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CNG FAQs

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In order to use natural gas as a transportation fuel, it must either be compressed or liquefied to provide energy density similar to gasoline or diesel.  Compressed natural gas is put under pressure and stored at approximately 3600 psi.  Liquefied natural gas is chilled to -260° F until it becomes a liquid.  Neither liquefying nor compressing change the chemical properties of natural gas and it can then be burned just as in other applications, with only minor modifications needed to inject it into the engine.  Approximately 5.7 lbs of compressed natural gas provide the same energy content as an equivalent gallon of gasoline.

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Because it is a gas, CNG natural gas is often referred to in “gallon gasoline equivalents,” or GGE, to provide a comparison between CNG and gasoline and diesel.  Nationally, the price of a gallon equivalent of CNG has averaged $1.90 since 2008, while gasoline and diesel have an average price of $2.86 and $2.90 respectively.  Additionally, crude oil is nearly 60% of the price of diesel at the pump; natural gas is only 1/3 of the price of CNG, which acts as a natural hedge for CNG prices against commodity price shocks.[i]



[i] U.S. Energy Information Administration 

 

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Estimates of vehicle emissions can vary, depending on factors such as engine usage, model design, and even the characteristics of specific engines. Several recent models show the lifecycle reduction of greenhouse gases to vary in magnitude from 4-28% when switching from diesel engines to natural gas. While pre-2007 heavy-duty diesel engines are much more polluting than CNG in terms of regulated emissions (NOx, particulate matter, CO), the EPA’s new heavy-duty diesel standards implemented in 2007 bring diesel engine compliance to similar levels as natural gas engines. Volatile organic compounds (VOCs) are portions of gasoline and diesel that are often released by evaporation during fueling and storage; they contribute to formation of ground level ozone and are also greenhouse gases. Use of natural gas vehicles almost completely eliminates evaporative VOCs due to the sealed nature of the natural gas fueling and storage process, although there are occasional system leakages that result in the release of methane.

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Colorado has the 3rd largest natural gas reserves of any state . As a state we produce about 4 times more natural gas than we consume each year, but only produce 1/3 of the state petroleum consumption. As a nation, 98% of the natural gas that we consume comes from North America. It is estimated that over 51,200 direct jobs in the State of Colorado come from the oil and gas industry, providing $3.8 billion in income.

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Natural gas has a narrow flammability range and, because it is lighter than air, dissipates quickly if released. NGV fuel tanks are strong and extremely puncture resistant and must meet standard safety specifications . All legal CNG vehicles and conversion kits must meet the same safety and environmental requirements as other vehicles.

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Natural gas vehicles are very similar in nature to gasoline and diesel vehicles that we drive today. Generally speaking, the biggest change is a hardened fuel tank that is capable of storing pressurized gas. Some modifications must be made to the engine and fuel delivery system as well, to allow for the efficient injection of gas into the cylinders.

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Currently the Honda Civic Natural Gas is the only consumer vehicle that is available from automobile manufacturers, with the natural gas model costing approximately$6,900 more than its gasoline counterpart. In a transit application, estimates from one bus manufacturer approximate the incremental cost of natural gas buses to be $42,000. For comparison, a diesel-hybrid bus costs approximately $200,000 more than a pure diesel bus.

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Advances in natural gas engine technologies have allowed CNG vehicles to run at high elevation just like diesels. At a recent conference for the Colorado Association of Transit Agencies, several bus manufacturers demonstrated this ability by taking CNG buses up Rabbit Ears Pass near Steamboat Springs.

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CNG is typically used in light to medium-duty vehicles as a substitute for either gasoline or diesel while LNG is typically used in medium to heavy duty vehicles as a diesel substitute. Because LNG is more energy dense, it can meet the needs of long-range heavy-duty vehicles using smaller sized tanks.

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Forward markets provide the option to purchase fuel through 2018 with a price differential of nearly $2/gallon between diesel and CNG. The U.S. Energy Information Administration forecasts natural gas prices to remain under $5/mmBtu in real terms for over a decade whereas petroleum price increases are expected to be higher and more volatile .

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Yes. Hybrid technology increases fuel efficiency and lowers the tailpipe emissions of a vehicle. While it is traditionally implemented on gasoline and diesel vehicles, hybrid technology is also applicable to CNG vehicles. Denver was the first to demonstrate this with CNG hybrid buses on the 16th Street Mall.