International Conference on Petroleum Engineering 2019 (ICPE-2019)
Bangladesh University of Engineering & Technology (BUET)
Dhaka-1000, Bangladesh
ICPE – (2019-10)
Liquid Petroleum Gas (LPG) as an Alternative
to Compressed Natural Gas (CNG) in Vehicle
Fuels and Its Future Directions
Srimonta Roy1*,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1,
Md. Shaheen Shah1
1
Department of Petroleum and Mining Engineering, Jashore University of Science
and Technology,
2
Dept of Electrical and Electronic Engineering. American International University of
Bangladesh.
Jashore-7408, Bangladesh
ABSTRACT
Bangladesh is a small country, full of natural resources such as coal, natural gas,
stone etc. In Bangladesh, octane, petrol and diesel etc are very well known as vehicle
fuel. Compressed natural gas (CNG) is used as an alternative fuel in the country to reduce
driving costs. The price of this gas is low, but it is very dangerous for the engine. Cars
that are usually imported into our country are made to run with liquid fuel. A new fuel
has become popular without reducing oil prices and damaging the engine. This fuel is
called Liquefied Petroleum Gas (LPG),also known as Autogas. Increasing the
prominence on liquid petroleum gas (LPG) as a relatively low and abundant energy
source for delivering affordable fuel-efficient transport, encourages the search for the best
method of fuel, air and combustion management to achieve the best results.
Consequently, it is used at home and is now beginning to be used in vehicles. This article
compares one of these two types of vehicle fuel. The comparison includes breaking point,
* Corresponding Author address
Email: srimontojust@gmail.com
2 Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md.
Shaheen Shah1
volumetric energy density, energy produced, availability, fuel comparison, environmental
effect, luggage space, power loss, emission, mileage & running cost. Finally, after all
these considerations, it can be concluded that LPG vehicle fuel is better than CNG
vehicle fuel.
Keywords: Compressed natural gas (CNG), Liquefied Petroleum Gas ( LPG), alternative
fuel, vehicle fuel.
INTRODUCTION
Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas) is mixture of
flammable hydrocarbon gases which consists of propane (C3H8), mostly butane (C4H10), and,
most commonly mixes including both propane and butane. When LPG is used to fuel internal
combustion engines is defined as autogas or auto propane[1]. LPG is used for home heating,
cooking, hot water, and autogas(fuel for LPG cars and vehicles).LPG has lower energy
density than other petrol, diesel or fuel oil which equivalent fuel consumption is higher[2].
CNG is Compressed Natural Gas, which is mainly methane compressed at a pressure of 200
to 248 bars[3].CNG is a fuel which can be used in place of gasoline, diesel fuel and
propane/LPG. It is stored and distributed in hard containers at a pressure of 20–25 MPa
(2,900–3,600 psi), usually in cylindrical or spherical shapes[4]. CNG obtained from natural
gas-and-condensate wells, oil wells, coal bed methane wells[3].
2.HISTORICAL BACKGROUND
LPG was first identified as a significant component of propane and butane mixture
comes from as early as 1910. It was then that Walter O. Snelling, an American chemist
researching properties of petrol, separated gaseous fractions from liquid ones, thus
discovering the existence of propane.In 1912, he started his first domestic propane
installation, and in 1913 he patented producing propane on an industrial scale[5]. Information
concerning practical use of LPG dates to 1918, when the fuel was utilised for brazing lamps
and metal-cutting blowtorches. LPG sales in the US topped 223 thousand gallons in 1922,
while within the next 3 years the figure grew to 400 thousand gallons. Snelling soon realised
that the LPG could be used for lighting, metal cutting, and cooking.That discovery marked
the origin of the LPG industry[6]. In 1928, LPG was first used as motor fuel (in a truck) and
the first LPG refridgerator was made. In 1929, the level of sales of the fuel was as much as 10
million gallons in the US[5].
CNG are an alternative fuel vehicle that use natural gas as fuel rather than the typical
gasoline or diesel.CNG were first manufactured in United States during the 1930s. They were
used during World War II in Europe and interest for these vehicles rose during the early
Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md. 3
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1950s. As of 2009, there were over 11 million compressed natural gas (CNG) vehicles
worldwide[7][8].
