Using multi-stage Wiebe to characterize the combustion of a marine natural gas lean-burn SI engine

Abstract

Marine natural gas SI engines are a potential solution for mitigating GHG impacts of the maritime sector.
However, SI engines encounter challenges related to combustion stability, including knocking and partial burning. Employing fast thermodynamic simulation models can aid in understanding the combustion characteristics of these engines and identifying optimization routes. Previous studies have shown that these converted engines exhibit three distinct combustion stages due to the different transport and chemical phenomena occurring when cylinder geometry remains unchanged.
This study aims to utilize this approach to characterize the combustion of a converted marine NG-fueled SI engine using a multi-Wiebe modeling approach. In this paper, we developed a closed in-cylinder thermodynamic model based on measurements from a 500 kW marine NG-SI engine and validated it through additional measurement points. Furthermore, we analyzed the impact of operating parameters such as spark timing (ST) and air excess ratio (λ) on the Wiebe parameters and their corresponding combustion stages.
Our findings indicate that the triple-Wiebe modeling approach effectively simulates the combustion processes in this type of NG-SI marine engine. Additionally, diluting the mixture increased the shape factor of all three Wiebe functions. The first combustion stage was found to be the most sensitive to both dilution and delayed ST effects, as reflected by the Wiebe parameters. This sensitivity may explain the observed deterioration in combustion and emission performance, as more fuel combusts in the later combustion stage. In our efforts to accelerate the defossilization of the shipping industry, this study highlights the importance of various combustion modeling approaches in understanding and optimizing the performance of marine SI engines.