Study On The Injection And Atomization Process Of Biodiesel On The Condition Of The High Temperature And Pressure In-Cylinder

Biodiesel is an oxygenated clean fuel with physical and chemical properties similar to diesel fuel.Biodiesel is widely sourced and can be directly applied in diesel engines.The continuous development of electronically controlled fuel high-pressure injection technology and combustion mode for diesel engines can improve combustion efficiency and reduce emissions.The fuel injection and atomization process is the key to the combustion process,especially in the later part of the injection duration.The transport characteristics of the fuel are changed by temperature and pressure,leading to changes in the mixture formation process.The paper addresses the injection development and atomization process of biodiesel.The paper uses a combination of experimental measurements and simulations to investigate the transport characteristics of biodiesel in high temperature and high pressure environments.Based on this,the paper carries out a study on the development and atomization process of in-cylinder injection under different environmental conditions.This paper analyzes the change law of thermodynamic and transport properties of biodiesel under different temperature and pressure conditions based on PR equation,and determines the critical temperature of 630 K and critical pressure of 3.15 MPa for biodiesel.This paper studies the transport properties of biodiesel such as thermal conductivity,diffusion coefficient and kinematic viscosity,and the results show that: as the temperature rises from 300 K to near the critical temperature of phase change,the thermal conductivity of biodiesel decreases by 60%,the kinematic viscosity and Prandtl number decrease rapidly,and the surface tension disappears sharply;with the increase of temperature(T>300K),the diffusion coefficient increases and the compression factor decreases,and with the increase of pressure(P > 1MPa),the diffusion coefficient decreases and the compression factor increases.The development history of biodiesel injection was investigated by using the injection process in the diesel engine cylinder as the environmental condition.A high-pressure thermal atmosphere internal combustion engine optical diagnostic test platform consisting of a high-pressure volume setting device,an optical system,a high-pressure common rail injection system and an image acquisition device is built.In this paper,spray images are processed based on the principle of temporal standard deviation and Canny operator.The test acquired images of biodiesel injection development process under different environmental conditions in six cylinders.The spray gray histogram is applied to determine the gas-liquid transition threshold of the mixed layer.Based on the structural characteristics of the oil beam atomization,the characterization parameters of the gas-liquid interface mixing degree were proposed.The spray cone angle,spray penetration distance,spray penetration velocity,gas-liquid interface mixing layer,mixing layer expansion angle and gas coiled suction of biodiesel during the development course of injection were investigated.Based on the experimental data of the biodiesel injection process in a constant volume combustion bomb(400K≤T≤800K,2MPa≤P≤6MPa),the paper analyzed the effect of the change of biodiesel from subcritical to supercritical state on the biodiesel atomization process.The results showed that with the increase of ambient temperature and pressure,the atmosphere in the cylinder changed from subcritical to supercritical;the increase of ambient temperature and pressure accelerated the mixing of fuel and gas,the gas-liquid mixing layer area gradually expanded,the spray front area increased significantly,and the "comb-like" structure appeared on both sides of the spray area.As the spraying process proceeded(ASOI>0),the spray projection area gradually increased.Compared with the subcritical state(T=400K,P=2MPa),the spray cone angle of biodiesel in the supercritical state(T=800K,P=6MPa)increased by 3.5°,the maximum penetration distance decreased by 13 mm,and the penetration speed did not change much;the gasliquid interface at the periphery of biodiesel spray in the supercritical state The expansion of the mixed layer intensifies,the expansion angle of the mixed layer increases significantly,and the gas coiled suction is enhanced.It shows that when the biodiesel is in the supercritical state,the droplets at the periphery of the oil beam are easy to mix with the gas,which is more conducive to the rapid phase change and atomization process.To further explore the effects of ambient temperature and pressure on the biodiesel atomization process,a biodiesel spray model was established based on the actual ambient conditions of the in-cylinder spray process of diesel engines,and the atomization process was simulated under different pressure and temperature conditions,and the temperature distribution,concentration distribution,velocity distribution and SMD of biodiesel were investigated.The results show that as the ambient temperature in the cylinder increases from 300 K to 700 K and the ambient pressure increases from 0.1 MPa to 4 MPa,the maximum width of the liquid phase spray of biodiesel decreases by 69.2%,flocculation is produced at the end of the spray,and the spray changes from a "triangular" structure to a "comb-like" structure.The spray changed from a "triangular" structure to a "comb" structure.When the ambient pressure was 4MPa and the ambient temperature increased from 700 K to 1000 K,the low temperature region in the central of the spray temperature field gradually decreased,the temperature gradient at the periphery decreased,the concentration in the spray front region gradually decreased,the velocity distribution range in the spray liquid core region gradually became larger,the velocity at the distal end of the spray was more uniform and the SMD gradually decreased.When the ambient temperature is 800 K and the ambient pressure increases from 4 MPa to 7 MPa,the diffusion of the spray temperature and concentration fields is inhibited,the velocity field at the spray nucleus decreases and the SMD gradually decreases.The research work is of reference value to the atomization and evaporation process of biodiesel in diesel engine cylinders and is of great significance to the application of biodiesel in diesel engines.