A CFD Model of Supercritical Water Injection for ICEs as Energy Recovery System

Supercritical water injection for ICEs may be a valid option to recover engine wall heat transfer and energy from exhaust gases, with benefits in terms of efficiency and performances. Water is recovered from exhaust gases and is brought up to supercritical conditions by employing the waste heat during engine operations. A preliminary study of this energy recovery approach has already been performed in an authors’ previous work, by employing a port fuel injection (PFI) internal combustion engine quasi-dimensional model, which has been validated against experimental data, returning satisfactory results in terms of overall efficiency gain. In this work, in order to obtain a more reliable and accurate evaluation of the achievable energy recovery with supercritical water injection, a multidimensional CFD model of the engine has been set and validated. As regards the engine geometry, a simplified axial symmetric engine has been used, in order to reduce the computational time and storage. The combustion has been modelled with an ECFM model using an 88-species and 349-reactions chemical kinetics mechanism, in order to evaluate the pollutant emissions and their potential reduction due to supercritical water injection. The water injector has been modelled as a convergent-divergent nozzle which is located along the cylinder axis. The first part of this work focuses on the validation of the engine model with experimental data. Then, the influence of supercritical water injection on engine performances has been analyzed, by considering two different setup as concerns the water injection process. The gross indicated work per cycle increases by 11.6% and 13.4% when supercritical water is injected at 40 and 35 CAD ATDC, respectively, with respect to the case without injection.