Clean Burning Natural Gas Vehicles

Mention alternative fuels, and most Americans think ethanol, biodiesel, or hydrogen. Forgotten is one of the most promising alternative fuels: natural gas. Clean burning and available from mostly domestic sources, natural gas is already used by most Americans every day for heating and cooking. The technology challenges facing its widespread use in natural gas vehicles, or NGVs, are nil. So why does natural gas get so little attention?

Natural gas, mainly methane (CH4), is obtained mostly from natural gas wells or as a byproduct of crude oil production. It can also be a renewable fuel when biogas - also called digester gas, swamp gas, or marsh gas - is produced by the fermentation of organic matter including manure, wastewater sludge, municipal solid waste, or any other biodegradable feedstock.

According to the U.S. Energy Information Administration (EIA), 84 percent of the natural gas used in the U.S. comes from domestic sources. By comparison, less than 40 percent of the crude oil we use is produced domestically. Imported natural gas comes mostly via pipeline from Canada and Mexico. A small but growing amount of natural gas is super cooled into liquefied natural gas (LNG) and shipped in on huge tankers, then it's warmed up and turned into a gas upon arrival in the U.S. What LNG is imported now primarily comes from places like Bolivia and the Republic of Trinidad and Tobago. The bottom line is that natural gas comes from much more reliable locations compared to crude oil.

One of the most important advantages of natural gas is that it's extremely clean burning when used in internal combustion engines. According to the U.S. Department of Energy, exhaust emissions from NGVs are much lower than those of gasoline-powered vehicles. For instance, carbon monoxide (CO) and nitrogen oxides (NOx) are reduced by more than 90 and 60 percent, respectively, and carbon dioxide (CO2), a greenhouse gas, is reduced by 30 to 40 percent. When used in medium- and heavy-duty engines, CO and particulate matter (PM) reductions of over 90 percent, and NOx reductions of over 50 percent, have been demonstrated compared to diesel engines.

While there are only about 130,000 NGVs in the U.S., there are nearly 4.5 million of these alternative fuel vehicles worldwide, mainly in Argentina, Brazil, Pakistan, Italy, and India. This shows that the fundamental technology needed for NGVs is not highly sophisticated. It also shows that drivers in these countries are willing to accept some of the well-known shortcomings of this lower cost alternative fuel, most notably a higher vehicle purchase price, a very slight decrease in horsepower in most cases, and the lack of an extensive public refueling infrastructure. Acceptance by American drivers is sure to grow if fuel prices continue to climb or conventional gasoline or diesel fuels become scarce.

Because it is a gas, this fuel must be stored aboard a vehicle either as compressed natural gas (CNG) or as liquefied natural gas (LNG). Typically, CNG is compressed to 3,000-3,600 pounds-per-square-inch (psi). LNG is stored at a much lower 20-150 psi, but must be kept at a cryogenic temperature of -260? F. Because heavily insulated tanks must be used for storing LNG, this form of natural gas is typically limited to heavy-duty applications like garbage trucks, delivery trucks, and urban buses.

NATURAL GAS VEHICLES
There are two basic types of natural gas vehicles: dedicated NGVs operate only on natural gas, while bi-fuel NGVs can operate on either natural gas and traditional gasoline or diesel fuel. In some cases this is driver selectable with the flip of a switch, while others offer either manual switching or automatic switchover to conventional fuel operation when the on-board natural gas fuel supply is exhausted.

In general, dedicated NGVs demonstrate better performance and have lower emissions than bi-fuel vehicles because their engines can be optimized to run on natural gas alone. In addition, dedicated vehicles do not carry two types of fuel, which means they don't sacrifice cargo capacity or carry around additional weight. The plus for bi-fuel vehicles, of course, is that they reduce the possibility of being stranded if natural gas fueling isn't readily available since they can also run on conventional fuel.

Today, consumers in this country have few light-duty NGVs to choose from at the showroom. That short list includes the Honda Civic GX sedan and the Chevrolet Silverado and GMC Sierra pickups. Ford no longer offers the natural gas models it once did and General Motors has trimmed its NGV line to these two full-size pickup models, reportedly due to overall poor natural gas vehicle sales. While this might be partly due to marketing that was aimed primarily at fleet sales, there are other factors that limited private buyer sales. Other choices are available from small volume manufacturers like BAF Technologies with its 2006 Ford natural gas powered Crown Victoria, Grand Marquis, and Town Car, and Baytech with its dedicated natural gas GM vans, pickups, and SUVs.

As with virtually all alternatives to conventional gasoline and diesel vehicles - with the notable exception of hybrids - the inability to refuel anywhere, anytime is a major drawback to NGVs. There are over 1,300 CNG and LNG refueling stations in the U.S., but a large number of these are for fleet operators. Even if all of them were available to consumers, challenges would remain since this number pales in comparison to the 175,000 gasoline stations scattered conveniently in every town and city across the nation. Natural gas is great for centrally-fueled fleets like buses, delivery trucks, refuse trucks, and taxis since there is no need for a widespread refueling infrastructure. In fact, about 20 percent of all new transit buses in the U.S. are now powered by this gaseous alternative fuel. Natural gas has also provided a principal strategy for fleets in urban non-compliance areas that must meet emissions requirements.

