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5 <br />present in the earth, and consists primarily of methane (CH4) with smaller <br />elements of ethane and very small amounts of hydrogen, helium and nitrogen.. <br />Methane is formed from organic matter decomposing in presence of heat, <br />organic matter converted by microorganisms (as in landfills), and releases from <br />oil and coal. <br />Very large reserves of natural gas are believed to exist at depths of 15,000- <br />20,000 feet below the Earth's surface (referred to as "deep gas"). Since methane <br />remains stable up to its auto-ignition temperature of 1022 OF, it is found at depths <br />where oil is not found. Natural gas is a very good spark-ignition internal <br />combustion engine fuel, and was actually used as a fuel in the early days of <br />engine development. However, for many years the ability to store large quantities <br />of natural gas for onboard vehicles created barriers to use as a transportation <br />fuel. In terms of domestic production, the United States produces 87% of natural <br />gas that is consumed - the remaining 13% comes from Canada. <br />Very little processing is needed to make natural gas suitable as a fuel. Water <br />vapor, sulfur and heavy hydrocarbons are removed before it is piped. Methane <br />mixes readily with air and has a high octane rating, which makes it a very good <br />engine fuel, and it barely participates in atmospheric reactions that produce <br />ozone (03). Because of its high hydrogen to carbon ratio, methane combustion <br />produces 20% - 30% less carbon dioxide (the primary greenhouse gas <br />component that contributes to global warming) than gasoline or diesel engines. <br />CNG vehicles also reduce emissions of carbon monoxide by 70% and nitrogen <br />oxides or NOx (the primary contributor to ozone) by 87%. Finally, CNG vehicles <br />emit virtually no particulate matter (PM2), which affects respiratory and <br />cardiovascular systems and contributes to atmospheric haze. As a result, <br />manufacturers have been able to certify CNG vehicles to California's Ultra Low <br />Emission Vehicle standard, the most stringent in the U.S. <br />In the last 20 years, significant advances have been made in lightweight <br />aluminum and carbon fiber high-pressure cylinders that can store natural gas at <br />high pressure. As such, compressed natural gas has become the preferred <br />method for storage and fueling of vehicles for natural gas use. Typical use of <br />natural gas for transportation fuel involves connection to a natural gas pipeline. <br />The gas is then run through a dryer to take out any remaining hydrocarbons, and <br />a compressor pressurizes the gas to the appropriate pounds per square inch <br />(psi) for dispensing. <br />CNG vehicles can increase their power and efficiency by increasing the <br />compression ratio, and thus 3600 psi vehicles are currently the most popular <br />choices on the market. Older CNG vehicles were manufactured at 2400 and <br />3000 psi. <br />With all of the above benefits of CNG, there are two detriments to CNG vehicle <br />performance. The weight of a natural gas system will always be more than that of