Seoksu Moon

Biodiesel effects on transient needle motion and near-exit flow characteristics of a high-pressure diesel injector

In this study, biodiesel effects on transient needle motion and near-exit flow characteristics of a single-orifice high-pressure diesel injector were investigated in terms of needle-lift, needle speed, exit velocity and near-exit flow structure under various injection pressures. Ultrafast x-ray phase-contrast imaging technique was employed in this study to analyze the transient needle motion and near-exit flow characteristics. High-energy sub-nanosecond x-ray pulses have a potential to visualize the needle inside the nozzle and near-exit dense supersonic flow which speed reaches over 600 m/s. Transient needle motion and the structure and velocity of near-exit supersonic flows can be obtained by fabricated analysis of the x-ray images regardless of fuel, injection condition and type of injector. High bulk modulus and viscosity of biodiesel normally slow down the needle movement and decrease the flow performance. During opening-transient, sharp increase and following overshoot in needle speed and exit velocity were observed with a concurrent increase in spray width. The biodiesel showed a slower increase in needle speed, exit velocity and spray width but a higher degree of velocity overshoot during opening-transient. At steady-state, the biodiesel showed less turbulent flow structure and smaller spray width than diesel. During closing-transient, an abrupt increase in needle speed and decrease in exit velocity were observed with a concurrent increase in spray width. The biodiesel showed the retarded start of closing-transient and longer total injection duration under same energizing pulse duration. The difference between biodiesel and diesel became insignificant at low injection pressures roughly below 100 MPa.

The Effects of Injector Temperature on Spray and Combustion Characteristics in a Single Cylinder DISI Engine

The authors would like to thank the support of NRL (National Research Laboratory) project of Korea.

End-of-Injection Behavior of Diesel Sprays Measured With X-Ray Radiography

The behavior of diesel fuel sprays at the end of injection is poorly understood, yet has important implications regarding diesel engine emissions. Recent research has shown that at the end of injection, an entrainment wave is created, causing the fuel spray to rapidly entrain ambient gas. This rapid entrainment creates a dilute mixture of fuel that may be a source of unburned fuel emissions. In this study, x-ray radiography is used to examine the end-of-injection behavior of diesel sprays. X-ray radiography permits quantitative mass distribution measurements in dense sprays, providing data that cannot be obtained with optical techniques. Analysis of the spray velocity at steady-state suggests an entrainment wave speed of several hundred m/s, which is supported by the appearance of a travelling entrainment wave at low ambient density. The spray density declines most rapidly near the nozzle, behavior that matches the expected entrainment wave behavior. In several cases, the spray distribution in a cross-section across the nozzle axis becomes smoother at the end of injection. Three-dimensional reconstructions of the spray density at the end of injection show that the spray plume widens considerably, enhancing the dilution caused by the reduction in spray mass in the flowfield. Measurements of injector needle motion with x-ray phase contrast imaging show that throttling across the needle seat may cause a smearing of the ideally sharp entrainment wave.Copyright

Development and Evaporation of Group-Hole Nozzle Sprays under Various Surrounding and Impinging Conditions of Direct-Injection Diesel Engines

In the present study, penetration and evaporation of the diesel sprays injected by a group of two closely spaced orifices (a group-hole nozzle) were investigated and compared with those of conventional single-hole nozzle sprays under various engine loads and wall-impinging conditions of direct-injection (DI) diesel engines. Both free and wall-impinging conditions were considered. The experiments were performed inside a constant-volume vessel under simulated ambient conditions for low and high engine loads of DI diesel engines. To investigate the effect of spray targeting, two impinging conditions (impingement angles of 45° and 90° with the same impingement distance) were applied. Geometry and liquid/vapour mass distributions of the evaporating diesel sprays were analysed using a laser absorption scattering (LAS) technique. Under a free spray condition, fuel evaporation of the group-hole nozzle spray was improved compared with that of the single-hole nozzle spray at low load conditions, while it showed simultaneous deterioration in fuel evaporation and spray tip penetration at high load conditions. Jet axes deflection of the two jets from the group-hole nozzle, which generated a dense liquid region at the central region of the spray, was responsible for this deteriorated evaporation at high load conditions. Under a vertical impingement condition (impingement angle of 90°), the group-hole nozzle spray showed simultaneous improvement in spray tip penetration and fuel evaporation at both low and high load conditions from strong momentum interaction of the two jets on the impingement wall. However, this improvement from the group-hole nozzle did not appear at an inclined wall-impingement condition (impingement angle of 45°) owing to weakened and delayed momentum interaction of the two jets. Both spray tip penetration and fuel evaporation of the group-hole nozzle spray were deteriorated at the inclined wall-impinging condition.

