Correlation of Exhaust Emission Test Facilities

Current legally specified test procedures for measuring hydrocarbon and carbon monoxide concentrations in vehicle exhaust gases contain intrinsic test variables which significantly affect test results. These variables constantly hamper efforts to correlate test data generated at one or more exhaust emission test facilities. This paper will provide a general description of some of the more prominent test variables such as vehicle repeatability, test driver repeatability, instability of calibrating gases and changing ambient test conditions. In addition to describing test variables and their effects, the paper will describe the success of various measures which were undertaken to reduce or eliminate the influence of some of the variables on test repeatability and facility correlation.