Compressed Natural Gas (CNG) is a substitute for
gasoline
(petrol),
diesel, or
propane
fuel. It is
considered to be a more environmentally "clean" alternative to those fuels
and it is much safer than other motor fuels in the event of a
fuel spill: natural gas is lighter than air, so it disperses quickly
when leaked or spilled.
It is made by compressing
natural gas (which is mainly composed of
methane
(CH4)), to less than 1% of its volume at
standard atmospheric pressure. It is stored and distributed in hard
containers, at a normal pressure of 200–220
bar
(2900-3200 psi), usually in cylindrical or spherical shapes.
Compressed natural gas is used in traditional gasoline cars that are
thus turned into bi-fuel (gasoline/CNG) cars. CNG/gasoline cars are
increasingly used in Europe and South America due to raising gasoline
prices.
In response to high fuel prices and environmental concerns,
compressed natural gas is starting to be used also in
light-duty passenger vehicles and
pickup trucks,
medium-duty delivery trucks, and in
transit and
school buses.
Technology
CNG can be used in
Otto-cycle (gasoline) and modified
Diesel
cycle engines. Lean-burn Otto-cycle engines can achieve higher thermal
efficiencies when compared with
stoichiometric Otto-cycle engines at the expense of higher NOx and
hydrocarbon emissions. Electronically-controlled stoichiometric engines
offer the lowest emissions across the board and the highest possible power
output, especially when combined with
EGR, turbocharging and intercooling, and three-way catalytic
converters, but suffer in terms of heat rejection and fuel consumption. A
suitably designed natural gas engine may have a higher output compared
with a petrol engine because the octane number of natural gas is higher
than that of petrol.
CNG may be refueled from low-pressure ("slow-fill") or high-pressure
("fast-fill") systems. The difference lies in the cost of the station vs.
the refueling time. There are also some implementations to refuel out of a
residential gas line during the night, but this is forbidden in some
countries. Fueling a vehicle from a home natural gas fuel line is becoming
more popular in the United States, especially in California and New York,
and tax credits are available for installing the necessary appliance.
CNG cylinders can be made of
steel,
aluminum, or
plastic.
Lightweight
composite (fiber-wrapped thin metal "ISO 11439 CNG-3"/fibre-wrapped
plastic "ISO 11439 CNG-4") cylinders are especially beneficial for
vehicular use because they offer significant weight reductions when
compared with earlier generation steel and aluminum cylinders, which leads
to lower fuel consumption. The CNG cylinders bundled with safety-valve
generally follow the ISO 11439 standard.
[1]
The equipment required for CNG to be delivered to an
Otto-cycle engine includes a pressure regulator (a device that
converts the natural gas from storage pressure to metering pressure) and a gas mixer or gas injectors (fuel metering devices).
Earlier-generation CNG conversion kits featured
venturi-type gas mixers that metered fuel using the
Venturi effect. Often assisting the gas mixer was a metering valve
actuated by a
stepper motor relying on feedback from an exhaust gas oxygen sensor.
Newer CNG conversion kits feature electronic multi-point gas injection,
similar to petrol injection systems found in most of today's cars.
Drawbacks
Compressed natural gas vehicles require a greater amount of space for
fuel storage than conventional gasoline power vehicles. Since it is a
compressed gas, rather than a liquid like gasoline, CNG takes up more
space for each GGE (Gallon of Gas Equivalent). Therefore, the tanks used
to store the CNG usually take up additional space in the trunk of a car or
bed of a pickup truck which runs on CNG. This problem is solved in
factory-built CNG vehicles that install the tanks under the body of the
vehicle, thanks to a more rational disposition of components, leaving the
trunk free (eg.
Fiat Multipla, New
Fiat
Panda,
Volkswagen Touran Ecofuel,Chevy Taxi (sold in countries such as Peru)
etc). While CNG-powered vehicles are considered to be safer than
gasoline-powered vehicles
[2][3],
there are concerns about how best to fight fires involving CNG vehicles.[4]
Since its calorific value is far less than other fuels it needs
comparatively large volume of Gas to get desired energy.
CNG cars
CNG cars available in Europe are actually bi-fuel vehicles. Their
engine is a standard gasoline engine. This means that they can
indifferently run on either gasoline or CNG (this is why some extra space
is needed to for the CNG storage cylinder (separate from the gasoline
tank) that is usually located in the trunk). The driver can select what
fuel to burn by simply flipping a switch on the dashboard.
Several manufacturers (Fiat, Opel(General Motors), Peugeot, Volkswagen,
opel Zafira 1.6 CNG and others) sell bi-fuel cars.
Almost any existing gasoline car can be turned into a bi-fuel
(gasoline/CNG) car. Authorized shops can do the retrofitting, this
involves installing the CNG cylinder in the trunk and installing the CNG
injection system and electronics.
