Numerical analysis of methane slip source distribution in a four-stroke dual-fuel marine engine
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ORIGINAL ARTICLE
Numerical analysis of methane slip source distribution in a four‑stroke dual‑fuel marine engine Michael Vincent Jensen1 · Rasmus Faurskov Cordtz1 · Jesper Schramm1 Received: 21 December 2019 / Accepted: 6 August 2020 © The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2020
Abstract We present the results of a numerical model which has been developed for estimating the contribution to the methane slip from different sources in a four-stroke dual-fuel marine engine running on natural gas. The model is a thermodynamic threezone zero-dimensional full engine cycle model and considers methane slip contributions from short-circuiting, crevices and wall quenching. The model is applied to analyze the methane slip from a four-stroke dual-fuel medium speed marine engine using natural gas as primary fuel. At low loads, wall quenching is found to be the dominant contribution to the methane slip. At full load, the wall quenching contribution is comparable to the level of the short-circuiting and crevice contributions which only vary relatively little with load. At 75% load, the contribution from short-circuiting is highest. In addition, we found that in-cylinder post-oxidation of unburned fuel remaining after the main combustion is negligible. Keywords Methane slip · Dual-fuel engine · Marine engine · Four-stroke engine · Natural gas · Numerical model
1 Introduction Due to increasing environmental concern, the maritime emission limits for nitrogen oxides ( NOx ) and sulfur oxides ( SOx ) (via fuel sulfur content limitation) have been tightened in recent years through the International Maritime Organization’s (IMO) MARPOL treaty Annex VI [1, 2]. Further tightening of the fuel sulfur content limitation will enter into force in 2020, and further limitations on maritime emissions may be expected in the future. Consequently, marine engine manufactures are currently highly focused at further improving the marine engine technology to meet these emission limits. A way to comply with the SOx emission limit is to use liquefied natural gas (LNG) as a primary fuel instead of fuel oils since LNG has virtually no sulfur content, contrary to fuel oils, resulting in significantly less SOx emissions [3]. LNG is also seen as a promising marine fuel for the future due to the large natural gas world reserves [3, 4]. When applied in four-stroke dual-fuel marine engines, LNG is evaporated and injected as a gas into the charge air in the * Michael Vincent Jensen [email protected] 1
Department of Mechanical Engineering, Technical University of Denmark, Nils Koppels Allé 403, 2800 Kgs. Lyngby, Denmark
intake manifold to form a premixed charge in the engine cylinder, which is ignited by a pilot injection of diesel fuel in the end of the compression stroke. The premixed charge is typically lean which lowers the combustion temperature and accordingly the NOx formation, beneficial for meeting the reduced NOx emission limit as well [5–7]. The emissions of particulate matter (PM) from the engines are also lowered si
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