The Optimization of the Dual Fuel Engine Injection Parameters by Using a Newly Developed Quasi-Dimensional Cycle Simulation Combustion Model

The paper presents the optimization of injection parameters of directly injected fuel in the dual fuel engine operation. The optimization is performed numerically by using a cycle simulation model of the considered engine. In the cycle simulation model, combustion is simulated by a newly developed quasi-dimensional dual fuel combustion model. The model is based on the modified multi-zone combustion model and the quasi-dimensional combustion model. The modified multi-zone combustion model handles the part of the combustion process that is governed by the mixing-controlled combustion, while the modified quasi-dimensional combustion model handles the part that is governed by the flame propagation through the combustion chamber. The developed dual fuel combustion model features a phenomenological description of spray processes, i.e. the liquid spray break-up, fresh charge entrainment, droplet heat-up, and evaporation processes. In order to capture chemical effects on the ignition delay, special ignition delay tables are made. Additionally, to capture the effect of entrained methane on the chemical reaction rate, a special table that features the chemical reaction time scale is also created. The turbulence is calculated by the modified k-ε turbulence model that takes into account the effect of diesel pilot injection on the increase in the in-cylinder turbulence level. Before being used for the optimization, the engine model is validated through a comparison with experimental data. After that, the direct injection parameters are changed in search for the optimal solution. The objective is to obtain the maximum efficiency while maintaining the limits on emissions and on the mechanical load. The study is conducted at the mid load point at a constant engine speed.