Clean combustion of a hydrogen-doped elliptical rotary engine based on turbulent jet ignition: Synergistic enhancement of thermodynamic and emission performance via flow field coupling

The elliptical rotary engine (ERE) is expected to replace the conventional reciprocating engine as a special power due to its high energy density and compact design. However, the special eccentric structure results in a flattened chamber at ignition timing, which is not conducive to complete combustion. To optimize thermodynamic efficiency and emission characteristics, this paper develops a turbulent jet ignition configuration for ERE (TJI-ERE) based on in-cylinder compression flow field through numerical simulation. Three different jet directions – forward jet (FJ), vertical jet (VJ), and backward jet (BJ) − are engineered with orifice diameters of 1 mm (D1), 2 mm (D2), and 3 mm (D3). The synergistic interaction between jet flame propagation and bi-directional vortex formation is systematically investigated through mechanistic analysis. Comparative evaluations of thermodynamic performance and emissions are conducted across various configurations. Key findings reveal that FJ and BJ configurations predominantly influence forward and backward vortex development respectively, while vertical jetting induces horizontal flame expansion against vertical compression flows. The orifice diameter of 2 mm demonstrates optimal balance between jet momentum and flow capacity. The indicated thermal efficiency under FJ-D2 condition achieves the peak of 0.329 (14.63 % improvement over VJ-D1), while increases NO_x emissions to 0.18 %. By contrast, BJ-D2 and FJ-D3 configurations maintain indicated mean effective pressure at 7 bar while suppressing CO and HC emissions below 0.026 %, showcasing enhanced emission control capabilities. This research can provide experience in addressing the combustion degradation of ERE and advance its practical application in field of UAV power system.