Tier 3 Certification Fuel Impacts Test Program
Test Program Overview
The U.S. Environmental Protection Agency has the responsibility to determine the test procedures to be used when performing emission and fuel economy testing for vehicles and engines. Part of this responsibility involves defining the properties of the test fuels that are required for the testing performed by manufacturers and laboratories, and also providing the proper analytical equations to calculate both emission and fuel economy for the test fuels. When test fuel properties change, as they have recently for the Tier 3 vehicle emissions program, EPA must make the proper test procedure adjustments to maintain the intended level of stringency for existing or new emission and fuel economy (FE) standards. The test procedure adjustments include changes to the method of calculating the emission and FE results that are subject to applicable standards.
To determine the appropriate test procedure adjustments from the changes to the test fuel properties included in the Tier 3 program, the agency performed a study on eleven vehicles operating over the two required test cycles using the two test fuels, the Tier 2 and the new Tier 3 test fuel. The overall results across the test fleet showed a reduction in CO2 of 1.78% for the FTP and 1.02% for the HFET tests for Tier 3 compared to Tier 2 test fuel. For fuel economy the overall reduction was 2.29% for the FTP and 2.98% for the HFET tests for Tier 3 compared to Tier 2 test fuel. Throughout, the high levels of statistical significance observed, both for CO2 and fuel economy, suggest that the measured differences in these parameters are actual and in reasonable agreement with the difference projected during the planning of the study.
Tier 3 Certification Fuel Impacts Test Program (pdf) (1.4 MB, January 2018, EPA-420-R-18-004, updated with editorial changes January 2018)