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The sealing characteristics of an annular power cylinder based on the Twin-rotor piston engine are studied, which provides a theoretical foundation for the sealing design of a new high-power density piston engine. In this paper, the basis thermodynamic realization process of an annular power cylinder is presented. The Runge Kutta equation is used to establish the coupled leakage model of adjacent working chambers under annular piston seal. And the sealing performance of the annular power cylinder is analyzed in detail. Moreover, the influence of rotor speed and compression ratio on the sealing characteristics and leakage is studied. Finally, some tests are carried out to verify the sealing principle and simulation results, which verifies the theoretical basis of simulation analysis. Results show that there are double pressure peaks in the leakage chamber between two working chambers, which is beneficial to reduce the leakage rate. Besides, increasing the speed and decreasing the compression ratio can help to reduce gas leakage. Furthermore, the effects of speed variation on the leakage are only significant when rotating at low speed. Changing the compression ratio has a greater effect on the slope of the leakage curve at a low compression ratio, and the lower the compression ratio, the better the sealing effect.

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Combining the structural features of cam engines and opposed engines, a kind of opposed cam piston engine is designed, in which a kind of variable sine curves family applied to the cam working surface. Based on the structure of this engine, a thermodynamic zero-dimensional model of the working cycle was established, and the accuracy of it was verified by the numerical simulation model utilizing the engine simulation software AVL BOOST. Based on the zero-dimensional model, the changes in the pressure, temperature, and quality of the working fluid in the cylinder under different cam profiles were calculated, and on this basis, the engine’s thermal efficiency, mechanical efficiency, overall machine efficiency, and power per liter were solved. Compared with common civil vehicle engines, OCPE has higher power per liter and has better economic performance and power performance.

In this paper, a novel type of twin-rotor piston engine (TRPE) is proposed, and the circumferential oil film thickness for the piston ring in TRPE is analysed. Different from the integrated cylinder of a typical engine, the combined annular cylinder (CAC) of TRPE has unique structural composition and differential velocity motion characteristic, making the tribological performance more complicated. The main purpose of this paper is to reveal and explain the special tribological performance of TRPE, which has never been studied. Firstly, the special structural composition of CAC is introduced and the relative velocity between the piston ring and CAC wall at different circumferential positions of the piston ring is analysed. Then, based on the Greenwood-Trip asperity contact theory, radial and axial quasi-static equilibrium equations of the piston ring are both derived. The circumferential oil film thickness is calculated by solving the equilibrium equations and the two-dimensional average Reynolds equation within a cycle. Results indicate that there are significant differences in circumferential oil film thickness of the piston ring due to the special structure and motion of CAC, and the differences become greater as the output shaft speed increases. A long-time engine reverse towing experiment shows an obvious uneven wear phenomenon of the piston ring and CAC wall, which well validates the simulation results of the circumferential oil film thickness. The research work can be used as the basis of equal-wear design for the piston ring in TRPE with the help of surface texture technology, thereby greatly reducing the wear loss.