Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h Vo lume 3, Issue 3, Marc h -2012 1

ISS N 2229-5518

Performance and Emissions of LPG Fueled

Internal Combustion Engine: A Review

Albela H.Pundkar, S.M. Lawankar, Dr. Sameer Des hmukh

Abs tract- Alternative f uels f or both spark ignition (SI) and compression ignition (CI) engines have become very important ow ing to incr eased environmental protection concern, the need to reduce dependency on petroleum and even socioeconomic aspects. The investigatio ns have been concentrated on decreasing f uel consumption by using alternative fuels and on low ering the concentration of toxic components in combustion products. Realizing the gravity of the problem, steps are being taken to introduce better technologies, better f uel quality, shif t to environment f riendly f uels. Alternative fuels like LPG, CNG, hydrogen etc has emerged as a solution to depleting crude oil resources as w ell as to the deteriorating urban air quality problem. As a gaseous f uel, gains f rom LPG have already been established in terms of low emissions of carbon monoxide, hydroc arbon. Air-fuel ratio, operating cylinder pressure ignition timing and compression ratio are some of the parameters that need to be analyzed and opt imally exploited for better engine perf ormance and reduced emissions. In the present paper a comprehensive review of various oper ating parameters and concerns have been prepared f or better understanding of operating conditions and constrains f or a LPG f ueled internal combustion engine.

Ke ywords - LPG, Spark ignit ion engines, Dual f uel engine, Combustion characteristics, perf ormance characteristics and Emissions.

INTRODUCTION

Air pollution is fast becoming a serious urban as w ell

necessary to under stand its combustion under the appropr iate conditions and to study the effects of various parameters on it.
as global pr oblem with the incr easing population and its subsequent demands.Finding an alter native to conventional fuels w ould help to r educed it. Vehicles r unning on cleaner fuels pr oduce few er harmful emissions, and can offer some savings on fuel costs, compar ed with petr ol or diesel. In

Propane Production

Natural gas purification 55%

crude oil

refining 45%

addition to cleaner , low sulphur versions of the conventional
vehicle fuels petr ol and diesel, the main alternatives ar e curr ently r oad fuel gases LPG and CNG bio-fuels and, mor e distantly, hydr ogen fuels, including methanol; fuel cells, and electric vehicles. Kirti Bhandari et.al [1]LPG as a fuel for spar k ignition engines, it has many of the same advantages as
natur al gas with the additional advantage of being easier to carry aboar d the vehicle. Its maj or disadvantage is the limited supply, which rules out any lar ge-scale conversion to LPG fuel. LPG is typically a mixtur e of several gases in varying pr oportions. Major constituent gases ar e pr opane (C3 H8 ) and butane (C4 H10 ), w ith minor quantities of pr opane (C3 H6 ), various butanes (C4 H8 ), iso-butane, and small amounts of ethane (C2 H6 ). The composition of commer cial LPG is quite variable. Being a gas at normal temper atur e and pr essur e LPG mixes r eadily with air in any pr oportion. Figur e 1 shows that about 55% of the LPG processed fr om natural gas pur ification. The other 45% comes fr om crude oil r efining. LPG is der ived fr om petr oleum, LPG does less to r elieve the country’s dependency on for eign oil than some other alter native fuels.LPG does help addr ess the national secur ity component of the nation’s over all petr oleum dependency pr oblem. [2]To benefit fr om the use of LPG in IC engines, it is

Fig ure 1: Pro pane Pro duc tio n

This r eview aims to pr epar e a concise state of art that pr ovides an idea of var ious concer ns r elated to employment of LPG as a vehicular fuel in or der to impr ove the rapidly deter iorating air quality conditions in urban r egions. Comparative Pr operties of LPG, Gasoline, Diesel and CNG as follows.

