of its vehic les to run on CNG.

In Indi a, two-whee lers are popul ar because of its low cost operation inc luding suppl y of fu e l. Many manufacturers are in the process of converting ex isting petro l and diesel operated two-wheelers petrol and diesel to CNG operation . The full replacement of petrol in a pe tro l engine with CNG is not a problem but full replacement of d iesel in a di esel engine possess a lot of problems because of the low cetane number of diese l. As per Indian context, automobil e manufacturers are looking forward for the complete replacement of diesel with CNG, demanding an extens ive research work in the use of CNG in the diesel eng ine.

GHOSH et al.: APPLICATION OF CNG IN TRANSPORTATION SECTOR 23

Conclusions

Going through the research work carried out by researchers at national and inte rnational level the following fac ts have corne to li ght :

( i) The ex isting SI engines can be operated with 100 per cent substitution o f CNG in place of petro l.

( ii ) It is diffi cult to operate the CI eng ines with the substituti on of 100 per cent CNG in place of di ese l. However, hi gher percentage of substitution of CNG is poss ible at the operati on of hi gh loads.

( iii ) The C I engines can be completely operated with CNG by convertin g the CI engines to SI engines, though it is not economica l.

( iv) The na tural gas fro m the source can be ava ilable in three forms such as Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG), Lique fi ed Pe troleum Gas (LPG), out of these CNG appears to be economi ca l because of the following reasons:

(a) The convers ion of NG to CNG needs a compressor.

(b) The convers ion of NG to LNG needs cryogenic set up to maintain the NG at -40 DC which is uneconomi ca l.

(c) LPG is the byproduc t o f c rude petroleum. During the process in g o f c rude petro leum it becomes ex pens ive and ava il ab ilit y is also limited.

(v) The convers ion of existing S I and C I eng ines needs kits the manufacture o f w hi ch has been ve ry popular all over the world. It appears throu gh the I ite rature survey that the devel opment of kit s has a w ide scope re lated to the proper des ign and fa bri ca ti on. As per the diffe rent SI and C I engines ha ving diffe rent horse powers (hp) the careful des ign and fabrication of C G kit s require proper thou ght. Thus the des ign and fabri ca ti on of CNG kits for diffe rent capacity eng ll1es has been a chall enging global issue.

(v i) On the basis of works carried out by Prof. Karim at Unive rsity of Calgary Canada . Prof. Evan at the Uni vers ity of Colombia, Canada.

Prof. Rene at the University o f Auc land , New Zeland. Prof. Bill at the University of Allabama, USA Prof. L.M . Das at lIT De lhi , India . Prof. B.B . Ghosh at lIT Kharagpur, Indi a Prof. H.B . Mathur at lIT De lhi , Indi a Prof. Probir Kr. Bose, at Jadavpur Univers ity, Jadavpur, India .

(v ii ) ]t has been realised that CNG is a c lean fuel in compari son to petrol and diese l as pe r the engine ex haust emi ss ion.

(v iii) On the whole on the bas is eng ine performance and e mi ss ions, in future the dedicated CNG engines have to be des igned and manufactured .

( ix) It is the proper time to go in for ded icated CNG engines which can be operated at hi gher compression rati o in order of 14 to have very good eng ine effi c ie ncy.

ex) As per the safety po int of view the operation on CNG engines is more safe r because of its hi gh

ignition te mperature as compared to petro l a nd

diese l.

References

DcLuchi A M. John ston R A & Spcrlin g D. M ethanol 1'.1'

natllml gas I'echiclesn: a cOlllllarison. SAE Paper No. 88 1656. 1988.

2 Singhal S, Sharma J & Gandhi K K. Stratcgy 1'01' use or natural gas as a transport ation rucl in In dia, PmI' TI \'e/jih Nllt

Conj'l C t:ng COII/bllst liP. D ehradlln , 1<)<)2.

3 Kimbara Y. Kat sumata S. Iehimi ya T, Kan M & Kondo S Dcvclopment or toyoto clectroni ca ll y co nt rollcd comp rcsscd natural gas vchi clc. Con/, Pall Gaseons FilI' I Tran .I·I }()r!. 0 I August 1<)86, Vanco uvcr B C, Canada .

4 Su lli van 0 P J & Gcttc l L E, Elcctroni c du al-rucl diesel ('ontrol systcms, Con/, Pal l Gas F llels TraIlSI }(} I' /. 0 I August 86, Vancou ver B C, Canada .

:) Nagaraj A Ramcsh. D S Khatri & Gajcndra Bahu M K. Ascssmcnt o r thc pcr l<lrmancc and cmi ss ion characteri sti cs or an automoti vc passengcr car cnginc opcrating on gaso line :lI1d CNG. Pmc Nat Cont' I C I :'ng COIII IJIIst . .fadell 'liIIl' Un iversitr . 2000.

6 Das L M & Rcddy Y V. Ex haus t cmi ss ion characteristics oj' a CNG-ruell cd cnginc. Proc Sixteenth Nut CrJllt' I C EI/g Combllst . .fadm'lmr Unil 'ersitr , 2000 .

7 Flcming R D & All sup J R. Ellliss ion characterist ics o/'

I/at l/ ral gas as in a ll/ol/ lOt i )'/' .fi{(' I , SAE papcr No. 7 1 08JJ m 1<)7 1.

