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J. Fruehhaber, A. Peter, S. Schuh, T. Lauer, M. Wensing, F. Winter, P. Priesching, K. Pachler:
"Numerical investigation of inert and reactive spray characteristics during pilot injection of a dual fuel injector";
Talk: 7th European Conference on Computational Fluid Dynamics, Glasgow | United Kingdom (invited); 2018-06-11 - 2018-06-15.

Dual fuel combustion will become more important in the field of maritime propulsion, due to the introduction of the so called Emission Controlled Areas within the IMO Tier III legislation. To meet the stringent emission targets, ships propelled with HFO may switch to dual fuel operation mode in the protected areas. The combustion process is characterized by the injection of a small amount of fuel oil, which ignites a premixed natural gas-air mixture. The resulting short injection durations oblige the injector into the ballistic working regime. This influences spray penetration, mixture formation and ignition behavior.

In the present work, a CFD model of a dual fuel injector was developed using the commercial code AVL FIRE®. Due to the ballistic working regime, the main challenge for the modeling is to capture the opening and closing behavior of the injector. Therefore, optical investigations were carried out in an injection bomb to characterize the liquid and the vapor phase at an early stage of spray propagation. Based on the experimental observations, a methodology assuming constant momentum along the spray axis was applied to estimate the initial penetration velocities. The injection profile is adjusted for different fuel quantities to investigate the resulting spray characteristics. To realize the observed dependencies of the spray penetration from chamber conditions in simulation and to depict the decrease of liquid length after the end of injection, a suitable initial droplet spectrum was defined. The developed model is able to predict the experimental observed penetration and contour of the spray plume. The spray model is extended by a detailed reaction mechanism to simulate the combustion process of the diesel jet. The ignition delay was validated using measurements of the OH* emission of the flame. Measured OH* intensities enable a detailed characterization of the development and the propagation of the first flame structures. The distribution of the simulated OH concentration shows a good correlation with the experimental data concerning the contour und the penetration behavior of the flame.