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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.

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.

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.

An experimental study of sprayod structures from a regular dual-stream (RDS) injector and an air-shrouding dual-stream (ASDS) injector was carried out extensively to understand the spray characteristics of dual-stream (DS) port fuel injector for applications to 4-valve gasoline engines. The injectors were tested under steady and transient conditions at different injection pressures. The global spray structures were visualized using planar laser Mie scattering (PLMS) technique and spray atomization processes were quantified using phase Doppler anemometry (PDA) technique. The experimental results showed that at the beginning of fuel injection, the spray tip penetration for the RDS injector decreases with an increase in injection pressure; however, at the later stage of fuel injection, it increases when the injection pressure is increased. It is also found that the ligaments are dominant near the injector tip for the RDS injector with threads connecting the two streams.

The requirement of meeting the emission standards for low emission vehicles (LEV) and ultra low emission vehicles (ULEV) has resulted in a more stringent examination of all elements of the automotive internal combustion engine that contribute to emission formation. The fuel system, as one of the key elements, is the subject of renewed and expanded research in an effort to understand and optimize the important parameters. Only through such enhanced understanding of the basic processes of fuel injection, metering, atomization, targeting, pulse-to-pulse variability and induction of fuel under cold, normal and elevated temperature conditions can the very low emissions of today's vehicles be further reduced to ULEV values.

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.

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.

An experimental study was made to investigate the spray characteristics of high pressure fuel injectors for direct-injection gasoline engines. The global spray development process was visualized using two-dimensional laser Mie scattering technique. The spray atomization process was characterized by Phase Doppler particle analyzer. The transient spray development process was investigated under different fuel injection conditions as a function of the time after the fuel injection start. The effects of injector design, fuel injection pressure, injection duration, ambient pressure, and fuel property on the spray breakup and atomization characteristics were studied in details. Two clear counter-rotating recirculation zones are observed at the later stage or after the end of fuel injection inside the fuel sprays with a small momentum. The circumferential distribution of the spray from the large-angle injector is quite irregular and looks like a star with several wings projected out.

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.

Diesel engine cold-start problems include long cranking periods, hesitation and white smoke emissions. A better understanding of these problems is essential to improve diesel engine cold-start. In this study computer simulation model is developed for the steady state and transient cold starting processes in a single-cylinder naturally aspirated direct injection diesel engine. The model is verified experimentally and utilized to determine the key parameters that affect the cranking period and combustion instability after the engine starts. The behavior of the fuel spray before and after it impinges on the combustion chamber walls was analyzed in each cycle during the cold-start operation. The analysis indicated that the accumulated fuel in combustion chamber has a major impact on engine cold starting through increasing engine compression pressure and temperature and increasing fuel vapor concentration in the combustion chamber during the ignition delay period.

A two phase, global combustion model has been developed for quiescent chamber, direct injection diesel engines. The first stage of the model is essentially a spark ignition engine flame spread model which has been adapted to account for fuel injection effects. During this stage of the combustion process, ignition and subsequent flame spread/heat release are confined to a mixing layer which has formed on the injected jet periphery during the ignition delay period. Fuel consumption rate is dictated by mixing layer dynamics, laminar flame speed, large scale turbulence intensity, and local jet penetration rate. The second stage of the model is also a time scale approach which is explicitly controlled by the global mixing rate. Fuel-air preparation occurs on a large-scale level throughout this phase of the combustion process with each mixed fuel parcel eventually burning at a characteristic time scale as dictated by the global mixing rate.

The study relates air/fuel ratio, fuel injection timing, and engine speed to exhaust smoke levels and performance of the diesel engine. Additional data were obtained under supercharged and turbocharged inlet air conditions to investigate the applicability of the derived relationships under these conditions. Limited data using a variance in fuel type were obtained. Insight into the basic mechanism of smoke formation in diesel engines was gained. The relative percentages of fuel injected before ignition (i.e., premixed fuel) and after initiation of combustion (i.e., unmixed diffusion burning fuel) were found to be extremely significant in determining smoke levels. A smoke factor (the ratio of equivalence ratio in the combustion chamber at initial ignition to overall equivalence ratio) was formulated and found to be useful in predicting smoke phenomena in diesel engines.

