Development and calibration of an enhanced quasi-dimensional combustion model for HSDI diesel engines

The paper describes the development and validation of a quasi-dimensional combustion model, applicable to any type of high-speed direct-injection (HSDI) diesel engines. In this model, the fundamental in-cylinder processes are taken into account, including turbulence, fuel injection, spray dynamics, ignition, and combustion. In comparison with similar models presented in the literature, a more physical description of average in-cylinder turbulence properties and their interaction with spray dynamics is introduced, as well as a detailed modelling of fuel jet wall impingement. Some experimental measures available in the literature and three-dimensional computational fluid dynamics simulations were considered to calibrate the modelling parameters. These improved sub-models make results accuracy less dependent on the calibration carried out on each engine, so that the same parameter setting can be successfully applied to different combustion chamber configurations. The model was first applied to a small HSDI turbocharged diesel engine. The specific calibration was supported by both experimental and simulation results, the latest being obtained from the three-dimensional computational fluid dynamics analyses. Then, a different diesel engine was simulated, adopting the same set-up of the model parameters. For both engines, the comparison between experiments and simulation showed a very good agreement in terms of in-cylinder pressures and heat release rates, as well as of average in-cylinder turbulence properties. It is worth mentioning that the two engines had a quite different unit displacement, i.e. 312 and 697 cm3, respectively. As a conclusion, this model was demonstrated to be a reliable tool for addressing the optimization of the main engine design parameters, such as injection rates and timings, combustion chamber base geometry, and so forth