Investigation on jet controlled diffusion combustion (JCDC) mode applied on a marine large-bore two-stroke engine

Ships with large-bore marine engines are essential for international trade and transportation. However, a large number of fuel energy consumption and waste emissions are produced. Future lower fuel consumption and cleaner marine natural gas engines needs technological innovation. One approach is the use of a prechamber, providing high ignition energy. In this study, diesel injected into the prechamber and the prechamber jet controlled diffusion combustion (JCDC) mode was applied to a marine two-stroke natural gas/diesel engine. A three-dimensional simulation method was employed to optimize the combustion control parameters and compare the performance of JCDC mode with the traditional pilot controlled diffusion combustion mode (PCDC). The diesel compression ignition in the prechamber generated turbulent jet in the main chamber, which ignited the direct-injection natural gas. The key parameters influencing the JCDC mode, including the direct-injection interval and diesel energy percentage, were optimized in this study. A small direct-injection interval of 0.15°CA between diesel and natural gas was achieved, resulting in good ignition performance. By utilizing a 1.8% diesel energy percentage in the prechamber, a high indicated thermal efficiency (ITE) of 53.6% was obtained. Compared to the PCDC mode, the JCDC mode demonstrated a maximum reduction of approximately 1.4g/kWh in equivalent indicated specific fuel consumption (EISFC), indicating very large improved fuel economy for the marine two-stroke engine. Furthermore, the JCDC mode exhibited notable reductions of greenhouse gas in CO₂ and unburned CH₄ emissions, with a maximum decrease of 1.6% and 89%, respectively. The JCDC mode indicates a cleaner marine natural gas engine.