Characterization and Reduction of In-Use CH₄ Emissions from a Dual Fuel Marine Engine Using Wavelength Modulation...

In-use exhaust stream CH₄ emissions from two dual fuel marine engines were characterized and strategies for CH₄ reduction were identified and evaluated. For this, a low-cost, portable, wavelength modulation spectroscopy (WMS) system was developed. The performance of the developed WMS sensor was assessed using gas standards and demonstrated on a heavy-duty, diesel pilot ignited, direct-injection natural gas research engine through comparison to a flame ionization detector. The WMS sensor was subsequently used to measure the exhaust-stream CH₄ concentration from two diesel pilot-ignited, port-injected natural gas engines on a coastal vessel while under normal operation. Using cylinder deactivation to reduce the excess air ratio, λ, and vessel operation changes to minimize operation at lower loads, the total CH₄ emission were reduced by up to 33%. The measured, load specific CH₄ emissions were subsequently used to identify an improved vessel operation strategy, with an estimated 56-60% reduction in CH₄ emissions. These results demonstrate the importance of considering the real-world engine operation profile for accurate estimates of the global warming potential, as well as the utility of a WMS sensor for characterizing and mitigating in-use CH₄ emissions.