Nitrous oxide (N₂O) 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 N₂O emissions from
light-duty vehicles (LDV) to 0.010 g/mile. For LDV, N₂O measurement
should be done from sample storage bags over the light-duty FTP
drive cycles. N₂O emission standard of 0.10 g/bhp-hr for heavy-duty
engines (HDE) is also finalized. The final N₂O 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 N₂O 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 N₂O measurement. In the previous study, the authors
had developed an instrument based on mid-infrared laser
spectroscopy for measuring ultra-low level N₂O in automobile
exhaust gas sampled in a sample storage bag. In this study,
comparative measurement of automobile exhaust N₂O 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, CO₂, and H₂O usually observed in the
automobile exhaust gas in significantly amount and have absorption
in the same wavelength region as of N₂O used in this analyzer. The
test vehicle emits very low N₂O and most of them are emitted within
first 100 seconds of the FTP driving cycle when tested under cold
start condition.