HD41 - Study of Compressed Natural Gas Vehicle Pilot Projects

  • Published: 1996
  • Author: Department of Transportation
  • Enabling Authority: House Joint Resolution 481 (Regular Session, 1991)

Executive Summary:
In 1991, the Virginia General Assembly requested the Virginia Department of Transportation to study alternative motor fuels. Three pilot projects were undertaken using compressed natural gas (CNG) as a vehicle fuel. The primary objectives of the projects were to increase the familiarity and acceptance of clean fuels by the general public and local governments, and to determine any operational and cost differences between CNG powered and gasoline powered vehicles. It is believed the first objective was accomplished because of the publicity given the projects, the visibility of VDOT vehicles to the public, and the interest shown by local governments. The operational and cost differences are reported here, although they are somewhat immaterial due to the rapid changes in CNG vehicle technology.

The projects were developed as a result of the 1991 General Assembly passing HJR 481/S5JR 206. A total of 50 vehicles were selected for conversion and 50 corresponding control vehicles were selected as comparisons. Six dedicated CNG pickups were purchased in 1994 and added to the project.

Project sites were selected on the basis of the availability of the vehicles and the availability of a natural gas line nearby. Of the 50 vehicles selected, there were 20 passenger cars, 29 pickup trucks, and one van. Specifications for conversions were developed based on the latest information available from industry sources. Conversion prices ranged from approximately $2800 for cars to $4500 for some of the pickup trucks. Data was collected from VDOT's computerized Equipment Management System, weekly forms sent in by operators, fuel records, oil analysis and periodic emissions tests.

Fuel costs were compared using 120 cubic feet of natural gas as an equivalent to one gallon of gasoline, and monitored throughout the projects. Since VDOT does not pay federal or state fuel taxes, in some cases the cost of CNG exceeded the cost of gasoline.

Three converted vehicles and three control vehicles were chosen to have emission tests performed by the IM240 process. It was found that on our conversions the air/fuel adjustment was critical to emission output. Repair history was evaluated for all vehicles in the project by reviewing the work orders generated throughout the projects. In the categories of no-start and driveability, the CNG vehicles exceeded the gasoline vehicles by as much as three to one. In most cases there was substantially higher repair costs to the converted vehicles.

Periodic oil analysis was performed on each of the 50 converted vehicles as well as the 50 control vehicles. These were reviewed, concentrating on iron contamination and soot contamination. It was found the CNG vehicles had slightly more iron contamination, indicating slightly more internal wear, but much less soot contamination, indicating that CNG vehicles could require less frequent oil changes than gasoline vehicles.

Vehicle performance was tested on VDOT's chassis dynamometer and by timed acceleration tests. The CNG vehicles had less power and slower acceleration than the control vehicles.

As expected in any project of this magnitude, problems arose. Probably the most troublesome was the conversion companies' performance. Many instances of poor wiring connections, loose and leaking lines, and component failures were encountered. Throughout all this the gas companies were very helpful and assisted with correcting problems. The gas companies additionally had their own problems to deal with because of problems with the fueling stations.

CNG conversion technology has improved so much in the last few years that many of the results of these projects are not applicable to the type of conversions available today. However, at least partly as a result of these projects, there is a small but growing infrastructure of CNG stations including several commercial stations.

The experience gained from these projects will aid VDOT in complying with upcoming federal clean fuel fleet regulations. Both the Clean Air Act and Energy Policy Act will require large percentages of the VDOT fleet to be alternatively fueled in the near future. VDOT is working with other agencies to develop a plan so that the Commonwealth's fleet purchases will meet the criteria of both laws.