While developing one of the first commercialized Super Ultra Low Emission Vehicles, one vehicle manufacturer also improved the method for measuring low level hydrocarbons [1]. This was accomplished by enhancing the Constant Volume Sample System, and correcting hydrocarbon measurements from the Flame Ionization Detector hydrocarbon analyzer for the effect of oxygen quench. Based on the manufacturer's results, it appears that the variation in oxygen content of the calibration gas, span gas, zero gas, and sample gas can affect the accuracy of low level hydrocarbon measurement.
Within the last couple of years, the United States Environmental Protection Agency and the California Air Resources Board approved the Bag Mini Diluter method for emission sampling [2,3]. This method was developed by the American auto industry in cooperation with government agencies within the American Industry/Government Emissions Research Consortium. The method was primarily designed to measure the lowest vehicle emission levels [4]. Due to a constant low dilution ratio, exhaust samples contain a lower oxygen content than the hydrocarbon calibration gases, resulting in underreported hydrocarbons.
This paper describes a method for optimizing the Flame Ionization Detector hydrocarbon analyzer and correcting for oxygen quench effect. For one test vehicle, the oxygen quench effect on Non-Methane Hydrocarbon emission measurements was -8 percent for the Bag Mini Diluter system and -2 percent for the Constant Volume Sample system.