Understanding the Effects of Fuel Type and Injection Conditions on Spray Evaporation Using Optical Diagnostics

Comparing with port-fuel-injection (PFI) engine, the fuel sprays in spark-ignition direct-injection (SIDI) engines play more important roles since they significantly influence the combustion stability, engine efficiency as well as emission formations. In order to design higher efficiency and cleaner engines, further research is needed to understand and optimize the fuel spray atomization and vaporization. This paper investigates the atomization and evaporation of n-pentane, gasoline and surrogate fuels sprays under realistic SIDI engine conditions. An optical diagnostic technique combining high-speed Mie scattering and Schlieren imaging has been applied to study the characteristics of liquid and vapor phases inside a constant volume chamber under various operating conditions. The effects of ambient temperature, fuel temperature, and fuel type on spray atomization and vaporization are analyzed by quantitative comparisons of spray characteristics. Experimental results indicate that the evaporation of n-pentane, gasoline, light surrogate fuel and heavy surrogate fuel is affected by fuel temperature and ambient temperature. Under the same condition, the evaporation of n-pentane is strongest, and the evaporation of gasoline and light surrogate fuel spray is stronger than that of heavy surrogate fuel spray. Moreover, the fuel temperature and ambient temperature have significant effects on spray penetration length of liquid phase as well as the two-phase interaction between liquid and vapor. Therefore, changing the environment temperature and fuel temperature are effective ways to control the spray penetration and evaporation.