Compressed Natural Gas (CNG)
Overview
CNG is a readily available alternative to gasoline that’s made by compressing natural gas to less than 1% of its volume at standard atmospheric pressure. Consisting mostly of methane, CNG is odorless, colorless and tasteless. It's drawn from domestically drilled natural gas wells or in conjunction with crude oil production.
Natural gas powers more than 12 million vehicles on the road today. Unfortunately, only about 250,000 of these are being used in the U.S.,
according to GE.
The average growth rate in the U.S. shows a 3.7% increase per year since 2000, as contrasted with a booming global growth rate of 30.6% per year.
CNG OVERVIEW & BASICS
What is Natural Gas?
Natural gas occurs deep beneath the earth's surface. Natural gas consists mainly of methane, a compound with one carbon atom and four hydrogen atoms. Natural gas also contains small amounts of hydrocarbon gas liquids and nonhydrocarbon gases. We use natural gas as a fuel and to make materials and chemicals.
Why Natural Gas?
Natural gas powers about 150,000 vehicles in the United States and roughly 22 million vehicles worldwide.1 Natural gas vehicles (NGVs) are a good choice for high-mileage fleets— such as buses, taxis, and refuse vehicles—that are centrally fueled or operate within a limited area or along a route with natural gas fueling stations. The advantages of natural gas as an alternative fuel include its domestic availability, established distribution network, relatively low cost, and emissions benefits.
What is Natural Gas?
Natural gas is an odorless, gaseous mixture of hydrocarbons—predominantly methane (CH4 ).
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Energy Efficiency & Renewable Energy
Natural gas is an odorless, gaseous mixture of hydrocarbons—predominantly methane (CH4 ). The fuel is widely used for heating and cooking, electric power production, and industrial use. Although it is a proven, reliable alternative fuel that has long been used to power vehicles, only about one-tenth of 1% of natural gas is currently used this way. Because it is a gas, it must be stored onboard a vehicle in either a compressed gaseous or liquefied state. Compressed natural gas (CNG) is typically stored in a tank at a pressure of 3,000 to 3,600 pounds per square inch. Liquefied natural gas (LNG) is super-cooled and stored in its liquid form at -260°F in insulated tanks. Because liquid is more dense than gas, more energy can be stored by volume. This makes LNG favorable for trucks that need a longer range. Natural gas is sold in units of gasoline- or diesel-gallon equivalents, which is based on the energy content of a gallon of gasoline or diesel fuel.
How and where is natural gas produced and distributed?
Most natural gas is drawn from wells or extracted in conjunction with crude oil production.
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Energy Efficiency & Renewable Energy
Most natural gas is drawn from wells or extracted in conjunction with crude oil production. The production of fossil natural gas in the United States has increased significantly in recent years as advances in hydraulic fracturing technologies have enabled access to shale gas. Most of the natural gas used in the United States is produced in North America. The United States has a vast natural gas distribution system, which can quickly and economically distribute natural gas to and from most locations in the lower 48 states. Renewable natural gas (RNG), or biomethane, is produced from decaying organic materials like municipal solid waste from landfills, sewage from wastewater treatment plants, animal manure, or food waste. After impurities are removed, the gas produced from these operations is ready for use in vehicles or for distribution through existing pipelines. Because it is produced from non-fossil fuel sources, RNG qualifies as a renewable fuel under the federal Renewable Fuels Standard (RFS) and a low carbon fuel under California’s Low Carbon Fuel Standard. Thus, RFS credits are available to offset the higher cost of RNG as compared to fossil natural gas. In 2014, roughly 20 million gasoline-gallon equivalents of RNG received credits under the RFS. This is less than one percent of estimated production potential. Learn more about RNG on the AFDC website.
Is Natural Gas safe for use in vehicles?
Just like conventional vehicles, NGVs must comply with all applicable regulations, including Federal Motor Vehicle Safety Standards (FMVSS).
