Browse Topic: Engine mechanical components
To solve the poor mobility of traditional camping vehicle chassis in complex terrains and confined spaces, this paper proposes an underactuated omnidirectional mobile chassis for outdoor camping vehicles. The chassis adopts a coupled commutation mechanism (double-crank elastic special-shaped connecting rods cross sliders), allowing each wheel to realize two motion modes (omnidirectional translation, in-situ rotation) with just one drive motor, reducing system complexity and cost. A control system based on the RoboMaster Development Board C Type integrates PID angle-loop control and motor speed-current dual closed-loop control for motion stability. Kinematic models for these two modes are established to derive the wheel parameter-chassis motion relationship. MATLAB R2023b-ADAMS 2024 co-simulations show the chassis maintains attitude stability under S-shaped curve, circular curve, and in-situ rotation; Qualisys 3D motion capture experiments confirm its stable attitude in omnidirectional movement.
The cam mechanism, as an extremely important transmission method in mechanical transmission, is widely used in automatic machinery and automatic control devices. In small and medium-sized high-speed automatic guns, high-speed camshafts are often used to achieve intermittent movement of the supply and transport of ammunition during high-speed shooting. Due to the possible vibrations, wear, and instability that may occur during the movement of high-speed camshafts, the design of camshafts needs to meet the requirements of continuous third-order derivatives of the curve, while minimizing angular acceleration as much as possible. This article focuses on the design requirements of a high-speed intermittent motion mechanism, with continuous angular velocity and angular acceleration as design constraints. It establishes segmented function motion equations for the acceleration, deceleration, and uniform speed sections of a high-speed conjugate parallel indexing cam while ensuring that the design cam curve does not have knots. The theoretical profile and the actual profile of the cam, considering roller radius offset, are calculated. Based on this, dynamic simulations are carried out on the acceleration and deceleration sections of the cam roller, and the structural response considering structural elastic deformation and contact collision conditions is obtained. The calculations show that the cam and roller meet the structural strength requirements during high-speed motion. Experimental verification shows that the structure is stable and reliable during high-speed motion.
In recent years, especially in high-performance spark-ignition engines, the thermal stress of pistons has gradually increased due to the implementation of various technologies, aimed at meeting emission reduction and specific power increase requirements. If the heat is not properly dissipated, cracking and plastic deformation of the material as well as formation of hot spots triggering pre-ignition in the combustion chamber mixture can occur. This last aspect is even more true considering innovative fuels such as hydrogen. To overcome these problems, one or more jets of oil are directed towards the piston under-crown region, impacting at high speed. This technique ensures immediate cooling and allows the engine performance to be increased without compromising the useful life. In order to optimize the oil jet effectiveness, 3D-CFD can be proficiently adopted. In this regard, the aim of this work is to define a robust numerical methodology able to simulate oil jet impingement and piston thermal field. In particular, a 3D-CFD Volume-of-Fluid (VoF) simulation is used to numerically assess the oil jet impact and provide a map of heat transfer coefficients, which, in turn, is adopted in a 3D-CHT model to estimate the piston thermal field. The proposed methodology is validated against experimental data on a high-performance engine piston. In particular, a pair of oil jets is investigated and the resulting heat transfer coefficient map is exploited to obtain the thermal field of the piston, which is finally compared to the available experimental temperature measurements. The results show that the predicted temperatures agree with the experimental data within an error lower than 2.5%.
A valve developed by NASA Stennis Space Center consists of a solid piston floating in a medium to control the flow stream. The piston is designed to be axially and radially balanced within the flow stream whether the valve is in the open or closed position. The only force imparted onto the piston is that which the operator chooses to input on to it.
Ammonia is emerging as a promising energy vector for decarbonising the maritime sector. However, its low flame speed can lead to incomplete combustion, reduced engine efficiency, and increased emissions of unburned ammonia (NH3). Blending hydrogen with ammonia helps to address these issues, but the fundamental combustion characteristics of such mixtures remain insufficiently understood. This study examines the combustion dynamics of an NH3–H2 blend containing 30% hydrogen at 3 bar initial pressure. Experiments were performed in a 1.2 L optically accessible constant-volume combustion chamber fitted with a wall-mounted surface spark plug. High-speed shadowgraph imaging with 6,000 fps captured the flame evolution throughout the combustion process. The pressure and temperature values were monitored using piezoresistive pressure transducers and K-type thermocouples. Combustion times and flame extensions were extracted via post-processing of flame images using custom MATLAB algorithms. The combustion process was examined from the initial start to a diameter of 60mm. Complementary CFD simulations were carried out in CONVERGE using the C3MechV3.5 chemical mechanism. To match the experimental conditions, the numerical studies were conducted at an ambient pressure of 0.3 MPa and an equivalence ratio of 1.0. The model predicted flame propagation times accurately, achieving an average relative error of 2.95% and an R2 value of 0.991. A third-order polynomial correlation was derived to predict instantaneous flame diameter as a function of time, enabling interpolation for intermediate combustion stages for both simulation and experimental results. Error analysis indicated that the model achieved its best performance for medium-sized flames (30–45 mm) but exhibited larger discrepancies at the smallest and largest diameters. Nevertheless, within the 20–60 mm range, deviations remained between −9.5% and +3.4%.
Items per page:
50
1 – 50 of 15000