Meta-Model Optimization of Dual-Fuel Engine Performance and Emissions Using Emulsified Diesel with Varying Water Percentages and Injection Timing

As emission restrictions become more stringent and conventional fuel supplies become more limited, dual-fuel engines are emerging as a promising solution that offers both environmental and economic benefits. However, the performance of these engines is often hampered by the issue of knocking, which can negatively impact their overall operation, and also by the increase in NOx emissions at high load. This work investigates the use of pilot injection properties by combining the use of emulsified diesel of different water percentages with injection timing to reduce both knock intensity and NOx emission rate. Specifically, a dual fuel operation case at full load with high enrichment of the primary fuel (natural gas) with hydrogen is considered in order to create conditions for high knocking and high NOx emission rates. The online optimization principle is used for the creation of the meta-model, utilizing the Radial Basis Functions technique (RBF), and the search for the optimum in parallel using the Non-Dominated Sorting Genetic Algorithm (NSGA-II) to handle two objective functions: the minimization of the knock intensity and NOx emissions, and the maximization of the engine thermal efficiency, based on two decision variables: the volume percentage of water in the emulsified diesel (0-30%) and the injection time of this pilot fuel (5-30° CA BTDC). The evaluation of the cases is provided by a CFD calculation model (Converge©) after validation by experimental results. The results indicate that the amount of water contained in the diesel and the injection time have a significant influence on the knock intensity (a decrease of 74%) and the rate of pollutant emissions (a decrease of 61%). The Pareto front summarizes the non-dominated cases according to the two objective functions and indicates that increasing the percentage of water and delaying the pilot injection decrease both the intensity of the knocking and the NOx emissions but penalizes the thermal efficiency of the engine. Therefore, choosing the optimums is crucial in achieving a compromise between the two objective functions.