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.
Highlights
The importance of toxic effects and global warming potential of emission compounds from industrial activities in our daily life have been investigated for decades, and environmental legislation is going to be more strict for these applications
Considering the essence of utilizing natural gas in a very lean burn mixtures, these sources still will produce a substantial volume of Unburned hydrocarbons (UHC) in the lean-burn natural gas engines
The model estimates the contribution to the total unburned hydrocarbon emissions from three sources: crevices, wall quenching, and short-circuiting due to valve overlap
Summary
The importance of toxic effects and global warming potential of emission compounds from industrial activities in our daily life have been investigated for decades, and environmental legislation is going to be more strict for these applications International standards such as the Euro norms and the IMO regulations [1, 2] have imposed more strict levels for emission compounds, especially from engines; for instance, Tier III [3] only allows almost one-fifth of NOX emissions compared to Tier I for marine Diesel engines. Rosli Semin [7] reported up to 85% NOx reduction and 30% CO2 and 95% CO reduction in natural gas engines These engines allow manufacturers to a high extent to meet emission legislations without any fundamental modification on the engine or even using aftertreatment systems [8]. Since the engine is designed for marine applications, time-based harmonic loads are imposed on the engine
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