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Energy Efficiency & Renewable Energy
Just like conventional vehicles, NGVs must comply with all applicable regulations, including Federal Motor Vehicle Safety Standards (FMVSS). Compared to gasoline and diesel fuel, natural gas has a higher autoignition temperature (the point at which a gas or vapor can ignite in air without a spark or flame being present), making unintentional autoignition less likely. In addition, because it is lighter than air, natural gas dissipates quickly. Fuel tanks on natural gas vehicles are strong and extremely puncture resistant, and they undergo testing according to stringent standards. Once in use, they must be inspected in a qualified service facility every three years (36 months) or 36,000 miles, whichever comes first.
Considerations for CNG Tanks:
How do NGVs work?
A CNG fuel system transfers highpressure natural gas from the tank to the engine while reducing the fuelpressure to meet the operating requirements of the engine’s fuelmanagement system.
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Energy Efficiency & Renewable Energy
A CNG fuel system transfers highpressure natural gas from the tank to the engine while reducing the fuelpressure to meet the operating requirements of the engine’s fuelmanagement system. Just as in a gasoline engine, the fuel-air mixture is compressed and ignited by a spark plug to produce power. LN engines operate similarly; the LNG is converted to a gas before it is injected into the engine.
There are three types of NGVs:
Light-duty vehicles are typically configured as dedicated or bi-fuel models, and heavy-duty vehicles ar configured as dedicated or dualfuel models. Dual fuel engines are traditionally limited to heavy-duty applications and are slightly more fuel-efficient than their sparkignited, dedicated counterparts, but a dual-fuel system is more complex and requires onboard storage of both types of fuel.
How well do NGVs perform?
NGVs are similar to gasoline or diesel vehicles with regard to power, acceleration, and cruising speed..
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Energy Efficiency & Renewable Energy
NGVs are similar to gasoline or diesel vehicles with regard to power, acceleration, and cruising speed. Natural gas has a higher pump octane number than gasoline (120+ compared to 84-93 for gasoline), and some original equipment manufacturers (OEMs) offer dedicated engines optimized to take advantage of this higher rating.4 This can result in improved performance and fuel economy overnon-optimized engines. The driving range of NGVs is generally less than that of comparable gasoline and diesel vehicles. This is because natural gas has a lower energy content and less overall energy can be stored in the same size tank as the more energy-dense gasoline or diesel fuels. Extra storage tanks or the use of LNG can help increase range.
What NGVs are available?
A wide variety of light-, medium-, and heavy-duty NGVs are available and suitable for various applications.
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Energy Efficiency & Renewable Energy
A wide variety of light-, medium-, and heavy-duty NGVs are available and suitable for various applications. Buyers can purchase vehicle through OEM dealerships or have existing vehicles converted to natural gas after they’ve already been in service.
How can I find reliable and EPA-compliant vehicles?
All natural gas fueling systems must be certified to meet U.S. Environmental Protection Agency (EPA)or California Air Resources Board (CARB) emissions standards.
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Energy Efficiency & Renewable Energy
All natural gas fueling systems must be certified to meet U.S. Environmental Protection Agency (EPA)or California Air Resources Board (CARB) emissions standards. Fo a list of EPA-certified natural gas conversion systems and engines, see the EPA website (epa.gov/otaq/ consumer/fuels/altfuels/altfuels.htm and epa.gov/otaq/certdata.htm#lsi).
Note that, as EPA states, the list is not comprehensive and there may be certified conversions that do not appear on the list. EPA adds conversion systems upon request of the conversion manufacturer and advises checking the list periodically for updates. Customers should ask to see and verify a manufacturer’s EPA or CARB certificate.
Purchasing New Vehicles:
Converting In-Service Vehicles:
How much do NGVs cost?
The price of an NGV is higher than that of a comparable conventional fuel vehicle; however, NGVs can provide an acceptable return on investment (ROI) for many fleets because of the fuel’s relatively low price.
