EKC2023

Improving cylinder airflow process in a low speed two stroke marine diesel engine at low load using variable-sized scavenge port approach

Aug 15, 2023, 9:50 AM

20m

Taurus 1 (Science Congress Center Munich, Technical University of Munich)

Marine Applications [MaApp] IND2-1: Marine Application - Demonstration

Speaker

Antony John Nyongesa (Korea Maritime and Ocean University)

Description

The shipping sector plays a vital role in global trade, with 80% of the goods being transported via the ocean [1]. Two-stroke marine diesel engines are the most preferred propulsion system in the marine sector because they offer superior fuel economy and high reliability [2]. However, the combustion of fossil fuels in these engines produces harmful emissions [3]. The scavenge air flow process and fuel injection process are the main factors affecting engine performance and exhaust gas emissions. At low engine load, the turbocharger efficiency is reduced, which leads to reduced scavenging efficiency. Enhancing the in-cylinder air flow swirl is important because the diffusion combustion of the injected fuel depends on the mixing rate of the fuel/air mixture[4]. A good cylinder swirl ratio improves airflow stability, which results in a stable engine operation. This study evaluates the effects of the variable-sized scavenge ports on the airflow process inside the engine cylinder using a numerical approach. Simulations were conducted at 25% engine load. The original port height is 122mm, the height was modified to 80, and 100mm, respectively. Simulations were conducted using CONVERGE CFD software and the scavenging processes were evaluated from -260CA before opening the exhaust valve to the top dead center 0CA to analyze the in-cylinder turbulence kinetic energy (TKE), trapped air mass, scavenge air velocity temperature distribution, and the swirl ratio.
As a result, the port height of 100 mm produced promising results. TKE and the trapped air mass were significantly increased by 21% and 9.5%, respectively. The swirl ratio was increased by 30% and the airflow velocity was significantly improved. Decreasing the scavenge port height past 80mm decreases scavenging efficiency, in-cylinder swirl, and the trapped air mass. By reducing the port height at low engine load, higher TKE and swirl can be achieved, which is important for the fuel-air is mixing process. The variable ports should be adjusted to an optimum height to achieve high air flow characteristics and to improve engine performance.
In this study, cold flow analysis of a marine two-stroke engine with variable-sized scavenge ports was analyzed and revealed a significant improvement in the in-cylinder flow characteristics at different port heights. The results of this study will be coupled with the combustion process to analyze the engine performance and exhaust gas emission characteristics in future work

References

1. Al-Enazi, A., E.C. Okonkwo, Y. Bicer, and T. Al-Ansari, A review of cleaner alternative fuels for maritime transportation. Energy Reports, 2021. 7: p. 1962-1985.
2. MAN, D., Basic principles of ship propulsion. 2004, Turbo Publication.
3. Ni, P., X. Wang, and H. Li, A review on regulations, current status, effects and reduction strategies of emissions for marine diesel engines. J Fuel, 2020. 279: p. 118477.
4. Lu, T., Z. Lu, L. Shi, T. Wang, M. Liu, and H. Wang, Improving the fuel/air mixing and combustion process in a low-speed two-stroke engine by the IFA strategy under EGR atmosphere. J Fuel, 2021. 302: p. 121200.