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, and 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 200–248 bar (2900–3600 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.
CNG can be used in Otto-cycle (gasoline) and modified Diesel cycle engines. Lean-burn Otto-cycle engines can achieve higher thermal efficiencies than 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 exhaust gas recirculation, 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 as this would allow for an engine design with a higher compression ratio.
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.
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 gasoline gallon equivalent (GGE). 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)]. CNG-powered vehicles are considered to be safer than gasoline-powered vehicles.
Scientists are developing methods of storing methane in a new form known as ANG (Absorbed Natural Gas) at 35 bar (500 psi, the pressure of gas in natural gas pipelines) in various sponge like materials, such as activated carbon and metal-organic frameworks (MOFs). The fuel is stored at similar or greater energy density than CNG. The benefits are that vehicles can be refuelled from the natural gas network without extra gas compression, the fuel tanks can be made of lighter, less strong materials, and the tank designed to be much slimmer.
Worldwide, there are more than 7 million NGVs on the roads as of 2008, with the largest number of NGVs in Argentina, Brazil, Pakistan, Italy, India, China, Thailand, and Iran, with South America leading with a global market share of 48%.
CNG cars available in Europe are bi-fuel vehicles burning one fuel at a time. 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, Toyota, Honda and others) sell bi-fuel cars. In 2006, Fiat introduced the Siena Tetrafuel in the Brazilian market, equipped with a 1.4L FIRE engine that runs on E100, E25 (Standard Brazilian Gasoline), Gasoline and CNG.
Any existing gasoline vehicle can be converted to a bi-fuel (gasoline/CNG) vehicle. Authorized shops can do the retrofitting, this involves installing a CNG cylinder in the trunk, installing the plumbing, installing a CNG injection system and the electronics.
Due to the absence of any lead or benzene content in CNG, the lead fouling of spark plugs is eliminated. CNG-powered vehicles have lower maintenance costs when compared with other fuel-powered vehicles. CNG fuel systems are sealed, which prevents any spill or evaporation losses. Increased life of oils is another advantage. Other practical advantage observed is the increased life of lubricating oils, as CNG does not contaminate and dilute the crankcase oil. CNG mixes easily and evenly in air being a gaseous fuel. CNG is less likely to auto-ignite on hot surfaces, since it has a high auto-ignition temperature (540 °C) and a narrow range (5%-15%) of inflammability.
CNG produces significantly lesser emissions of pollutants like carbon dioxide (CO2), hydrocarbons(UHC), carbon monoxide (CO), nitrogen oxides (NOx), sulfur oxides (SOx) and particulate matter (PM), as compared to petrol . For example, an engine running on petrol for 100kms emits 22,000 grams of CO2, while covering the same distance on CNG emits only 16,275 grams of CO2. The corresponding figures are 78 and 25.8 grams respectively, for nitrogen oxides. Carbon monoxide emissions are reduced even further. Due to lower carbon dioxide and nitrogen oxides emissions, switching to CNG can help mitigate greenhouse gas emissions
CNG Locomotives are operated by several railroads. The Napa Valley Wine Train successfully retrofit a diesel locomotive to run on compressed natural gas before 2002. This converted locomotive was upgraded to utilize a computer controlled fuel injection system in May 2008, and is now the Napa Valley Wine Train's primary locomotive Ferrocarril Central Andino in Peru, has run a CNG Locomotive on a freight line since 2005. 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.
CNG is often confused with liquefied natural gas (LNG). While both are stored forms of natural gas, the key difference is that CNG is gas that is stored at high pressure, while LNG is in uncompressed liquid 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).
CNG vehicles are commonly used in South America, they represent 48% of the world's total fleet, where these vehicles are mainly used as taxicabs in main cities of Argentina and Brazil. Normally, standard gasoline vehicles are retrofitted in specialized shops, which involve installing the gas cylinder in the trunk and the CNG injection system and electronics. Argentina and Brazil are the two countries with the largest fleets of CNG vehicles, with a combined total fleet of more than 3 million vehicles by 2008. Conversion has been facilitated by a substantial price differential with liquid fuels, locally-produced conversion equipment and a growing CNG-delivery infrastructure.
Argentina has some 1.69 million NGV's as of 2008, with 1767 refuelling stations across the nation, or 15% of all vehicles. By July 2008 there were 1.56 million retrofitted vehicles in Brazil, or about 5% of the total light vehicle fleet, with 1585 refueling stations, and most of the fleet is comprised of taxis operating in the cities of Rio de Janeiro and São Paulo.
Bolivia has increased its fleet from 30,000 in 2004 to 90,163 units in April 2008, Colombia has an NGV fleet of 257,468 vehicles, and 378 refueling stations as of June 2008. Peru has 41,411 NGV as of July 2008, but that number is expected to skyrocket as Peru sits on South America's largest gas reserves.
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 rising petrol prices. The initial cost of converting a regular vehicle to dual fuel at the German conversion workshop of C. Melchers, for example, is around S$3,800 (US$2,500); with the promise of real cost-savings that dual-fuel vehicles bring over the long term.
