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CO vs. RVP
CRC Project No. E-74
Leaders: M. C. Ingham
M. Valentine
Scope and Objective
The objective of this project is to generate data that will confirm the effects of gasoline vapor pressure and ambient temperature on CO exhaust emissions from the in-use vehicle fleet. It is anticipated that these data will be used to update the predictive relationships regarding vapor pressure, temperature, and CO exhaust emissions embodied in the EPA MOBILE6.2 emission factor model.
Current Status and Future Program
This project was a new start in 2004. The program consists of two tasks to be performed in sequence. Task 1 involved a statistical analysis of existing emissions certification data contained in the EPA database. The database contains Federal and California emissions certification data for the vehicle model years 1979 through 2004. Specifically, there is interest in an analysis of the subset of these vehicles for which both standard FTP and low temperature CO certification results are available. EPA began phasing in the low temperature CO certification test in model year 1994; with 100% compliance required beginning model year 1996. This task sorted through the available certification data for 1994 through 2004 model year vehicles and extracted the data for those vehicles where both standard FTP and low temperature CO certification results were provided. The low temperature CO test is run at 20°F, while the standard FTP is run between 68°F and 86°F, but manufacturers have also provided some data at 50°F. These intermediate temperature data were also of interest. Statistical analysis of the data were conducted to identify the response of vehicle CO emissions to changes in temperature and, perhaps, to changes in vapor pressure. The results of this analysis were useful in designing the experimental test program being conducted in Task 2 of this program.
A Task 2 plan was designed assuming that both vapor pressure and temperature effects need to be evaluated. The actual test program design was finalized based upon the outcome of Task 1. The original Task 2 plan called for two fuels to be prepared for testing, having nominal vapor pressures of 9.0 and 13.0 psi. Other fuel properties were targeted to be typical of regular-grade winter conventional gasolines blended with alcohol. In addition, both fuels meet the quality levels specified in ASTM D4814 and contain a detergent additive. Both fuels were blended from standard refinery gasoline blending streams, without use of special chemicals or chemical blendstocks, such that all carbon numbers of each HC type are represented in the blends.
The contractor acquired 15 vehicles for testing. The objective of the fleet selection was to balance several requirements:
- Combination of existing and advanced emission control technology.
- Representative of current and future US vehicle fleet.
- Tier 1-, NLEV- and Tier 2-certified vehicles.
- Generally split between cars and trucks.
- High volume vehicle/engine/emission control systems.
Air Improvement Resources (AIR) was selected to conduct Task 1. AIR completed their analysis, and the Final Report, “Examination of Temperature and RVP Effects on CO Emissions in EPA’s Certification Database,” was issued in April 2005, and is posted on the CRC Website. The results from Task 1 were used to guide the Task 2 program content.
For Task 2, a contracting team led by HHA, and including ATL and Sierra Research, was selected and Contract E-74b was issued in September 2006. After discussions with EPA on how this project could help meet their data needs, the project was expanded to include additional fuel formulations. The key fuel parameters that varied among the final test fuel set are vapor pressure (7, 9 and 13 psi) and ethanol content (0, 10 and 20 volume percent). The testing is complete and the data set has been reviewed by the Committee, with analysis and reporting in process. The Final Report is expected to be released in the Fall of 2008.
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