1993-03-01

Study on Parameters Affecting NMOG Measurements and a Method to Improve its Accuracy 930387

Nissan has developed a non-methane organic gas (NMOG) emission measuring method based on California Air Resources Board (CARB) procedures.1) In addition, a system to analyze the chemical species present in the exhaust gases at Low Emission Vehicles (LEV) and Ultra Low Emission Vehicles (ULEV) levels has been created.
It was found that when using an electrically heated catalyst (EHC) to achieve the low emissions for LEV and ULEV levels, the interference between exhaust HC species and the contamination of the analyzing system are a serious problem for the measurement of speciated emissions.
The methyl tertiary butyl ether (MTBE) contained in reformulated gasoline can interfere with HC speciation in the Chromatogram, requiring that the automatically speciated results be checked by a trained operator.
The low exhaust HC emissions of bags 2 and 3 in the Federal Test Procedure (FTP) are nearly equal to that of the background air utilized in the constant volume sampler (CVS) dilution. For this reason, the HC level in the background air affects the result of speciated emissions and the Specific Reactivity (SR, refer to Appendix A). Measurements using purified dilution air were effective to the speciated emissions stability. In addition, the contamination of the exhaust sampling bags must be minimized to maintain the analysis accuracy. The accuracy of speciation measurements was improved by these procedure modifications.

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