Based on a large six cylinder intake port injection ignition M100 methanol engine, the effects of injection timing on engine performance at 1100 r/min and 100% load were studied using a combination of bench tests and CFD fluid simulation software CONVERGE. In this paper, five different injection timings (449, 439, 429, 419, 409°CA ATDC) are set for simulation calculations. A comprehensive comparison of the simulation results shows that in terms of combustion, the forward movement of the injection timing can effectively improve the combustion quality of the engine. As the injection timing advances, the peak combustion pressure, cumulative heat release, and peak temperature in the cylinder gradually increase, and the phases corresponding to CA10, CA50 and CA90 gradually move forward. The combustion duration gradually decreases, the quality of the incylinder mixture gradually increases, and the ignition speed gradually accelerates. In terms of emissions, the forward shift of fuel injection timing can effectively improve the engine's CO, HC and SOOT emissions, but the NOx emissions have increased.

The heat transfer efficiency of the solar air collector with smooth heat absorption plate is very low. Using artificial roughness on the absorption plate can interrupt the boundary layer and improve the heat transfer efficiency of the system. The improvement is made based on the rectangular artificial roughness, and a twodimensional simulation of the solar air collector with the rightangle hexagonal artificial roughness is performed using ANSYS FLUENT. The influence of artificial roughness spacing on heat transfer efficiency and flow characteristics in the specific Reynolds number range is discussed, and the thermohydraulic performance is evaluated under different working conditions. The governing equations are solved using the finite volume method and the transport equations of the turbulent kinetic energy and the turbulent dissipation rate are solved using the RNG kɛ turbulence model. The result show that the heat transfer characteristic of the system is significantly improved by the addition of the rightangle hexagonal artificial roughness compared to the smooth plate. The rightangle hexagonal artificial roughness with p = 10mm had the maximum THPP of 1.76 at Re=4000, which is 1.6 times the artificial roughness of the rectangle under the same geometric parameters.

The thermal efficiency of the traditional bottomheated solar still is low, and the interfacial evaporation technology can limit the heat to the evaporation interface, and then quickly generate water vapor to realize the efficient utilization of solar energy. In this paper, a composite interface evaporator with carbon nanopowder as photothermal conversion material and coated with polyvinyl alcohol hydrogel was prepared, and on this basis, a singleeffect solar still was designed. In this paper, firstly, the energy distribution in the process of water production in the still is analyzed by theoretical calculation, and it is found that the sunlight reflection on the condensation surface and the heat conduction on the evaporation interface are the two biggest factors leading to the energy loss of the still. Then, by adjusting the wettability of the condensation surface, the light transmittance is improved, and the sunlight reflection is reduced, so that the evaporation interface can receive more solar energy. It was found that the thermal efficiency of the still was increased from 36.1% to 55.4% by adjusting the wettability of the condensing surface; the heat conduction loss of evaporation interface is reduced by optimizing the water supply structure of evaporator. When the proportion of water supply area is 20%, its thermal efficiency is improved to 64.6%. Finally, the water production performance of the still under outdoor practical conditions was tested, and the system operated stably without salt crystallization. The evaporation interface temperature and water production rate change synchronously with the change of irradiation intensity, and the wholeday water production reaches 2.89 kg/m². This study can provide theoretical guidance for the design and performance improvement of solar still.

China's "Whole County PV" programme has been dramatically expanding the use of solar power in rural areas, by building on government, comnmercial, industrial and residential rooftops. However, a large number of dispersed residential PV will have an impact on the power system, and accurately predicting the shortterm power generation of residential PV is a prerequisite for addressing the impact. However, in addition to its original volatility, residential rooftop PV also has the characteristics of small capacity, decentralized and offline operation, together with the lack of accurate meteorological data, making PV power prediction exceptionally complex. Therefore, under the limited data, this paper longitudinally detects similar samples from the previous power data of the residential PV to be predicted,and horizontally collects similar samples from the power data of neighboring residential PV, ultimately jointly realizing two dimensional data expansion, which overcomes the dependence of PV power generation prediction on some key input features to a certain extent. And then a residential PV generation prediction method is proposed based on LSTNet neural network, which has the functions of shortterm local features capture, longterm time series information reinforcement, and cyclical linear component extraction.

