CNG - AN ALTERNATIVE FUEL

GOAL:

To understand the problems involved in the use of Compressed Natural Gas (CNG) as an optional fuel.

OBJECTIVES:

The students will learn CNG's effects as an alternative fuel with respect to:

1. vehicle fuel economy,

2. the environment, and

3. technical changes in the vehicle.

LESSON/INFORMATION:

Several factors affect the use and selection of any fuel. Some important properties are engine design, net energy per pound, net energy per gallon and the sulphur content of alternative fuel.

SELECTED PROPERTIES OF PRESENTLY AVAILABLE FUELS.

Physical State	Gasoline Liquid	Liquified Petroleum Gas	Compressed Natural Gas	Methanol Liquid	Ethanol Liquid
Net Energy Content BTU/lb	18,700 19,100	19,800	21,300a	8,600	11,500
Octane Number Range (R + M) ÷ 2	87 - 93	104b	120b	99	100
Sulfur Content (W + %)	0.02 - 0.045	Negc	Negc	None	None

a - Pure Methane

b - Octane ratings above 100 are correlated with given concentration of tetraethyl lead in 150-octane

c - Natural sulfur content very low but measurable.
Source: Steering A New Course: Transportation, Energy, and the Environment, pages 75, 76.

Measuring a fuel's relative potential energy can easily be done by defining that fuel's Btu content. A Btu is defined as the amount of heat necessary to raise one (1) pound of water, one (1) degree fahrenheit.

For a gasoline engine designed to run on CNG, significant modifications are needed. If the vehicle is dual fueled, gasoline and CNG, then weight is added to the vehicle (approximately 350 - 400 pounds) and space is sacrificed (up to 20 cu. ft. of space under the hood and in the trunk.) See Figure 1.

Figure 1. Typical trunk installation for dual-fueled CNG/gasoline.

These dual fueled vehicles are known as hybrid-demonstration vehicles to let the public know that natural gas powered vehicles perform well. Many states and cities are taking advantage of federally subsidized programs to convert portions of their fleet to vehicles designed to operate solely on CNG. These conversions (See Figures 2A and 2B) operate very well and alleviate bulk and the complexities imposed by a dual fuel system. Optimum CNG performance requires vehicle manufacturers to redesign some engine systems such as valves, fuel injectors, NO_x emissions controls, and ignition systems.

Figure 2A and Figure 2B. Typical under hood installation

CNG has a significant emission-based advantage; it produces much less (19%) CO and CO₂ emissions when compared to gasoline. The oxides of nitrogen emissions for converted vehicles are higher but this increase in emissions could be overcome by catalytic converter redesign. Other inhibitors to widespread CNG usage are increased refueling stops, refueling time with low pressure systems, and building a distribution network. The present gasoline refueling stations are supplied by the oil industry. Government regulations have kept the oil and gas businesses as separate entities. If current standards apply, then an entirely new distribution network would need to be developed. Government must also face the highway tax revenue issue. Gasoline taxes support the highway system. Natural gas is presently used in 35% of U.S. homes for heating purposes. How could highway fuel taxes be levied when an individual could feasibly refuel his vehicle at home? Home CNG refueling stations are presently being designed and tested! Presently, CNG is the cheapest, cleanest, and least environmentally impacting alternative fuel available.

Several manufacturers have begun offering CNG powered engines. Some "dual fuel" gasoline and CNG conversion kits are being offered to provide a transitional system. To change operation from gasoline to CNG or visa-versa, the operator flips a select switch to select for the fuel desired. See Figure 3.

Figure 3. Typical Fuel Selection Switch Installation.

Initial fleet test data indicates driver acceptance of vehicle driveability, cold starting, and net vehicle performance. Fuel mileage equivalent to a gallon of gasoline is significantly lower. However, net operating costs compared to gasoline are approximately equal. Other positive indications include reduced oil contamination and decreased engine wear, thus, reduced operational costs result. Operators are concerned with fuel fill rates. Early fill systems took up to twelve hours to completely charge the fuel tank. Newer, high-pressure, fast fill systems completely refill a typical tank in five minutes or less, but these systems are more expensive to install. Opponents to CNG warn of potentially costly maintenance for these high pressure, multi-staged pump systems. The U.S. Department of Energy and independently sponsored CNG "demonstration projects are incomplete. More analyses and additional testing needs to be completed prior to mass, widespread manufacturing of dedicated CNG vehicles. For the 1993 model year, General Motors and Chrysler have committed to producing at least 2,000 dedicated CNG vehicles. CNG powered public transit buses and medium duty trucks for 1993 are also scheduled.

