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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.

Mie-Scattering and laser induced exciplex fluorescence (LIEF) were used to visualize the distribution of liquid fuel and fuel vapor inside an optical accessible one-cylinder research engine with gasoline direct injection (GDI). Using a tracer which was developed especially for the environments of gasoline combustion engines, LIEF enables an extensive separation between liquid and vapor phase and delivers a signal proportional to the equivalence ratio. Simultaneous images of LIEF and Mie scattering proof the high quality of the phase separation using this tracer concept. The mixture formation process will be shown exemplary at one operation point with homogeneous load and another with stratified load. First results of determining the air/fuel ratio by means of linear Raman spectroscopy will be presented and compared with the two-dimensional qualitative distribution of the fuel vapor (LIEF).

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.

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.

The vapor phase of an evaporating spray from a heavy-duty Diesel common-rail injection system has been investigated with an optical diagnostic technique based on linear Raman scattering, which has been extended to the application in fuel sprays. One-dimensional spatially resolved Raman measurements of the air/fuel-ratio have been performed in the spray region with high local and temporal resolution in an injection chamber at an air pressure of 4.5 MPa and at a temperature of 450°C. The influence of different parameters, such as rail pressure, nozzle geometry and injection duration on the temporal evolution of the local air/fuel-ratio in the vapor phase has been studied quantitatively, and results from a selected spatial location are compared. Furthermore, the effect of physical/chemical fuel properties on the evaporation dynamics has been investigated by performing measurements with two different fuels.

Propagation-based and phase-enhanced x-ray imaging was developed as a unique metrology technique to visualize the internal structure of high-pressure fuel injection nozzles. We have visualized the microstructures inside 200-μm fuel injection nozzles in a 3-mm-thick steel housing using this novel technique. Furthermore, this new x-ray-based metrology technique has been used to directly study the highly transient needle motion in the nozzles in situ and in real-time, which is virtually impossible by any other means. The needle motion has been shown to have the most direct effect on the fuel jet structure and spray formation immediately outside of the nozzle. In addition, the spray cone-angle has been perfectly correlated with the numerically simulated fuel flow inside the nozzle due to the transient nature of the needle during the injection.

Two-Color imaging optics were developed and used to observe soot emission processes in a modern heavy-duty diesel engine. The engine was equipped with a common rail, electronically-controlled, high-pressure fuel injection system that is capable of up to four injection pulses per engine cycle. The engine was instrumented with an endoscope system for optical access for the combustion visualization. Multidimensional combustion and soot modeling results were used for comparisons to enhance the understanding and interpretation of the experimental data. Good agreement between computed and measured cylinder pressures, heat release and soot and NOx emissions was achieved. In addition, good qualitative agreement was found between in-cylinder soot concentration (KL) and temperature fields obtained from the endoscope images and those obtained from the multidimensional modeling.

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 global characterization of the spray distribution of various current and development types of automotive fuel injectors was obtained. Axial and radial measurement of droplet sizes, velocities and volume fluxes were made with a phase Doppler particle analyzer (PDPA) for a transient port injector spray in quiescent atmospheric conditions. Time-resolved measurements involving the time-of-arrival of each droplet associated with its size and velocity components were also acquired. Additionally, the liquid sprays emanating from various types of port fuel injectors were visualized, through planar laser induced fluorescence (PLIF) technique, at different time instants. Such detailed study provides an improved understanding of the temporal or unsteady behavior of port injector spray.

Engine-out CO emission and fuel conversion efficiency were measured in a highly-dilute, low-temperature diesel combustion regime over a swirl ratio range of 1.44-7.12 and a wide range of injection timing. At fixed injection timing, an optimal swirl ratio for minimum CO emission and fuel consumption was found. At fixed swirl ratio, CO emission and fuel consumption generally decreased as injection timing was advanced. Moreover, a sudden decrease in CO emission was observed at early injection timings. Multi-dimensional numerical simulations, pressure-based measurements of ignition delay and apparent heat release, estimates of peak flame temperature, imaging of natural combustion luminosity and spray/wall interactions, and Laser Doppler Velocimeter (LDV) measurements of in-cylinder turbulence levels are employed to clarify the sources of the observed behavior.

An experimental study was carried out to characterize the spray atomization process of automotive port fuel injectors retrofitted to a novel pressure modulation piezoelectric driver, which generates a pressure perturbation inside the fuel line. Unlike many other piezoelectric atomizers, this unit does not drive the nozzle directly. It has a small size and can be installed easily between regular port injector and fuel lines. There is no extra control difficulty with this system since the fuel injection rate and injection timing are controlled by the original fuel-metering valve. The global spray structures were characterized using the planar laser Mie scattering (PLMS) technique and the spray atomization processes were quantified using phase Doppler anemometry (PDA) technique.

A multi-dimensional model was used to calculate interactions between spray drops and gas motions close to the nozzle in dense high-pressure sprays. The model also accounts for the phenomena of drop breakup, drop collision and coalescence, and the effect of drops, on the gas turbulence. The calculations used a new method to describe atomization (a boundary condition in current spray codes). The method assumes that atomization and drop breakup are indistinguishable processes within the dense spray near the nozzle exit. Accordingly, atomization is prescribed by injecting drops (‘blobs’) that have a size equal to the nozzle exit diameter. The injected ‘blobs’ breakup due to interaction with the gas as they penetrate, yielding a core region which contains relatively large drops. The computed core length agrees well with available measurements of core length in high-pressure sprays.

