Search

With the tightening of emission regulations for marine engines, it has become increasingly important to explore efficient and clean combustion strategies in diesel–natural gas dual–fuel marine engines. This study, for the first time, compared and analyzed the effects of single and split injection strategies on the combustion process in a marine medium-speed dual-fuel engine with a natural gas substitution rate of 93.3%. Optimal strategies were compared for single injection [Case A: start of injection (SOI)=−15° crank angle (CA) after top dead center (ATDC)] and split injection (Case B: SOI1=−60°CA ATDC, SOI2=−10°CA ATDC). The analysis of Cases A and B revealed that employing a split pilot diesel injection strategy enhances engine thermal efficiency—Case B had a 0.77% increase in efficiency compared with Case A. More importantly, the split injection strategy proved to be more effective in reducing emissions; compared with Case A, Case B had a 36.3% and 49.4% decrease in NOx and CH4 emissions, respectively. A deeper examination of the combustion process in Case B revealed that the reactivity in specific cylinder regions was enhanced, thereby increasing the flame propagation speed in those areas. Moreover, the strategy reduced the proportion of pilot diesel diffusion combustion, leading to lower high temperatures and aiding in the reduction of NOx formation. These findings provide a technological reference for improving energy conversion efficiency and facilitating cleaner combustion in future applications of low-carbon fuels in dual-fuel marine engines. [ABSTRACT FROM AUTHOR]

In this study, the influence of direct steam injection (DSI) on the performance and emissions of marine engines is investigated. Simulation models are developed and tested based on experimental data. Steam is obtained by waste heat recovery in a marine engine. The limitations of DSI parameters are investigated based on the exhaust gas temperature. The steam quantity and temperature decrease with a decrease in load. The results show that steam mass plays an important role in NOx reduction and improving power. For a steam/fuel ratio of 1.27 at 100% load, the brake power improved by 3.09% and NOx emissions decreased by 4.67%. A higher degree of improvement is obtained with an increase in steam mass. The steam temperature and injection timing only slightly influenced the brake power and NOx emissions. When steam-injection timing improved to 12°CA at 100% load with injection duration decreasing from 85°CA to 25°CA, brake power improved from 3,485.7 to 3,529.7 kW. All of this demonstrates that the DSI approach has excellent energy-saving and emission reduction potential for marine engines. The steam-injection strategy should be optimized in the future. [ABSTRACT FROM AUTHOR]

Emission reduction from marine engines can be supported by implementing multiple injection strategies. In the present study, the effect of fuel post-injection on the performance and exhaust emissions of a large two-stroke marine diesel engine is investigated by using computational fluid dynamics (CFD). An optimization procedure is formulated by coupling a KIVA-3-based CFD code with an optimization tool based on evolutionary algorithms (EAs). A fuel-injection profile consisting of two pulses (main and post-injection) is considered and parameterized in terms of four design variables. The specific fuel oil consumption (SFOC) and the final concentration of nitric oxides (NOX) and soot constitute the objective functions. Using a parametric study, two multiobjective optimization problems are formulated, an unconstrained and a constrained one; in the latter, the work output per engine cycle and the maximum in-cylinder pressure are the problem constraints. For both problems, significant reductions in pollutant emissions are attained, in comparison with a reference case characterized by continuous injection; for the constrained problem, the reductions reach 23 and 32% for NOX and soot, respectively. [ABSTRACT FROM AUTHOR]