Heavy-fuel aviation piston engines (HF-APEs) are widely used in general aviation and unmanned aerial vehicle (UAV) due to their safety and fuel economy. This paper describes a numerical and experimental study of scavenging and combustion processes on a 2-Stroke Direct Injected HF-APEs for light aircraft, with its cylinder specifically designed as cross scavenging. A 3-Dimentional transient model of in-cylinder flow and combustion process is established by the Forte platform, and the engine test system is set up. By comparing the simulation results to the experimental results, it showed that multi-ports cross scavenging can generate unbalanced aerodynamic torque in the cylinder. In the compression process, the swirl ratio (SR) gradually increases, and the peak SR reaches 15. Moreover, approximately 25% of exhaust residual gas in the cylinder is conducive to the fuel atomization and evaporation process in a high-altitude environment. When the injection timing is between −8 °CA and −16 °CA, the engine has the optimal power and economy performance at different altitudes. Finally, when the injection advance angle moves forward by 4 °CA, the maximum pressure increases by 2 MPa, with the rising rate decreasing gradually. The results have important significance for the development of the combustion system of small 2-Stroke Direct Injected HF-APEs.
Bump foil journal bearings (BFJBs) are widely used in the superchargers of aviation piston engines (APEs). This paper proposes a method to evaluate the operating state of superchargers by monitoring the bearing temperature. A numerical model with a repeating symmetrical structure in the axial direction is established based on a certain type of supercharger, which solves the temperature field of BFJBs with the non-isothermal Reynolds equation and energy equation. It can be used to analyze the effect of thermal expansion on lift-off speed and stop-contact speed. A new test rig and six various BFJBs were designed to check the temperature characteristics of the BFJBs with variable load and speed. By comparing the numerical results with the experimental results, it was shown that the air film temperature increased almost linearly with the increase in bearing load and speed. However, the temperature increase caused by the rotation speed was significantly greater than the load. The structural parameters of the BFJB affected the bearing support stiffness, which had a nonlinear effect on the lift-off speed and air film temperature. Therefore, the proposed method to evaluate the state of superchargers with BFJBs was effective. These thermal characteristics can be used to guide BFJB design and predict the life cycle of BFJBs.
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