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Energy Efficiency & Renewable Energy
The price of an NGV is higher than that of a comparable conventional fuel vehicle; however, NGVs can provide an acceptable return on investment (ROI) for many fleets because of the fuel’s relatively low price. New OEM light-duty NGVs cost approximately $6,500 to $10,000 more than comparable gasoline vehicles, and heavy-duty NGVs cost $30,000 or more than their counterparts. The price depends on the fuel-tank capacity and whether the vehicle is purchased from a dealer or is an in-service vehicle that has been converted.
The maintenance and operation costs of NGVs are similar to those of their gasoline or diesel counterparts. Fleet managers will also need to consider both the cost of fueling infrastructure, if they do not currently have access to existing fueling sites (see page 4), as well as the potential cost of any upgrades that may be required to their maintenance facilities. Tax credits and other incentives may also be available to help reduce the cost of fuel, vehicles, and infrastructure.
Is it easy to fuel an NGV?
CNG vehicles are fueled with easyto-use, pressure-sealed dispensers. The amount of time it takes to fill a tank depends on several factors, including how the fueling station is configured.
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Energy Efficiency & Renewable Energy
CNG vehicles are fueled with easyto-use, pressure-sealed dispensers. The amount of time it takes to fill a tank depends on several factors, including how the fueling station is configured. Time-fill stations fuel vehicles overnight, taking advantage of off-peak electricity rates an smaller (and less expensive) compression equipment. Fast-fill stations fill vehicles rapidly using larger compression equipment and high-pressure gas storage systems. Ambient air temperature and fill speed also affect the final fill volume in CNG vehicle tanks. See an illustrated interactive animation of these effects on the AFDC website (afdc.energy.gov/vehicles/ cng_tank_animation.html).
LNG stations are structurally similar to gasoline and diesel stations because they deliver a liquid fuel. There are three options for LNG fueling: mobile, containerized, and customized large stations. In mobile fueling, LNG is delivered by a tanker truck that has on-board metering and dispensing equipment. A containerized station, or starter station, includes a storage tank, dispensing equipment, metering, and required containment (for spills or leaks). A custom station has greater storage capacity and is tailored to meet fleets’ needs. Fueling LNG vehicles requires special procedures, training, and protective equipment, but the process is not difficult. As with all vehicles, proper safety precautions must be taken when fueling NGVs.
How much does natural gas cost and where is it available?
Historically, the average retail price of natural gas has been lower an more stable than that of gasoline and diesel.
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Energy Efficiency & Renewable Energy
Historically, the average retail price of natural gas has been lower an more stable than that of gasoline and diesel. This makes natural gas a good option for fleets that use large amounts of fuel. However, fleet managers should carefully consider their options when establishing private fueling or using public sites.
Public Fueling Stations:
Private Fueling Stations:
How do I calculate the ROI for NGVs?
The ROI associated with natural gas depends on a variety of factors. Because natural gas fuel is often less expensive than gasoline and diesel, fleets with higher annual vehicle mileage will experience shorter payback periods. Payback is therefore linked to fleet size and type.
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Energy Efficiency & Renewable Energy
The ROI associated with natural gas depends on a variety of factors. Because natural gas fuel is often less expensive than gasoline and diesel, fleets with higher annual vehicle mileage will experience shorter payback periods. Payback is therefore linked to fleet size and type. Tax credits and other incentives may also be available to help reduce the cost of natural gas fuel, vehicles, and infrastructure, thereby shortening the payback period. For more information, contact your local Clean Cities coordinator and see the AFDC Federal and State Laws and Incentives section (afdc.energy.gov/laws).
Two helpful tools include the Fuel Life-Cycle Environmental and Economic Transportation (AFLEET) tool (greet.es.anl.gov/afleet), which estimates petroleum use, emissions, and cost of ownership of lightduty and heavy-duty vehicles for a variety of fuels; and the Vehicle and Infrastructure Cash-Flow Evaluation (VICE) model (afdc.energy.gov/ vice_model), which can be used to evaluate ROI and payback period for both natural gas vehicles and infrastructure.