An experimental study was carried out to investigate the spray behavior inside engine intake ports. Production-type intake ports of four-valve gasoline engines were modified for the optical access at directions. The global spray formation process was visualized through laser Mie scattering technique. The spray breakup and atomization processes, spray targeting and fuel dispersing characteristics were investigated as a function of elapse time after fuel injection. The spray interaction with the port wall and port air flow were examined with different types of port fuel injectors including single-stream, multi-stream, and air-shrouded ones. The spray targeting and dispersing characteristics inside two different intake ports were examined. It was found that spray targeting and fuel dispersion inside the intake port are strongly dependent on the spray characteristics, as a result of different injector designs and injector installation positions.

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.

This paper describes a computer simulation of Diesel spray formation and the locations of self-ignition nuclei. The spray is divided into small elementary volumes in which the amounts of fuel and fuel vapours, air, mean, maximum and minimum fuel droplet diameter are calculated, as well as their number. The total air-fuel and air-fuel vapour ratios are calculated for each elementary volume. The paper introduces a new criterion for determining self-ignition nuclei, based on assumptions that the strongest self-ignition probability lies in those elementary volumes containing the stoichiometric air ratio, where the fuel is evaporated or the fuel droplet diameter is equal to or lower than 0.0065 mm. The most efficient combustion in regard to consumption and emission will be in those elementary volumes containing stoichiometric air ratio, and fuel droplets with the lowest mean diameters. Measurements of injection and combustion were carried out in a transparent research engine.

A quantitative and time-resolved technique has been developed to probe the dense spray structure of direct-injection (DI) gasoline sprays in near-nozzle region. This technique uses the line-of-sight absorption of monochromatic x-rays from a synchrotron source to measure the fuel mass with time resolution better than 1 μs. The small scattering cross-section of fuel at x-rays regime allows direct measurements of spray structure that are difficult with most visible-light optical techniques. Appropriate models were developed to determine the fuel density as a function of time.

A measurement technique is described which permits quantitative, multi-point, in-cylinder fluid composition measurements in an internal combustion engine. The technique is based on spontaneous Raman scattering with broadband signal collection, and provides simultaneous determination of the mole fractions of H2O, CO2, N2, O2, and fuel (C3H8). Calibration and data reduction procedures which largely eliminate interference between the signals from the various species are discussed. Mean mole fractions obtained in an optical access engine from the beginning of the intake stroke to the end of the compression stroke are reported. The mean mole fractions of the individual species are used to obtain independent estimates of the mean mole fraction of burnt residual gases, which, in turn, are used to evaluate the accuracy and consistency of the data. An over-prediction of the CO2 mole fraction in hot exhaust gases is found to be the most significant shortcoming of the technique.

In diesel injector nozzles, the shape of the orifice entrance and the sac-volume play a significant role in determining the orifice internal flow characteristics and the subsequent spray formation process. The sac-volume of the injector nozzle determines injection characteristics like injection rate shape and discharge coefficients. The sac-volume is also important from emissions point of view, in that it controls the amount of Un-Burnt Hydrocarbons (UBHC). This paper demonstrates the use of commercial dynamic and computational fluid dynamics (CFD) programs in predicting the flow characteristics of various nozzle orifice and sac-volume configurations. Three single orifice nozzle tips with varying sac configurations and orifice entrance shapes are studied. Transient simulations are carried out in order to compare the injection rates, discharge coefficients and internal flow characteristics for the nozzle tips. The simulation results are compared with experimental results.

Measurements of ignition behavior, homogeneous reactor simulations employing detailed kinetics, and quantitative in-cylinder imaging of fuel-air distributions are used to delineate the impact of temperature, dilution, pilot injection mass, and injection pressure on the pilot ignition process. For dilute, low-temperature conditions characterized by a lengthy ignition delay, pilot ignition is impeded by the formation of excessively lean mixture. Under these conditions, smaller pilot mass or higher injection pressures further lengthen the pilot ignition delay. Similarly, excessively rich mixtures formed under relatively short ignition delay conditions typical of conventional diesel combustion will also prolong the ignition delay. In this latter case, smaller pilot mass or higher injection pressures will shorten the ignition delay. The minimum charge temperature required to effect a robust pilot ignition event is strongly dependent on charge O2 concentration.

In the Atomization regime, liquid jets breakup either within the nozzle or immediately upon entering the chamber gas and drops much smaller than the jet diameter are formed. The mechanism of Atomization, which is presently unknown, was investigated by the simultaneous use of two photographic techniques. The initial transient was observed with a 106 frames/s camera and the steady state by a technique similar to spark photography. The experiment range was: liquid pressure 500 to 2500 psia; five mixtures of water and glycerol to vary the liquid viscosity; air, nitrogen, helium, and xenon at up to 600 psia as chamber gases to separate gas pressure from gas density effects; and 14 nozzle designs. Not changed were the temperature (room value), the nozzle diameter (340 μ), and the surface tension (70 dyne/cm).