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Nozzle length has been proven influencing fuel spray characteristics, and subsequently fuel-air mixing and combustion processes. However, almost all existing related studies are conducted when fuel is subcooled, of which fuel evaporation is extremely weak, especially at the near nozzle region. In addition, injector tip can be heated to very high temperature in SIDI engines, which would trigger flash boiling fuel spray. Therefore, in this study, effect of nozzle length on spray characteristics is investigated under superheated conditions. Three single-hole injectors with different nozzle length were studied. High speed backlit imaging technique was applied to acquire magnified near nozzle spray images based on an optical accessible constant volume chamber. Fuel pressure was maintained at 15 MPa, and n-hexane was chosen as test fuel.

High fuel injection pressure has been regarded as a key controlling factor for internal combustion engines to achieve good combustion performance with reduced emissions and improved fuel efficiency. For common-rail injection system (CRS) used in advanced diesel engines, fuel injection pressure can often be raised to beyond 200 MPa. Although characteristics of diesel spray has been thoroughly studied, little work has been done at ultra-high injection pressures. In this work, the characteristics of CRS diesel spray under ultra-high injection pressure up to 250 MPa was investigated. The experiments were conducted in an optically accessible high-pressure and high-temperature constant volume chamber. The injection pressure varied from 50 MPa to up to 250 MPa. Both non-evaporating condition and evaporating condition were studied. A single-hole injector was specially designed for this investigation.

In this study, the spray characteristics of three multi-hole injectors, namely a 2-hole injector, a 4-hole injector, and a 6-hole injector were investigated under various superheated conditions. Fuel pressure was kept constant at 10MPa. Fuel temperature varied from 20°C to 85°C, and back pressure ranged from 20kPa to 100kPa. Both liquid phase and vapor phase of the spray were investigated via laser induced exciplex fluorescence technique. Proper orthogonal decomposition technique was applied to analyze the cycle-to-cycle variations of the liquid phase and vapor phase of the fuel spray separately. Effects of fuel temperature, back pressure, superheated degree and nozzle number on spray variation were revealed. It shows that higher fuel temperature led to a more stable spray due to enhanced evaporation which eliminated the fluctuating structures along the spray periphery. Higher back pressure led to higher spray variation due to increased interaction between spray and ambient air.

In spark ignition direct injection (SIDI) engines, the injector configuration plays an important role on influencing the spray atomization and evaporation. In order to optimize the injector configuration to generate a better fuel spray, the further study to understand the effect of injector configuration is needed. In this study, the influence of the hole length to diameter ratio (L/D) on the fuel spray evaporation is investigated in a constant volume chamber under various operating conditions. The laser induced exciplex fluorescence (LIEF) technique is utilized to capture the vapor fluorescence signal of fuel spray. The fuel sprays with the fuel temperature ranging from 45°C to 85°C and ambient pressure ranging from 20kPa to 100kPa are investigated to study the influences of superheated degree (SD) on the spray evaporation.

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.