ACTIVITY:

Use the chart on the following page for this activity.

1. Determine what type of vehicles are available in your area which use gasoline and CNG or CNG only. For dual fueled vehicles, what are the recommended operational procedures? If any, how do these differ from gasoline only operational procedures?

2. Determine if CNG conversion systems are available in your area.

3. For each vehicle or conversion system, determine each of the following:

a. extra cost for a new vehicle; cost (materials and labor) attributed to the system;

b. additional maintenance requirements or reductions or changes if any;

c. changed operational characteristics;

d. available (number) fueling stations in immediate area;

e. cost for fuel compared to pure, standard gasoline.

Note: Local natural gas utility companies, fleets, taxi cabs, or city, parish, and state motor pools are good places to begin locating this information.

CNG FUELED VEHICLES
Type of Vehicle		Type of System		Fuel System
Make, Model, etc.	Type of Fuel(s) possible	Factory Installed	Locally Installed	Cost (Materials and Labor)	Maintenance Changes	Operational Characteristics Changes	Available Fuel Station (Number Locally)	Cost of Fuel (Equivalent to one gallon of gasoline)
				$
				$
				$
				$
				$
				$

COST PER GALLON (OR EQUIVALENT)

CNG: $ _______________________________

STANDARD GASOLINE: $_______________________

INFORMATION CHECK

Directions: Indicate whether the following statements are true or false. If the statement is false, explain why it is false.

1.______ All CNG systems require a long time (more than fifteen minutes) to refill the cylinder(s) (fuel tank).

2.______ By-products of sulphur are sources of acid rain, a serious environmental consideration.

3.______ Only additives can raise gasoline's octane ratio.

4.______ Lead additives produce harmful by-products.

5._____ Benzene emissions are harmless.

TEACHERS NOTES:

Students MUST complete the guide "Alternative Fuels - What are They?" before they attempt this activity. A comparative understanding of alternative fuels is necessary before they can successfully proceed with this guide.

Recent media attention on CNG touts CNG as "the" new alternative fuel. Domestic natural gas supplies are deemed to be more adequate than oil. Potentially, vehicles powered by CNG produce less CO and HC tailpipe emissions. Current reducing NO_x catalytic converters are ineffective on CNG produced emissions. Duel fueled - gasoline/CNG - vehicles require both fuel tanks. The extra weight and trunk space lost due to utilizing two fuel tanks presents a barrier to public acceptance of CNG as a viable automotive fuel. Public perceptions hinder acceptance of CNG. Among the many public unknowns, driveability, safety, and available fuel stations rate highest. Duel fueled vehicles help relieve many public apprehensions. This guide will assist technically oriented students in discovering CNG as a viable alternative motor fuel.

ANSWERS TO INFORMATION CHECK:

1. False. CNG may be fast refilled with high pressure systems in approximately the same time as a gasoline refill.

2. True. Sulphur based tailpipe emissions create significant portions of acid rain.

3. False. Gasoline octane rating may be raised through the refining process; however, this process is costly and consumes more fuel in the process.

4. True. Airborne lead oxides are considered harmful to humans.

5. False. Benzene based tailpipe emissions are said to be carcinogenic.

REFERENCES:

New Transportation Fuels, American Petroleum Institute, Washington, D.C.-1991. Special Issue Department, Public Affairs Group, _______.

The Automobile. Earth Day, 1990, Fact Sheet, Stanford, CA. 1990.

Gordon, Deborah, Steering A New Course: Transportation, Energy, and the Environment. A Report by the Union of Concerned Scientists, Cambridge, MA 1991.

Motor - Vehicle Fuel Efficiency and Global Warming. Union of Concerned Scientists Briefing Paper: Cambridge, MA. 1991.

Duffy, James E., editor and Howard Bud Smith. Auto Fuel Systems. Goodheart Wilcox Co., South Holland, Illinois. 1987.

UPS Chooses CNG. Carol Birkland. Fleet Equipment. Vol. 19, No. 8.

Comments or questions to: TechAsmt@LA.GOV

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