TABLE I

COMP ARATIVE P ROP ERTIES OF LPG, GASOLINE, DIESEL AND CNG. [14][19][20

Amongs the spar k ignition and the compr ession ignition engines, diesel engines tend to be mor e ener gy efficient than Gasoline engines, pr ovide higher tor que output and operate over limited engine speeds; however , such engines typically do not pr ovide the thr ottle r esponse and flexibility desir ed for

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lighter weight vehicles. The par ameter s of particular inter est ar e engine tor que, pow er and specific fuel economy. Engines ar e basically air pumps,ability of an engine to pump air is called Volumetric efficiency (VE), which if r educed; the maximum pow er output w ill be r educed.
As the gaseous fuel r equir es 4 to 15 percent of mor e intake
passage volume than liquid fuels which r educes the VE and hence maximum pow er output will also be r educed(by 4%).

120

100

80

60

40

20

0

Gasolinepropanepropane

Type of Fuel

60%le ss CO2

20%le ss Nox gasoline

SI engines burn a pr emixed air -fuel mixtur e follow ed by compr ession befor e a spar k ignites the mixtur e. Octane rating of a fuel indicates how slowly the fuel w ill burn and how w ell the fuel will r esist pr e-ignition befor e the spar k plug fir es. Higher octane fuels can be burned at high compr ession ratios (CR). The higher CR of an engine, the mor e efficient is the
engine and mor e is the pow er generated w ith given amount of the fuel. LPG has high octane r ating 110+ that allows CR to be high up to 15:1, w hich is in the r ange of 8:1 to 9.5:1 for gasoline engines.Kirti Bhandari et.al[1]

1. LP G AS AN ALTERNATIVE FUEL FOR IC ENGINE

The gaseous natur e of the fuel/air mixtur e in an LPG vehicle’s combustion chambers eliminates the cold-start pr oblems associated with liquid fuels. LPG defuses in air fuel mixing at low er inlet temperatur e than is possible w ith either gasoline or diesel. This leads to easier starting, mor e r eliable idling, smoother acceler ation and mor e complete and efficient burning with less unburned hydr ocarbons pr esent in the exhaust. In contrast to gasoline engines, w hich pr oduce high emission levels while r unning cold, LPG engine emissions r emain similar whether the engine is cold or hot. Also, b ecause LPG enters an engine’s comb ustion chamb ers as a vapor , it does not str ip oil fr om cylinder walls or dilute the oil when the engine is cold. This helps to have a longer service life and r educed maintenance costs of engine. Also helping in this r egar d is the fuel’s high hydr ogen-to-carbon ratio (C3 H8 ), which enables pr opane-pow er ed vehicles to have less carbon build-up than gasoline and diesel-pow er ed vehicles. LPG deliver s r oughly the same pow er , acceler ation, and cr uising speed character istics as gasoline. Its high octane rating means engine’s power output and fuel efficiency can be incr eased beyond what w ould be possible with a gasoline engine without causing Destructive Knocking. Such fine-tuning can help compensate for the fuel’s low er ener gy density.

Figur e 2: Vehicle Emissions

The higher ignition t emperatur e of gas compar ed w ith petr oleum based fuel leads to r educed auto ignition
delays,less hazar dous than any other petr oleum based fuel and expected to pr oduce less CO, NOx emissions and may cause less ozone formation than gasoline and diesel engines .

2. ENGINE MODIFICATIONS REQUIRED

Many pr opane vehicles ar e converted gasoline vehicles the r elatively inexpensive conver sion kits include a r egulator /vapor izer that change liquid pr opane to a gaseous form and an air /fuel mixer that meters and mixes the fuel with filter ed intake air befor e the mixtur e is dr awn into the engine’s comb ustion chamb er s. Also included in conversion kits is closed-loop feedback circuitry that continually monitor s the oxygen content of the exhaust and adj usts the air /fuel ratio as necessary.LPG vehicles additionally r equir e a special fuel tank that is str ong enough to withstand the LPG stor age pr essur e of about 130 pounds per squar e inch.