How do NGV emissions compare to other emissions?
All new vehicles are equipped with effective emission control systems and must meet the same emissions standards, regardless of fuel type.
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Energy Efficiency & Renewable Energy
All new vehicles are equipped with effective emission control systems and must meet the same emissions standards, regardless of fuel type. Consequently, tailpipe emissions from NGVs (or any alternative fuel vehicles) are comparable to those of gasoline and diesel vehicles equipped with modern emissions controls. According to ANL’s Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model, light-duty vehicles running on conventional and shale natural gas can reduce life cycle greenhouse gas emissions by 11% (83% if running on RNG). In addition, because CNG fuel systems are completely sealed, the vehicles produce no evaporative emissions. For details, see the AFDC Natural Gas Vehicle Emissions page (afdc.energy. gov/vehiclesnatural_gas_emissions.html).
Natural Gas Vehicles
Overview
Natural gas powers more than 150,000 vehicles in the United States and roughly 15.2 million vehicles worldwide. Natural gas vehicles (NGVs) are good choices for high-mileage, centrally fueled fleets. Compressed natural gas (CNG) tanks and safety are improving, and in many cases CNG can provide adequate range for the required vehicle application. For vehicles needing to travel long distances, liquefied natural gas (LNG) is a good choice. The advantages of natural gas as a transportation fuel include its domestic availability, widespread distribution infrastructure, and reduced greenhouse gas emissions compared to conventional gasoline and diesel fuels.
CNG and LNG are considered alternative fuels under the Energy Policy Act of 1992. The horsepower, acceleration, and cruise speed of NGVs are comparable with those of equivalent conventional vehicles. Also, compared with conventional diesel and gasoline vehicles, NGVs offer other air-quality benefits.
There are light-, medium-, and heavy-duty natural gas vehicles available from original equipment manufacturers, as well as medium- and heavy-duty vehicle options available through qualified system retrofitters. Qualified system retrofitters can also economically, safely, and reliably convert many vehicles for natural gas operation with aftermarket conversion systems.
FACTS AND STATS
Overview
The United States used about 27.49 trillion cubic feet (Tcf) of natural gas in 2016, the equivalent of 28.4 quadrillion British thermal units (Btu) and 29% of total U.S. energy consumption.
Natural gas use by U.S. consuming sectors by amount and share of total U.S. natural gas consumption in 2016:
Electric power—9.987 Tcf—36%
Industrial—9.31 Tcf—34%
Residential—4.35 Tcf—16%
Commercial—3.11 Tcf—11%
Transportation—0.74 Tcf—3%
Advantages
- About 96% of U.S. natural gas used is domestically produced
- Roughly 20% to 45% less smog-producing pollutants
- About 5% to 9% less greenhouse gas emissions
- Less expensive than gasoline
Disadvantages
- Limited vehicle availability
- Less readily available than gasoline and diesel
- Fewer miles on a tank of fuel
Natural Gas is Clean
Natural gas is the cleanest commercially available transportation fuel.
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Natural Gas Vehicles for America
- Natural gas is the cleanest commercially available transportation fuel. Per unit of energy, natural gas is less carbon intensive than any other fossil fuel. This means using natural gas as a motor vehicle fuel typically produces lower carbon dioxide (CO2 ) emissions than gasoline and diesel fuel. Numerous studies and reports attempt to rate the relative well-to-wheels greenhouse gas (GHG) emission benefits of different fuels. Such studies look not only at the end-use impact of burning a fuel but also the energy intensity and other emissions associated with the upstream production of different fuels. In 2012, the National Petroleum Council (NPC) produced an exhaustive study on the future of transportation fuels. The NPC study summarizes the findings of available studies with respect to natural gas vehicles (NGV) as follows: light duty NGVs provide a 7–30 percent reduction in GHG emissions and heavy duty NGVs provide an 11–29 percent reduction in GHG emissions.
- Transit buses that use natural gas can expect a fuel cost savings of $20,000 or more annually when compared to conventional diesel buses.
