Testing of a Modern Wankel Rotary Engine - Part IV: Overall Mechanical and Thermal Balance

The present work extends the performance analysis of a rotary Wankel engine for range extender applications already introduced in the companion papers of this series. Specifically, in this work, an overall balance was carried out on mechanical and thermal parameters inferred from the indicated pressure cycles and those measured by the dynamometer and the data acquisition system during steady-state engine testing, highlighting the energy fluxes within the machine. The evaluation of the in-chamber heat transfer coefficient, by means of an adapted Woschni model, and the related heat rejected to the coolant represent the additional and necessary analysis to complete the experimental assessment already presented in the previous papers. The tested engine is the Advanced Innovative Engineering 225CS and the experimental testing was conducted using a combustion analyser specifically developed for rotary machines. The results reported in this work are representative of the performance of current rotary engine technology. The engine was tested in steady-state motored and firing conditions while collecting all the usual engine data. The indicated torque, the net heat release and the rate of heat release were computed from the indicated pressure cycle taking into account the engine geometrical parameters and employing analytical relations and numerical procedures. The indicated torque at different operating points was compared under further simplifying assumptions (friction torque curve measured in motoring condition considered unaltered in firing condition) with the motoring and firing torque measured by the dynamometer while the net heat released was compared with the instantaneous fuel flow rate, the mechanical power delivered and the heat rejected in the coolant. The results show a good balance closure of the aforementioned parameters with a low level of imbalance mainly due to simplifying assumptions and measurement uncertainties, hence validating the methodologies extensively reported in Part II and III of this suite of papers. The data reported here and in the previous works also represent the initial steps in validating CFD models and the optimisation of fuel consumption and emissions for the aforementioned engine to be employed as a range extender in Series Hybrid (or Range-Extended) Electric Vehicles.