Compressed natural gas (CNG)
Compressed natural gas (CNG) is a cleaner alternative fuel derived from natural gas, stored at high pressure in steel or composite tanks. Used primarily for transportation, CNG helps reduce fuel costs and harmful emissions compared to traditional fossil fuels like gasoline and diesel. It plays a significant role in various vehicles, including dedicated natural gas vehicles (NGVs) and dual-fuel options that accommodate both CNG and another fuel type. By 2024, approximately 28 million NGVs were in operation globally, predominantly in countries such as Pakistan, China, and Iran, supported by around 24,000 natural gas refueling stations.
CNG offers environmental advantages, including lower carbon dioxide emissions and reduced particulate matter, which can contribute to improved air quality and potentially lower maintenance costs for vehicles. Despite its benefits, challenges such as higher initial costs, fewer refueling stations, and limited range remain barriers to broader adoption. Technological advancements and government incentives are gradually addressing these issues, promoting CNG as a viable alternative fuel amid rising interest in cleaner energy sources.
Compressed natural gas (CNG)
Summary: The use of compressed natural gas as fuel for cars, trucks, and buses can reduce fuel costs and harmful emissions. By 2024, about 28 million natural gas vehicles were in use all over the world. These were supported by the world's 24,000 natural-gas refueling stations.
Compressed natural gas (CNG) is natural gas stored under high pressure of about 200 bars (2,900 pounds per square inch), usually in steel tanks or cylinders. CNG tanks made of carbon fiber and fiberglass are available but not yet widely used. Like natural gas supplied by pipeline, CNG can be used as fuel for gas turbines, boilers, furnaces, and heating and cooling systems. The bulk transport of CNG by truck, rail, or ship can be an alternative to long-distance pipelines or the use of liquefied natural gas (LNG) ships. CNG can also be used in place of liquid fossil fuels (gasoline or diesel) as fuel for internal combustion engines.
CNG for Transportation
The most widespread application of CNG is for land transportation. Pakistan has the highest concentration of natural gas vehicles (NGVs) in the world: In 2021 it had about 4 million NGVs comprising about 80 percent of the country’s vehicle fleet.
There are dedicated NGVs that run only on CNG, as well as dual-fuel NGVs that use CNG and gasoline or CNG and diesel. NGVs appear to be particularly well suited for fleet applications that have defined routes or areas, centralized refueling facilities, and high mileage. Examples include buses and taxis for public transport, city and municipal fleets, school buses, airport shuttles and support vehicles, garbage trucks, and delivery trucks. The city of Los Angeles, California, operates a refueling station that can dispense CNG and LNG for use by its NGVs (including street sweepers, transit buses, aerial lift trucks, dump trucks, and passenger vehicles).
CNG for land transport has been available since the 1920s, but it did not gain wide acceptance. Early versions of CNG fuel storage included the use of inflatable bags and trailers. Compared to gasoline- or diesel-powered vehicles, some disadvantages associated with CNG are lower engine efficiency, a higher initial cost, a small number of refueling stations, a more limited range for each refueling, and the extra space taken up by the storage system. Technological improvements coupled with government support have helped to mitigate these issues.
Energy Consumption for Transportation
Energy consumption for transportation is closely tied to the issues of energy security, affordability, and climate change. Transportation accounts for about 25 percent of global greenhouse gas emissions (including carbon dioxide, CO2). In 2023, global oil consumption was estimated at 100.2 million barrels per day, of which 64 percent was used for transportation (by land, air, and sea). More than 90 percent of the energy supply for transportation was from liquid fossil fuels (mainly gasoline and diesel). Gasoline was used by 98 percent of light-duty vehicles; 98 percent of heavy-duty vehicles; 100 percent of planes; and 52 percent of trains. However, these percentages were expected to greatly reduce in the future, as more people transitioned to electric vehicles. In 2024, there were 40 million electric cars in the world.
In addition to the environmental impact associated with the high level of dependence on liquid fossil fuels, higher oil prices and political instability in oil-producing regions have helped to spur interest in alternative fuels and advanced vehicles. Many governments (including those of the United States and China) promote the use of alternative fuels such as biofuels, liquefied petroleum gas (LPG), and CNG, as well as advanced vehicles such as hybrids and electric vehicles. In doing so, they seek to achieve policy objectives, including greater energy security and lower greenhouse gas emissions and air pollution, by reducing dependence on imported oil. Stricter emissions standards, coupled with government incentives in the form of subsidies, rebates, tax credits, and exemptions, have helped to increase the adoption of NGVs.
Benefits of CNG in Transportation
For private motorists, commercial users, and fleet operators, fuel price is a key issue, and the low prices of CNG compared to gasoline and diesel remained an important driver to encourage a shift to NGVs. Subsidies for gasoline and diesel continued to be provided in several countries, often serving as a barrier to the wider use of alternative fuels. However, there has often been strong political opposition to the removal or reduction of these subsidies.
The use of CNG has significant environmental benefits. Using CNG in place of gasoline and diesel can reduce CO2 emissions (which are about 68 grams per megajoule for CNG as opposed to 96 grams per megajoule for gasoline) and emissions of particulate matter and nitrogen oxides. Cleaner-burning CNG can also extend engine life, reduce maintenance costs, and produce less engine noise.
Natural gas reserves are more dispersed geographically compared to crude oil reserves and can be less at risk of supply disruptions and volatile prices. There are potentially abundant supplies of natural gas from unconventional sources such as shale. The US Energy Information Administration estimated that recoverable shale gas in the United States was about 827 trillion cubic feet, a volume that is more than thirty-four times the annual US gas consumption. Global shale gas reserves could reach 7,300 trillion cubic feet in forty-one countries. However, the environmental impact of the shale gas production process on water resources has been debated. New technology and investment could also enable large-scale biogas production from sewage, agricultural and industrial waste, and landfills—and in the process create a renewable source of CNG.
Growth in CNG Use
There were about 28 million NGVs globally by 2024. The leading countries in terms of the number of NGVs were China (5.35 million), Iran (4 million), India (3.045 million), Pakistan (3 million), and Argentina (2,295). There were an estimated 175,000 NGVs in the United States.
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