- Natural gas costs, on average, over one-third less than conventional gasoline at the pump. Depending on the market, that savings can be $1.50 or more per gasoline gallon equivalent (GGE).
Natural Gas is American
Ninety-eight percent of all the natural gas consumed in the U.S. is produced in North America, while nearly 55 percent of the crude oil we use is imported.
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Natural Gas Vehicles for America
- Ninety-eight percent of all the natural gas consumed in the U.S. is produced in North America, while nearly 55 percent of the crude oil we use is imported.
- There are about 1,250 NGV fueling stations in the U.S. and more than half are available for public use.
- The necessary natural gas fuel distribution infrastructure is already in plac — more than 1.5 million miles of natural gas pipelines and distribution lines blanket the U.S., making supplies readily available for new fueling stations.
Natural Gas is Abundant
Domestic reserves of natural gas are estimated to be twice that of petroleum based upon current consumption—more than 100 years.
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Natural Gas Vehicles for America
Domestic reserves of natural gas are estimated to be twice that of petroleum based upon current consumption—more than 100 years.
- Approximately 22–23 trillion cubic feet of natural gas have been consumed each year in the United States since 1995.
- Can U.S. natural gas supply sources meet growing market demand for natural gas?
The simple answer is yes, and this is supported by a number of natural gas supply analyses.
- For 15 of the last 16 years, the U.S. has added more gas to its domestic reserves than it has produced and used.
- Worldwide, natural gas reserves are greater than petroleum.
- A 1998 U.S. Department of Energy study estimated that, worldwide, between 25 and 37 quadrillion Btu of methane is released each year into the atmosphere due to the natural decomposition of organic material. In the U.S., the report states that it is feasible to capture and use about 1.25 quadrillion Btu produced from landfills, sewage and animal waste alone. This is equivalent to approximately 6 percent of all the natural gas used in the U.S.
Natural Gas is Affordable
Natural gas has been 25–42 percent cheaper than diesel over the last 14 years; EIA’s Annual Energy Outlook projects that this favorable cost-spread will continue into the future.
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Natural Gas Vehicles for America
- Natural gas has been 25–42 percent cheaper than diesel over the last 14 years; EIA’s Annual Energy Outlook projects that this favorable cost-spread will continue into the future.
- Transit buses that use natural gas can expect a fuel cost savings of $20,000 or more annually when compared to conventional diesel buses.
- Natural gas costs, on average, over one-third less than conventional gasoline at the pump. Depending on the market, that savings can be $1.50 or more per gasoline gallon equivalent (GGE)
Natural Gas Vehicles are Widely Used
Use of NGVs is widespread and growing—there are approximately 120,000 NGVs on U.S. roads today and about 15 million worldwide.
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Natural Gas Vehicles for America
- Use of NGVs is widespread and growing—there are approximately 120,000 NGVs on U.S. roads today and about 15 million worldwide.
- Major companies using NGVs in the U.S. include AT&T, UPS, Verizon, Waste Management and Republic Services; and natural gas-powered buses operate in many of the largest metropolitan areas such as Los Angeles, New York, Dallas-Ft Worth, Atlanta, Boston, Washington, D.C. and dozens of secondary markets and small communities.
- About 30 different manufacturers produce 100 models of light-, medium- and heavy-duty natural gas vehicles and engines in the U.S.
- In the U.S., natural gas vehicles can be factory ordered from a variety of original equipment manufacturers (OEM), including companies such as Allianz-Johnston, American Honda, American LaFrance-Condor, Autocar, Blue Bird, Capacity, Chrysler Ram Commercial Truck, Crane Carrier, ElDorado, Elgin, Freightliner Truck, General Motors, Gillig, Kalmar, Kenworth, Mack, Motor Coach Industries, Navistar, New Flyer, North American Bus Industries (NABI), Peterbilt, Schwarze, Thomas Built, Tymco, Vehicle Production Group and Volvo.