Compressed Natural Gas (CNG) is made by compressing natural gas to less than 1% of its volume at standard atmospheric pressure . It is an alternative to gasoline. Natural gas powers more than 12 million vehicles on the road but only 112,000 of these are being used in the U.S today . With gasoline price continues to rise and the booming shale gas plays in the domestic US for their promising exploration and development for the next 50 plus years, natural gas powered vehicles can be of good potential to reduce America’s reliance on imported oil.
CNG vehicles have been around for decades. They have been introduced in a wide variety of commercial applications including light-duty trucks, sedans, taxi cabs, medium-duty van (e.g. UPS delivery vans and postal vehicles) to heavy-duty vehicles like transit buses, street sweepers and school buses . Today, natural gas accounts for only 2% of U.S. demand for transportation fuel. But is there any opportunity for natural gas to make important contributions to transportation? What are the existing and future challenges?
Honda is currently the only major car maker producing new CNG vehicles for the general public . The benefits of CNG cars include cheaper fuels, cause less damage to the engine (lower maintenance cost), low emissions, and a variety of existing tax credits . The cons are the filling stations are hard to find and the compressed gas tank takes up part of the trunk space . However, the CNG vehicles are nearly 25% more expensive than conventional gasoline vehicles and 10% more expensive than the hybrid car, based on equivalent models .
Infrastructure is another concern. For people who wants to fuel up on CNG cars as easily as they do today on gasoline, the US government would have to build an entirely new network of pipelines and service stations to accommodate high-pressure fueling . And a single CNG station will cost anywhere from $300,000 to $3 million more than a regular gas station .
California has the fastest growing NGV industry. It has more than 33,000 vehicles fueled with CNG or LNG . In California, single-occupant CNG vehicles under 14,000 pounds can use High Occupancy Vehicle (HOV) lanes. In major metropolitan areas from LA to the Mexican border, there are more than 100 public fueling stations. In 2005, California has more than 200 CNG fueling stations.
2. PERFORMANCE (LOW ENERGY DENSITY)
CNG has relatively low energy density – it contains almost 70 % less energy per gallon equivalent than gasoline . This means that we have to fill tanks more often to go to the same distance. The large and heavy CNG fuel tanks (200 pounds versus 10 pounds for gasoline) take up lots of space and reduced car fuel economy too.
Can NGV play an important role in the future with all these given factors? Commercial and municipal fleets with limited driving distances definitely will benefit from CNG and we should encourage people to take public transportation. In addition, the Next Generation Natural Gas Vehicle (NGNGV) R&D Activity, the U.S. Department of Energy (DOE) funded NGV research has reached some significant progress. In Phase (I), the medium-duty engines have demonstrated NOx emissions below 0.2 g/bhp-h . So far, Phase II research activity has suggested that stoichiometric natural gas engines with three-way catalysts are one likely path to the ultra low NOx emissions . This is even a better new for NG powered public transportation systems.