Unburned hydrocarbon formation in a natural gas engine under sea wave load conditions

Although natural gas is documented as a low-emission fuel compared to the other traditional fossil fuels in internal combustion engines, recent research indicates large amounts of methane emission released by lean burn gas engines and highlights the importance of this emission on global warming. This paper aims at illustrating the main sources of unburned fuel in internal combustion engines with an emphasis on spark ignited natural gas engines. In addition, two unburned hydrocarbon modeling patterns, empirical and thermodynamic, are proposed. Moreover, a verified engine model including all components with an implemented dynamic load based on harmonic sea waves has been set up and coupled to the unburned hydrocarbon formation models. Results show that load variation may contribute to further methane slip and this increment rises sharply when the load amplitude enlarges. The maximum amount of methane slip occurs at reduced loads when the time lag of the control system of the turbocharger causes additional fresh air to flow towards the combustion chamber and brings the flame into the quenching area. As well, inspecting unburned hydrocarbon emission in diverse air–fuel ratios but with the same wave frequency and amplitude uncovers the sensitivity of lean burn gas engines to the dynamic load.