What is Compressed Natural Gas (CNG)?
CNG or compressed natural gas is a domestically available, economical,
clean burning, alternative fuel source for vehicles.
Rather than burn gasoline or diesel fuel, a consumer would fuel their
vehicle with natural gas. In order to provide enough range, the gas is
compressed and stored on the vehicle in pressurized tanks. Tanks that
can hold up to 3,600 psig.
Sounds a little scary doesn't it? Not when you compare the physical properties
of Natural Gas and gasoline. The fact is that natural gas is a much safer
fuel than gasoline. Natural gas readily disperses in air because of its simple molecular structure. (Ever wonder why the stove in your home doesn't burn
gasoline instead of natural gas?) Just take a look at the charts below
for some interesting facts:
Natural Gas - a simple hydrocarbon
As you can see from the first chart at left, natural gas has a ratio of
four (4) hydrogen atoms to one (1) carbon atom. This makes CNG the lowest
carbon fuel available today: with the exception of hydrogen itself, natural
gas (NG) has the highest hydrogen content of any fuel.
Its simple molecule structure makes complete combustion easy and results
in less tailpipe pollution than petroleum fuels. Natural Gas Vehicles
(NGVs) produce approx. 93 - 95% less emissions than similar petroleum
fueled vehicles. (source: EIA)
Incomplete Combustion - Why Petroleum is More Polluting
The second chart at left shows the molecular structure typical of gasoline
- you can see that it's much more complex than the simple structure of
methane (natural gas) shown above at left . You'll notice that there are
eight (8) carbon atoms and eighteen (18) hydrogen atoms in each molecule.
Because of the complexity of the molecule, gasoline tends not to completely
combust in an engine.
When a hydrocarbon fuel (that is one that's made of a combination of
hydrogen and carbon) burns completely, the oxygen in our air combines
with the hydrogen to form water (H2O) and with the carbon to
form carbon dioxide (CO2). If the combustion is not complete,
then some of the carbon atoms only combine with one oxygen instead of
two, and form carbon monoxide (CO) as a result - a poisonous gas that
is lethal to humans if concentrated.
The third chart below shows the very complex molecule structure typical
of diesel. There are sixteen (16) carbon molecules and thirty-four (34)
hydrogens. The ratio of carbon to hydrogen is nearly double to the ratio
of carbon to hydrogen found in methane (CNG). Because of its complex structure,
diesel fuel does not completely combust in an engine.
Along with carbon monoxide pollution resulting from incomplete combustion,
other carbon atoms may remain stuck together with each other and with
some of the hydrogen atoms also; these unburned hydrocarbon molecules
come out of the tailpipe. The unburned hydrocarbons then react with nitrogen
oxides (another pollutant from combustion) in the presence of sunlight
to form ozone, which is a lung irritant.
FACT: high level ozone in the stratosphere
is a shield against the sun's ultraviolet light, but ground level ozone
is the main component of "smog". Carbon atoms can also remain
stuck to one another with few or no hydrogen atoms attached, especially
during incomplete combustion of diesel fuel, producing soot. Soot
has been linked to a significant increase in respiratory illness in school
age children. Find out more about health risks of diesel from the EPA:
http://www.epa.gov/otaq/schoolbus/humanhealth.htm (link opens in new window)
Because alternative fuels such as CNG have simpler molecules, they burn
more completely in an engine, so that less carbon monoxide, soot, and
unburned hydrocarbons come out the tailpipe. Methane, or natural gas,
in particular is almost incapable of forming smog. These are reasons that
CNG is much less polluting than gasoline and diesel.
How is Compressed Natural Gas (CNG) used for powering vehicles?
This is accomplished by the following steps:
- Natural gas is compressed and enters the vehicle through the natural
gas dispenser or fill post
- It flows into high-pressure cylinders that are located on the vehicle.
- When the driver steps on the accelerator, the natural gas leaves the
on-board storage cylinder, passes through the high-pressure fuel line
and enters the engine compartment.
- Gas then enters the regulator, which reduces pressure from up to 3,600
psi to approximately atmospheric pressure.
- The natural gas solenoid valve allows natural gas to pass from the
regulator into the gas mixer or fuel injectors.
- Natural gas mixed with air flows down through the carburetor or fuel
injection system and enters the engine's combustion chambers.
Are Natural Gas Powered Vehicles safe?
Natural Gas an ideal fuel source for many reasons, including safety.
Natural Gas is lighter than air. This means that it will not puddle (like
gasoline) or sink to the ground like propane, which is heavier than air.
Instead, Natural Gas will rise and dissipate in the atmosphere.
Natural gas also has a higher ignition temperature. This means that it
is much harder to ignite. Also the storage systems used for compressed
natural gas are infinitely stronger that the gasoline tanks found on cars
and trucks today.
gCNG® – Natural Gas from Renewable Resources
What's the Difference?
Natural gas, or methane, is a
gas composed of four hydrogen molecules, and one carbon molecule.
Up to 95% less emissions when used in similar petroleum fueled
From a renewable,
sustainable biogas resource*
* Natural gas (methane) is often associated with petroleum exploration
as both are commonly found together in the same reservoir. Non-associated
natural gas is gas that is found without oil.
gCNG is a
sustainable biofuel that comes from resources such as landfills,
municipal waste water treatment plants, and livestock operations.
FirmGreen's patented process enables economical cleanup of biogas
to pipeline quality – improving air quality while producing
a clean alternative fuel from local renewable resources!
Safe: Lighter-than-air compressed natural
gas is nontoxic and disperses quickly. It has a higher ignition
temperature than gasoline and diesel fuel, which reduces the chances
of accidental ignition.