Test Variability of Emission and Fuel Economy Measurements Using The 1975 Federal Test Procedure

Several sets of repetitive test data using the 1975 Federal Test Procedure ('75 FTP) have been analyzed to establish the variability of each component measured during each phase of the test.

The variability characteristics of four different emission control systems have been discussed and compared. The overall variabilities of the '75 FTP composite values have been assessed at ±6% for hydrocarbons and CO, ±3% for NO_x, and ±1% for CO₂.

The extremely repeatable behavior of the CO₂ emissions is utilized to calculate the fuel economy during the test. This calculation is discussed and some fuel economy results from repetitive tests are presented.