A preliminary numerical study on the use of methanol as a Mono-Fuel for a large bore marine engine. (15th February 2022)

• Record Type: Journal Article
• Authors: Leng, Xianyin; Deng, Yicheng; He, Dongze; Wei, Shengli; He, Zhixia; Wang, Qian; Long, Wuqiang; Zhu, Shulin
• Is Part Of: Fuel. Volume 310:Part B(2022)
• Publication Date: 2022-02-15
• Subjects: Large bore engine -- Methanol -- Mono-fuel -- Distributed jets ignition -- Numerical simulation -- Excess air ratio -- Ignition timing; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2021.122309
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Distributed jets were used to ignite in-cylinder lean mixture on a large bore engine using methanol as a mono-fuel. Heat release rates showed a firstly slow and then rapid trend. The lean limit was found to be at excess air ratio of 2.4 with a combustion efficiency of 99%. A strategy was proposed for the methanol engine to balance efficiency and power density. Abstract: To use methanol as a mono-fuel in large bore marine engines, a distributed jets ignition combustion mode was applied on a 320 mm-bored engine, in which pre-chamber initiated jets were employed to ignite the in-cylinder lean mixtures and to enhance the flame propagation. A preliminary numerical study was carried out to investigate the effects of in-cylinder excess air ratio and ignition timing on combustion characteristics and performances of the engine. Conditions with excess air ratios ranged from 2.0 to 2.8 and ignition timings ranged from −8°CA ATDC to the top dead center were calculated. The numerical results show that, under the distributed jets ignition combustion mode, the in-cylinder lean methanol-air mixtures could be reliably ignited and the heat release rates showed a firstly slow and then rapid trend, resulting in high thermal efficiencies and low NO x emissions, which could meet for the IMO Tier III emission regulations without aftertreatment. Moreover, with the increase of the in-cylinder excess air ratio and the delaying of the ignition timing, the in-cylinder pressure, the peak pressure rising rate, the ringing intensity and the NO x emissions were continuously decreased. As the in-cylinder mixture becoming leaner, the combustion efficiency firstly kept constant and then rapidly dropped when the excess air ratio increased to 2.4, resulting in a peak value of the indicated thermal efficiency (49.2%) at this excess air ratio. According to the numerical results, a combustion control strategy was proposed: when the brake mean effective pressure was below 1.8 MPa, the in-cylinder excess air ratio was controlled at 2.4 and coupled with an earlier ignition timing to obtain high thermal efficiency, and when the brake mean effective pressure was higher than 1.8 MPa, the in-cylinder excess air ratio was controlled at 2.1 and coupled with a later ignition timing, thereby to achieve high power density.