3. ENGINE TECHNOLOGY FOR LPG VEHICLES

As the LPG is stor ed in liquid form under high pr essur e,it is need to convert it into vapor ized for m befor e drawn into the combustion chamber . As engine technology for LPG vehicles is similar to that for natural gas vehicles, with the exception that LPG is not commonly used in dual-fuel diesel applications due to its r elatively poor knock r esistance Hutcheson1995[21].
For Spar k ignition engine ther e ar e tw o types of LPG engines
ar e pr imar ily studied
1. LPG which is stor ed in composite vessel at high pr essur e approximately at 10-20 bar ,supply to the engine is contr olled by a r egulator or vapor izer , w hich converts the LPG to a vapour . The vapour is fed to a mixer located near the intake manifold, w her e it is meter ed and mixed with filter ed air
befor e being drawn into the combustion chamber w her e it is burned to pr oduce power , just like gasoline.
2. LPG fueled dir ect inj ection SI engine, especially in or der to impr ove the exhaust emission quality while maintaining high thermal efficiency comparable to a conventional engine. In- cylinder dir ect inj ection engines developed r ecently wor ldwide utilizes the str atified char ge formation technique

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at low load, wher eas at high load, a close-to-homogeneous char ge is formed. Thus, compar ed to a conventional port inj ection engine, a significant impr ovement of fuel consumption, pow er can be achieved and these system have pr oven to be r eliable in terms of engine dur ability and cold starting.
Recently, sever al wor ks have been carried out for inj ecting the
fuel dir ectly into the combustion chamber to meet the low
emission standar d and high efficiency.And those methods have been used in practical gasoline engines. How ever , a lar ge amount of unburned hydr ocarbon emission is a new pr oblem w ith GDI engines, when they operate near th e Stochiometric mixing condition. Kirt i Bhandari et.al[1 traditional pr emixed char ge combustion engine has lower
thermal efficiency due to high occurr ence of engine knock and the unavoidable thr ottling at intake. Homogeneous- char ge lean combustion engines can r ealize a high thermal efficiency due to the low pumping and heat loss and incr ease in the specific heat ratio, at the expense of moder ately high NOx emissions due to ineffectiveness of the catalyst. How ever , the lean operation limit for this type of l ean homogeneous engine was not high compar ed to the value of diesel engine. The char ge stratification in the combustion chamber permits extr emely lean combustion that incr eases the thermal efficiency but gives the penalty of high NOx. Noise, pr oduced by the combustion pr ocess cause immediate annoyance and physiological change. Combustion noise occurs in tw o for ms, dir ect and indir ect. Dir ect noise is generated in and r adiated fr om a r egion under going turbulent combustion. The indir ect noise is generated dow nstr eam of the combustion r egion due to interactions betw een str eamlines of differ ent temper atur es. Main factor that affects the combustion noise is the pr essur e rise rate dur ing combustion.

4. PRESENT STATUS OF LP G ENGINES: PERFORMANCE AND COMB USTION CHARACTERISTICS

Follow ing literatur e survey is done to study the pr esent status of LPG engines per formance and combustion char acter istics Shinichi Goto 2000 [6] has been carr ied out to investigate the effect of var ious piston cavities and swirl ratio on combustion char acteristics as w ell effect of fuel composition on engine per formance w ith a single cylinder r esearch engine (Nissan Diesel Co. FD1L.Fr om the r esults he found that Lean burn operation of an LPG SI engine r esulted in impr oved fuel consumption for both the full and half load cases. As the in- cylinder flow was made mor e turbulent by suitable piston cavity modification, the cyclic var iation and combustion
dur ation both declined. The dog dish cavity achieved the low est thermal efficiency, wher eas the bathtub cavity showed the highest value. Although the nebula cavity showed impr oved combustion character istics, had the highest NOx emissions than pr oduced with dogdish cavity. The nebula cavity showed a better thermal efficiency than the bathtub cavity, since the nebula cavity could achieve leaner combustion. High swirl impr oved combustion stability and thermal efficiency, and enabled engine oper ation at low NOx levels.
Ki HyungLee, Chang Sik Lee, Jea Duk Ryu And Gyung-Min

Choi2002[8] investigate the combustion character istics and

flame pr opagation of the LPG (liquefied petr oleum gas) and gasoline fuel.The flame pr opagation of both LPG and gasoline
fuels was investigated by the laser deflection method and the high-speed Schlier en photogr aphy. The flame pr opagation speed of the fuel is incr eased with the decr ease of initial pr essur e and the incr ease of initial temperatur e in the constant volume chamber . The r esults also show that the equivalence ratio has a gr eat effect on the flame speed, combustion pr essur e and the combustion dur ation of the fuel- air mixtur e.

