MODELING THE OPERATION PROCESS OF A SHIP DUAL-FUEL GAS-DIESEL GENERATOR UNIT

Abstract

The article addresses the urgent task of modeling the operation of ship dual-fuel gas-diesel generator units (GDGU), in particular Wärtsilä 50DF engines widely used on LNG carriers and LPG carriers. The rapid development of liquefied gas transportation has led to the replacement of steam turbine installations with more economical electric propulsion systems based on dual-fuel engines capable of operating both on diesel fuel and on boil-off gas (BOG) from cargo tanks. The authors emphasize the need for reliable stabilization of pressure in cargo tanks, safe utilization of excess vapor, and minimization of fuel costs through maximum replacement of diesel fuel with natural gas. A mathematical dynamic model of the GDGU is proposed that takes into account the influence of the turbocharger (represented as an aperiodic link with positive feedback), nonlinear properties of the object, and real parameters of the gas-air mixture supply system. The model is presented in the form of a structural diagram and implemented in Simulink, which made it possible to adequately reproduce transient processes when the load is suddenly applied/dropped. Particular attention is paid to the correct selection of PID-controller settings, since the amplification factor of the object changes significantly depending on the load level. It is shown that tuning the regulator at minimum load provides the greatest margin of stability when moving to nominal and maximum modes. The features of the electronic speed control and fuel mode switching system are considered: instantaneous (within 1 s) transfer from gas to diesel mode at any load, longer (up to 2 min) controlled transfer from diesel to gas with mandatory leak testing and combustion verification, automatic blocking of gas mode in case of faults or blackout start. The advantages of isochronous load sharing in multi-generator ship power plants and the possibility of forced transfer to backup diesel mode are noted. The developed model and recommendations for regulator optimization ensure high stability of voltage and frequency in the ship electric power system under sharp load fluctuations, increase the safety of liquefied gas transportation and contribute to the reduction of operating costs due to efficient use of boil-off gas as the main fuel.