Numerical studies on the flow characteristic of the marine two-stroke engine integrated with the high-pressure exhaust gas recirculation system

Abstract

The high-pressure exhaust gas recirculation (HP-EGR) has been well-proven for marine engines complying with the IMO Tier Ⅲ NOx regulation. Considering different turbocharged scavenging schemes and emission control modes, intake and exhaust gas management is critical to the HP-EGR design. However, few theoretical studies on it were reported. This paper aims at providing a case study on the flow characteristic of the turbocharged HP-EGR system. With the proposed topology structure of the typical HP-EGR layout, numerical studies on the turbocharged scavenging and EGR design were conducted based on the 6EX340 two-stroke engine. The result showed that the flow characteristic of the turbocharged two-stroke engine can be graphically depicted by simplifying the cylinder and turbine as multi-nozzle in series. According to the nozzle flow equation of uniflow scavenging, there exists an optimum turbine flow area to maximize the scavenging mass flow. Effects of EGR, cylinder bypass, and exhaust gas bypass on the flow characteristic of the two-stroke engine depend on the turbocharger matching. The out-cylinder scavenging and in-cylinder combustion should be optimized interactively to fully explore the fuel economy and NOx trade-off. Finally, the proposed design procedure can provide good guidance for the design and control of the HP-EGR system.

Keywords

• Marine engine
• Turbocharged scavenging
• Flow characteristic
• Exhaust gas recirculation
• Graphical analysis