UBC Theses and Dissertations
Development of a fast methane sensor based on wavelength modulation spectroscopy for exhaust methane emission measurement Son, Donghyun (Jeff)
Natural gas is an attractive alternative fuel with a lower price and carbon dioxide emission compared to liquid fossil fuels. Methane (CH₄) in natural gas, however, has a high global warming potential (GWP), thus the emission of unburnt CH₄ can offset the cleaner combustion of natural gas and should be carefully monitored in dual-fuel natural gas/diesel engines. To develop cleaner engines, a high-speed methane sensor in the exhaust gas stream is required to capture emissions during real-world, transient engine operation. While CH₄ measurements using Fourier-transform infrared (FTIR) spectroscopy in dual-fuel engines have been demonstrated, its speed is insufficient for cycle-resolved measurements. To this end, a fast, robust, and inexpensive CH₄ sensor based on wavelength modulation spectroscopy (WMS) was developed using a relatively inexpensive IR diode laser with a centre wavelength of 1651 nm. The WMS sensor was assessed using gas standards and validated against a flame ionization detector (FID). The 508 mm heated gas cell reliably detects CH₄ from 50 ppm to over 2% at a temporal resolution of over 200 Hz. The WMS sensor can resolve transient methane emission with a time delay and time constant of 0.55 s and 0.44 s respectively. When demonstrated on a heavy-duty dual-fuel research engine, the WMS sensor and FID agreed with a mean percentage difference of 4.2%. The field measurement capability of this portable sensor, which can continuously measure for seconds to hours, was demonstrated on dual-fuel marine engines of a coastal vessel. The GWP of dual-fuel engine exhaust heavily depends on operational profiles, and the fast WMS methane sensor will assist engineers and policy makers to characterize and reduce in-use CH₄ emissions.
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