Development of a Combustion Model for Medium Speed Dual-Fuel Engines

In the present work a predictive combustion model for medium speed dual-fuel engines is developed and implemented in GT-Power. To predict the start of combustion, a detailed physically/chemically based ignition delay model is developed. Therefore, detailed correlations for the ignition delay times of the 2-stage ignition process are derived from reaction kinetics calculations. Using these correlations, the reaction progress inside the spray is calculated until ignition. The spray zone and the homogenous natural gas/air mixture are burned with different combustion models, to account for the effect of the inhomogeneous fuel distribution. Due to the implemented state-of-the art sub-models for laminar and turbulent flame speed, a wide range of air-fuel ratios is covered by the combustion model. To account for the HC emissions two flame quenching models are included and ex-tended with an empirical correlation. NOx emissions are modelled using a standard Extended Zeldovich Mechanism and for the prediction of knocking combustion a detailed knock model from literature is implemented. The models are calibrated and validated with measurement data from a single cylinder medium speed dual-fuel engine. The combustion parameters are predicted reasonably for a wide range of injection timings and operation conditions. Furthermore, the included HC models allow for a satisfactory prediction of the engine operation parameters brake specific fuel consumption and indicated mean effective pressure. Due to the detailed description of the different combustion phases, the influence of the injection timing on the NOx emission is captured well with the standard NOx-model. The knock limit is also predicted within an acceptable range for different air-fuel ratios and charge air temperatures.