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Operation of flex fuel vehicles requires operation with a range of fuel properties. The significant differences in the heat of vaporization and energy density of E0-E100 fuels and the effect on spray development need to be fully comprehended when developing engine control strategies. Limited enthalpy for fuel vaporization needs to be accounted for when developing injection strategies for cold start, homogeneous and stratified operation. Spray imaging of multi-hole gasoline injectors with fuels ranging from E0 to E100 and environmental conditions that represent engine operating points from ambient cold start to hot conditions was performed in a spray chamber. Schlieren visualization technique was used to characterize the sprays and the results were compared with Laser Mie scattering and Back-lighting technique. Open chamber experiments were utilized to provide input and validation of a CFD model.

In present GDI engines, multiple injection strategies are often employed for engine cold start mixture formation. In the future, these strategies may also be used to control the combustion process, and to prevent misfiring or high emission levels. While the processes occurring during individual injections of GDI injectors have been investigated by a number of researchers, this paper concentrates on the interactions of multiple injection events. Even though multiple injection strategies are already applied in most GDI engines, the impact of the first injection event on the second injection event has not been analyzed in detail yet. Different optical measurement techniques are used in order to investigate the interaction of the two closely timed injection events, as well as the effect of dwell time and the in-cylinder conditions. The injector investigated is a GDI piezo injector with an outwardly opening needle.

Effects of fuel cell material properties on water management were numerically investigated using Volume of Fluid (VOF) method in the FLUENT. The results show that the channel surface wettability is an important design variable for both serpentine and interdigitated flow channel configurations. In a serpentine air flow channel, hydrophilic surfaces could benefit the reactant transport to reaction sites by facilitating water transport along channel edges or on channel surfaces; however, the hydrophilic surfaces would also introduce significantly pressure drop as a penalty. For interdigitated air flow channel design, it is observable that liquid water exists only in the outlet channel; it is also observable that water distribution inside GDL is uneven due to the pressure distribution caused by interdigitated structure. An in-situ water measurement method, neutron imaging technique, was used to investigate the water behavior in a PEM fuel cell.

Liquid and vapor penetration of sprays from a multi-hole gasoline fuel injector operating under engine-like conditions were systematically investigated utilizing a high-speed imaging system capable of acquiring schlieren and Mie scattering images in a near-simultaneous fashion. The influences of ambient conditions and fuel properties on the formation of liquid and vapor envelopes were evaluated. In addition to the compilation of an extensive data set, results of the investigation indicate that mixing-limited vaporization modeling can be utilized to predict the maximum liquid penetration of short-duration, multi-plume sprays.

The objective of this research is to investigate the behavior of interacting sprays, so-called spray clusters, under typical Diesel combustion conditions. Visualizations and Phase-Doppler Anemometry are employed to characterize the macro- and microscopic spray properties. A significant effect of the cluster geometry on spray formation is noticed. Direct spray-spray interaction is found in all cases, with varying intensity depending on the included angle of the orifices within a cluster. The sprays from all investigated cluster nozzles penetrated significantly slower than those of a comparable conventional nozzle. The stability of the sprays is found to be very sensitive to the orientation of the cluster. Depending on this parameter the sprays from one cluster penetrate very similar or exhibit significant instabilities, especially at lower injection pressures.

Stringent emission standards are driving the development of diesel-fuel injection concepts to mitigate in-cylinder formation of particulates. While research has demonstrated significant reduction in particulate formation using micro-orifice technology, implementation requires development of industrial processes to fabricate micro-orifices with diameters as low as 50 μm and with large length-to-diameter ratios. This paper reviews the different processes being pursued to fabricate micro-orifices and the advanced techniques applied to characterize the performance of micro-orifices. The latter include the use of phase-contrast x-ray imaging of electroless nickel-plated micro-orifices and laser imaging of fuel sprays at elevated pressures. The experimental results demonstrate an industrially viable process to create small uniform orifices that improve spray formation for fuel injection.

Liquid and vapor envelopes of sprays from a multi-hole fuel injector operating under closely-spaced double-injection conditions were investigated using a combination of high-speed schlieren and Mie scattering imaging. The effects of mass split ratio and dwell time between injections on liquid and vapor penetration have been investigated under engine-like pressures and temperatures. For the conditions evaluated, the results indicate that closely-spaced double-injection generally reduces liquid and vapor penetration.