G.H.Choi et.al 2002[9] carried out to quantify the combustion and emissions char acteristics of LPG fuelled SI engine w ith minor modification in original SI engine to r un on LPG fuel with varying volume per centage of LPG at 5%,10%,20% w ith the help of PLC contr oller . Engine speed maintained at

4000r pm,the r elative air -fuel ratio var ies fr om 0.8 to
1.3.The exhaust gas constituents (CO2 ,CO,uHC and NOx) w er e measur ed using the 5-gas analyzer . Percentage of LPG in gasoline means that the combustion shifted towar ds complete phase and ‘gr eener ’ exhaust pr oducts w er e subsequently r eleased to the atmospher e. For each pr oportion of LPG in gasoline investigated, it was also obser ved that the CO2 emissions peaked at ar ound λ=1 and exhibits lower per centages at r ich and lean mixtur es. An incr easing pr oportion of LPG in gasoline pr omotes faster
burning velocity of mixtur e and hence r educe the combustion duration and subsequently the in-cylinder peak temperatur e incr eases. At high r elative air-fuel ratio, the amount of NOx measur ed was much higher , uHC also shows mar ked r eduction as the r elative air -fuel ratio exceeds Stochiometr ic.

Ki hyung Lee et.al 2005[7] study to clar ify the combustion pr ocess of the heavy duty LPG engine, the flame pr opagation and combustion char acteristics w er e investigated using a CVCC and a port inj ection type heavy duty LPLi engine system. Both the laser deflection method and the hi gh-speed Schlier en photography method w er e employed to measur e

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the flame pr opagation speed of LPG fuel. In addition, the single cylinder heavy duty LPLi engine was manufactur ed to analyze the combustion char acter istics of the LPG. Accor ding to the CVCC and heavy duty LPLi engine experimental r esults, the flame pr opagation r eached a maximum speed at the Stochiometr ic equivalence ratio, r egar dless of operating conditions, and the effect of the equivalence ratio on both flame pr opagation and combustion charact er istics was gr eater than that of ambient conditions. In addition, w e found that the coefficient of variation of combustion duration incr eased when the equivalence r atio decr eased.

M.A. Ceviz, F.Yuksel 2006[14]compar e the cyclic var iability and emission char acter istics of LPG and gasoline-fuelled spar k ignition engine at lean operating conditions. Cylinder pr essur e, indicated mean effective pr essur e (imep), mass fr action burned (MFB) and combustion duration ar e pr esented in r elation to cyclic var iability. Var iations in the CO, CO2 and HC emissions ar e also discussed. The lean operation decr eases the flame speed and the b urning r ate, r esult in an incr ease in the over all combustion duration, How ever , the incr eases in the combustion duration when in operation w ith LPG is lower than that of gasoline despite wor king on mor e lean conditions. The r eason for the lower combustion duration is the higher laminar burning velocity of LPG (0.46 m/s) when compar ed with gasoline (0.42m/s) and low er ed the emission also. Orhan Durgun et.al2007[15] Studied a quasi-dimensional spar k ignition (SI) engine cycle model is used to pr edict the cycle, per formance and exhaust emissions of an automotive engine for the cases of using gasoline and LPG. Combustion is simulated as a turbulent flame pr opagation pr ocess and during this pr ocess, two differ ent thermodynamic r egions consisting of unburned gases and bur ned gases that ar e separated by the flame fr ont ar e consider ed. A computer code for the cycle model has been pr epar ed to per form numerical calculations over a range of engine speeds and fuel–air equivalence r atios. In the computations per formed at differ ent engine speeds, the same fuel–air equivalence ratios ar e selected for each fuel to make r ealistic comparisons fr om the fuel economy and fuel consumption points of view . Comparisons show that if LPG fueled SI engines ar e operated at the same conditions w ith those of gasoline fueled SI engines; significant impr ovements in exhaust emissions can be achieved.

