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

Abstract

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.

The Effect of Air Throttle on Combustion Process and Emission Formation in Marine Lean-Burn Gas Engines

“…The engine speed operated around the constant value by adjusting the fuel rack position with a PID controller. The measured data and simulation results confirmed that the engine had satisfying stability around the speed setpoint [17]. The results of this section are divided into two groups: Performance output and emission formation.…”

“…12 displayed the variation of unburned hydrocarbon in these two operational modes, with and without throttle. These authors' previous work [17] revealed that the UHC compound directly correlates with the air-fuel ratio, and a higher amount of excess air ratio deteriorated the combustion quality and resulted in the flame quench. Besides, flame quench was one of the three primary UHC sources in lean-burn spark-ignition gas engines together with gas exchange and crevice volume.…”

Transient Performance of Gas-Engine-Based Power System on Ships: An Overview of Modeling, Optimization, and Applications

“…The majority of current studies focus on thermal efficiency and methane slip problems in steady states [81]. In sea conditions, time-varying loads have to be considered due to the fact that a decrease in the energy efficiency has been obtained at the part loads of gas engines [82], and the increase in emissions has been observed when gas engines work at wave load conditions [83,84]. To further reduce the emissions from gas engines, especially the methane slip, several methods have been proposed and examined [85][86][87].…”