Civil Engineering Reference
In-Depth Information
Source: General Motors Company. Reprinted by permission.
Figure 3. Cross-Section of a CNG Vehicle. 2015 Chevrolet Impala Components that
differ from a gasoline-powered vehicle.
The CNG fuel system transfers the highly pressurized natural gas from the
storage tank to the engine, reducing pressure during the transfer to equate to
the operating pressure of the engine's fuel-management system.
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A CNG
engine functions like a gasoline engine: The fuel and air mixture are
compressed and then ignited by a spark plug, expanding gases to drive pistons
to propel the vehicle. Certain changes are required to accommodate the
pressurized, gaseous CNG, such as new valves and fuel injectors and a
pressure regulator.
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While much of a natural gas vehicle's composition is
similar to that of gasoline-powered internal combustion engine vehicle,
modifications required for CNG use currently add up to $11,000 to the price of
a passenger vehicle.
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Some current models of CNG vehicles are bifuel, with tanks for both CNG
and gasoline, thereby allowing for extended driving range.
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When a bifuel
vehicle runs out of CNG, it automatically shifts into gasoline mode. Drivers
can also shift from one fuel to another by selecting a dashboard button.
In addition to passenger vehicles, CNG has been adopted as a fuel for
taxis; regional-haul trucks used in local freight and package delivery;
construction, residential refuse pickup, and municipal fleets; and transit buses.
The vehicles return each day to a central garage or maintenance yard, where
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