Range between fill-ups is limited because of the amount of CNG or LNG that can be carried on-board. For example, the natural gas Honda Civic GX has a range of 200-250 miles on the 7.2 gasoline equivalent gallons of CNG it carries. A conventional Honda Civic can travel up to 400 miles on its 13.2 gallons of fuel and the hybrid version can go over 600 miles on the same quantity of fuel. The shortfall is notable, but not unreasonable considering the many advantages brought to bear by the popular GX.

The refueling challenge can be partially alleviated by the use of home refueling appliances like Phill, manufactured by Honda's strategic partner FuelMaker. While providing the convenience of on-site home or small business refueling and eliminating the need to regularly visit fueling stations, Phill does require electric vehicle-like times to refuel the Honda Civic GX - about four hours for 100 miles worth of fill-up and up to 12 hours for a full tank of CNG. That said, this isn't an issue for those who start the fueling process when their CNG vehicle is parked for the night, since every morning brings a full fuel tank and a fresh 200-250 miles worth of driving range.

Today, NGVs cost more than their conventional counterparts. In the case of the Honda Civic GX, that's about an additional $4,500 in the cost equation, but that's not the true bottom line since this cost can be reduced by substantial federal and state incentives, plus tax deductions. Then there are the intangible benefits like the ability to drive vehicles like the Civic GX solo in high occupancy vehicle lanes in some states. While choices are very limited when it comes to new NGVs, virtually any gasoline or diesel engine can be converted to natural gas by a number of aftermarket companies. Conversions can cost from $2,000 to $4,000, but that cost can be eventually recouped by the lower cost of natural gas.

And how much would that cost be? Of course, this depends on many factors including location and who's marketing the product. CNG is almost always substantially less than gasoline or diesel at the pump. Vehicles filled at home with a Phill appliance, using natural gas priced at favorable home rates, can operate at the now-unbelievable cost of about $1.25 to $1.50 per gallon, on a gallon-of-gasoline-equivalency (GGE) basis. On the commercial front, fleet operators not only achieve emissions reductions by operating their light-, medium-, and heavy-duty vehicles on natural gas, but also realize significant operational savings due to lower fuel prices. Those prices are sometimes as low as $1.50 to $2.00 GGE if a fleet works with a fuel supplier like Clean Energy on a contract basis.

Several other technologies exist that could make NGVs more attractive to certain buyers, such as flexible-fuel vehicles that could operate on multiple fuels. For instance, Brazilians already can select vehicles that run on any combination of alcohol, gasoline, and CNG. Such capability could demand a premium price that would be paid by those who want the ability to buy the lowest priced fuel available and as a hedge against a shortage of any single fuel type. Another technology is hybrid electric vehicles where the internal combustion engine operates on natural gas. Besides being a very environmentally friendly vehicle using domestically produced natural gas, or even renewable biogas, a CNG-electric hybrid could provide the performance and range of a conventional gasoline or diesel vehicle.

NATURAL GAS SUPPLY
Since transportation has to compete with the use of natural gas for utility, industrial, commercial, and residential purposes, one of the concerns surrounding the widespread use of NGVs is natural gas availability.

Today, only 0.1 percent of the natural gas in the U.S. is used to fuel 130,000 NGVs. Extrapolating this to only one percent, a tenfold increase, means fueling well over a million NGVs. According to natural gas utility sources, even a substantial influx of millions of NGVs in the short term would not impact natural gas usage by more than 5 percent, which could be readily handled within the current infrastructure.

The potential for shifting electric power generation from the growing trend toward natural gas to other energy sources such as nuclear, wind, solar, and biomass could result in vast amounts of additional natural gas available for transportation, which some consider this fuel's ideal use.

ROAD TO RENEWABLES
Biogas offers intriguing possibilities for both industry and vehicles. Presently, GM is the largest direct corporate user of LFG (landfill gas) as a replacement for natural gas in the U.S. The automaker has reduced its natural gas consumption at seven GM operations by an astonishing 25 percent through the use of LFG. This is equivalent to the amount of energy needed to heat over 25,000 homes. Sweden is a world leader when it comes to using biogas transportation fuel produced by the anaerobic digestion of organic waste materials, with nearly 800 biogas fueled buses and more than 4,500 cars on the road that run on a mixture of gasoline and either biogas or natural gas.

Natural gas could be the catalyst to get the hydrogen economy rolling. How? Vehicles fueled with a blend of CNG and hydrogen represent the initial step toward future hydrogen-based transportation. HCNG, a blend of 10 to 50 percent hydrogen with the balance CNG, is touted as a way to build early demand for a hydrogen infrastructure long before hydrogen fuel cells are ready for prime time. As an added benefit, CNG engines running on HCNG have demonstrated significantly reduced emissions.

All this leads to an interesting conclusion: While attention is being focused elsewhere, one of the oldest and most potentially viable transportation fuels may well be moving from its marathon stride to a sprint toward its end goal. That goal is no less than fueling millions of cars and trucks on a clean-burning, domestically abundant, and readily usable fuel that's well-suited for consumers, private and government fleets, and large commercial operations nationwide.