Code of Federal Regulations Title 40. Protection of Environment 40 CFR Pt. 86, App. IX—Experimentally Determining the R–Factor for Bench Aging Durability Procedures

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.

1. 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.

2. Estimate the value of R and calculate the effective reference temperature (T_r ) for the bench aging cycle for each control temperature according to the procedure described in § 86.1826–08(d)(4).

3. 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.

4. Calculate the slope of the best-fit line for each aging temperature.

5. 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.

6. 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.

7. Compare the R–factor determined separately for each constituent. Use the lowest R–factor (worst case) for the BAT equation.