C-L Myung,S Park,J Kim,K Choi,I G Hwang 2011[22] focuses on the exper imental comparison of combustion phenomena and nanoparticle emission character istics fr om a wall-guided DI spar k ignition engine for gasoline and LPG. A r eturnless GDI fuel supply system was r ew or ked for the r etur n-type liquid- phase LPG inj ection fuel supply sy stem that w as composed of

an LPG tank with a br ushless d.c. pump and a low -pr essur e r egulator to supply the stable liquid-phase LPG for the DI engine. To ver ify the clean combustion character istics of the LPG DI engine, nanoparticle concentrations obtained with a differ ential mobility spectr ometer and the total hydr ocarbon and nitr ogen oxide emission levels w er e compar ed with those of a gasoline-fuelled engine.In conclusion, the nanoparticle and exhaust emissions of the LPG DI engine wer e much low er than those of the GDI engine. And the combustion stability in a part-load condition of LPG w as better than that of gasoline because it evaporated very r apidly and mixed w ell with the air .
Fr om the above liter atur e r eview showed the impr oved combustion char acter istics, per formance and emissions char acteristics w ith LPG as alter native fuel to gasoline at various condition such as changing the piston cavities, air fuel ratio, speed etc.Further r esear ch has to be carried out by changing compr ession r atio/ignition timing to compar e the per formance and emissions character istics.

5. NOISE AND AIR P OLLUTION WITH LPG ENGINES

The study of engine noise has been carr ied out since the ear ly stages of engine development. In 1931, Ricar do fir st found a descr iptive r elationship between the combustion pr essur e r ise and the noise pr oduced . Later , a number of parameters in determining the noise developments w er e investigated w hich include the fir st and the second der ivative of cylinder pr essur e . These methods w er e effective in r evealing the r elationship betw een engine combustion and noise. Some of them still play an important r ole in identifying the source of engine noise Ando. H.et.al[3].Although ther e ar e a number of engine noise sour ces, one of the most fundamental is the combustion -induced noise. It occurs towar d the end compr ession str oke and subsequent expansion str oke. The r apid pr essur e change due to the combustion transmits thr ough engine str uctur es and forms a part of the airbor ne noise . This pr essur e change also causes the vibration of the engine components such as the cylinder head, pistons, connecting r ods and engine body.Because of its super ior knock-r esistance, pr opane is pr eferr ed to butane as an automotive fuel.The lean combustion limit of pr opane-gasoline mixtur es is considerably leaner than for gasoline, allowing the use of lean-bur n calibrations, which pr ovides mor e r esistant to knocking and per mit the use of still higher compr ession ratios.LPG has many of the same emission characteristics as natur al gas. Graph shows IANGV emissions compar ison study betw een Gasoline, LPG and CNG.Sw itching fr om gasoline to LPG and CNG r esults in a substantial r eduction in the CO emission. CNG also r educed HC and NOX emissions.

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50

40

30

20

10

0

Gasoline LPG CNG

Fuel

Nox*10

CO HC*10

thr ee-way catalyst can easily meet (Eur o 2 and 3) str ingent heavy-duty emission standar ds. Lean burn engines in combination w ith an oxidation catalyst can also achieve very low emission r esults (Hutcheson 1995). The very low levels of particulate emissions with both stoichiometr ic and lean- burning LPG engines continue to be their str ongest point, particular ly as this is attainable with low NOx emissions. LeeS.etal [17] per for med exper imental study on per formance