Singapore currently has five 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 own a second station on Serangoon North Ave 5 which was set up end of March 2009; The fifth and largest station in the world was opened by the UNION Group in September 2009. This station is recognized by the Guniness World Records as being the laregst in the world with 46 refuelling hoses. This station is located in Toh Tuck. The Union Group, which operates 1000 CNG Toyota Wish taxis plan to introduce another 3 daughter stations and increase the CNG taxi fleet to 8000 units.
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. This initiative will end at the end of 2012 as the government believes the 'critical mass' of CNG vehicles would then have been built up.
The Ministry of Transport of Myanmar passed a law in 2005 which required that all public transport vehicles - buses, trucks and taxis, be converted to run on CNG. The Government permitted several private companies to handle the conversion of existing diesel and petrol cars, and also to begin importing CNG variants of buses and taxis. Accidents and rumours of accidents, partly fueled by Myanmar's position in local hydrocarbon politics, has discouraged citizens from using CNG vehicles, although now almost every taxi and public bus in Yangon, Myanmar's largest city, run on CNG. CNG stations have been set up around Yangon and other cities, but electricity shortages mean that vehicles may have to queue up for hours to fill their gas containers. The Burmese opposition movements are against the conversion to CNG, as they accuse the companies as being proxies of the junta, and also that the petrodollars earned by the regime would go towards the defense sector, rather than towards improving the infrastructure or welfare of the people.
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.
In China, companies such as Sino-Energy are active in expanding the footprint of CNG filling stations in medium-size cities across the interior of the country, where at least two natural gas pipelines are operational.
India has the highest number of vehicles running on CNG. CNG has grown into one of the major fuel sources used in car engines in India and Bangladesh as well. 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–$1000. In the Bangladesh capital of Dhaka not a single auto rickshaw without CNG has been permitted since 2003.
In India CNG costs are at Rs. 22.00 (US$ 0.48) per kg compared with Rs. 47.53 (US$ .92) per liter of petrol (prices as of 06th Sept. 2009 in Mumbai, India). The cost saving is immense along with reduced emissions and environmentally friendlier cars.
In Pakistan the majority of private vehicles have converted to CNG because of cheaper price as compared to petrol. Only luxury cars and official vehicles now run on petrol. Recently, new CNG Buses had been introduced CDGK. Almost all car manufacturers in Pakistan (except Honda and Toyota) now produce company fitted CNG kit versions. Recent hikes in CNG prices has downplayed the ambitious ventures of some of the stakeholders in this sector. It is expected that price of the CNG and Kits will come down as competition among manufacturers grows. LandiRenzo Pakistan is also exporting CNG kits to various countries including China, Brazil and Italy. Almost 2 million vehicles on the country's roads have dual fuel options with Suzuki having the highest in quantity.
Egypt is a top ten country in the world with more than 63,000 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 Iran as part of a government mandated plan to ensure energy security and to save on petrol imports a dual track plan of both producing dual fuel vehicles as well as conversion of existing vehicles to CNG has been undertaken. As of January 2009, there are some 1.3 million CNG equipped vehicles on the road. There is also a government mandate that forces local car manufacturers to produce 60% of all their new vehicles as dual fuel vehicles.
The vast majority 780000 have been produced as dual fuel vehicles by the auto manufacturer in the last two years, and the remainder have been converted utilizing after market conversion kits in workshops. There are 750 active refueling stations country wide with an additional 660 refueling stations under construction and expected to come on stream. Currently the major problem facing the industry as a whole is the building of refueling stations that is lagging behind dual fuel vehicle production, forcing many to use petrol instead.
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 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 automotive aftermarket 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).
In Sweden there are currently 90 CNG filling stations available to the public (as compared to about 10 LPG filling stations), primarily located in the southern and western parts of the country as well the Mälardalen region Another 70-80 CNG filling stations are under construction or in a late stage of planning (completions 2009-2010). Several of the planned filling stations are located in the northern parts of the country, which will greatly improve the infrastructure for CNG car users. There are approx. 14,500 CNG vehicles in Sweden (2007), of which approx. 13,500 are passenger cars and the remainder includes buses and trucks. In Stockholm, the public transportation company SL currently operates 50 CNG buses but have a capacity to operate 500. The Swedish government recently prolonged its subsidies for the development of CNG filling stations, from 2009-12-31 to 2010-12-31. In Spain the EMT Madrid bus service use CNG motors in 351 regular buses. Is rare to see another kind of CNG vehicle, and there's no CNG refueling stations.
There are almost 30 CNG filling stations in the Czech republic, mainly in the big cities.
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.
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 buses), and there are 90 public fueling stations in Southern California alone. 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, 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 heavy vehicles has been recently started by oilman and entrepreneur T. Boone Pickens. California voters defeated Proposition 10 in the 2008 General Election by a significant (59.8% to 40.2%) margin. Proposition 10 was a $5 Billion bond measure that, among other things, would have given 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.
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. At the peak of natural gas use, 10 percent of New Zealand's cars were converted, around 110,000 vehicles.
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.
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.