The improvement of spray atomization and penetration characteristics of GDI multi-hole injector sprays is a major component of the engine combustion developments, in order to achieve the fuel economy and emissions standards. Significant R&D efforts are directed towards optimization of the nozzle designs, in order to achieve optimum multi-objective spray characteristics. The Volume-of-Fluid Large-Eddy-Simulation (VOF-LES) of the injector internal flow and spray break-up processes offers a computational capability to aid development of a fundamental knowledge of the liquid jet breakup process. It is a unique simulation method capable of simultaneous analysis of the injector nozzle internal flow and the near-field jet breakup process. Hence it provides a powerful toll to investigate the influence of nozzle design parameters on the spray geometric and atomization features and, consequently, reduces reliance on hardware trial-and-tests for multi-objective spray optimizations.

The performance of Gasoline Direct Injection (GDI) engines is governed by multiple physical processes such as the internal nozzle flow and the mixing of the liquid stream with the gaseous ambient environment. A detailed knowledge of these processes even for complex injectors is very important for improving the design and performance of combustion engines all the way to pollutant formation and emissions. However, many processes are still not completely understood, which is partly caused by their restricted experimental accessibility. Thus, high-fidelity simulations can be helpful to obtain further understanding of GDI injectors. In this work, advanced simulation and experimental methods are combined in order to study the spray characteristics of two different 3-hole GDI injectors.

Two-dimensional pulse-laser Mie scattering visualization of the direct-injection gasoline fuel sprays and wall impingement processes was carried out inside a single-cylinder optically accessible engine under motoring condition. The injectors have been first characterized inside a pressurized chamber using identical technique, as well as high-speed microscopic visualization and phase Doppler measurement techniques. The effects of injector cone angle, location, and injection timings on the wall impingement processes were investigated. It was found that the fuel vaporization is not complete at the constant engine speed tested. Fuel spray droplets were observed to disperse wider in the motored engine when compared with an isothermal quiescent ambient conditions. The extent of wall-impingement varies significantly with the injector mounting position and spray cone angle; however, its effect can be reduced to some extent by optimizing the injection timing.

Most previous measurements of diesel sprays have yielded few details regarding the near-nozzle structure of the sprays. X-ray radiography measurements have provided quantitative, time-resolved measurements of spray behavior, but the radiography data are projections of the actual fuel distribution. In this study, diesel sprays from two axial, single-hole nozzles are measured using x-ray radiography from several viewing angles. A model-based reconstruction is used to determine the actual density distribution from the projected data. The spray from the hydroground nozzle is eccentric and relatively dense, while the spray from the non-hydroground nozzle is asymmetric and far less dense. Even several mm from the nozzles, the calculated density values are high enough to call into question the assumptions underlying many standard CFD spray models.

By taking advantage of high-intensity and high-brilliance x-ray beams available at the Advanced Photon Source (APS), ultrafast (150 ps) propagation-based phase-enhanced imaging was developed to visualize high-pressure high-speed diesel sprays in the optically dense near-nozzle region. The sub-ns temporal and μm spatial resolution allows us to capture the morphology of the high-speed fuel sprays traveling at 500 m/s with a negligible motion blur. Both quality and quantitative information about the spray feature can be readily obtained. In the experiment, two types of single-hole nozzles have been used, one with a hydroground orifice inlet and the other with a sharp one. Within 3 mm from the nozzle, the sprays from these nozzles behave differently, ranging from laminar flow with surface instability waves to turbulent flow. The sprays are correlated with the nozzle internal geometry, which provides practical information for both nozzle design and supporting numerical simulation models.

Because of their robustness and cost performance, multi-hole gasoline injectors are being adopted as the direct injection (DI) fuel injector of choice as vehicle manufacturers look for ways to reduce fuel consumption without sacrificing power and emission performance. To realize the full benefits of direct injection, the resulting spray needs to be well targeted, atomized, and appropriately mixed with charge air for the desirable fuel vapor concentration distributions in the combustion chamber. Ethanol and ethanol-gasoline blends synergistically improve the turbo-charged DI gasoline performance, especially in down-sized, down-sped and variable-valve-train engine architecture. This paper presents the spray imaging results from two multi-hole DI gasoline injectors with different design, fueled with pure ethanol (E100) or gasoline (E0), under homogeneous and stratified-charge conditions that represent typical engine operating points.

Results of Computational Fluid Dynamic (CFD) analyses of different diesel fuel injector nozzle configurations using a commercial CFD code are presented here. The emphasis of this study is on comparing cavitation models available in the commercial code with respect to their mathematical approach. One of the models is a simple single-phase model based on the Barotropic equation of state, while the other model is a two-phase model based on the bubble dynamic considerations. Results are compared for various 3-D diesel injector nozzles using the two cavitation-modeling approaches. Simulation results are observed to substantiate some of the experimentally established facts like; nozzle efficiency improvements by using techniques like rounded orifice inlets and conical orifices. Also, simulation results agree well with the experimental results. Spray characteristics are predicted based on a primary breakup model.