The pitch Angle is generally set to a fixed value in the design of vertical axis wind airfoil, which leads to the problem that the aerodynamic performance of the airfoil can't be fully utilized. In this paper, a design method of vertical axis wind turbine considering variable pitch Angle is proposed and applied to airfoil optimization. Then, based on the braking cylinder theory, the power coefficient is iteratively calculated, and the maximum power coefficient is directly taken as the objective function, and the profile and pitch Angle distribution are optimized by using genetic algorithm coupled with RFOIL software. Finally, the new airfoil VAWT250 of vertical axis wind turbine is optimized. Compared with the reference airfoil AIR001, the optimization results show that the aerodynamic performance of the new airfoil is significantly improved under both smooth and rough conditions, especially under rough conditions, the maximum lift coefficient and liftdrag ratio are increased by 16.1% and 17.1% respectively. Under rough conditions, the maximum power coefficient of the wind turbine is increased by 6.81% considering the pitch Angle. The results have a certain guiding significance for the optimal design of vertical axis wind turbine airfoil.

The rotating blade of wind turbine generates trailing vortex, which affects the flow on the surface of the blade. The vortex generator is installed on the blade surface, and its flow control effect is inevitably affected by the trailing vortex. In order to explore the influence of the trailing vortex, this paper takes the PhaseVI wind turbine as the research object, and establishes a simulated blade with the same spanwise circulation distribution under its rotation condition for numerical calculation. The results are compared with the smooth blade and the airfoil section with VG respectively. It is found that the airflow velocity on the suction surface is larger, the Cp value is smaller, and the pressure difference between the suction and pressure surfaces is increased.

Wind resource analysis is crucial for the establishment of a wind farm, and the acquisition of wind measurement data is an important prerequisite for wind resource analysis. The layout scheme of the wind tower directly affects the accuracy of wind measurement data. Taking a wind farm under complex terrain as an example, based on computational fluid dynamics method, Meteodyn WT software is used to simulate the wind resources of the wind farm, and by comparing and analyzing the wind tower wind speed and annual power generation of the wind farm from different numbers and locations under the layout scheme of wind towers, the results show that the range represented by wind towers in complex terrain is extremely small, and when selecting representative wind towers, it is necessary to divide different terrains, and it is recommended to use the multitower comprehensive method. Wind towers in special terrain cannot be used as a representative choice for the entire wind farm, but when there is occlusion or crossterrain, a separate wind tower needs to be set up at this location to reduce errors. The research results can provide a reference for the site selection and number of wind towers under complex terrain in the future, so as to improve the accuracy and rationality of wind resource analysis.

Microgrid has problems such as poor dynamic response performance and large overshoot when subjected to external disturbances under traditional droop control. In accordance with the above issues, this paper proposes a control strategy for photovoltaicenergy storage microgrid based on improved virtual oscillator and sliding mode control. The photovoltaic system adopts a twostage structure, and the front stage DCDC converter adopts sliding mode control to enhance the robustness of the microgrid against external interference; The back stage inverter uses a virtual oscillator control with MPPT algorithm to achieve maximum power point tracking control for photovoltaic cells, while improving the dynamic response speed of the microgrid. The energy storage system uses a battery model, and the inverter uses a virtual oscillator control that introduces virtual inertia. Inertia and damping characteristics are introduced into the virtual oscillator control to provide reliable power and frequency support for the microgrid. Finally, based on the Matlab/Simulink platform, a simulation model of the photovoltaicenergy storage microgrid is built. By comparing the simulation results with traditional droop control strategies, the feasibility and effectiveness of the control strategy proposed in this paper are verified.

The significant uncertainty of highproportion wind power can make the scenarios of cascading failures in the power system more numerous and the mechanisms more complex. Identifying the key propagation modes of cascading failures is of great significance for preventing major power outages. This paper first considers factors such as wind power output uncertainty and component failure, establishes a dynamic analysis model for cascading failures. On this basis, failure propagation path data under massive initial scenarios are generated. Besides, an influence correlation diagram describing the sequential propagation process of cascading failures is established. Moreover, a method for identifying key failure propagation modes is proposed in combination with probabilityconsequences to screen highrisk propagation links of cascading failures under highproportion wind power access. Finally, the IEEE 118 node is used to verify the effectiveness of the proposed method in identifying key propagation modes.

In the islanded DC microgrid, the energy storage converters play the role of grid forming. The random characteristics of distributed generation and electric loads lead to the fluctuation of DC microgrid bus voltage, affecting system safety and power supply reliability. In this paper, to suppress the fluctuations and improve the transient response of bus voltage, a perturbation suppression strategy based on state feedback is designed, when the droop control strategy is adopted to form the grid. In this paper, the influencing factors of the transient response of the bus voltage are first analyzed, and the feedforward compensation method is proposed, which can realize the decoupling of the voltage loop and the current loop. Then, the equivalent simplification of the control system is completed without affecting the transient characteristics, and the application of the disturbance observer is achieved. The power disturbance is fed forward to the voltage loop by means of a disturbance observer, and disturbance suppression based on state feedback is realized. Finally, experimental results are given to verify the effectiveness of the proposed control strategy.