Abstract
In this study, a first application of a high fidelity Conditional Moment Closure (CMC) combustion model is presented for autoigniting Diesel sprays with dimensions and time-scales of large marine Diesel engines. Results have been compared with data available from an optically accessible large two-stroke marine Diesel engine reference experiment. A one-hole co-axial injector with an orifice diameter of 0.875 mm was employed. Four different test cases have been considered, where the gas temperature at start of injection (SOI) ranges from 730 to 910 K and the ambient density was kept constant at 33 kg/m^3. Validation is performed by means of ignition delay time, ignition location and flame lift-off length. Ignition delays were over/underpredicted by within 9 and 23 percent, whereas the highest errors for the flame lift-off length amounted to 13 percent. The trend of the ignition spot shifting to downstream locations for lower temperatures was correctly reproduced, while the accuracy of the predictions was within 40 percent. Experimental images of OH* chemiluminescence confirmed a flame region consistent with the simulation and the lateral deviation of the spray due to the characteristic swirling environment was well reproduced. The good agreement reported suggests that CMC is capable to reproduce the complex phenomenology of a lifted autoigniting spray flame also for a large injector size.
