Combustion performance optimization of marine diesel-natural gas dual-fuel engines under low operation loads

With the increasingly stringent IMO emission regulations, the diesel-natural gas dual-fuel engine is gradually applied to ship’s power systems. However, the misfire and unconventional emissions of dual-fuel engines under low operation loads limit its application. In this study, a marine diesel/natural gas dual-fuel engine was used as a prototype to develop a 3D CFD simulation model using CONVERGE, which was then validated by using the experimental data under different operation loads. The validated model was used to study the effect of injection timing, intake temperature, and EGR rate on the combustion and emission characteristics under low operation loads soon afterward. The effects of different operating parameters on engine performance and emissions were determined by observing the formation of combustion intermediates and in-cylinder temperature variation. Results show that under small load conditions, advancing diesel injection timing and increasing intake temperature can reduce the emissions of HC and CO while improving the misfire phenomenon partly, but NOx increases. A larger EGR rate can effectively reduce NOx emissions but cause an increase in unconventional emissions. After optimization, the effective power increased by 5.9%, while the HC and CO emissions decreased by 33.1% and 35.2%, respectively. The misfire phenomenon under low operation loads has been significantly improved, thus providing theoretical support for the de sign and operation of dual-fuel engines.