The Advanced Vehicle Testing Activity (AVTA) managed a series of light-duty vehicle chassis dynamometer emissions tests on alternative fuel vehicles (AFVs). Several emissions projects or projects with emissions components have been conducted, of which the most extensive effort was the AFV emissions test program initiated in 1994. Its purpose was to determine relative emissions from commercially available AFVs compared with otherwise identical gasoline vehicles taken from actual service. Test vehicles were scheduled for emissions testing once a year. The test matrix of vehicles, locations, and mileage levels was designed to optimize reliability of the data and to control variability in the emissions results.
In addition to testing the vehicles for regulated exhaust and evaporative emissions, detailed speciation of the hydrocarbon (HC) emissions was conducted on a subset of the test vehicles. Speciation of the HC emissions allows for an evaluation of the relative level of air toxic emissions and the reactivity or ozone forming potential of the HCs. In addition, a small number of vehicles were also tested using new or proposed chassis dynamometer driving cycles.
Extensive testing of in-use emissions of light-duty AFVs fueled by natural gas, ethanol, and methanol was conducted. This project focused on evaluating current technology AFVs in production and available from the original equipment manufacturers. The AFV emissions results were compared to emissions from standard gasoline models tested on a baseline gasoline fuel. The baseline gasoline used was California Phase 2 reformulated gasoline (RFG). This fuel was chosen because it represents a "best-case" scenario for gasoline emissions and it was believed that in order to compete, alternative fuels must be compared to the best gasoline available. RFG has lower sulfur, olefin, and aromatic content than standard unleaded gasoline. The alcohol blends (M85 and E85) were prepared with 85% alcohol (methanol or ethanol) and 15% RFG. The CNG fuel was designed to represent a national industry average fuel composition.
Emissions testing was performed on different vehicle models. For every AFV model tested, a similar number of vehicles of the corresponding standard gasoline model (controls) were also tested. A relatively large number of vehicles were selected for testing to account for the high variability observed in emissions from vehicles pulled directly from fleet service.
All the vehicles were original equipment manufacturer vehicles. The test vehicles included four passenger car models, one full-size passenger van, and one mini-van. Both alcohol- and CNG-fueled AFVs were tested. The alcohol fuels were M85 (a blend of 85% methanol and 15% gasoline) and E85 (a blend of 85% ethanol and 15% gasoline). The M85 and E85 vehicles were flexible-fuel vehicles (FFVs), capable of operating on unleaded gasoline or any blend of the alcohol and gasoline up to 85% alcohol blended with 15% gasoline. All of the CNG models tested were dedicated CNG vehicles (designed to operate on CNG only).
|Dodge Intrepid||1995||M85 FFV||24||89|
|Dodge Spirit||1993||M85 FFV||77||373|
|Ford Taurus||1994/95||E85 FFV||24||88|
|Chevrolet Lumina||1992/93||E85 FFV||25||144|
|Compressed Natural Gas|
|Dodge B250||1992/94||Dedicated CNG||54||144|
|Dodge Caravan||1994||Dedicated CNG||13||16|
|aMore tests than vehicles are reported because many vehicles were tested more than once over the course of the program (at increased mileage levels).|
Testing followed the U.S. Environmental Protection Agency's (EPA's) emissions certification test procedure known as FTP-75. The FTP-75 includes measurement of exhaust emissions on a chassis dynamometer and two one-hour evaporative emissions tests. Details of the test procedures are described in the Code of Federal Regulations (CFR 40 Part 86). The vehicles were scheduled for testing at certain targeted mileage intervals or once per year. On arrival at the test laboratory, each vehicle was inspected for any problems. Once approved for testing, the vehicles were subjected to an extensive fuel changeover procedure to switch over to the test fuel (see figure 1). Alcohol fuel vehicles were tested on both alcohol fuel (M85 or E85) and RFG. The corresponding control vehicles were tested on RFG. All CNG vehicles were tested on CNG fuel only, and their corresponding gasoline controls were tested on RFG.
The emissions samples collected during the FTP were analyzed for hydrocarbons, methane, oxides of nitrogen, carbon monoxide, and carbon dioxide. Alcohols (ethanol and methanol) in the emissions were collected using primary and secondary impingers. Gas chromatography was used to analyze the alcohols. Aldehydes were collected on specialized cartridges or impingers and analyzed using high-performance liquid chromatography.
The emissions from a subset of test vehicles were subjected to full hydrocarbon speciation. The following table lists the numbers and types of vehicles for which hydrocarbon emissions were speciated. Speciation is the quantification of individual HC components using gas chromatography. Up to 288 HC constituents in the emissions samples were identified. This data is used to evaluate the level of air toxics and ozone- forming potential of the HC emissions.
Other Emissions Projects
Some of the following documents are available as Adobe Acrobat PDFs. Download Adobe Reader.
- Light-Duty Alternative Fuel Vehicles: Federal Test Procedure Emission Results, September 1999
- Testing of CNG and LPG Conversion Vehicles, April 1996 (PDF 262 KB)
- Emissions Certification Procedures for Aftermarket Conversions
- High-Mileage Fleet Studies
- Off-Cycle Emissions Results, June 1998 (PDF 793 KB)