Tao Nie

Cavitation flow inside an injector control valve significantly affects the injection performance and operational reliability of diesel engines, and the selection of turbulence and cavitation models is crucial for accurately predicting cavitating flows. To evaluate the predictive performance of different model combinations, a numerical model was established based on the Winklhofer microchannel experiment. Three large eddy simulation (LES) subgrid-scale (SGS) models were coupled with three cavitation models, and their performance was assessed by comparing the predicted outlet mass flow rate, centerline pressure distribution, and cavitation distribution with the experimental results. The results show that the outlet mass flow rate increases with the inlet–outlet pressure difference. When the pressure difference reaches approximately 70 bar, the growth rate decreases significantly, indicating the onset of typical cavitation-induced flow choking. Under low pressure differences, the prediction results of different model combinations are generally similar, whereas significant discrepancies are observed under high-pressure-difference conditions with intense cavitation. In terms of mass flow rate prediction, the Dynamic Smagorinsky + FRP model combination shows the best agreement with the experimental results in the pressure difference range of 70–85 bar, with an error of 3.06%. For pressure distribution prediction, the Dynamic Smagorinsky + FRP and Smagorinsky + FRP model combinations exhibit relatively smaller errors than the other combinations. The cavitation distribution results indicate that, compared with the LES subgrid-scale model, the cavitation model has a more pronounced influence on the extent and evolution of the cavitation region. Overall, the Dynamic Smagorinsky + FRP model demonstrates the best comprehensive predictive performance. Furthermore, this model was applied to the simulation of cavitating flow in a two-dimensional injector control valve, and the predicted results agree well with the visualization experiments. The present study provides a useful reference for the numerical simulation and structural optimization of cavitating flows in injector control valves.

With the increasingly stringent mandatory emission regulations for engines and the continuous growth of energy consumption, reducing energy consumption and emission pollution has become an inevitable choice for engine development. Against this backdrop, biodiesel and boot-shaped injection rates have attracted widespread attention. However, research results on the combination of boot-shaped injection and biodiesel applied to engines have not yet been reported. In order to provide direction for the optimal matching of the combustion system parameters of biodiesel engines under saddle-shaped injection conditions, this paper achieves boot-shaped injection using a dual solenoid valve control strategy for ultra-high-pressure fuel injection devices, establishes a simulation model of biodiesel engines under saddle-shaped injection conditions using software and validates the model based on experiments. Subsequently, the model is used to study the influence of nozzle numbers, swirl ratio and bore-to-stroke ratio on the performance of biodiesel engines under saddle-shaped injection conditions. The results show that under saddle-shaped injection conditions, appropriately increasing the nozzle hole can refine the fuel spray, which is beneficial for fuel–air mixing and combustion in the cylinder. However, too many nozzle holes can lead to interference between adjacent fuel sprays. When the swirl ratio is large, air flow accelerates, and the oxygen concentration in the cylinder increases, which can effectively control soot formation. When the bore-to-stroke ratio is large, the fuel spray is farther away from the combustion chamber side wall, facilitating sufficient contact between fuel and air, resulting in better fuel–air mixing and effectively reducing soot formation. However, the cylinder temperature also increases, leading to higher NOx formation.

The combustion characteristics of ammonia/hydrogen premixed laminar flow and the effect of hydrogen on the combustion performance of ammonia fuel were studied. First, the corresponding model of ammonia/ hydrogen premixed laminar combustion is established by using GRI3.0 mechanism, Konnov mechanism, Mei mechanism, Okafor mechanism, and Otomo mechanism respectively. Second, the simulation results are compared with the experimental results. It is found that the Mei mechanism and Okafor mechanism are more suitable for ammonia/ hydrogen premixed laminar combustion. On this basis, the effects of equivalent ratio, hydrogen ratio, and initial temperature on laminar flame velocity, maximum combustion temperature, and NO mole fraction were studied. The results show that the laminar flame velocity, the maximum combustion temperature, and the mole fraction of NO first increase and then decrease with the increase of the equivalent ratio, and the laminar flame velocity reaches the maximum when the equivalent ratio is 1.1. At the same time, with the increase of hydrogen ratio and initial temperature, the maximum combustion temperature increases first and then decreases. The mole fraction of NO increased with the increase of hydrogen ratio and initial temperature. The results show that mixing hydrogen in ammonia can improve the combustion characteristics of ammonia.

The heat transfer model of difference in temperature is used in the heat transfer analysis for platelet nosetip. The temperature distribution of platelet construction unit and transpiration cooling medium is got by analytical solution. Hot dipping depth is used for range of influence. The results show that the maximum temperature and hot dipping depth decrease with transpiration flux increasing, and decreasing trend of hot dipping depth is slowing. Hot dipping depth and the maximum temperature increase with the heat flux on the wall increasing, and increasing trend of hot dipping depth is slowing. Temperature increasing trend of platelet construction unit in heat-affected zone is slowing with thermal conductivity of structural material increasing. The temperature change tendency is basically unchanged with the length of distribution channel increasing, but only heat-affected zone of platelet move some distance to the exit. So simply increasing the length of the distribution channel does not improve the thermal protective effect.

In order to study the main bearings lubrication characteristics for diesel engine under elastic deformation conditions, an elastic fluid dynamics simulation model of diesel engine main bearing is established. The law of the load, minimum oil film thickness and maximum oil film pressure of the seven main bearing for the diesel engine is studied. The results show that the minimum oil film thickness decreases gradually with increasing of the bearing clearance of the main bearing, but the maximum oil film pressure gradually increasing. The maximum oil film pressure and the minimum oil film thickness of the main bearing appears in the 3^# and 5^# main bearings.