{"data":{"id":"us/40-cfr-appendix-ix-to-part-86","jurisdiction":"us","citation":"40 CFR Appendix IX to Part 86","heading":"Appendix IX to Part 86—Experimentally Determining the R-Factor for Bench Aging Durability Procedures","body":"The R-Factor is the catalyst thermal reactivity coefficient used in the bench aging time (BAT) equation [Ref. § 86.1826-08(d)(3)]. Manufacturers may determine the value of R experimentally using the following procedures.\n1. Using the applicable bench cycle and aging bench hardware, age several catalysts (minimum of 3 of the same catalyst design) at different control temperatures between the normal operating temperature and the damage limit temperature. Measure emissions (or catalyst inefficiency (1-catalyst efficiency)) for each constituent. Assure that the final testing yields data between one- and two-times the standard.\n2. Estimate the value of R and calculate the effective reference temperature (Tr) for the bench aging cycle for each control temperature according to the procedure described in § 86.1826-08(d)(4).\n3. Plot emissions (or catalyst inefficiency) versus aging time for each catalyst. Calculate the least-squared best-fit line through the data. For the data set to be useful for this purpose the data should have an approximately common intercept between 0 and 4000 miles. See the following graph for an example.\n4. Calculate the slope of the best-fit line for each aging temperature.\n5. Plot the natural log (ln) of the slope of each best-fit line (determined in step 4) along the vertical axis, versus the inverse of aging temperature (1/(aging temperature, deg K)) along the horizontal axis, Calculate the least-squared best-fit lines through the data. The slope of the line is the R-factor. See the following graph for an example.\n6. Compare the R-factor to the initial value that was used in Step 2. If the calculated R-factor differs from the initial value by more than 5%, choose a new R-factor that is between the initial and calculated values, then repeat Steps 2-6 to derive a new R-factor. Repeat this process until the calculated R-factor is within 5% of the initially assumed R-factor.\n7. Compare the R-factor determined separately for each constituent. Use the lowest R-factor (worst case) for the BAT equation.","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER C—AIR PROGRAMS","PART 86—CONTROL OF EMISSIONS FROM NEW AND IN-USE HIGHWAY VEHICLES AND ENGINES"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"6597073652ff6d5df91f815e04076f6c85b1011901138d0a364dcc843c9cb9db","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-appendix-viii-to-part-86","next":"us/40-cfr-appendix-x-to-part-86"},"notice":"GroundRules: Original legal text. Not legal advice."}