Just the Facts on Natural Gas and Propane

This is the first article of a series dedicated to "clearing the air" about alternative fuels, because while the World Wide Web is a vast source of information, it is not always accurate or up to date. The NAFTC is a non-profit, unbiased organization that develops curricula and conducts training to educate and inform people about alternative fuels and advanced technology vehicles. This first installment of "Just the Facts…" focuses on providing facts and erasing misconceptions about natural gas and propane.

High fuel prices always seem to spark interest in alternative fuels. With a national average of over $3.00 a gallon for gasoline, many of America's commuters are seeking information to reduce high costs at the pump. Some of the most frequently asked questions we receive at the NAFTC, when fuel prices increase, include "What are my options for using alternative fuels?" and "How much does it cost?" The only simple answer to these types of questions is awareness through research and investigation.

While the Internet is the most common source of information of this type, as is the case with many subjects, the World Wide Web contains some very reliable sources for alternative fuels information and others that are often more opinion-based and may in fact publish incorrect information. Fact-based sources include non-profit organizations and government Web sites. (See links provided below.)

Natural Gas and Propane Vehicles

If you wish to convert a vehicle to run on compressed natural gas (CNG) or propane (LPG), you are limited to which model, year, and engine size for which a company produces and certifies its conversion system. After you have conducted your research and know the facts about alternative fuels, you will be able to make an informed decision concerning the conversion of your vehicle to run on CNG or LPG.

The cost of a conversion varies among location, year, model, and type of system you choose to purchase. In making this decision, you also need to be aware that if you choose to convert your vehicle to CNG or LPG, you may be limited to the availability of fueling stations. You also have the choice of bi-fuel (an engine that can operate on two fuels independently by using two separate fuel storage systems) or a dedicated version which will only operate on one specific alternative fuel.

There are options other than converting to CNG or LPG. Some manufacturers are producing engines that operate on natural gas or propane only. Honda has a natural gas version of its popular Civic that is available to fleets nationwide and to the public in New York and California. The CNG Honda is the GX model that operates on compressed natural gas. Cummins Westport also offers the world's widest range of natural gas engines to replace its existing 5.9L diesel version. Cummins Westport has converted its existing compression ignition engine to a lean burn spark ignition (LBSI) to operate on CNG or propane, depending on which model is chosen. These low-emissions commercial engines are used in trucks and buses.

So what are the benefits of operating a CNG or LPG-fueled vehicle? We can look at this question in two ways. First, they help reduce emissions and dependence on foreign oil (unfortunately this alone is not enough to convince most Americans to begin using them), and secondly, the rising cost of gasoline.

When we compare the efficiency of CNG or LPG to gasoline, there are some differences people neglect to note. We compare the fuel prices at the pump, and the initial cost of conversion to make our decision whether to begin using alternative fuels, but the answer lies much deeper than the price at the pump. While there is an initial cost to convert to CNG or LPG, that money can be justified over the life of the vehicle if we concentrate on the facts.

In order to ignite the fuel in an engine it must be turned into a vapor. This rapid vaporization is known as volatility. Unfortunately, gasoline is made up of several hundred hydrocarbons consisting of a wide range of light to heavy carbon molecules. It is this process which makes gasoline an inefficient fuel. Gasoline is stored in liquid under normal pressure, pumped to the injectors, sprayed into the combustion chamber, and ignited by the spark plug. The problem lies when trying to vaporize several hundred different hydrocarbons of different weights in gasoline, Volatility is important because solids and liquids do not burn, only vapor burns. When we try to vaporize the several hundred different hydrocarbons in gasoline, they all do not turn to vapor, leaving a small amount of liquids and/or solids in the combustion chamber. This will result in unburned hydrocarbons in the exhaust emissions and lead to carbon build-up in the combustion chamber.

Shown here is a comparison of gasoline, natural gas and propane hydrocarbon molecule chains. The diagrams show the simpler molecular structure of natural gas and propane, which allows for a cleaner burn. NAFTC Image.

Compressed natural gas and propane are made up of lighter and simpler hydrocarbons. CNG and LPG are in vapor form under ambient temperature and pressures. The fuels are stored under pressure or as a liquid, but the fuels are brought to ambient temperatures and pressures prior to combustion, allowing a more complete burn compared to gasoline. A more complete burn will reduce the amount of carbon build-up and oil life is extended due to the reduced amount of HCs entering into the crankcase.

Over the life of the vehicle, using CNG or LPG can save money above and beyond the prices at the pump. If we look at the facts, low tire pressure can cause a loss of 5 percent fuel efficiency, clogged air filter create a 5-7 percent loss, lack of tune-up is a 10 percent loss, carbon build-up from gasoline causes 10-15 percent loss, and mechanical resistance of worn engine components also causes loss of fuel efficiency. Operating on clean burning alternative fuels increases engine life, reduces engine wear and carbon build-up, and allows for extended oil life—all reducing total operating costs to the owner.

If we only compare pump prices and Btu's (British Thermal Units) of gasoline to CNG or LPG it can be proven that these alternative fuels will have 5 percent reduction in fuel efficiency. The long-term use of alternative fuels will prove to reduce total costs of operating the vehicle and extend engine life.

Counting the Cost

It's more difficult to answer the question "How much does it cost?" Depending on all the options discussed above, even a range of total operating cost is difficult to pinpoint. Costs of conversions will vary due to location, year, model, and type of system you choose to purchase. Several government sites take the guesswork out of acquiring alternative fuel vehicles. The U.S. Department of Energy's (DOE's) Alternative Fuels Data Center (AFDC) has a great cost analysis of buying and fueling a Honda Civic GX including state, and tax rate (http://www.eere.energy.gov/afdc/progs/cost_anal.cgi?490). Also, the AFDC has several great resources for those interested in alternative fuel conversion in addition to the cost calculator including an alternative fuels station locator, toolkits, and industry contacts.

Hopefully this article has provided you with a better understanding of natural gas and propane and their use as alternative fuels. Alternative fuels will play an important role and are already beginning to have an impact. The more that is learned about their adoption, use, and benefits, the more likely that energy independence and clean air will be achieved in the near future.

Supplemental Links:

National Alternative Fuels Training Consortium (NAFTC) – http://www.naftc.wvu.edu
U.S. Department of Energy (DOE) – http://www.doe.gov
U.S. Environmental Protection Agency (EPA) – http://www.epa.gov
U.S. Department of Energy's Clean Cities Program – http://www.eere.energy.gov/cleancities
Alternative Fuels Data Center – http://www.eere.energy.gov/afdc/