Natural Gas Basics 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 lim- ited area or along a route with natural gas fueling stations. The advantages of natural gas as an alternative fuel include its domestic availability, estab- Heavy-duty natural gas vehicles are a good choice for long-haul fleets that operate along a lished distribution network, route with natural gas fueling stations. Photo by Saturn Lounge Photography, NREL 28496 relatively low cost, and emis- sions benefits. range. Natural gas is sold in units distribute natural gas to and from of gasoline- or diesel-gallon equiva- most locations in the lower 48 states. What is natural gas? lents, which is based on the energy Natural gas is an odorless, gaseous content of a gallon of gasoline or Renewable natural gas (RNG), or mixture of hydrocarbons—pre- diesel fuel. biomethane, is produced from decay- dominantly methane (CH4 ). The ing organic materials like municipal fuel is widely used for heating and How and where is solid waste from landfills, sewage cooking, electric power production, natural gas produced from wastewater treatment plants, and industrial use. Although it is and distributed? animal manure, or food waste. After a proven, reliable alternative fuel impurities are removed, the gas pro- Most natural gas is drawn from wells that has long been used to power duced from these operations is ready or extracted in conjunction with vehicles, only about one-tenth for use in vehicles or for distribution crude oil production. The produc- of 1% of natural gas is currently through existing pipelines. Because tion of fossil natural gas in the used this way. Because it is a gas, it it is produced from non-fossil fuel United States has increased signifi- must be stored onboard a vehicle sources, RNG qualifies as a renew- cantly in recent years as advances in either a compressed gaseous or able fuel under the federal Renew- in hydraulic fracturing technologies liquefied state. Compressed natural able Fuels Standard (RFS) and a have enabled access to shale gas. gas (CNG) is typically stored in a low carbon fuel under California’s Most of the natural gas used in the tank at a pressure of 3,000 to 3,600 Low Carbon Fuel Standard. Thus, United States is produced in North pounds per square inch. RFS credits are available to offset America. The United States has a the higher cost of RNG as com- vast natural gas distribution system, Liquefied natural gas (LNG) is pared to fossil natural gas. In 2014, which can quickly and economically super-cooled and stored in its liquid roughly 20 million gasoline-gallon form at -260°F in insulated tanks. equivalents of RNG received credits Because liquid is more dense than gas, more energy can be stored by 1. “Worldwide NGV Statistics,” NGV Journal, volume. This makes LNG favor- accessed August 6, 2015. www.ngvjournal. able for trucks that need a longer com/worldwide-ngv-statistics/ VEHICLE TECHNOLOGIES OFFICE cleancities.energy.gov VEHICLE TECHNOLOGIES OFFICE • June 2016 • Page 2 under the RFS. This is less than one inspected and, if the vehicle has Light-duty vehicles are typically percent of estimated production ever been in an accident, whether configured as dedicated or bi-fuel potential. Learn more about RNG the tank was inspected afterwards. models, and heavy-duty vehicles are on the AFDC website (afdc.energy. CNG fuel tanks have a useful life configured as dedicated or dual- gov/fuels/natural_gas_renewable.html). of 15, 20, or 25 years, depending fuel models. Dual fuel engines are on how they were certified by the traditionally limited to heavy-duty Is natural gas safe for original manufacturer. All CNG applications and are slightly more use in vehicles? tanks carry a label that states the fuel-efficient than their spark- Just like conventional vehicles, expiration date. This date can also ignited, dedicated counterparts, but NGVs must comply with all appli- be found on a label near the fueling a dual-fuel system is more complex cable regulations, including Federal connector, and on the label under and requires onboard storage of Motor Vehicle Safety Standards the hood of the vehicle. both types of fuel. (FMVSS). Compared to gasoline and diesel fuel, natural gas has a How do NGVs work? How well do NGVs higher autoignition temperature A CNG fuel system transfers high- perform? (the point at which a gas or vapor pressure natural gas from the tank NGVs are similar to gasoline or can ignite in air without a spark or to the engine while reducing the fuel diesel vehicles with regard to power, flame being present), making unin- pressure to meet the operating acceleration, and cruising speed. tentional autoignition less likely. In requirements of the engine’s