CNG compared to LNG
CNG is often confused with
liquefied natural gas (LNG). While both are stored forms of
natural gas, the key difference is that CNG is in compressed form,
while LNG is in liquefied form. CNG has a lower cost of production and
storage compared to LNG as it does not require an expensive cooling
process and cryogenic tanks. CNG requires a much larger volume to store
the same mass of gasoline or petrol and the use of very high pressures
(3000 to 4000 psi, or 205 to 275
bar).
Worldwide
Canada
Canada is a large producer of natural gas, so it follows that CNG is
used in Canada as an economical motor fuel. Canadian industry has
developed
CNG-fueled truck and bus engines,
CNG-fueled transit buses, and
light trucks and taxis. Both CNG and propane refueling stations are
not difficult to find in major centres.
United States of America
In the US, federal tax credits are available for buying a new CNG
vehicle. Use of CNG varies from state to state. In California, CNG is used
extensively in local city and county fleets, as well as public
transportation (city/school busses), and there are 90 public fueling
stations in Southern California alone. Although natural gas prices are
rising, compressed natural gas is available at 30-60% less than the cost
of gasoline, as a rule of thumb, in much of California. Personal use of
CNG is a small niche market currently, though with current tax incentives
and a growing number of public fueling stations available, it is
experiencing unprecedented growth. The state of Utah offers a subsidised
statewide network of CNG filling stations at a rate of $0.85/gge[5],
while gasoline is above $4.00/gal. Elsewhere in the nation, retail prices
average around $2.50/gge, with home refueling units compressing gas from
residential gas lines for approx $1.50/gge. Other than aftermarket
conversions, and government used vehicle auctions, the only currently
produced CNG vehicle in the US is the
Honda Civic GX sedan, which is made in limited numbers and available
only in a few states. An initiative, known as
Pickens Plan, calls for the expansion of the use of CNG as a standard
fuel for cars has been recently started by oilman and entrepreneur
T. Boone Pickens.
Europe
Italy currently has the largest number of CNG vehicles in Europe and is
the 4th country in the world for number of CNG-powered vehicles in
circulation.
The use of methane (CNG) for vehicles started in the 1930's and has
continued off and on until today.
Currently (06/2008) there is a large market expansion for natural gas
vehicles (CNG and LPG) caused by the rise of gasoline prices and by the
need to reduce air pollution emissions.
Before 1995 the only way to have a CNG-powered car was by having the
retrofitted with an after-market kit. A large producer was Landi Renzo,
Tartarini Auto, Prins Autogassystemen, OMVL, BiGAs,... and AeB for
electronic parts used by the most part of kit producer.
Landi Renzo and Tartarini have divisions selling vehicles in Asia and
South America.
After 1995 bi-fuel (gasoline/CNG)cars became available from several
major manufacturers. Currently
Fiat,
Opel(GM),
Volkswagen,
Citroen,
Renault,
Volvo and
Mercedes
sell various car models and small trucks that are gasoline/CNG powered.
Usually CNG parts used by major car manufacturers are actually produced by
after-market kit manufacturers, e.g.
Fiat use
Tartarini Auto components,
Volkswagen use Teleflex GFI[1]
and Landi Renzo components.
In
Germany, CNG-generated vehicles are expected to increase to two
million units of motor-transport by the year 2020. The cost for
CNG fuel is between 1/3 and 1/2 compared
to other fossil fuels in
Europe.[citation
needed] in 2008 there are around 800 gas(CNG)
stations in Germany
In Portugal there are 4 CNG refueling stations but 3 of them do not
sell to the public. Only in Braga you can find it on the local city bus
station (TUB).
South America
Argentina and
Brazil
are the two countries with the largest fleets of CNG vehicles. Conversion
has been facilitated by a substantial price differential with liquid
fuels, locally-produced conversion equipment and a growing CNG-delivery
infrastructure. A 'Blue-network' of CNG stations is being developed on the
major highways of the Southern Cone (including
Chile and
Bolivia)
to allow for long-haul transportation fuelled by CNG.
Asia
CNG Radio Taxi in New Delhi, India
CNG costs are at Rupees 18.90(USD $0.46) per kg compared with Rs.56.00
(US$ 1.45) per liter of petrol. The cost saving is immense along with
reduced emissions and environmentally friendlier cars.
CNG has grown into one of the major fuel sources used in car engines in
Iran,
Pakistan,
Bangladesh and
India. The
use of CNG is mandated for the public transport system of India's capital
New
Delhi as well as for the city of
Ahmedabad in the state of
Gujarat.
The
Delhi Transport Corporation operates the world's largest fleet of CNG
buses. The government of
Punjab, Pakistan, the most populous province of that country, has
mandated that all public-transport vehicles will use CNG by 2007. Today
many rickshaws as well as personal vehicles in India and Bangladesh are
being converted to CNG powered technology, the cost of which is in the
range of $800-$1000. In the Bangladesh capital of Dhaka not a single auto
rickshaw without CNG has been permitted since 2003. As of July 2007
Pakistan is the largest user of CNG in Asia, and second largest user in
the world.[6]
According to the International Association for Natural Gas Vehicles,
Pakistan has the second-largest number of
natural gas vehicles.[6]
Recently Landi Renzo of Italy has set up a production subsidiary in
Karachi to cater to the growing demand of CNG Kits in Pakistan. OEM's like
Toyota Pakistan and Suzuki Pakistan is producing company fitted CNG cars.