Table-01 :Properties of LPG and CNG
Properties CNG - Methane LPG – Propane
Chemical Formula CH4 C3H8
Energy Content 9MJ/L 25MJ/L
Storage Pressure 20 – 25 MPa 2 MPa
Air:Gas Combustion Ratio 10:01 25:1
Operating Pressure 1.1 kPa 2.75 kPa
Density (vs Air) .5537:1 1.5219:1
Cylinder Weight 1 ≈3x
State Gas Liquid or Gas
3. STUDY ABOUT FOR LPG AND CNG
3.1 Production
LPG gas (propane) comes from oil and gas wells, as it is a fossil fuel. Then LPG process
continues with LPG coming from two LPG gas manufacturing process sources: natural gas
processing and crude oil refining, where it is a co-product of both. 60% of LPG-propane
comes from natural gas processing "stripper plants" and 40% of LPG-propane comes from the
crude oil refinery process[9].
The production facility for CNG is simpler than other remote gas utilization options such
as liquefied natural gas (LNG), gas to liquid (GTL), ammonia, or methanol. It typically
consists of compression, cooling, dehydration, and possibly liquefied petroleum gas (LPG)
separation. The extent of compression and cooling is different for the various CNG processes.
The scope of the production facility depends on the quality of the gas and reservoir pressure,
but is a small fraction of that of a comparably sized LNG or GTL facility[10].
3.2 Cost
CNG is generally cheaper than LPG. However, propane produces over twice the amount
of energy than natural gas. So LPG could be more cost effective than natural gas depending
upon local prices (which tend to fluctuate)[12].
Table-02 : Statement showing comparative cost analysis of CNG and LPG vehicle per km[11]
Sr no. Particulars LPG vehicle CNG vehicle
01 Capital cost in BDT (chassis 13 lacs 12 lacs
and body building)
02 KMPL 6.5 4
03 Fuel cost in BDT 50 42
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3.3 Availability
There is an extensive distribution network for both CNG and LPG. But the retail
availability of LPG is more compared to that of CNG[12].CNG distribution is mainly via
pipeline networks that run from natural gas production wells to various distribution centers
and finally into residential neighborhoods and commercial areas.LPG is available in 18 cities
and CNG is available in 40 cities[13].
Figure-01 :LPG Filling Station
3.4 Energy Produced
LPG, vaporized and at atmospheric pressure, has a higher calorific value (94 MJ/m3 or
26.1kWh/m3) than natural gas (38 MJ/m3 or 10.6 kWh/m3). This LPG produces more energy
than the equivalent amount of natural gas[12][13].
3.5 Safety and Environmental Impact
Although CNG does produce greenhouse gases upon combustion, it is a more
environmentally clean alternative to other fossil fuels like gasoline or LPG. CNG is also safer
than other fuels in the event of a spill because natural gas, being lighter than air, disperses
quickly when released[12].The environmental comparison of CNG and LPG vehicles
includes two separate time hori-zons, i.e. the present situation (2018) and a future scenario
(2030)[14].
Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md. 5
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Time Horizon Vehicle Fuel Supply pathway Emissions
2018 Passenger Car LPG Crude Oil CO2 eq
2030 CNG Natural Gas NMVOC
City Bus
... ...
Figure-02:Structure Of The Environmental Comparison[14].
3.6 Emission comparison
LPG vehicles provide less air quality benefits than CNG vehicles mainly because the
hydrocarbon emissions are photo chemically more reactive and emissions of CO are
higher[13].
Table-03:CO2 Emissions From Fuel Combustion[14].
Fuel Petrol Diesel CNG LPG
g CO2 per MJ 72 74 56 65
CO2 Emissions From Fuel Combustion
80
70
60
50
40
gCO2 per MJ
30
20
10
0
Petrol Diesel CNG LPG
Figure-03: CO2 Emissions From Fuel Combustion
6 Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md.
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Table-04:Energy Flows And Emissions For The Production And Processing Of LPG[14].
I/O Unit Amount
Natural Gas Input MJ/MJ 0.053
LPG Input MJ/MJ 1
LPG Output MJ 1
Emissions
CO2 - g/MJ 3.1
CH4 - g/MJ 0.015
N2O - g/MJ 0
NOx - g/MJ 0.009
Dust/PM - g/MJ 0
SO2 - g/MJ 0
NMVOC - g/MJ 0.011
CO - g/MJ 0.001
3.7 Uses
LPG
i. Heating: LPG is used an alternative to heating oil and electricity in places where
there is no natural gas pipe line.
ii. Cooking: LPG is the most common cooking fuel in India and urban Brazil.
iii. Refrigeration: Gas absorption refrigerators and air conditioning systems use
LPG. But its use in motor vehicles for air conditioning has been discouraged due
to the risk of fire.
iv. Automobiles: A large number of vehicles, light, medium and heavy duty, around
the world are fueled by LPG. There about 1,600 bi-fuel Ford F-150 pickup trucks
in the California state fleet. Propane fueled forklifts are used both inside and
outside warehouses and at construction sites[12].
Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md. 7
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Sector wise use of LPG
Large Industry Industry Domestrics Transport(Auto Gas) Others
2% 3% 2%
14%
79%
Figure-04 :Sector wise use of LPG[15].
CNG
i. Automobiles: Any vehicle running on gasoline can be converted to a bi-fuel
vehicle (gasoline/CNG). It involves installing a CNG cylinder in the trunk,
installing the plumbing system, installing CNG injunction system and the
electronics. In the US, CNG vehicles have been introduced in a wide variety of
commercial vehicles, from light duty trucks and sedans like taxi cabs to medium
duty trucks like UPS delivery vans and postal vehicles to heavy duty vehicles
like transit buses, street sweepers and school buses. In California, transit agency
buses run on CNG. Coco Cola Enterprises delivered its beverages to London
Olympics Games 2012 in bio methane fueled lorries.
ii. Locomotives: Napa Wine Valley Train has been converted to be run with CNG.
FerroCarril Central Andino in Peru has been running a freight line on CNG run
locomotive since 2005. Iran, Pakistan, Argentina, Brazil and India have the
highest number of CNG vehicles run[12].
3.8 Advantages of using CNG and LPG in vehicles
LPG
i. It has a higher calorific value which equivalent to the octane and petrol.
ii. It contains very less amount of carbon in it, hence LPG powered vehicles
produce almost 50% less CO2 than petrol.
8 Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md.
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iii. It mixes with air at all temperatures.
iv. It provides a uniform charge for combustion, in case of multi cylinder engine.
v. It has very high compression ratios.
vi. It has very high antiknock characteristics.
vii. The engine may have 50% longer life.
viii. LPG is easy to transport.
ix. LPG burns consistently, making it more reliable than other forms of
energy[12][16].
CNG
i. Lead or benzene is not used. Hence lead fouling of spark plugs is eliminated.
ii. Natural gas vehicles have lower maintenance costs when compared with other
fossil fuel-powered vehicles.
iii. The fuel systems are sealed. This prevents any spill or evaporation losses.
iv. CNG does not contaminate or dilute the crank case oil thus increasing the life of
lubricating oil.
v. The emission of greenhouse gases is reduced 80% when compared to gasoline
vehicles.
vi. Natural gas disperses easily in air and is not flammable. Hence CNG vehicles are
safer than gasoline vehicles.
vii. CNG is cheaper than gasoline or diesel
3.9 Disadvantages of using CNG and LPG in vehicles
LPG
i. LPG has lower energy density than gasoline or diesel and hence the equivalent
fuel consumption is more.
ii. LPG provides less upper cylinder valve lubrication. If a LPG-fueled engine is not
suitable modified, it will lead to valve wear.
iii. It does not disperse easily and is readily inflammable.
Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md. 9
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CNG
CNG occupies more space than gasoline. Additional space in the trunk of a car or the bed
of a pickup truck is used to store the CNG tanks. This problem has been mitigated in factory-
built CNG vehicles by installing the tanks under the vehicle body[12][16].
4.COMPARISON BETWEEN LPG AND CNG
Table-05 :Comparison between LPG and CNG are given below :
Sl Feature LPG CNG
No.
01 Constituents Propane and Butane Methane
02 Source Automatically generated from Obtained from natural
gas fields when natural gas is gas-and-condensate wells,
extracted from the reservoir. oil wells, coal bed
By-product of cracking process methane wells.
during crude-oil refining.
03 Environmental effects Releases CO2 which is a Releases lesser
greenhouse gas but is cleaner greenhouse gas.
when compared to gasoline.
04 Properties Highly inflammable. It is It is lighter than air and
heavier than air and on leakage hence disperses quickly in
will settle to ground and the event of spillage.
accumulate in low lying areas.
05 Safety Since it is difficult to disperse Easily disperses, hence
risk of fire is more. risk of ignition is
minimized.
