Modal Measurements of Some Important NMOG Species by FT-IR Spectroscopy

The EPA and the State of California are phasing in tighter emissions requirements for hydrocarbons. Designing emissions control systems to meet these standards requires detailed information of the composition of the exhaust stream. Of particular interest is the ability to determine non-methane organic gases (NMOG) to meet reactivity index (RI) specifications.

Fourier transform infrared (FT-IR) spectroscopy is a technique widely used to measure organic compounds. Many NMOG compounds have unique infrared signatures that can be speciated by FT-IR. Because FT-IR can analyze samples in real time, the effects of driving cycle events such as the cold start and acceleration modes may be studied.

This paper gives a brief overview of the new regulations being phased in for hydrocarbons, as well as the techniques currently used for these measurements. FT-IR instrumentation and sampling techniques for exhaust gas analysis are explained. A discussion of the different gases which may be analyzed by FT-IR is presented, with the gases divided into their functional groups. Finally, the capabilities and limitations of FT-IR will be summarized.