Improving diesel mixture preparation by optimization of orifice arrangements in a group-hole nozzle:

Abstract The factors affecting the free and wall-impinging spray characteristics of closely spaced micro-orifices (group-hole nozzles) are investigated to determine the optimal orifice arrangement for improved in-cylinder air utilization. To determine the optimized arrangement of the nozzles, different types of group-hole nozzles with different intervals and angles between the orifices have been studied. The spray tip penetration and fuel evaporation were analysed using a laser absorption scattering technique for non-axisymmetric sprays. In the case of a free spray, the spray tip penetration of the group-hole nozzle increased as the included angle and the distance between orifices decreased. The shortest spray tip penetration was observed when the two jets injected by a group-hole nozzle began to separate, but the periphery of each jet still touched. On the contrary, fuel evaporation deteriorated when the distance and angle between the two orifices decreased since the severe collision/coalescence of the two jets hindered evaporation. In the case of a wall-impinging spray, the spray tip penetration of the group-hole nozzle was strongly related to the distance χ between the arbitrary centres of each jet at the impingement wall. Maximum spray tip penetration of the group-hole nozzle was observed at a specific range of χ. In this range, the strong momentum regions of the jets began to meet just after wall impingement, therefore collision/coalescence before wall impingement was minimized and the interaction between the two wall-impinging jets was maximized. The fuel evaporation in the wall-impinging spray also improved at a distance of χ for maximum tip penetration. The mechanism causing this phenomenon is discussed in terms of near-field spray interaction and wall-impinging jet interaction after wall impingement.

Measurements of droplet size distribution and in-cylinder mixture formation from a slit injector in a direct-injection gasoline engine

The droplet size distribution and in-cylinder mixture formation of a slit injector were investigated under varied fuel temperature and air flow conditions. This variance in fuel temperature and air flow represents the altered spray momentum and external forces acting upon the spray. Phase Doppler anemometry (PDA) was used to investigate the effect of fuel temperature and air flow on droplet size distribution. The in-cylinder mixture formation process and the factors affecting the in-cylinder mixture distribution were analyzed under various fuel temperature and air flow conditions using laser induced fluorescence (LIF). When the fuel temperature and air flow velocity increased, the smaller droplets were entrained to the upper and central parts of the spray altering the initial droplet size distribution. The reduced spray momentum decreased the spray penetration in the combustion chamber, and the interaction between the spray and piston bowl was degraded. This phenomenon eventually caused a relatively lean and dispersed mixture distribution near the spark plug at high fuel temperatures. The optimal spray momentum and external force depend on the fuel quantity (air-fuel ratio) and piston bowl shape. Consequently, the spray momentum and the external forces acting upon the spray should be optimized to form the stoichiometric and well-distributed mixture near the spark plug.

Pink-beam focusing with a one-dimensional compound refractive lens

The performance of a cooled Be compound refractive lens (CRL) has been tested at the Advanced Photon Source (APS) to enable vertical focusing of the pink beam and permit the X-ray beam to spatially overlap with an 80 µm-high low-density plasma that simulates astrophysical environments. Focusing the fundamental harmonics of an insertion device white beam increases the APS power density; here, a power density as high as 500 W mm(-2) was calculated. A CRL is chromatic so it does not efficiently focus X-rays whose energies are above the fundamental. Only the fundamental of the undulator focuses at the experiment. A two-chopper system reduces the power density on the imaging system and lens by four orders of magnitude, enabling imaging of the focal plane without any X-ray filter. A method to measure such high power density as well as the performance of the lens in focusing the pink beam is reported.

Generation of robust and well-atomized swirl spray

The authors would like to thank for the financial support of the Combustion Engineering Research Center (CERC).

The Gasoline Atomization Characteristics and Static Pressure Distribution of Tapered Nozzle Swirl Spray

The static pressure distribution, atomization characteristics and velocity distribution of tapered nozzle swirl spray is analyzed and then compared with original swirl spray. The static pressure distribution inside the swirl spray is measured using a piezoresistive pressure transducer. Phase Doppler anemometry (PDA) is applied to measure and analyze the droplet size and velocity distribution of tapered nozzle and original swirl spray. The static pressure inside the spray shows the lower value compared to the atmospheric pressure and this pressure drop is getting attenuated as the taper angle is increased. The droplet size of tapered nozzle spray shows similar value compared to the original swirl spray at the horizontal mainstream while it shows increased value at vertical mainstream. The deteriorated atomization characteristics of tapered nozzle spray is improved by applying high fuel temperature injection without causing the spray collapse. The velocity results show that the larger portion of fuel is positioned with higher injection velocity, and the smaller portion of fuel is positioned with lower injection velocity with causing spatially non-uniform mixture distribution.