8 Paul G. Majumdar S & Ghosh B B. Use rl colllll r e.I'serl natllral gas il/ COIII/II('1'cia l cO/llpression ignitiol/ (' I/g il/ e. Vol 73 , Thc Instituti on or Engineers (India ), Seplcmhcr 1992.

24 J SCIIND RES VOL 61 JANUARY-FEBRUARY 2003

Das R K & Ghosh F3 S, COIIII,arali ve sllldies ()fgasoline and cOIIII,re.l·sed natllral gas as .lile! for spark ignilion engines , Vol. 75 , The Instituti on or engineers (India), November 1994,

1 0 Das R K & Ghosh B B, SOlli e Sl lIdies on Ih e {'({se (lj' CNG in research and cOllllllercial diesel engines, Vol. 76, The Institution of Engineers (India), November 1995.

~ r~!,~"

A./ier being gradllated \\'ilh honollrs ill Mechanical Engineering .frolll GlasgoII' Universily in 1904, Prof 8 8 Ghosh j oilled Vickers E'ngin eering Ltd, England .for IIVO rears 10 have sOllie indllslrial e.r/'t'rimce. He also receil'('(l ARCST (Associale Melllher of Royal College of Science & Technology) Hons in Mechan ico l Engineering fm lll Slralhvcirde Universilv in 1964. He joined Mechanical Engineering Deparllllenl o.f I I T. Khamglillr, India. He cOlllpleled his PhD and sen'ed I I T. Kharagpllr for 33 vears in leaching and research in Ih(' area o.f I C Engines. He gllided 60 B Tech, 40 M Tech and seven PhD Ih esis re!aled 10 I C Engines. He IJllblislll'd 60 nalional and Inlemalirmalpllhlicalionsandisa.fello\\.lIIelllber oj. Inslilllleo.fEngineers (lndia). Lij.e lll elllher oj COlllhllslion /nslillll e, Inlemalional, Melllher(ASMC),Melllber(SAE). He hasll'onvariolls nalional and inlemalional{lll.ards.AII.res£.nl he is working as Vice-chair ( Malhs and Science ) in ElIslem SAE Seclion, India. I ({In lI 'orking as {lfl l:'J}/erililS proj'essor (A ll India COllncil For Technical Edllcation) (II .Jadavpllr /J III I'('f's i/r ({IIII Indian InSlilllle (~j'Technologv, Khargpllr afler relirelllelllfrolll 1fT, Kharagllllr, His dillies are related 10 re,l'earch in glliding PhD Iheses, coordinaling research projecls, ele.

PJ'()f P K 80SI' did his 8/~' in Mechanical Engineering in Ihe year 1975frolll Ih e Regional En gineering College, Dllrgapllr and passed 0 111 lI 'ilh Firsl Class (H(II/s.), He cOlllpleled MaSler of F;ngineering. (ME) ill Mechallical F;ngineer;'lIg / i'Oln .Jadm'lllIr Unil 'ersily in Ih e vear 1978 and aim did his PhD in Engineering./imi/ Indian In Slillll£' oj' Teclu/Ologv, Bom!Jar in 1993. He has golll/Ore Ihan 80 pllblications ill inlemational and nalionu/jollmuis (111(1

conj'erence,I' 10 his ('{'edil (lnd has gllided 17 PhD sllIdenls lill n (}\I '. He is a II 11'111 her or 11/(/11.1' Ilm/('ssiollal hodies and Associations of En gineers and has also delil'ered leel llr('s ill variolls inslilllles (~j'diff'er('l/I ('ol(//Iri l's allm'er

Ih(' I\·or/d. He is presenlil' Proj'l'ssor of Mechanical Enginl'ering in .Jadavp/(r Unil 'ersil.", Kolka/(l,

Shri R K Clwkra!Jarti gradllated in Mechanical /:.'ngineering Ivilh Firsl Class (1-lons).fi'Olll .Jadal'llIIr Unil'ersilr ill 198 1. !-II' did Posl-Gradllalioll ill Mechanical engineering froll/ In dian Inslil/(Ie of'Tec//I/Olo/?I·, Khamgp/(r in 1984, !-Ic has lI'orked ill II/(/n.\' Indllslries like Mil- Telco, .Jall/shedp/(r, Mil- Usha Telehoisl Ltd, Cuic/(Ila and Mil­VOLTAS' Ltd. BOlllhav and CalclIlIlI. !-I(' jo ill al acar/l'lI/ie,I' in 1990 alld presenlll' is a Sl'nior Let'IWer, Mechanical Engin('cring IJeparlll/('I/l, .Jad(/\ 'llIIr Universil.\', Kolkata,

Kail'an KIIII/ar Das oiJlained his BE degree in Mechanical Engineering FOil/ Ihe Universi/r of' No rth Bengal Oil

1972, He is a cons/(Italll to vario/(s Indllslries and ca /'lying 0 111 research work on allematil'e alllolllOhilejil!'1 ill Ih l' MI'c/wllicai Engineering Dell(lr/lnelll or .Jadavp/(r Universil.\', In dia. !-Ie is a II/ell/ber (If IIISlillllion of En gineers, India and SAE Inlemalional, USA.