The process of spray atomization has typically been understood in terms of the Rayleigh-Taylor instability theory. However, this mechanism has failed to fully explain much of the measured data. For this reason a number of new atomization mechanisms have been proposed. The present study intends to gain an understanding of the spray dynamics and breakup processes in the near-nozzle region of heavy-duty diesel injector sprays. As this region is optically dense, synchrotron x-rays were used to gain new insights. This spray study was performed using a prototype common-rail injection system, by injecting a blend of diesel fuel and cerium-containing organometalic compound into a chamber filled with nitrogen at 1 atm. The x-rays were able to probe the dense region of the spray as close as 0.2 mm from the nozzle. These x-ray images showed two interesting features. The first was a breakup of the high density region about 22 μs After the Start Of Injection (ASOI).

Unburned hydrocarbon (UBHC) emissions from gasoline engines remain a primary engineering research and development concern due to stricter emission regulations. Gasoline engines produce more UBHC emissions during cold start and warm-up than during any other stage of operation, because of insufficient fuel-air mixing, particularly in view of the additional fuel enrichment used for early starting. Impingement of fuel droplets on the cylinder wall is a major source of UBHC and a concern for oil dilution. This paper describes an experimental study that was carried out to investigate the distribution and “footprint” of fuel droplets impinging on the cylinder wall during the intake stroke under engine starting conditions. Injectors having different targeting and atomization characteristics were used in a 4-Valve engine with optical access to the intake port and combustion chamber.

A quantitative and time-resolved technique has been developed to probe the fuel distribution very near the nozzle of a high-pressure diesel injector. This technique uses the absorption of synchrotron x-rays to measure the fuel mass with good time and position resolution. The penetrating power of x-rays allows measurements that are difficult with other techniques, such as quantitative measurements of the mass and penetration measurements of the trailing edge of the spray. Line-of-sight measurements were used to determine the fuel density as a function of time. The high time resolution and quantitative nature of the measurement also permit an accurate measure of the instantaneous mass flow rate through the nozzle.

The direct injection spray-wall interactions were investigated experimentally using high-speed laser-sheet imaging, shadowgraphy, wetted footprints and phase Doppler interferometry techniques. A narrow-cone high-pressure swirl injector is used to inject iso-octane fuel onto a plate, at three different impact angles inside a pressurized chamber. Heated air and plate conditions were compared with unheated cases. Injection interval was also varied in the heated case to compare dry- and wet- wall impingement behaviors. High-speed macroscopic Mie-scattering images showed that presence of wall and air temperature has only minor effect on the bulk spray structure and penetration speed for the narrow-cone injector tested. The overall bulk motions of the spray plume and its spatial position at a given time are basically unaffected until a few millimeters before impacting the wall.

Cavitating flows inside a two-dimensional valve covered orifice (VCO) nozzle were simulated by using the Space-Time Conservation Element and Solution Element (CE/SE) method in conjunction with a homogeneous equilibrium cavitation model. As a validation for present model, cavitation over a NACA0015 hydrofoil was predicted and compared with previous simulation results as well as experimental observations. The model was then used to investigate the effects on internal cavitating flows of different nozzle design parameters, such as the hole size, hole aspect-ratio, hydro-erosion radius, and orifice inclination. Under different conditions, cavitating flows through fuel injectors generated hydraulic flip, supercavitation, full cavitation, and cyclical cavitation phenomena, which are commonly observed in experiments.

A time-resolved x-radiographic technique has been employed for measuring the fuel distribution close to a single-hole nozzle fitted in a high-pressure diesel injector. Using a monochromatic synchrotron x-ray beam, it is possible to perform quantitative x-ray absorption measurements and obtain two-dimensional projections of the mass of the fuel spray. We have completed a series of spray measurements in the optically dense, near-nozzle region (< 15 mm from the nozzle orifice) under ambient pressures of 1, 2, and 5.2 bar N2 and 1 bar SF6 at room temperature with injection pressures of 500 and 1000 bar. The focus of the measurements is on the dynamical behaviors of the fuel jets with an emphasis on their penetration in the near-nozzle region. Careful analysis of the time-resolved x-radiographic data revealed that the spray penetration in this near nozzle region was not significantly affected by the limited change of the ambient pressure.