Compressed Natural Gas (CNG) is a fossil fuel substitute for gasoline (petrol), diesel, or propane fuel. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill (natural gas is lighter than air, but disperses quickly when released).
CNG 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.
CNG is used in traditional gasoline internal combustion engine cars that have been converted into bi-fuel vehicles (gasoline/CNG). Natural gas vehicles are increasingly used in Europe and South America due to rising gasoline prices.
In response to high fuel prices and environmental concerns, CNG is starting to be used also in light-duty passenger vehicles and pickup trucks, medium-duty delivery trucks, transit and school buses, and trains.
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.
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.
CNG cars available in Europe are actually flexible-fuel vehicles. Their engine is a standard gasoline internal combustion engine (ICE). This means that they can indifferently run on either gasoline from a gasoline tank or CNG from a separate cylinder 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. Besides the lower costs, a major benefit is that CNG cars can reduce pollution.
CNG Locomotives are operated by several railroads, including Ferrocarril Central Andino in Peru, which has run a CNG Locomotive on a freight line since 2005 , and the Napa Valley Wine Train, which replaced its diesel locomotive with a CNG locomotive in May 2008. CNG locomotives are usually diesel locomotives that have been converted to use compressed natural gas generators instead of diesel generators to generate the electricity that drives the motors of the train. Some CNG locomotives are able to fire their cylinders only when there is a demand for power, which, theoretically, gives them a higher fuel efficiency than conventional diesel engines.
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. California voters will be voting on Proposition 10 in the 2008 General Election. Proposition 10 is a $5 Billion bond measure that, among other things, will give rebates to state residents that purchase CNG vehicles.
Congress has encouraged conversion of cars to CNG with a tax credits of up to 50% of the auto conversion cost and the CNG home filling station cost. However, while CNG is much cleaner fuel, the conversion requires a type certificate from the EPA. Meeting the requirements of a type certificate can cost up to $50,000.
The use of methane (CNG) for vehicles started in the 1930s 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 and Landi Renzo components.
In Italy, there are more than 800 CNG stations
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. 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).
Ankara has got 1050 CNG Bus.
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......
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. 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.
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.
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. The practice of using CNG remained largely confined to taxicabs predominantly in the Klang Valley and Penang 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.
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% increase in the number of new CNG tanks installed. National car maker Proton considered fitting its Waja, Saga and Persona models with CNG kits from Prins Autogassystemen by the end of 2008, while a local distributor of locally assembled Hyundai cars offers new models with CNG kits. 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.
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.