Calibration-free wavelength modulation spectroscopy approach for practical logging measurements of methane slip from natural gas engines

Natural gas (NG) is a potential substitute for diesel in engine applications because of its potential to reduce greenhouse gas and toxicant emissions. To maximize the benefits of NG, robust diagnostic methods are required to quantify concentration of unburned methane in the exhaust stream, without requiring frequent sensor recalibration. A wavelength modulation spectroscopy sensor has been developed to measure CH 4 slip from NG engines. The sensor uses the first-harmonic-normalized, second-harmonic (2 f /1 f ) processing method to perform long-duration, logging measurements at 20 Hz on an NG-powered marine vessel. Calibration-free 2 f /1 f measurements were shown to match calibrated 2 f /1 f measurements with an average error of 2.17% over the course of a 3 h sailing.