Measurement of Automobile Exhaust N_2O in Continuous Dilute and in Sample Storage Bag by a Mid-IR Laser Spectroscopic Motor Exhaust Gas Analyzer

摘要

Nitrous oxide (N_2O) emission reduction has gained large prominence recently due to its contribution to the climate change as a greenhouse gas. The United States Environment Protection Agency (US-EPA) together with the United States Department of Transport (DOT) has already regulated the N_2O emissions from light-duty vehicles (LDV) to 0.010 g/ mile. For LDV, N_2O measurement should be done from sample storage bags over the light-duty FTP drive cycles. N_2O emission standard of 0.10 g/bhp-hr for heavy-duty engines (HDE) is also finalized. The final N_2O standard becomes effective in 2014 model year for diesel engines. Usually raw or diluted exhaust is measured for HDE emission testing. Therefore, an analyzer capable of measuring N_2O from bag and from diluted sample continuously is required to support both LDV and HDE regulations. Nondispersive infrared (NDIR) analyzer, Fourier transform infrared (FTIR) analyzer, Laser infrared analyzer, Photoacoustic analyzer (PAS), and Gas chromatograph (GC) analyzer have been recommended for N_2O measurement. In the previous study, the authors had developed an instrument based on mid-infrared laser spectroscopy for measuring ultra-low level N_2O in automobile exhaust gas sampled in a sample storage bag. In this study, comparative measurement of automobile exhaust N_2O in continuous dilute and in sample storage bag has been attempted. A modern vehicle meeting 2008 Japanese emission standards has been evaluated. Tests are conducted on a chassis dynamometer cell under different test cycles. In addition, verification of the interference of co- existing gases commonly observed in automobile exhaust gas has also been performed. In this study, it is found that the laser based exhaust gas analyzer has sufficient detection capability for bag measurement and fast response for continuous dilute measurement. There is no interference caused by CO, CO_2, and H_2O usually observed in the automobile exhaust gas in significantly amount and have absorption in the same wavelength region as of N_2O used in this analyzer. The test vehicle emits very low N_2O and most of them are emitted within first 100 seconds of the FTP driving cycle when tested under cold start condition.