fuel- Natural gas has a higher pump addition, because it is lighter than management system. Just as in a octane number than gasoline air, natural gas dissipates quickly. gasoline engine, the fuel-air mix- (120+ compared to 84-93 for Fuel tanks on natural gas vehicles ture is compressed and ignited by a gasoline), and some original equip- are strong and extremely puncture spark plug to produce power. LNG ment manufacturers (OEMs) offer resistant, and they undergo testing engines operate similarly; the LNG dedicated engines optimized to take according to stringent standards. is converted to a gas before it is advantage of this higher rating.4 Once in use, they must be inspected injected into the engine. This can result in improved per- in a qualified service facility every formance and fuel economy over three years (36 months) or 36,000 There are three types of NGVs: non-optimized engines. The driving miles, whichever comes first.2 The range of NGVs is generally less National Fire Protection Associa- • Dedicated vehicles are designed to than that of comparable gasoline tion, U.S. Department of Trans- run only on natural gas. and diesel vehicles. This is because portation, and other organizations • Bi-fuel vehicles have two separate natural gas has a lower energy con- provide these and other safety fueling systems that enable them tent and less overall energy can be guidelines for NGVs, as well as for to run on either natural gas or stored in the same size tank as the 3 natural gas fueling equipment. A gasoline. This provides the flex- more energy-dense gasoline or diesel list of applicable codes and stan- ibility of using either fuel or both, fuels. Extra storage tanks or the use dards is available on the AFDC effectively increasing overall of LNG can help increase range. (afdc.energy.gov/pdfs/48611.pdf). vehicle range. What NGVs are available? Considerations for CNG tanks • Dual-fuel vehicles use natural A wide variety of light-, medium-, When purchasing a CNG vehicle, gas with some diesel fuel for and heavy-duty NGVs are available customers should be mindful of the ignition assistance, allowing and suitable for various applica- FMVSS inspection requirements them to operate much like tions. Buyers can purchase vehicles and the useful life of the fuel tank. conventional compression- through OEM dealerships or have If the vehicle is used, it is important ignition (e.g., diesel) engines. existing vehicles converted to natu- to determine when the tank was last ral gas after they’ve already been in service. 2. Compressed Natural Gas Fuel Container Integrity, 49 C.F.R. 571.304 (Oct. 1, 2011). 3. “NFPA 52: Vehicular Gaseous Fuel Systems Code,” National Fire Protection Association, accessed August 6, 2015, nfpa.org/codes-and-standards/ document-information-pages?mode=code&code=52. 4. AFDC Fuel Properties Comparison (afdc.energy.gov/fuels/fuel_properties.php). CLEAN CITIES CLEAN VEHICLE TECHNOLOGIES OFFICE • June 2016 • Page 3 important to understand these and ask to review documentation on emissions compliance as well as the conversion practices, procedures, and training. Consult the Natural Gas Vehicle Conversions page on the AFDC website for additional details (afdc.energy.gov/vehicles/ natural_gas_conversions.html). 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. New OEM light-duty NGVs cost approximately $6,500 to CNG vehicles are fueled with easy-to-use, pressure-sealed fueling connectors. Photo by Pat Corkery, NREL 18188 $10,000 more than comparable gaso- line vehicles, and heavy-duty NGVs cost $30,000 or more than their How can I find reliable and Natural Gas Vehicles for America counterparts. The price depends on EPA-compliant vehicles? (NGVAmerica) Vehicle Availability the fuel-tank capacity and whether page (ngvamerica.org/vehicles/vehicle- All natural gas fueling systems must the vehicle is purchased from a availability/). be certified to meet U.S. Environ- dealer or is an in-service vehicle that mental Protection Agency (EPA) has been converted. The mainte- In some cases, buyers can order or California Air Resources Board nance and operation costs of NGVs select OEM models with gaseous- (CARB) emissions standards. For are similar to those of their gasoline fuel “prep packages,” which allow a list of EPA-certified natural gas or diesel counterparts. Fleet manag- a qualified system retrofitter or conversion systems and engines, ers will also need to consider both vehicle modifier (QSR or QVM) to see the EPA website (epa.gov/otaq/ the cost of fueling infrastructure, install the EPA- or CARB-certified consumer/fuels/altfuels/altfuels.htm if they do not currently have access natural gas fuel delivery system and epa.gov/otaq/certdata.htm#lsi).