Engine Efficiency Optimization under Consideration of NO _X - and Knock-Limits for Medium Speed Dual Fuel Engines in Cylinder Cut-Out Operation 2018-01-1151

As a consequence of the global warming, more strict maritime emission regulations are globally in force or will become applicable in the near future (e.g. NO_X and SO_X emission control areas). The tough competition puts economic pressure on the maritime transport industry. Therefore, the demand for efficient and mostly environmental neutral propulsion systems that meet the environmental legislations and minimize the cargo costs are immense. Medium speed dual fuel engines are in accordance with the strict maritime emissions legislation IMO Tier III. They do not require any exhaust gas aftertreatment, are economically competitive, and allow fuel flexibility. These engines deliver the highest efficiency in high load operation. A valuable approach to improve the efficiency and reduce the environmental impact in low and part load is represented by the electronic cylinder cut-out. Thereby, the natural gas admission is deactivated and the valves are kept activated. It is investigated with the help of a developed 1D GT-Power simulation model of a medium speed dual fuel engine. The predictive model is adjusted to a measured engine map (test bench data) by an optimization workflow that is set up in Optimus. The cylinder cut-out is analyzed with special emphasis on efficiency, NO emissions, and methane slip. Different static cut-out scenarios are simulated and assessed for constant relative air/fuel ratios and varying load. An optimization workflow is developed and set up in Optimus. The selected evolutionary algorithm changes the number of cut-out cylinders and the relative air fuel ratio to optimize the engine efficiency under consideration of IMO Tier III NO_X emission regulations and the knock onset. The optimization is conducted for discrete engine operation points in a load range from 10% to 50%. The optimization predicts a significant increase of the brake efficiency and reduced methane slip at low and part load operation. This depends on an increased turbocharger efficiency, reduced pumping work, richer combustion, and higher indicated mean effective pressures of the fired cylinders that leads to an improved combustion (shifted from diffusion to premix) and engine efficiency without exceeding the NO_X - and knock-limits.