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.

Ultraviolet chemiluminescence has been observed in a diesel engine cyclinder during compression, but prior to fuel injection under engine starting conditions. During a portion of the warm-up sequence, the intensity of this emission exhibits a strong correlation to the phasing of the subsequent combustion. Engine exhaust measurements taken from a continuously misfiring, motored engine confirm the generation of formaldehyde (HCHO) in such processes. Fractions of this compound are expected to be recycled as residual to participate in the following combustion cycle. Spectral measurements taken during the compression period prior to fuel injection match the features of Emeleus' cool flame HCHO bands that have been observed during low temperature heat release reactions occurring in lean HCCI combustion. That the signal from the OH* bands is weak implies a buildup of HCHO during compression.

Analysis of flow field and charge distribution in a gasoline direct-injection (GDI) engine is performed by a modified version of the KIVA code. A particle-based spray model is proposed to simulate a swirl-type hollow-cone spray in a GDI engine. Spray droplets are assumed to be fully atomized and introduced at the sheet breakup locations as determined by experimental correlations and energy conservation. The effects of the fuel injection parameters such as spray cone angle and ambient pressure are examined for different injectors and injection conditions. Results show reasonable agreement with the measurements for penetration, dispersion, global shape, droplet velocity and size distribution by Phase Doppler Particle Anemometry(PDPA) in a constant-volume chamber. The test engine is a 4-stroke 4-valve optically accessible single-cylinder engine with a pent-roof head and tumble ports.

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.

A long-distance microscope with pulse-laser as optical shutter up to 25kHz was used to magnify the diesel spray at the nozzle hole vicinity onto 35-mm photographic film through a still or a high-speed drum camera. The injectors examined are high-pressure valve-covered-orifice (VCO) nozzles, from unit injector and common rail injection systems. For comparison, a mini-sac injector from a hydraulic unit injector is also investigated. A phase-Doppler particle analyzer (PDPA) system with an external digital clock was also used to measure the droplet size, velocity and time of arrival relative to the start of the injection event. The visualization results provide very interesting and dynamic information on spray structure, showing spray angle variations, primary breakup processes, and spray asymmetry not observed using conventional macroscopic visualization techniques.

One of the most challenging problems in diesel engines is to reduce unburned HC emissions that appear as (white smoke) during cold starting. In this paper the research is carried out on a 4-cylinder diesel engine with a common rail fuel injection system, which is able to deliver multiple injections during cold start. The causes of combustion failure at lower temperature limits are investigated theoretically by considering the rate of heat release. The results of this clearly indicate that in addition to low cranking engine speed, heat transfer and blow-by losses at lower ambient temperatures, fuel injection events would contribute to the failure of combustion. Also, combustion failure takes place when the compression temperature is lower than some critical value. Based on these results, split-main injection strategy was applied during engine cold starting and validated by experiments in a cold room at lower ambient temperatures.

The nozzle configuration for an injector is known to have an important effect on the fuel atomization. A comprehensive experimental and numerical investigation has been performed to determine the influence of various internal geometries on the primary spray breakup and development using the electronically controlled high-pressure diesel injection systems. Different types of multi-hole minisac and VCO nozzles with cylindrical and tapered geometries, and different types of single-hole nozzles with defined grades of Hydro Grinding (HG) were investigated. The global characteristics of the spray, including spray angle, spray tip penetration and spray pattern were measured from the spray images with a high-speed drum camera. A long-distance microscope with a pulsed-laser as the optical shutter was used to magnify the diesel spray at the nozzle hole vicinity. A CFD analysis of the internal flow through various nozzle geometries has been carried out with a commercial code.