Effects of split injection strategy on combustion characteristics and NOx emissions performance in dual-fuel marine engine

• Published in: Applied thermal engineering 2024-07, Vol.248, p.123153, Article 123153
• Main Authors: Jiang, Longlong, Xiao, Ge, Long, Wuqiang, Dong, Dongsheng, Wei, Fuxing, Cao, Jianlin, Wang, Yang, Tian, Hua
• Format: Article
• Language: English
• Subjects: Diesel ignition of natural gas; High natural gas substitution rates; Large Eddy simulation; Reduce NOx emissions; Split injection strategy
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2024.123153

•Exploring and optimizing the piloted diesel injection strategies in medium-speed diesel/natural gas marine engine under 93.3% natural gas substitution rate.•The single and split injection strategies exhibit different trade-offs in terms of their impact on ISFC and NOx emissions.•Low-temperature reactions of n-heptane primarily lead to the production of CH2O through reactions R170 (CH3O + O2 = HO2 + CH2O), R344 (C7KET21 = C7H11CO + CH2O + OH), and R424 (C2H2 + OH = CH2O + CH3).•The optimized split injection strategy increases thermal efficiency by 0.77% while reducing NOx emissions by 36.3%. In order to address environmental concerns and promote sustainable development, the maritime industry is facing a demand to reduce emissions from ship engines. To address this, a growing trend in the development of diesel natural gas dual-fuel marine engine involves implementing more flexible diesel injection strategies, with the aim of enhancing performance and minimizing harmful emissions. This study utilized a numerical investigation based on the Large Eddy Simulation (LES) method to examine pilot diesel injection strategies in a dual-fuel marine engine operating at a high degree of natural gas substitution rate. Specifically, the analysis focused on the start of injection (SOI) in the single injection strategy and the first start of injection (SOI1) in the split injection strategy for pilot diesel. The findings highlight distinct trade-off relationships between these two injection strategies regarding their impact on indicated specific fuel consumption (ISFC) and NOx emissions. Compared to the optimized single injection strategy (Case A: SOI = -15°CA ATDC), the optimized split injection strategy (Case B: SOI1 = -60°CA ATDC, SOI2 = -10°CA ATDC) increases thermal efficiency by 0.77 % while reducing NOx emissions by 36.3 %. The split injection strategy induces low-temperature reactions of n-heptane in the squish region, resulting in the generation of active free radicals such as CH2O and OH, thereby accelerating the propagation speed of the flame in the squish region. Meanwhile, the split injection strategy diminishes pilot diesel accumulation in the piston bowl region, narrows the distribution range of high-temperature areas surpassing 2400 K, consequently leading to a reduction in NOx emissions.