06 Pressure It has 7.5 bar pressure. It has more than 200 bar
pressure.
07 Temperature The engine produces heat up to The engine produces heat
1310F up to 2000F - 3000F
08 System loss System loss 5 percentage System loss 25 percentage
09 Space LPG required less space than CNG occupies more
CNG storage space than LPG
10 Vehicle weight LPG vehicles are lighter than CNG vehicles are about
CNG vehicles. 100-150 kg.
Finally, after all these considerations, it can be concluded that LPG vehicle fuel is better than
CNG vehicle fuel.
10 Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md.
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5.PRESENT CONDITION OF LPG IN BANGLADESH
Demand of Liquefied Petroleum Gas (LPG) in Bangladesh is very high. In the public
sector 15,936 MT of LPG are bottling every year, out of which 10000 MT is obtained as
byproduct from processing of crude oil in Eastern Refinery and 6000 MT from is extracted
from natural gas in Kailashtila gas field. LPG is imported by only private sector. Around
537,686 MT of LPG is imported and marketed by private sector entrepreneurs every year. So
public and private sector combining do the marketing of 553,622 MT of LPG every year,
which is meeting a certain portion of LPG demand of the country. Considering the rising
demand for LPG, government has decided to enhance LPG bottling facilities for marketing
more imported LPG. For this purpose, two LPG bottling plants, each having capacity of 100
thousands MT per annum, will be set up in the coastal area. Of them, one plant will be
installed by Bangladesh Petroleum Corporation (BPC) and the in public private partnership
with BPC[17].
Present Condition of LPG
600,000
500,000
400,000 Public Sector Production MT
Import (Private) MT
300,000
Total MT
200,000
100,000
0
2014-15 2015-16 2016-17 2017-18
Figure-05: LPG scenario of last 4 year.
6.FUTURE DIRECTION OF LPG IN BANGLADESH
LPG, a green and clean hydrocarbon fuel, is an environment friendly vehicle fuel, which
can be critical to mitigate air pollution in Bangladeshi cities. An autogas user can halve the
fuel bills after paying for the cost of LPG conversion. Currently, a traditional conversion kit
costs between BDT 30,000-35,000, while price for the advanced kit ranges between BDT
Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md. 11
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50,000-60,000. The first digital LPG autogas filling station was established in Bogura in
October 2017 by Intraco Group. Presently, Omera Gas One (a subsidiary of Omera Petroleum
Ltd) is the country’s largest autogas provider having 10 stations in different parts of the
country. Beximco Petroleum Ltd (a subsidiary of the Beximco Group) has recently secured
approval for establishing 500 autogas filling stations and 25 workshops. At present, there are
around 10,000 autogas-run vehicles in Bangladesh, and every month, 90-100 new vehicles are
being converted to run on autogas[18].
The tax exemption policy for LPG import has played a major role in the growth of the
sector. Additionally, import tax on equipments used for assembling LPG cylinders have been
set below 5%.Additionally, the government has taken initiatives to gradually replace CNG
with LPG (Auto gas) in the transportation sector in order to reduce dependence on natural
gas. Accordingly, proposal for waiving import duties on LPG conversion kits is still under
consideration.
The Ministry of Power, Energy and Mineral Resources (MPEMR) published a gazette
notification in 2017. Under this policy, entities will be able to import, produce, store, supply
and export LPG cylinders after meeting the suggested compliances. Additionally, private
sector players can set up LPG terminals, auto-gas filling stations, auto-gas conversion plants
and LPG-bottling plants under the policy[18].
7.CONCLUSION
Based on the reviewed paper for the emission and performance, it’s concluded that LPG
represents a good fuel alternative for CNG,gasoline,petrol and therfore must be taken into
consideration in the future for transport purpose.Internal combustion engines running on
liquid petroleum gas (LPG) are well-proven technologies and work much like gasoline-
powered spark-ignition engines. Bi-fuel LPG cars can reduce greenhouse gas (GHG)
emissions by 15% as compared to petrol operation. In terms of modification cost LPG is
better than CNG vehicles. For intial cost and runnig cost, LPG is a sensible fuel. LPG vehicle
fuel is better than CNG vehicle fuel, but availabilty and fuel efficincy, CNG is still the most
widely available fuel. According to environment effects LPG is better than CNG for carbon
emission.
12 Srimonta Roy1,Sujan Kumar Mondal1, Milon Roy2,Sadakat sharif1, Md.
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