Evaluation of a Photoacoustic Gas Analyzer for Ethanol Vehicle Emissions Measurement

Certification of flex-fueled vehicles to US Environmental Protection Agency (EPA) and California Air Resources Board (CARB) emission standards requires a flame ionization detector (FID) analysis for hydrocarbons, plus a separate analysis for alcohols. Alcohol analysis methods, such as those found in the California Non-Methane Organic Gas (NMOG) Test Procedures and in the Code of Federal Regulations (40 Part 86), involve the bubbling of vehicle sample gas (exhaust or evaporative) through sample impingers filled with water. The water is then analyzed by gas chromatography (GC) equipped with a FID. This method requires significant manual sample handling and transport, and may take many hours for analysis to be complete. After analysis is completed, the vehicle test results are post-processed, sometimes manually, to generate the final sample results.

This report describes the direct bag analysis of ethanol with a photoacoustic gas analyzer. Analysis of gas standards and vehicle samples show that results from the photoacoustic gas analyzer correlate well with those from the standard impinger method. Linearity and sensitivity values exceed the requirements of the California NMOG Test Procedures. Real-world analyzer data, usage comments, and suggestions for emission bench integration are given.