Emissions Testing

Photo of Dynamometer Testing on Light-Duty VehicleThe 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.

Fuels Used

Photo of Man Refueling TruckExtensive 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.

Vehicles Tested

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).

FTP Emissions Tests Completed: Methanol
Model Model
Number of
Number of
Dodge Intrepid 1995 M85 FFV 24 89
Standard 25 47
Dodge Spirit 1993 M85 FFV 77 373
Standard 72 145
Ford Taurus 1994/95 E85 FFV 24 88
1995 Standard 24 45
Chevrolet Lumina 1992/93 E85 FFV 25 144
1993 Standard 16 45
Compressed Natural Gas
Dodge B250 1992/94 Dedicated CNG 54 144
Standard 53 138
Dodge Caravan 1994 Dedicated CNG 13 16
Standard 6 6
TOTAL 413 1280
aMore tests than vehicles are reported because many vehicles were tested more than once over the course of the program (at increased mileage levels).

Test Procedures

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.

Emission Test Procedure
Figure 1

Photo of Researcher in the LabThe 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.

Number and Type of Vehicles with
Hydrocarbon Speciation
Model Fuel Type Number of
Number of
Dodge Intrepid M85 FFV 6 16
RFG Standard 4 7
Dodge Spirit M85 FFV 10 28
RFG Standard 9 14
Ford Taurus E85 FFV 6 16
RFG Standard 5 8
Dodge B250 CNG Dedicated 8 17
RFG Standard 8 16
TOTAL 56 122

Other Emissions Projects

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