Research On Spray Characteristics Of Gasoline-Alcohol Blends And Injector Nozzle Optimization

With economic development and technology advancement, energy shortage and environmental pollution have become increasingly significant global problems. As the main power source for automobiles, internal combustion engines bring about massive consumption of petroleum as well as emission pollution. Therefore alternative fuels and emission reduction draw a great attention of public. As a large agricultural country with plenty of coal mines and other mineral resources, China can be benefited greatly from application of alternative fuels such as alcohol ether fuels. As the most popular alternative fuels available today, gasoline-methanol and gasoline-ethanol blends have shown great potentials of higher octane number, broader flammability limits, higher flame propagation speed and higher latent heat, which will improve engine efficiency and emission. Researches on the alcohol fuels have been focused on cold-start and erosion problem, but influences of fuel physical properties on spray and combustion have not been investigated enough.This paper mainly investigated density, viscosity and surface tension of gasoline-methanol and gasoline-ethanol blends, and relationships among ambient conditions, fuel physical properties and spray characteristics from a multi-hole low pressure direct-injection injector, using white light illumination technology. AVL FIRE code was applied to simulate injector inner flow and spray characteristics, and structure of low pressure DI injector was optimized to achieve better atomized spray.The results show that density, viscosity and surface tension of gasoline-alcohol blends decrease when temperature increase, and the mixture density and viscosity increase as the alcohol-to-gasoline ratio increases while the surface tension is relatively insensitive to the alcohol-to-gasoline ratio. The spray images show that increasing of density and viscosity results in reduced penetration of non-flash boiling spray, while higher saturation vapor pressure causes longer penetration of flash boiling spray. However spray angle varies with surface tension inversely. In terms of simulation results, for gasoline-methanol and gasoline-ethanol sprays, SMD on the plane 20mm below the nozzle tip takes much smaller values at the both ends (0% and 100% alcohol-to-gasoline ratio). SMD increases slightly as alcohol-to-gasoline ratio increases from 0% to 85%, but there is a sharp drop from 85% to 100% alcohol-to-gasoline ratio. By simulation of modified injectors, decreasing nozzle hole cone angle (decreasing angleα) or increasing thickness of liquid chamber upstream of the nozzle hole (increasing angleγ), can enhance atomization effect. Optimized spray characteristics can be achieved by matching ambient conditions, fuel physical properties and injector structure parameters. In the future research plan, special ambient conditions (such as flash boiling conditions) need intensive study. Spray and combustion testing under dynamic environment of the optical engine is also necessary. Besides, design parameters of the injector need to be further optimized in order to obtain the optimal spray characteristics.