Evaluation of a proportional sampler for automotive exhaust emissions

A test program was conducted to evaluate a proportional sampler for use in automotive exhaust gas emissions research. Automobile emissions test results obtained using the proportional sampler were compared with results obtained using the conventional constant volume sampler. Measurements obtained using the proportional sampler for hydrocarbons, carbon monoxide, nitrogen oxides, and carbon dioxide are within 19, 46, 20, and 14 percent, respectively, of measurements obtained using the constant volume sampler. Such differences render the proportional sampler unacceptable as a quantitative research tool. Inability of the exhaust gas flow meter to accurately measure pulsating exhaust flow is cited as the principal cause of error in the proportional sampler.