In the Middle East and Africa, Egypt is a top ten country in the world
with more than 63000 CNG vehicles and 95 fueling stations nationwide.
Egypt was also the first nation in Africa and the Middle East to open a
public CNG fueling station in January 1996.[7]
In
Singapore CNG is increasingly being used by public transport vehicles
like buses and taxis, as well as goods vehicles. However, according to
Channel NewsAsia on April 18, 2008, more owners of private cars in this
country are converting their petrol-driven vehicles to also run on CNG -
motivated no doubt by fiercely-escalating petrol prices these days. The
initial cost of converting a regular car to bi-fuel at the German
conversion workshop of C. Melchers-Galileo, for example, is around S$4,000
(US$2,300); with the promise of real cost-savings bi-fuel cars bring in
the long term.
Singapore currently has three operating filling stations for natural
gas. SembCorp Gas Pte Ltd runs the station on Jurong Island, and jointly
with Singapore Petroleum Company, the filling station at Jalan Buroh. Both
these stations are in the western part of the country. Another station on
the mainland is in Mandai Link to the north and is operated by SMART
Energy. SMART also plans a second station on Serangoon North Ave 5 which
will be set up the 2nd half of 2008; so will two more - at Jalan Bukit
Merah and Bedok in the central and eastern parts of the country.
As a key incentive for using this eco-friendly fuel
Singapore has a Green Vehicle Rebate (GVR) for users of CNG
technology. First introduced in January 2001, the GVR grants a 40%
discount on the Open Market Value (OMV) cost of newly-registered green
passenger vehicles.
In
Malaysia, the use of CNG was originally introduced for taxicabs and
airport limousines during the late-1990s, when new taxis were launched
with CNG engines while taxicab operators were encouraged to send in
existing taxis for full engine conversions; any vehicle converted to use
CNG is labelled with white rhombus "NGV" (Natural Gas Vehicle) tags,
lending to the common use of "NGV" when referring to road vehicles with
CNG engine. The practice of using CNG remained largely confined to
taxicabs predominantly in the
Klang Valley due to a lack of interest. No incentives were offered for
those besides taxicab owners to use CNG engines, while government
subsidies on petrol and diesel made conventional road vehicles cheaper to
use in the eyes of the consumers.
Petronas,
Malaysia's state-owned oil company, also monopolises the provision of CNG
to road users. As of July 2008, Petronas only operates about 150 CNG
refueling stations, most of which are concentrated in the Klang Valley. At
the same time, another 50 was expected by the end of 2008.[8]
As fuel subsidies were gradually removed in Malaysia starting June 5,
2008, the subsequent 41% price hike on petrol and diesel led to a 500%
growth in the number of new CNG tanks installed.[9][10]
National car maker
Proton considered fitting its
Waja,
Saga and
Persona models with CNG kits from Prins Autogassystemen by the end of
2008,[11]
while a local distributor of locally assembled
Hyundai cars offers new models with CNG kits.[12]
Conversion centres, which also benefited from the rush for lower running
costs, also perform partial conversions to existing road vehicles,
allowing them to run on both petrol or diesel and CNG with a cost varying
between RM3,500 to RM5,000 for passenger cars.[13][9]
Oceania
During the 1970s and 1980s, CNG was commonly used in
New
Zealand in the wake of the oil crises, but fell into decline after
petrol prices receded.
Brisbane Transport and
Transperth in Australia have both adopted a policy of only purchasing
CNG buses in future. Transperth is purchasing 451
Mercedes-Benz OC500LE buses and is undertaking trials with articulated
CNG buses from
Scania,
MAN, and
Irisbus,
while Brisbane Transport has purchased 216
Scania L94UB and 240 MAN 18.310 models as well as 30 MAN NG 313
articulated CNG buses. The
State Transit Authority of New South Wales (operating under the name
"Sydney Buses") operates 102
Scania L113CRB buses, two
Mercedes-Benz O405 buses and 300
Mercedes-Benz O405NH buses and are now taking delivery of 255
Euro 5-compliant Mercedes-Benz OC500LEs.
In the 1990s
Benders Busways of
Geelong,
Victoria trialled CNG buses for the Energy Research and Development
Corporation.[14]
Martin Ferguson, Ollie Clark, and Noel Childs featured on ABC 7.30
Report raising the issue of CNG as an overlooked transport fuel option in
Australia, highlighting the large volumes of LNG currently being exported
from the North West Shelf in light of the cost of importing crude oil to
Australia. The opportunity and pathways to industry development are mapped
out in summary on the
Rosetta Moon news site.
