Fluid flow characteristics of two types rotary engines

Abstract

Hydrogen fueled rotary engines are potential alternatives to be green engines in vehicles. In this study, a numerical approach is used to investigate and compare the internal flow field characteristics of two types of rotary engines: triangular rotary engine (TRE) and liquid piston engine (LPE) also known as elliptical rotary engine. First, the three-dimensional fluid analysis models are developed for the two engines based on geometric designs of the rotors. The fluid analysis is carried out using the computational fluid dynamics (CFD) tool by assuming two working fluids: air and H2, and the dynamic mesh and turbulent flow models are integrated and simulated with ANSYS Fluent solver. For simulation convenience, combustion and thermal effects are neglected. The results show that the flow rate fluctuation coefficient and gas moment fluctuation coefficient are higher in LPE as compared to TRE, indicating LPE has relatively lower stability than TRE. The vortex number is found to be higher in LPE, signifying higher combustion efficiency of LPE as compared to TRE. However, LPE may have more energy dissipations, reduced exhaust and suction efficiency and high risk of leakages. The TRE has more stable flow, larger exhaust, lesser vortex, lower leakages, and simpler flow path as compared to LPE. Comparison of the two fluids i.e. air and H₂ shows that in TRE, air has high magnitude of average gas moment, high mass flow rate, high pressure and low flow velocity as compared to H₂, implying that air is more stable than H₂ in TRE. Conversely, H₂ is more stable than air in the case of LPE. The vortex number is relatively lower in both LPE and TRE using air indicating that air has low leakages than H₂ in both rotary engine types. This study can be used as a reference for a better rotary engine design in the future.