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Good old gasoline and diesel fuels have been the staple of transportation energy since the inception of the automobile. But some estimates predict that at current consumption rates, oil will become a scarcity before the next century. What do we look to as the next thing after oil?
Besides reverting back to the "stone age" before cars became a lifestyle, many are looking at natural gas vehicles (NGVs) as the next logical step.
(<-- Image Credit: The Honda Portal)
Some Background on NGVs
NGVs store and use natural gas fuels as either compressed natural gas (CNG) or liquefied natural gas (LNG). CNG is gas stored at high pressure, while LNG is natural gas fuel in an uncompressed liquid form. LNG has over twice the energy density of CNG, making it more practical for shipment or transport of the fuel, and sometimes for use in larger vehicles (trucks and some buses) that require more energy. But in most applications, CNG makes more sense because it costs less to store.
Currently, CNG systems are used most readily in buses and other mass transportation systems that can more easily take advantage of this technology. The United States ranks 14th on the list of countries which own any notable number of CNG vehicles. Pakistan, Iran, Argentina, Brazil, and India all have over a million of these vehicles in use today.
Honda Civic GX - (Image Credit: Japanesesportcars.com -->)
What NGVs Can Brag About
In addition to displacing petroleum fuels, natural gas vehicles look very attractive for a number of reasons:
- Cleaner emissions - In comparison to gasoline in light-duty vehicles, CNG combustion emits ~80% less particulate matter, 20-40% less carbon monoxide, ~10% less VOCs, and an overall 20% decrease in greenhouse gases (source).
- Less expensive fuel (for now) - Costs for natural gas on a per unit energy basis are presently well below those of oil. In the U.S., this is largely due to the domestic abundance of natural gas: a majority (around 87% by one source) of U.S. natural gas is domestically produced.
- Proven technology - There are roughly 13.2 million NGVs in use today, worldwide. While only 112,000 of these (<1%) are in the U.S., the technology exists and can easily be implemented and developed if the conditions allow.
- Convenient construction - The design of NGVs is much closer to that of gasoline powered cars than many other alternative-fuel vehicles, since it runs on an internal combustion engine. Processes exist to convert gasoline-only cars to bi-fuel cars which can run on gasoline or natural gas. If it comes to choosing an alternative, the transition to NGVs from gasoline vehicles may be more favorable for car companies than fuel cell or electric vehicles.
- Safety - Because natural gas is lighter than air, it will dissipate into the air in the event of an accident or leak rather than spilling into a flammable pool on the ground. It has a higher auto-ignition temperature than gasoline (~842-1004°F vs. ~475-536°F) and narrower range of flammability. In addition, tanks for natural gas vehicles are said to be sturdier than gasoline tanks. LNG transportation is a separate issue that has some greater safety concerns.
- Refueling perks - Home refueling appliances for NGVs make it possible to tap into domestic natural gas and electric lines to slowly refuel overnight, allowing some consumers the ability to be less dependent on refueling stations.
The Flipside
While NGVs may seem like the natural choice for the future, there are some important limitations to consider:
- Less for more - While more reasonable than current electric cars, natural gas vehicles fall noticeably short of the range of comparable gas vehicles. This is due to the heavy CNG tanks and storage constraints for small cars. The old and new Honda Civic Natural Gas cars (the GX and Sedan respectively) have advertised fuel ranges between 170-250, as compared to their gasoline counterparts which are closer to 400 miles on a fuel tank. The extra $5K or more also buys you less power and less trunk space.
- Infrastructure - Like all alternative fuels, natural gas vehicles require a huge amount of infrastructure development to become commercially viable. In addition to many refueling stations, more piping networks and LNG trucking would be needed for adequate distribution of the fuel.
- Fossil fuel - Natural gas is still a fossil fuel, which means that there still is only a limited supply. Some estimates say that if the U.S. fueled all its transportation by natural gas, domestic reserves would last somewhere between 20-40 years (source). Environmental controversies surrounding its extraction (hydraulic fracturing) would also likely blow up even more if natural gas became a substantial transportation fuel in the U.S.
One Part of the Solution
While natural gas seems like it could be a great resource as an alternative transportation fuel, it cannot be the only answer. Certainly natural gas could be a great stepping stone [bridge fuel] in the transition to more sustainable fuels, but a complete overhaul to natural gas doesn't seem sensible considering the resource, like oil, is transitory. NVGs will also require a cooperative investment in their technology and supporting infrastructure to become economically viable for the average consumer.
What are your thoughts on NGVs? How much of a role do you think CNG will play in the transportation sector in years to come?
DOE - Natural Gas Emissions
The Oil Drum - How Much Natural Gas Do We Have to Replace Gasoline?
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