Figure 3: A Su mmary of Emis s ion with Non -Catalys t Vehic le
On an energy bas is LPG has a lower carbon content than gasoline or diesel fuel. W hen used in spar k-ignition engines, LPG pr oduces near -zer o particulate emissions, very little CO and moderate HC emissions. Variations in the concentration of differ ent hydr ocarbons in LPG can affect the species composition and r eactivity of HC exhaust emissions. As olefin (such as pr opene and butane) ar e much mor e r eactive in contr ibuting to ozone formation than paraffin’s (such as pr opane and the butanes), an incr ease in the olefin content of LPG is likely to r esult in incr eased ozone-forming potential of exhaust emissions. Due to the gas-tight seals r equir ed on the fuel system, evaporative emissions ar e negligible.Exhaust NMHC and CO emissions ar e low er with LPG than gasoline. CO2 emissions typically ar e also somewhat low er than those for gasoline due to the low er carbon-ener gy r atio and the higher octane quality of LPG. NOx emissions ar e sim ilar to those fr om gasoline vehicles, and can be effectively contr olled using thr ee-way catalysts. Over all, LPG pr ovides less air quality b enefits than CNG mainly b ecause the hydr ocarb on emissions ar e photochemically mor e r eactive and emissions of CO ar e higher . Moder n dual-fueled LPG car s have achieved impr essive r esults in r educing emissions. Average emissions and fuel consumption test r esults for five dual- fueled passenger cars fitted with closed-loop thr ee-way catalysts and thir d generation LPG equipment ar e summarized in table 2.The tests wer e conducted over the EDCE+EU DC cycle. Table 3 shows the limited emissions data
and emission char acter istics of an SI engine operated w ith
DME mixed w ith LPG. The r esults they obtained show ed that
knocking was significantly incr eased with DME due to the high Cetane number of DME. The output engine power of using 10% DME w as comparable to that of pur e LPG. Exhaust emissions such as HC and NOx wer e slightly incr eased when
utilizing blended fuel at low engine speeds. Using blended fuel, how ever , the engine power output was decr eased and br eak specific fuel consumption (BSFC) w as extr emely deter iorated because the ener gy content of DME is much low er than that of LPG.

IANGV Emission Report shown that unr egulated emissions like (1,3-butadiene,benzene,formaldehyde and methanol of all

the alter native fuel) of LPG give vehicles ar e gener ally less than formaldehyde levels for gasoline fuels. Graph shows Thr ee-way catalyst technology is efficient in r emoving not only r egulated emission components but also har mful unr egulated components. On gasoline, the TW C r educes 1,3-

butadiene, benzene and formaldehyde emissions by a factor of mor e than 10. For these thr ee components, LPG and CNG give low er emissions than gasoline.TNO data on acetaldehyde emissions fr om non-catalyst vehicle Switching fr om gasoline to gaseous fuels r educes PAH emissions by a factor of 10. How ever , one could estimate that the total toxic effects going fr om gasoline to natura l gas in non-catalyst vehicles will be r educed substantially.

10

1,3-butadie ne

available for LPG vehicles.

TABLE II

8

6 be nze ne

PASSENGER CAR AND HEAVY DUTY ENGINE EMISSIONS FOR LPG.[20] [21]

TABLE III

COMPARISON OF EMISSIONS AND FUEL CONSUMPTION FOR FIVE MODERN DUAL

FUELED CARS OPER ATING ON GASOLINE AND LPG.[20][21]

4

2

0

gasoline w/o

cat.*10

Gasoline LPG CNG

Fuel

formalde hyde

Ace talde hide

Modern spar k-ignition LPG-fueled engines equipped with a

Figur e. 4- Unr egulat ed emission component s (average values)

for differ ent fuel.

In all cases studied, LPG ener gy economy was low er than
EPA certification fuel economy data for the pr e-conversion

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gasoline vehicle (i.e. conversion appears to have r educed efficiency on gasoline). All the vehicles tested by EPA also yielded lar ge decr ease in acceler ation per for mance, measur ed by 5-60 mph and 30-60 mph. Finally, each of these DF vehicles had a low er r ange on LPG than on gasoline, typically at least at a 50 per cent r eduction. Efficiency, per formance and range character istics can be impr oved w ith dedicated and optimized LPG vehicles. Using accepted r elationship betw een weight, acceleration and fuel economy, it was estimated that a LPG w ith range and power equivalent to the gasoline model would be less efficient (25%). This tradeoff between efficiency, per formance and range is the r eason why many experts believe LPG and CNG is better suited for centralized urban fleet applications than for general public use.

20

15

CONCLUSION

Based on the r eview ed paper for the emissions and per formance, its concluded that the LPG r epr esents a good fuel alternative for gasoline and ther efor e must be taken into consideration in the futur e for transport pur pose. Apart fr om the fuel storage and delivery mechanism, LPG engines similar to petrol engines, and deliver nearly similar per for mance and good in combustion char acter istics than Gasoline. In the short term, LPG as a alter native fuels r eview ed could displace 10 per cent of curr ent usage of oil, or br ing significant r eductions in CO, CO2 emissions and help to r educe harmful gr eenhouse gas emissions. In the next five to ten year s, LPG will be mor e widely available and gaining mar ket shar e across vehicle ranges.

LIST OF SYMBOLS AND ABBREVIATIONS

SYMBOLS

10

5

0

Form al dehi de Acetal dehi de Acetone propi oal dehide

A/F=14.6

A/F=15.6

A/F=16.6

λ=r elative air-fuel r atio

ABBREVIATIONS AND CODES

CVCC- Constant Volume Combustion Chamber
CNG - Compr essed Natur al Gas
DF - Duel Fuel
DI - Dir ect Inj ection

Figur e. 5- Concentrat ion (ppmv) of aldehydes in exhaust gases of LPG fuelled engine.

Figur e 5 shown the concentration (ppmv) of aldehydes in exhaust gases of LPG fuelled engine at r ich,stoichiometr ic and lean Air /fuel ratio.

From the Study done by ETSAP LPG has a r elatively high ener gy content per unit of mass, but its ener gy content per unit volume is low . Thus, LPG tanks have mor e space and w eight than petr ol or diesel fuel tanks, but the range of LPG vehicles is equivalent to that of petr ol vehicles. Bi-fuel LPG car tests show ar ound a 15% r eduction in gr eenhouse gas emissions (per unit of distance) compar ed to petr ol operation. The best quality LPG bi-fuel engines produce few er NOx emissions and virtually zer o particulate emissions if compar ed to petr ol. [21]

Fuel Options for Contr olling Emissions. Both Stochiometr ic
and lean-bur n LPG engines have been developed with good r esults. Nearly all LPG vehicles curr ently in operation ar e aftermar ket r etr ofits of existing gasoline vehicles, mostly using mechanical (as opposed to electr onic) conversion systems.
DME - Di-Methyl Ether
ECE - Economic Commission for Eur ope/ECE test method
EGR - Exhaust Gas Recirculation
EPA - Envir onmental Pr otection Agency
EUDC - Extra Urban Driving Cycle
EURO - Eur opean Union test method/limit value
ETSAP - Ener gy Technology System Analysis
Pr ogramme
GDI - Gasoline Dir ect Inj ection
HD -Heavy -Duty
IANGV - International Association for Natur al Gas
Vehicles
LPG - Liquefied Petr oleum Gas
LPLi - Liquefied Petr oleum Liquid inj ection NMHC - Non-Methane Hydr ocarbons PAH - Polyar omatic Hydr ocarbons
TNO -TNO Road-Vehicles Resear ch Institute (Holland) TW C - Thr ee-Way Catalyst
VE - Volumetric efficiency

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J ourna l of Scie ntific & I ndus tria l Re search Vol. 64, Ma y 2005, pp 333-338.

2. U.S. De pa rtme nt of Energy ‚journa l of Ene rgy Efficie ncy a nd

Re ne wable Ene rgy‛Augus t 2003.

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Stra tegy for Engine Pe rforma nce I mproveme nt in a

Gas oline Direct I njection Engine ‛, SAE Pa pe r No.980158,

1998

4. Pre uss ne r, C., Doring, C., Fe hle r, S. a nd Kampma nn, S.,

‚GDI : I nteraction Betwee n Mixture Pre pa ration, Combus tion

Sys tem a nd I njector Pe rforma nce ‛, SAE Pa pe r No.980498,

1998.

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